I found this Vulcan clip and I think it's time to revisit this gem. I found a bag of parts with all the parts I need to rebuild it. I have no idea where the original pedal went. All of the sounds in the clip were just volume and pickup changes.
Check it out (https://aronnelson.com/sndz/vulcanAsh.mp3)
I'm pretty sure this was a Vulcan with a tone control.
(https://www.diystompboxes.com/analogalchemy/sch/vulcan.gif)
Wow, 15 years ago? I remember I built it just after Joe released the schematic! This is one of the most awesome hi gain od I've ever played with.
I know. I am going to build it again! I need DISTORTION!!!!!
And.... THANK YOU for being around for all of these years!!!!!!! WOW!
Quote from: aron on May 20, 2020, 01:19:04 AM
I need DISTORTION!!!!!
More than obtained with Insanity Box..?? :icon_eek:
Now you're making me want to rehouse the Blackfire and Highway 89 circuit boards I pulled and packed up in order to repurpose the enclosures (the priciest part of a pedal). The last 5 years of the previous century, and first 5 of this one, gave us some mighty circuits that still stand the test of time.
Yes, a great design indeed. The JFET version seems to have some fans but the BJT version is very under-appreciated imo. The diode-compression stages are a fantastic basis for amp-in-a-box style circuits. I tinkered with such a thing years ago but saw something shiny, got distracted... you know how it goes. About time I revisited that idea. Thanks for reminding me, Aron!
Andy
Would someone please educate me?
On the circuit diagram above, there are 6 voltage node arrows along the top, one of which is marked 9v.
Given the others are not marked, do they all connect together?
If so, is it normal practice to presume a single voltage supply unless explicitly stated (VCC, 5v etc)?
Sorry to be dumb
Quote from: antonis on May 20, 2020, 06:18:10 AM
Quote from: aron on May 20, 2020, 01:19:04 AM
I need DISTORTION!!!!!
More than obtained with Insanity Box..?? :icon_eek:
I have to side with Toni on this one. Insanity was one of the first veros I ever did, must be 10 years ago now. It's pretty.... insane.
Quote from: aron on May 20, 2020, 12:48:17 AM
I found this Vulcan clip and I think it's time to revisit this gem. I found a bag of parts with all the parts I need to rebuild it. I have no idea where the original pedal went. All of the sounds in the clip were just volume and pickup changes.
Nice! Makes me want to build one!
Best regards, Jack
Quote from: stallik on May 20, 2020, 11:58:17 AM
Would someone please educate me?
On the circuit diagram above, there are 6 voltage node arrows along the top, one of which is marked 9v.
Given the others are not marked, do they all connect together?
If so, is it normal practice to presume a single voltage supply unless explicitly stated (VCC, 5v etc)?
Sorry to be dumb
Here's a 2009 schematic for a 4 stage Vulcan and it shows 9v for all the top arrows.
https://www.ssguitar.com/index.php?PHPSESSID=94638097b4715075c6cc921f7720ada8&topic=4338.msg34732#msg34732
dave
Quote from: aron on May 20, 2020, 12:48:17 AM
Check it out (https://aronnelson.com/sndz/vulcanAsh.mp3)
Sold! :icon_cool:
I'm not going to lie, looking at the schematic I wasn't expecting to be impressed. But I am impressed :icon_eek: I'm working up my list for my next PCB order, looks like Vulcan will probably make its way on there!
Quote from: aron on May 20, 2020, 01:19:04 AM
I know. I am going to build it again! I need DISTORTION!!!!!
And.... THANK YOU for being around for all of these years!!!!!!! WOW!
I won't build it again because I already have one :icon_twisted:. And THANK YOU for keeping this so nice forum!
Quote from: Mark Hammer on May 20, 2020, 07:37:45 AM
Now you're making me want to rehouse the Blackfire and Highway 89 circuit boards I pulled and packed up in order to repurpose the enclosures (the priciest part of a pedal). The last 5 years of the previous century, and first 5 of this one, gave us some mighty circuits that still stand the test of time.
Those two are another awesome overdrives. HV89 is a pixed one on my pedalboard. Another one I really love is Joe Davisson's Obsidian, BJT version. I had to build one for a friend who was threatening to kidnap mine :icon_lol:
Quote from: stallik on May 20, 2020, 11:58:17 AM
On the circuit diagram above, there are 6 voltage node arrows along the top, one of which is marked 9v.
Given the others are not marked, do they all connect together?
Yep.
Quote from: vigilante397 on May 20, 2020, 01:33:07 PM
I'm not going to lie, looking at the schematic I wasn't expecting to be impressed. But I am impressed :icon_eek: I'm working up my list for my next PCB order, looks like Vulcan will probably make its way on there!
I have a verified layout, if you like. 1.93" x 1.38" with board mounted pots. Designed to fit inside a tuna (or sardine?) can, so it's smaller than a 1590B and can be modded to fit a 1590B better.
Quote from: Marcos - Munky on May 20, 2020, 05:03:59 PM
I have a verified layout, if you like. 1.93" x 1.38" with board mounted pots. Designed to fit inside a tuna (or sardine?) can, so it's smaller than a 1590B and can be modded to fit a 1590B better.
Thanks, probably through-hole though, right? I need SMD :P
Insanity box!
https://aronnelson.com/sndz/inFull.mp3
Obsidian!!!!
https://aronnelson.com/sndz/obsidian.mp3
Quote from: aron on May 20, 2020, 06:39:05 PM
Insanity box!
https://aronnelson.com/sndz/inFull.mp3
Obsidian!!!!
https://aronnelson.com/sndz/obsidian.mp3
But can they do "transparent"? :icon_mrgreen:
Someone actually asked me that about the Insanity box. They are insane.
