15 years ago - Vulcan

[antonis]

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..)

[Fancy Lime]

Hey boys and girls,

this is the glorious mess that lives on my bread board these days:



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

[antonis]

Don't quote me on the values, I haven't checked the schematic for errors

OK.. when you're ready, just let us know.. 

[Fancy Lime]

Don't quote me on the values, I haven't checked the schematic for errors

OK.. when you're ready, just let us know.. 

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

[Marcos - Munky]

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?

[rankot]

Hey boys and girls,

this is the glorious mess that lives on my bread board these days:



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!

[antonis]

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..

[Fancy Lime]

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

...

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

...

@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

[Marcos - Munky]

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 . 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

[rankot]

...

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!

[Ripthorn]

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...

[Fancy Lime]

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 . 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

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

[Marcos - Munky]

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.

[anotherjim]

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.

[pinkjimiphoton]

Insanity box!


https://aronnelson.com/sndz/inFull.mp3


Obsidian!!!!
https://aronnelson.com/sndz/obsidian.mp3

thats some pretty mean guitar for a keyboard guy

[Fancy Lime]

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

[antonis]

If it's still on breadboard, try to shunt D1/D3 with 10nF (or so) caps..
It might prevent popping by "slowing" diode responce..

[soggybag]

I made some boards at OSHPark. They came in the mail today.

[anotherjim]

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.

[Fancy Lime]

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