DIYstompboxes.com

Tonight breadboard experiment is the Shaka 5 (Thanks Jack @AMZ)
Its sounds good even with 2N7000 mosfet clippers.
I cant wait for the IRF520 to arrive.

Anyone built it?
Love it?
Hate it?
What's your fav mod?

Any preferred clippers etc.
I'm not mad keen on the tonestack so I might mod that.
Might just as well audition differant op amps while its on the breadboard too.

Kipper - haven't heard it.

Any chance you could toss up a sound clip??   Looks pretty interesting!  :)

Been playing around with an OCD sorta thing and mosfet clipping etc, not really the same but may as well throw in my 2c right?
Bought some CA3240 opamps, not all that cheap, but they sounded more pleasant than the tl072, ne5532 and opa2134 I tried - though that could just be me expecting that to be the case. They're Mosfet devices, so you have to be careful about static (not sure how that is inside the circuit, I've got another opamp in front of it with (perhaps unnecessary?) protection diodes and a resistor in front of it based on this: http://www.geofex.com/circuits/what_are_all_those_parts_for.htm). I feel like it's in the spirit of the circuit, too :P

Aside from that, maybe play around with series Zeners for clippers (they're kinda in a similar vein)? I think there's a page on them on AMZ, definitely some discussion around the forums (that's how I heard about it). I like 2.4V ones (the lowest I could find) but I've only played around with a few values in a couple of circuits.


Are IRF520s supposed to sound better than 2n7000s?

https://youtu.be/KqBINUl4Pik

Thanks for the clip, Kipper!  Nice sounding OD :)   You could play some AC/DC with that!   Tone control seems to have quite a big range, too.   Something for everyone.

Thanks Gibbo. It is really good. I'm tempted to use the midget clipping in another experiment.
Next on the list is Joe Davidson's obsidian and a few more from Joe
Cheers
Rich

I did a couple of Jacks suggested mods sounds even better to my ears (such as they are)
increased C5 to 10nf
Increased C5 to 100nf
I'm used the unused half of the op amp as a V bias buffer

yet to try;

Increasing C2. I fear this will muddy the low end.

Other op amps to TL072


Questions guys
I noticed from the oscope that the signal is inverted does the mini -booster?
Although ive seen signals inverted in other fet stage before I got it in my tiny brain that it depended on if the signal came from the source or drain.
but i could'nt figure out a reason why it would invert in this configuration.
Can anyone tell me a little more about this mini boosters configuration?
ie its name and a bit more on how it works, blah blah blah.

Thats all for now.


Here the schematic

http://www.muzique.com/schem/shaka5.gif


Rich

Very nice! It's been a while since I fired up my Shaka 3 - still have it. I use a lot less distortion now so will be interesting what the next "shaka" will sound like.

Thanks Think.   :icon_evil:
I haven't tried a series Zener yet, hmmm.


When did you make your Shaka 3 Aron ?

Looks like 1999!
http://www.diystompboxes.com/pedals/shaka3.jpg

>I noticed from the oscope that the signal is inverted does the mini -booster?...

The mu amp (http://www.geofex.com/Article_Folders/modmuamp/modmuamp.htm) is inverting. If that's not desirable, you could use the second op-amp to buffer and invert the output from the tone control - make a Shaka 6.

hhhhm I made a wiring mistake on the perf and I thik I fried both J201s.
I joined the blue smoke club too. My trimmer was glowing when I turned it and gave off the blue smoke.
First time I didnt use a socket Grrrr
I've replaced the Q1 jfet.
I think I'm gonna have to do Q2 too. The voltages are all wrong (compared to the breadboard)
I'm getting nearly 9v on the source.

Thanks Sam.
Mu Amp I cant get my head around it just yet. So I'll read the article a couple of times and see if i can take some in. I'll do some more reading too.
Cheers

Hi Rich- nice job on the clip. This one has grabbed my attention, there are a couple of builds in progress ahead of it, but hopefully it'll be on bread early next week. Thanks, and welcome to the magic smoke club.

Thanks Cozy I found the problem Q2 was back to front.
As you were.
All working now. It has a, i dont really know how to describe it but a nice sag. If thats what i mean.
I'll do some more this weekend. The three grandkids are coming for the day. Time to peel some spuds.

I'm contemplating using a Shunt regulated push pull as a replacement for the mini booster the one seen at the bottom of RG's article with noiseless biasing see here.

http://www.geofex.com/Article_Folders/modmuamp/modmuamp.htm
will this work with mpf102 2n5457 etc
looking to minimise usage of j201s at this time.


and changing the tonestack values

QuoteI'm contemplating using a Shunt regulated push pull as a replacement for the mini booster the one seen at the bottom of RG's article with noiseless biasing see here.

Good idea. A 470k or higher from 4.5v will do it.

Quotewill this work with mpf102 2n5457 etc
looking to minimise usage of j201s at this time.

I think you need a lo Vgs fet, below a 1.5v. Some MPF102 are above 4.5v.
Try BF245A, or high gain, low Vgs 2SK117.

mac

I'll check my stock fets data sheet when I get home and breadboard it thanks Mac

kipper - k30A jfets, with a funny pinout, are usually somewhere between j201 and 2N5457 specs. very bloody cheap, too.