What does that diode on the base do? That's a unique feature.
<The diodes in the bias network prevent hard-saturation of the transistors.>
From the web page. It really does sound great! Building another soon!
Quote from: vigilante397 on May 20, 2020, 05:47:00 PM
Thanks, probably through-hole though, right? I need SMD :P
Yep. Well, there are a few traces that runs under some resistors/caps, so I don't know how doable it is to be converted to an smd layout. Anywaym if you want the eagle files, just let me know.
Quote from: Marcos - Munky on May 21, 2020, 12:53:34 AM
Quote from: vigilante397 on May 20, 2020, 05:47:00 PM
Thanks, probably through-hole though, right? I need SMD :P
Yep. Well, there are a few traces that runs under some resistors/caps, so I don't know how doable it is to be converted to an smd layout. Anywaym if you want the eagle files, just let me know.
Yeah, converting layouts from through-hole to SMD doesn't usually work well, I'll just do it from scratch. I appreciate the offer though! ;D
Edit: Wasn't too bad, also added a tone control and reverse polarity protection 8)
(https://i.imgur.com/EiHyql4.jpg)
Quote from: aron on May 20, 2020, 12:48:17 AM
I found this Vulcan clip and I think it's time to revisit this gem. I found a bag of parts with all the parts I need to rebuild it. I have no idea where the original pedal went. All of the sounds in the clip were just volume and pickup changes.
Check it out (https://aronnelson.com/sndz/vulcanAsh.mp3)
I'm pretty sure this was a Vulcan with a tone control.
Any guesses which tone control you might have used? That's a pretty cool clip!
At that time, it was probably the tone control from Doug's sweet thing. Which is tacked on to the Hot Fuzz Schematic:
https://www.diystompboxes.com/pedals/hfuzz1.jpg (https://www.diystompboxes.com/pedals/hfuzz1.jpg)
Hi guys,
I just breadboarded the Vulcan again. Wow, what a fantastic circuit! I remember liking it when I first tried it but memory fades I suppose.
Some notes:
1. I played around with the R and C values in an attempt to optimize it. No such luck, Joe's original values are spot on for the best (or at least my favorite) sound. The only thing that turned out to be a big improvement, was to put a buffer in front of it. Makes interaction with the guitar volume more predictable. The sound itself is not affected by the buffer very much, it only gets a bit brighter and clearer on low gain settings, which is a plus in my book. I also added 2n7 caps in parallel with the collector resistors on the second and third stage to tame the highs a bit and put 100Ω resistors in series with the emitter bypass caps to control the gain and reduce noise.
2. What diodes you use makes a big difference. Higher voltage drops sound harsher, more "distortiony", lower voltage drops sound smoother, more "overdrivy". I settled on BAT42. Very smooth transition from clean to clipped, which to me is the essential quality for "amp-like" dis tortion. The other diodes do that too, but I find it most convincing with Schottkys.
3. Leaving out the third stage turns the Vulcan into a fantastic "base sound overdrive". The kind you want to have always on in front of a clean amp, or use it to dirty-boost a crunchy amp for fat lead sounds. I would use it the same way as a Red Llama or DOD250 or even a Klon. This thing cleans up with the guitar volume really well. I can definitely see me using this as my main overdrive / soft fuzz.
How is this thing not more popular? The Joe Davisson Diode Compression Stage is an absolutely fantastic building block for a wide variety of distortion tones. Try it today! Sure beats yet another Big Muff or Tube Screamer. I haven't tried slapping a BMP style tone control on the 3-stage version but I think that seems like a natural pairing.
Cheers,
Andy
You beat me. I was thinking I would build it tomorrow.
I put this board together this morning:
(http://www.bouron.org.uk/marc/pedals/vulcan_board.png)
Now I need to go drill an enclosure...
I put this into Eagle and made a layout. Totally untested. I made the schematic put the parts into a logical order and played with the auto router until I got something that looked reasonable.
(https://i.postimg.cc/dkpCdJm1/Vulcan-v1-bottom.png) (https://postimg.cc/dkpCdJm1)
(https://i.postimg.cc/kBr8gXgY/Vulcan-v1-parts.png) (https://postimg.cc/kBr8gXgY)
Here is a completed board.
(https://i.postimg.cc/R6GJ7FN1/8-CAEA73-B-9321-4221-9588-31-C4875-D6-C2-E.jpg) (https://postimg.cc/R6GJ7FN1)
Wow, that was fast!
Hopefully I didn't make a mistake! I put the schematic into Eagle last night. I started on a PCB but it was a total mess. This morning I took a second look, ignored the traces and organized the parts in a logical arrangement, really I just followed the schematic. Then I started experimenting with the auto router.
I took a look at the results of the auto router results. If I could see an improvement that could be made by rearranging parts I'd ripup make the changes and let the auto router figure it again. After following this process through a dozen or more iterations I had something I thought was acceptable.
Here's my Vulcan. I had a problem with the pad to output, it tore off the PCB, so injury rigged a jumper to the volume pot. It's working but I'm not sure it sounds quite right. It really loud. I had to make a couple part substitutions. I didn't have any 4m7 resistors so I used 3m9. I'm not sure how this would affect the bias here.
(https://i.postimg.cc/K1Kr9TT8/00-A0-D579-5957-49-D4-B971-D36654-F013-A8.jpg) (https://postimg.cc/K1Kr9TT8)
(https://i.postimg.cc/PCBb0qbz/09518229-8603-4-C8-E-AEA3-DA3421-D656-D0.jpg) (https://postimg.cc/PCBb0qbz)
Can I ask a silly question? How does the signal get past each of the three diodes? I've been trying to figure out this for a week now and still don't get it.
Only "part of half of it" does, distorted. Think about AC through a half-wave rectifier, minus the Vf.
Quote from: rockola on May 26, 2020, 02:47:41 AM
Can I ask a silly question? How does the signal get past each of the three diodes? I've been trying to figure out this for a week now and still don't get it.
If you redraw the circuit a little it will make more sense
from the base point the diodes "down" (vertical)
Connect the two resistors at the bottom side of the diodes
Transistors have a VBE drop
Si diodes have a voltage drop
Note the DC voltages at the bases and each end of the diodes
Quote from: Fancy Lime on May 23, 2020, 04:34:55 PM
Hi guys,
I just breadboarded the Vulcan again. Wow, what a fantastic circuit! I remember liking it when I first tried it but memory fades I suppose.
Some notes:
1. I played around with the R and C values in an attempt to optimize it. No such luck, Joe's original values are spot on for the best (or at least my favorite) sound. The only thing that turned out to be a big improvement, was to put a buffer in front of it. Makes interaction with the guitar volume more predictable. The sound itself is not affected by the buffer very much, it only gets a bit brighter and clearer on low gain settings, which is a plus in my book. I also added 2n7 caps in parallel with the collector resistors on the second and third stage to tame the highs a bit and put 100Ω resistors in series with the emitter bypass caps to control the gain and reduce noise.
2. What diodes you use makes a big difference. Higher voltage drops sound harsher, more "distortiony", lower voltage drops sound smoother, more "overdrivy". I settled on BAT42. Very smooth transition from clean to clipped, which to me is the essential quality for "amp-like" dis tortion. The other diodes do that too, but I find it most convincing with Schottkys.
3. Leaving out the third stage turns the Vulcan into a fantastic "base sound overdrive". The kind you want to have always on in front of a clean amp, or use it to dirty-boost a crunchy amp for fat lead sounds. I would use it the same way as a Red Llama or DOD250 or even a Klon. This thing cleans up with the guitar volume really well. I can definitely see me using this as my main overdrive / soft fuzz.
How is this thing not more popular? The Joe Davisson Diode Compression Stage is an absolutely fantastic building block for a wide variety of distortion tones. Try it today! Sure beats yet another Big Muff or Tube Screamer. I haven't tried slapping a BMP style tone control on the 3-stage version but I think that seems like a natural pairing.
Cheers,
Andy
Getting ready for the first run, used BAT 43 as Andy proposed. Really curious how it will sound!
(https://i.postimg.cc/hfS7zhsR/IMG-20200530-105446430.jpg) (https://postimg.cc/hfS7zhsR)
Quote from: rockola on May 26, 2020, 02:47:41 AM
Can I ask a silly question? How does the signal get past each of the three diodes? I've been trying to figure out this for a week now and still don't get it.
The diodes are normally on. Cathode voltage is at the bias minus the diode drop. Signal will get through until it's positive enough to take the cathode voltage too high compared to the anode at which point the diode starts to block further increase.
This is actually a diode "gate". If you take the resistor pulling down the cathode to a higher voltage than 0v and if that voltage was the + supply, the "gate" will be closed and no signal could get in because the diode will then be very much reverse biased. This was the basis of key gating in old organs letting a single key contact switch multiple footages - before cheap signal diodes, they had to have separate contacts for the footages.
That is VERY interesting. Not that you didn't try hard, but there is an enormous amount packed into a few short sentences that may not be fully comprehensible to a great many. For the broader audience here, could you elaborate a wee bit on what you said? Not a criticism, just a desire to polish up what might be a hidden gem.
Just finished the test - this thing is a killer! So nice, it goes to the enclosure first thing in the morning! <3
Quote from: Mark Hammer on May 30, 2020, 11:25:46 AM
That is VERY interesting. Not that you didn't try hard, but there is an enormous amount packed into a few short sentences that may not be fully comprehensible to a great many. For the broader audience here, could you elaborate a wee bit on what you said? Not a criticism, just a desire to polish up what might be a hidden gem.
If you're asking me Mark, there isn't many examples to be found to explain, although the "Analog Switch" in this article shows the principle again...
https://www.allaboutcircuits.com/textbook/semiconductors/chpt-3/diode-switching-circuits/
So long as the diode in the signal path has sufficient DC forward bias and the signal swing is not large enough to change that, the diode is a conductor. If diode forward bias is removed and it become reverse biased unless the signal swing is big enough to forward bias it - but while reverse biased, the signal won't get through.
...as to hidden gem, the problem for simple diode gating is that the control means a DC level shift, which could be heard as a click or thump and that the signal itself changes the diode threshold (this last is exploited in the Vulcan). This is not a problem in an organ since it acts on large square waves which it cannot distort and tone filtering happens later. In fact, it can also be a VCA when you only have square waves to control.
Nice diode VCA can be made, but as far as I know, they had to be balanced/differential so the DC shift gets cancelled out. Something about that here...
https://sound-au.com/articles/vca-techniques.html#s9
A thing is, the articles out there are very often working from a hi-fi perspective. Any distortion/artefacts might actually be interesting to us.
Thinking of another discussion about BJT control...
https://sound-au.com/articles/vca-techniques.html#s8
Perfed one up this evening. Nice work, Joe!
Experimentaly verified what Jim said above..
(SPST shunt switch added on evey diode, shorting them..)
Of course, shorted diode(s) stage(s) gain increased dramatically in a "harsly" way..
(glitches on top start of positive and botom end of negative waveforms.. - probably due to hard BJTs saturation..)
Hey boys and girls,
this is the glorious mess that lives on my bread board these days:
(https://i.postimg.cc/ns6df71H/OD707.png) (https://postimg.cc/ns6df71H)
A buffered two-stage Vulcan descendant with Boss-style bypass switching and a SWTC. Sounds fantastic. The Type switch makes it quite versatile and might as well be labeled Dist/OD/Fuzz. I love it. These Vulcan stages are somehow very pleasing and quite unusual sounding at the same time, which may have to do with them being very asymmetrical. Because they are asymmetrical in opposite directions, the symmetry of the harmonics has a beautifully complex relationship with the playing dynamics. Definitely a "players overdrive"; extremely responsive.
Don't quote me on the values, I haven't checked the schematic for errors, so experience tells me there is probably a bunch, as well as other errors. And sorry for the messy schematic, I need to figure out a better way of presenting this. Awfully confusing with all the connectors.
Cheers,
Andy
Quote from: Fancy Lime on June 02, 2020, 04:33:44 PM
Don't quote me on the values, I haven't checked the schematic for errors
OK.. when you're ready, just let us know.. :icon_wink:
Quote from: antonis on June 02, 2020, 04:43:44 PM
Quote from: Fancy Lime on June 02, 2020, 04:33:44 PM
Don't quote me on the values, I haven't checked the schematic for errors
OK.. when you're ready, just let us know.. :icon_wink:
Alright, I checked and found no errors. Not saying there are none... The starred resistors need adjusting for bias or led current draw, respectively.
Andy
Quote from: Fancy Lime on June 02, 2020, 04:33:44 PM
The Type switch makes it quite versatile and might as well be labeled Dist/OD/Fuzz.
I'm curious now. Do you think it's more interesting to use this switch or a switch between 2 and 3 stages?
Quote from: Fancy Lime on June 02, 2020, 04:33:44 PM
Hey boys and girls,
this is the glorious mess that lives on my bread board these days:
(https://i.postimg.cc/ns6df71H/OD707.png) (https://postimg.cc/ns6df71H)
A buffered two-stage Vulcan descendant with Boss-style bypass switching and a SWTC. Sounds fantastic. The Type switch makes it quite versatile and might as well be labeled Dist/OD/Fuzz. I love it. These Vulcan stages are somehow very pleasing and quite unusual sounding at the same time, which may have to do with them being very asymmetrical. Because they are asymmetrical in opposite directions, the symmetry of the harmonics has a beautifully complex relationship with the playing dynamics. Definitely a "players overdrive"; extremely responsive.
Don't quote me on the values, I haven't checked the schematic for errors, so experience tells me there is probably a bunch, as well as other errors. And sorry for the messy schematic, I need to figure out a better way of presenting this. Awfully confusing with all the connectors.
Cheers,
Andy
YOU ARE MY IDOL!
Quote from: Marcos - Munky on June 02, 2020, 09:51:07 PM
Do you think it's more interesting to use this switch or a switch between 2 and 3 stages?
It depends on what circuit behavior you like..
First stage gain is always more "drastical/critical" in such a circuit configuration..
@Andy: I presume R17 & R18 are for C9 & C11 anti-pop purpose only..
Quote from: Marcos - Munky on June 02, 2020, 09:51:07 PM
Quote from: Fancy Lime on June 02, 2020, 04:33:44 PM
The Type switch makes it quite versatile and might as well be labeled Dist/OD/Fuzz.
I'm curious now. Do you think it's more interesting to use this switch or a switch between 2 and 3 stages?
As Antonis said, it depends. What I like most about the Vulcan stages is the smooth breakup and complex harmonics at low to medium gain. It feels like a good amp to me, not like a "typical" pedal distortion, because it is very "transparent" in the sense that it reacts sensitively to playing dynamics, pickup selection and so on. It also plays really well with an additional booster or other distortion in front of it. With too much gain, you loose (some of) that behavior. With two stages you can already go to seriously high gain, just not crazy high like the 3-stage version. So for that purpose I prefer to be able to change the gain behavior of the first stage. Along with the bright cap on the gain pot, this makes for a very versatile setup without too many controls. For crazy gain, I prefer opamp circuits. They tend to be simpler, less noisy, and more predictable at those conditions and the virtues of the Vulcan stages don't get to shine as much at super high gain anyway. But of course no-one says you cannot use the Type switch AND an additional boost stage (maybe foot switchable). Or make a 2-stage version and a 3-stage version, tack on a Hiwatt or Marschall tone stack and have yourself a deluxe 2-channel amp-in-a-box :)
Quote from: rankot on June 03, 2020, 03:33:02 AM
...
YOU ARE MY IDOL!
I assume this is hyperbolic flattery but just in case it's not: Don't have idols. Idol worship is the path to the dark side. Besides, you have published plenty of great stuff here, so no need to find idols. That being said, thanks for the compliment, I'm glad you like my design :)
Quote from: antonis on June 03, 2020, 05:18:57 AM
...
@Andy: I presume R17 & R18 are for C9 & C11 anti-pop purpose only..
Yes, exactly. Not strictly necessary but the pops from these caps can get quite loud due to their position in the circuit, so I thing the resistors are worth having. The values are not critical, though. Can be anything between a few dozen kΩ and a few MΩ.
Cheers,
Andy
Quote from: Fancy Lime on June 03, 2020, 06:14:44 AM
But of course no-one says you cannot use the Type switch AND an additional boost stage (maybe foot switchable). Or make a 2-stage version and a 3-stage version, tack on a Hiwatt or Marschall tone stack and have yourself a deluxe 2-channel amp-in-a-box :)
Well... that is kinda what I have on Eagle right now :icon_mrgreen:. A Vulcan with Marshall tone stack and switchable between 2 and 3 stages. I was thinking on using it as a od channel in front of a little class d amp instead of as a stompbox, so the switch is pannel mounted. Well, guess it woudn't hurt to make the board a little bigger and add the type switch :icon_mrgreen:
Quote from: Fancy Lime on June 03, 2020, 06:14:44 AM
Quote from: rankot on June 03, 2020, 03:33:02 AM
...
YOU ARE MY IDOL!
I assume this is hyperbolic flattery but just in case it's not: Don't have idols. Idol worship is the path to the dark side. Besides, you have published plenty of great stuff here, so no need to find idols. That being said, thanks for the compliment, I'm glad you like my design :)
Just the expression of my gratitude for your generous and nice work!
I've never actually built one, but after listening to the clip, I'll need to give it a shot. I've been on a bit of an SMD kick lately, so maybe I'll make up a board for it with some modifications. Maybe have clipping diode selection, a tone control, input buffer, and switchable input volume. Hmm...
Quote from: Marcos - Munky on June 03, 2020, 09:58:46 AM
Quote from: Fancy Lime on June 03, 2020, 06:14:44 AM
But of course no-one says you cannot use the Type switch AND an additional boost stage (maybe foot switchable). Or make a 2-stage version and a 3-stage version, tack on a Hiwatt or Marschall tone stack and have yourself a deluxe 2-channel amp-in-a-box :)
Well... that is kinda what I have on Eagle right now :icon_mrgreen:. A Vulcan with Marshall tone stack and switchable between 2 and 3 stages. I was thinking on using it as a od channel in front of a little class d amp instead of as a stompbox, so the switch is pannel mounted. Well, guess it woudn't hurt to make the board a little bigger and add the type switch :icon_mrgreen:
I'd be interested in the result. Do you plan to have a recovery stage after the tome stack? I figure it is probably not necessary since the output swing from the Vulcan stages is pretty large, so loosing some volume to a passive tone stack is no big deal. On the other hand, I like to have a little clipping after the tone stack. Adds flavor, when done right. But also means that a Presence control after the recovery stage is often a good idea.
Something I wanted to ask: When switching on or off with the Boss switching system, I get a click noise that sounds like "tp". Not very loud but just enough to be annoying. Like a faint capacitor charge/discharge pop. I figure it may be a design problem or a problem with the wire and contact impedances on a breadboard. Does anyone spot a design problem? It may be worth noting that it sounds the same when switching on as when switching off. Any ideas?
Cheers,
Andy
Initially, I was thinking of no recovery stage. But I don't know how is the volume output of two stages. The layout can easily fit a recovery stage, so I'll probably add the traces/holes but built it first without the recovery stage to see how things goes. For the presence pot, it already will have 5 knobs and 2 switches, so I think I won't add anything else.
I don't know when exactly I'll be able to build it, since I have to finish one or two layouts to etch everything at the same time, and also I'm probably missing some pots and the center off switch. But I'll post the results here as soon as I have something to show, and maybe do a layout for something like a 1590BB.
R11 at 0v instead of Vr Andy? I suspect that could just be a drawing error though, since you have been consistent with Vr for the output switch.
Quote from: aron on May 20, 2020, 06:39:05 PM
Insanity box!
https://aronnelson.com/sndz/inFull.mp3
Obsidian!!!!
https://aronnelson.com/sndz/obsidian.mp3
thats some pretty mean guitar for a keyboard guy ;)
Quote from: anotherjim on June 03, 2020, 05:05:03 PM
R11 at 0v instead of Vr Andy? I suspect that could just be a drawing error though, since you have been consistent with Vr for the output switch.
Yes, R11 should go to VR instead of ground, thanks for catching that. It is correct on the breadboard, so that is not the source for the pop. I'll change the schematic as soon as I can.
Cheers,
Andy
If it's still on breadboard, try to shunt D1/D3 with 10nF (or so) caps..
It might prevent popping by "slowing" diode responce..
I made some boards at OSHPark. They came in the mail today.
(https://i.postimg.cc/p5KsSQV3/DB98424-C-7105-4113-BC70-C1-A245913-C8-E.jpg) (https://postimg.cc/p5KsSQV3)
Quote from: antonis on June 05, 2020, 05:00:25 AM
If it's still on breadboard, try to shunt D1/D3 with 10nF (or so) caps..
It might prevent popping by "slowing" diode responce..
Andy has quite large RC slowdowns on the flip-flop outputs. What could be happening is that the FET gates really super high impedance and breadboard/wire capacitance is bypassing the slowdown direct from BJT to Gate or the Flip-flop is popping the supply and it's not getting in the audio via the JFETs at all. Either way, it might be ok on a PCB.
So I went to play with the values of the slow-down caps C18 and C23 only to find that the 47n ceramics I had in there were not connected to ground. Fixed that, the result being a reduction in noise but no cigar. The slight click is now only audible on switching off, no longer on switchin on. Changed both caps to 100n ceramics and got a much louder "whoop" upon switching. What's that about? I will start experimenting with smaller caps and see what happens.
Another thing is biasing of the Vulcan stages. As it is now, I need to adjust one of four resistors (R12, R13, R14, or R15 for the first and R20, R21, R23, or R24 for the second stage) depending on the transistor I use. That's OK for the breadboard and only a bit annoying for a one-off pedal. But I would like to make several of these, so I would really like to avoid this sort of thing. Unfortunately, even after reading lots of stuff about biasing common emitter stages, I have still not found a *general* explanation on how to design these things in such a way that I can make sure that it will always bias OK as long as the transistors paramters fall in a given range. Lots of simplified explanations out there that are based on assumptions that are invalid here. Does anyone know where to find an actual, full, detailed explanation on BJT common emitter biasing? One that does not skip the dreaded math? Thanks, that'd be great!
I tried "feedback biasing with ground leg" or whatever the scheme is called that the Big Muff uses because I seem to remember reading somewhere that this is less sensitive to hfe variations of the transistor. Unfortunately, it also sounds a lot less good in case of the Vulcan. I may experiment some more with that (especially adding an AC killing cap in the feedback to keep gain and input impedance high) but is it even true that this the better scheme for dealing with hfe variations. Usually the voltage divider biasing scheme is considered "the most stable" but it is rarely specifies what that is supposed to mean.
Cheers,
Andy
Help me understand the bias situation here. If I understand correctly we need enough current at the base to get 4.5v at the collector? Since the stages are AC coupled there need to bias each stage?
Finally put it into the box - with a little mod, of course. I have added this switch, so I can switch it between two and three stages, as Andy proposed. But I noticed that this switch produce oscillations (or some kind of radio receiving, not sure), so adding 100p capacitor between base and collector of Q3 fixed it. Another 100p at the same place, but on Q2 removed lot's of noise, so I left both in place.
(https://i.postimg.cc/21PbBXnX/IMG-20200607-133844682.jpg) (https://postimg.cc/21PbBXnX)
Quote from: soggybag on June 06, 2020, 06:09:41 PM
Help me understand the bias situation here. If I understand correctly we need enough current at the base to get 4.5v at the collector? Since the stages are AC coupled there need to bias each stage?
Yes, that is the situation exactly.
Quote from: rankot on June 07, 2020, 07:48:18 AM
Finally put it into the box - with a little mod, of course. I have added this switch, so I can switch it between two and three stages, as Andy proposed. But I noticed that this switch produce oscillations (or some kind of radio receiving, not sure), so adding 100p capacitor between base and collector of Q3 fixed it. Another 100p at the same place, but on Q2 removed lot's of noise, so I left both in place.
(https://i.postimg.cc/21PbBXnX/IMG-20200607-133844682.jpg) (https://postimg.cc/21PbBXnX)
Nice!
Andy
Finally got my boards in and got one stuffed. I knew it was going to be heavy, but I didn't realize it was this heavy :icon_eek: Great sounding circuit, thanks for sharing, Aron!
(https://i.imgur.com/aM03oat.jpg)
Ranko, Nathan,
how did you guys bias the stages? You did not just use the values from Joe's schematic and hoped for the best, right? On my breadboard I get wildly different voltages at the collector depending on the individual transistor I use. They all "work" in the sense that they all produce a distorted sound but changing the bias point has a HUGE influence on the sound. Just by changing the bias you can go from muffled drive through nice overdrive/distortion to splatty fuzz. I'd love to have that be less of a hit or miss situation without having to individually select transistors or resistors or add trim pots. Tighter specced trasistor types would be a solution but ideally, I would like to have the freedom to use a range of different BJTs and experiment with the sound changes.
Andy
Honestly, I simply used default values and some generic 2N5088 transistors, all parked around 350 hFE. Maybe a lucky hit, but they seem to work fine and I like the sound. It could be interesting to add some trim pots for bias adjustment, but it would be too big for my intended 1590A enclosure. :)
I plan to play with it a little, because it basically goes from heavy to heavier to absurdly heavy, but I just went with default values from Joe's schematic. I may try 5088 instead of 5089 like Ranko, the 5089s are a bit over the top :P
I'm not sure if a traditional bias for 1/2 way collector voltage is all that relevant. What's the collector swing versus base swing? You could rig up a pot across the supply (with maybe 10k series from the wiper) to vary a voltage into the DC side of the input cap and see what limits the collector can swing between?
It already has emitter degen resistors, but there are large value base resistors suggesting it's aimed at high hfe transistors.
Another question about the bias. The 4m7 and 1m resistors formdivider that sits at about 1.5v. The diode doesn't change that until the voltage at the anode is less than 0.7v?
The transistor doesn't really "see" the Diode Vf in the steady-state. That voltage drop is on the 1M side. For DC, the voltage drop across the emitter resistor (raising the base voltage) should ensure there is always enough voltage at the anode to keep the diode forward biased.
Am I the only one hearing some radio-like noise with both volume and gain pots maxed? The pedal is complete, I also put some HF bypass capacitors in parallel with B/C pins of Q2 and Q3, but I still have that kind of noise. Not much on lower vol/gain settings, but it increase with amplification. Maybe my layout is not good???
(https://i.postimg.cc/XXf1S31Q/Vulcan-OD-contrast.jpg) (https://postimg.cc/XXf1S31Q)
There are few changes between this layout and my final pedal - I removed that 100n cap which was mounted below the volume pot and connected it with a switch, as show in this schematic, so I can switch between two or three stages. Maybe this switch is causing the circuit to be more prone to noise?
(https://i.postimg.cc/9RWbcwnb/Vulcan-ema.jpg) (https://postimg.cc/9RWbcwnb)
Makes me think of a point made by PRR in another thread recently, a PN junction in series is a radio detector. A pF value cap across the junction stops RF getting demodulated there without affecting audio frequencies. Try 22pF to 47pF across those diodes.
Across diodes? Good idea, I will. Tried 5, 10, 22, 33, 47 and 100p across B/C pins, but it doesn't help as much as I expected, and it seems I that with bigger values I lost some of the shimmer too.
Does the position of the 2-stage/3-stage make any difference?
Another option would be that you're experiencing some crosstalk from the third stage when it's not being used. i've seen this in HiFi Preamplifiers where outputs that were left open would cause noise. That was fixed by adding a (fairly small) resistor (to ground) to the third stage output in case it's not connected.
With high gain effects you need to be careful with wiring and even how the switch is wired
Think about it
Two gain stages is non inverting overall
Three gain stages is inverting overall
High gain
feedback, one adds one subtracts
IIRC years ago Doug H posted about placing the input and output connections to a 3PDT switch to the outsides and the led to the middle for more spacing between the in and out.
Try to cross signals at 90 degrees if you need to cross them
don't run traces with signals that can effect the circuit stability parallel to each other(unless you want the circuit to be at the edge of oscillating)
You can couple signals with a double sided PCB if they align top to bottom (sometimes you can make a few pf cap)
Can anyone compare this (or even better the JFET version of this) to the BSIAB soundwise? I've built BSIABs in the past, but given them all away. Thinking about building another, but might do this instead if it compares favorably.
I've got a small bag of 20 year old J201 from Mouser and I know I'm not ever getting anymore of those, so I want to choose my projects wisely.
Quote from: dennism on June 09, 2020, 10:40:27 AM
Can anyone compare this (or even better the JFET version of this) to the BSIAB soundwise? I've built BSIABs in the past, but given them all away. Thinking about building another, but might do this instead if it compares favorably.
I've got a small bag of 20 year old J201 from Mouser and I know I'm not ever getting anymore of those, so I want to choose my projects wisely.
Socket them so if you decide they'd be better served in another project you can easily remove them with no worries of damage.
dave
Quote from: Gus on June 09, 2020, 08:41:50 AM
With high gain effects you need to be careful with wiring and even how the switch is wired
Think about it
Two gain stages is non inverting overall
Three gain stages is inverting overall
High gain
feedback, one adds one subtracts
IIRC years ago Doug H posted about placing the input and output connections to a 3PDT switch to the outsides and the led to the middle for more spacing between the in and out.
Try to cross signals at 90 degrees if you need to cross them
don't run traces with signals that can effect the circuit stability parallel to each other(unless you want the circuit to be at the edge of oscillating)
You can couple signals with a double sided PCB if they align top to bottom (sometimes you can make a few pf cap)
Quote from: niektb on June 09, 2020, 03:17:36 AM
Does the position of the 2-stage/3-stage make any difference?
Another option would be that you're experiencing some crosstalk from the third stage when it's not being used. i've seen this in HiFi Preamplifiers where outputs that were left open would cause noise. That was fixed by adding a (fairly small) resistor (to ground) to the third stage output in case it's not connected.
Yes, I know all that, but I had not much options when wiring my switch - it came as an add-on after the PCB was already made and it was very tight build (1590A). So I presume I will try to bypass diodes with some capacitance.
There is some difference in noise when I switch between 2 or 3 stages, but it maybe also due to different amplification factor. I will see if I have enough space to use DPDT instead of SPDT switch, so I can ground stage 3 input or output if it is not connected. Also, it was noisy even before this addition, but I'm not sure if it was the same or less.
I played around with the biasing scheme a bit. Specifically, I tested the original Vulcan's voltage divider bias with high gain (MPSA18, 2N5088, 2N5089) and low(er) gain (2N3904, 2N5551) transistors. As expected, the bias point needs to be adjusted between types to get near half supply at the collector. Without readjusting, there is about 4V difference at the collector betweeen a 2N5551 and an MPSA18. Interestingly, I get very tight groupings within the same type. I tested all the MPSA18 and 2N5089 I have (about 15 each) and for each of them, the variation of collector voltage without readjusting any of the resistors, was within half a volt. The MPSA18 are from three different batches, purchased from different suppliers. I don't remember where I got the 2N5089 but some are straight and some are bent legged. So it seems that dispite the huge span of hFE in the data sheets, in practice we can probably use the voltage divider bias without adjusting it to individual transistors, as long as we have set it right for the transistor type and the individuals don't scatter too much.
I also tried the dual feedback with AC shunting to ground. This works much better in terms of accomodating different transistors without readjusting the resistors; only about 2V difference at the collector betweeen a 2N5551 and an MPSA18. However, this configuration is much noisier (on my breadboard). Can anyone tell me why? The sound is pretty much identical to the voltage divider version.
I also mucked about with the switching to get rid of the clicking. Mostly I tried different values for C18 and C23. No luck there yet, still the same clicking. I am aware that worse thing happen to better people every day but this is driving me nuts...
Cheers,
Andy
Quote from: dennism on June 09, 2020, 10:40:27 AM
Can anyone compare this (or even better the JFET version of this) to the BSIAB soundwise? I've built BSIABs in the past, but given them all away. Thinking about building another, but might do this instead if it compares favorably.
I've got a small bag of 20 year old J201 from Mouser and I know I'm not ever getting anymore of those, so I want to choose my projects wisely.
Two different beasts. BSIAB gives you that marshall mid boosted mid to hi gain sound (like 80's and beginning of 90's hard rock guitar sounds). Vulcan is more modern sounding, more aggressive and have more gain (way more gain).
IIRC, the NPN Vulcan sounds better than the jfet one.
I just tried to add some small caps in parallel with diodes and it brought no change, but I also noticed that my noise's pitch is actually not so high - it is somewhere around 90Hz according to my oscilloscope. And that noise is absent when guitar volume pot is low or at zero.
Also, voltage at collector of all three trannies is at 5.8V with default values for passive parts. All are 2N5088 with hFE around 350.
Hi there,
revised version:
(https://i.postimg.cc/zbfV1hZT/OD707-02.png) (https://postimg.cc/zbfV1hZT)
I am now using BC550C transistors, which are usually easier to get than MPSA18 and I cannot hear a difference. Another reason for doing that is the tighter hFE specs on the BC550C, which makes consistent biasing easier. 2N5089 are a very close equivalent to BC550C and probably easier to get in some places but has slightly wider hFE limits. For the switching I went with BC337-40, although any BC337 should work. 2N4401 works as well and 2N2222 should do also. Probably even 2N3904. I changed the switching slow-down cap for Q4 (C24) to a smaller value after figuring out that the switching of Q2, which is then amplified by the gain circuitry, contributes to the switching pop. It is better now but not quite gone completely. Will keep on experimenting.
Cheers,
Andy
Ooh it's sounding pretty good now. I just built up one of the boards from OSH Park. I made one small mistake, the ground on the volume pot wasn't connected to anything. That was easily fixed. I used the schematic on the first page of this thread.
I used 2n5088 transistors with gains of 430 hfe. I get about 6.3v at the collector at each. Which seems pretty good. If I understand it correctly we want to bias at about 3/4 the power supply.
At times I here a faint high high pitched oscillation. It comes and goes. Could be the power supply, I'm using the One Spot and there is no power filtering. Could something else this thing has a lot of gain!
(https://i.postimg.cc/bs7TpRXx/539-C6104-B9-C7-40-D7-83-AC-EC201780-C711.jpg) (https://postimg.cc/bs7TpRXx)
I remember that "cutting ac feedback" from an escobedo schem. I still don't quite get it. The feedback resistor is divided by the miller effect so it appears smaller, does splitting it in two with a cap to ground make matters better, or worse?
Voltage divider bias is less variable because instead of having the base voltage determined just by base current and collector voltage (and the negative feedback between the two with beta), you have a somewhat stable base voltage to work with (still influenced by base current depending on the divider values).
I'm interested to know more about this building block, I've seen the vulcan before but haven't heard it. The diode is obviously throwing half of the wave in the trash, then that gets inverted and decoupled and the process is repeated. I guess there's no crossover distortion because there's only one diode, so no "coring out", just clipping and losing everything above -0,6V?
Anyway great thread everyone. Sorry for not quoting properly the messages I'm answering to.
Version 2 of my PCB. I added power filtering and wiring for the LED.
(https://i.postimg.cc/2b4Jg2jd/2681-C9-FC-6900-42-A5-973-F-30-FAB2-F3-A099.jpg) (https://postimg.cc/2b4Jg2jd)
Great circuit, almost 4 years ago I added a Rat filter knob and called it good. Here's 8 pages of material, including perf and Filipe's PCB layout plus a shitty 10 minute iPhone demo!
https://www.diystompboxes.com/smfforum/index.php?topic=116171.0 (https://www.diystompboxes.com/smfforum/index.php?topic=116171.0)
Finally got around to building up these boards from OSHPark and confirming that they work. I made the project public. If you want to build a Vulcan, you can order boards from OSHPark, looks like $13 for 3 shipped.
https://oshpark.com/shared_projects/UgsLvqqP
(https://i.postimg.cc/9rcCD5hz/662-B38-D1-3942-4611-9-A2-F-74-D00-D2020-E6.jpg) (https://postimg.cc/9rcCD5hz)
Picture of the latest build. Built and tested!
Here's a link to a build doc:
https://docs.google.com/document/d/1RZGN90AS7-ltEiKo_XSCzGfeI8s1LfxNiioncr-u75I
Looks like a great preamp building block lay out for a SS amp....
This sounds so good I had to make another! Some build process pics.
(https://i.postimg.cc/d740bVCh/0-C6-B1-BB5-7-DE1-486-E-B7-EA-2-F50-F98-C858-E.jpg) (https://postimg.cc/d740bVCh)
(https://i.postimg.cc/NygMCHKh/5-E7-D39-E1-FE16-47-AE-AE24-535-AF27276-EB.jpg) (https://postimg.cc/NygMCHKh)
(https://i.postimg.cc/JD0hMC3P/5-E86-F642-04-AD-4978-9-DDD-7-AEBC46-B29-E9.jpg) (https://postimg.cc/JD0hMC3P)
(https://i.postimg.cc/bS2NS0Bn/765032-CC-BB6-D-4-BF0-9533-A3-BE09700-FEA.jpg) (https://postimg.cc/bS2NS0Bn)
(https://i.postimg.cc/3kQWp67x/897-C3-ED2-397-A-417-B-88-E1-BE25153-F6-A62.jpg) (https://postimg.cc/3kQWp67x)
(https://i.postimg.cc/G4PtjQhJ/CAC87-D4-C-6-F1-A-4597-A2-D2-5829-B7052480.jpg) (https://postimg.cc/G4PtjQhJ)
(https://i.postimg.cc/vgKZm23M/FEE330-C3-F7-B6-460-C-B618-3224-DC15-C706.jpg) (https://postimg.cc/vgKZm23M)
Considering doing it with BC108A, just for the look mainly ;-)
Ben