Thanks Duck Arse
10 on the way. I tried every type of fet i have and j201s work best in the srpp on my breadboard.
Some where less than unity.
Now I'm wondering if the srpp can be done with BJT. I searched and googled but found nothing useful.

QuoteNow I'm wondering if the srpp can be done with BJT. I searched and googled but found nothing useful.

There is a NPN NPN Si Harmonic Percolator version, the Barge Concepts
IIRC, it's self biased with base to collector resistors.

mac

> Some where less than unity.

What do you mean by this?

I set up a srpp from the RG page linked above
used
560k from Vbias to gate of top fet
1k from top fets source to bottom fets drain.rvrvrv
100nf from top fets gate to bottom fets drain
output from the top fets source

i tried 2n5485 mpf102 j113 2n3819 j201 2n5457
the j201s and 2n5485 where the only ones that actually boosted the signal all the others had less than unity gain. I hope this clarifys things Aron

What are you thoughts on the mini booster in this circuit. Does it make a significant contribution to the sound.
What if i was to use a common or garden booster instead say an lpb1.
why the lpb1 because its low parts count as opposed to an op amp booster.
The circuit is fine as is the reason I ask is because im looking to reduce the amount of j201s in use

This circuit is on my breadboard now. Overall very nice, super responsive to controls, the tone circuit needs work though. The Shaka Syrup?
And its got some gain to it!!

(http://i1362.photobucket.com/albums/r688/russrutledge/Shaka%20SRPP/DSCN2602_zpsjobe0oor.jpg)

Sure to end up in a 1590a too, cozy?!!

Maybe an LB

try swapping that c5 (220pf) for a higher value, Im using 10nf you might like it better.

What value resistor are you using between the source and drain on the srpp?

Have you tried the srpp with other fets?
I'm trying to preserve my stash of j201s.

Why add the op amp gain stage after the tonestack? i would have thought the mini booster (srpp) should have plenty to push the stack without the need for the extra stage.

Is the tone stack better with a 10k than  100k?
As it is in the original schematic the highs are needlessly high and harsh for my rig. Fender pj.

Cosy you'd be lucky to get that in a 1590a even with 2n7000s rather than the lrf520's.

Hi Rich-
The resistor is 1K (Q2-S to Q1-D). The Op-Amp is to invert the signal to be in phase with the input, the volume there works real well.

The 10K pot works a lot better in the tone circuit- larger values give a dead spot in the middle. Its ice picky at max treble, and wooly at bass- definitely needs work. I forgot to draw in the coupling cap- I stuck a 100n between Tone and the op-amp, it smoothed the response a bit- maybe my imagination?

I just breaded it this morning, haven't had a chance to try other JFETs or the other component values other than the vol and tone pots. I'm sure this can be improved, you and Sam Hay had some good ideas to try, so I did, and was surprised at how good it sounded from the start. Thats not usually the case. There are certainly a lot of things that can be tweaked, I'm looking forward to it.

Oooh, a challenge for a small box build!

Looks good Russ, but you should probably put a cap between the tone stack and second op-amp or connect the 22k to Vref rather than ground. You can loose the 470k resistor to the (+) input too.

Thank you Sam- there is a 100n cap there now, I neglected to draw it in. Another mistake, the cap from Q2-G to Q1-D is 33n, not 100n. :icon_redface:

I'll remove that 470K on pin 5.

This is definitely a work in progress, nowhere near ready to box.

Quote from: Kipper4 on June 15, 2015, 12:32:18 PM
Thanks Duck Arse
10 on the way. I tried every type of fet i have and j201s work best in the srpp on my breadboard.
Some where less than unity.
Now I'm wondering if the srpp can be done with BJT. I searched and googled but found nothing useful.

rich - you should be getting bucketts of boost outta the srpp, esp w/ j201, maybe summink 'off'? I think joe davisson has done srpp bjt, maybe. mosfet too.

I do get loads of gain with j201 but all the rest bar one or two where not functioning in this circuit as I have it set up. Maybe I'll try again asap with a 4m7 resistor to Vb

There are bjt srpp they are even simpler in terms of parts basically an npn and pnp emitter to collector arrangement.
some include the srpp in the feedback loop of an op amp IIRC for stability.

I havent found a suitable mosfet alternative but I'm not done yet.
Just finishing up my directo-matic with an xlr conector then I'm gonna work on the corner freqauncies of the bmp tonestack with the duncan calculator.

Cosy I didnt bother with the op amp at the end of the circuit yet.
I've got lots of spare room on the perf for upgrades.
I did try bs170s for clippers but the lrf520s are better IMO
How do the 2n7000s sound?
I will try the 10k tone pot too.

Smoke me one, I'm on my way.

Bugger me  :( look what I just found thanks DA

http://www.diystompboxes.com/analogalchemy/old/ccsdrive.gif

Rich- Nice find! Always great to have the option to use 2cent transistors instead, will have to try these out.

Mine was gated, so I spent the morning on a quest to sort out the right bias combination. Its simple, just add the 1M resistor back in, to the ground side of the 100K trim pot to gate of Q1. Now on to reducing 60 cycle hum, adjusting the tone stack, and trying some component value changes.

I think I know the one.
Similar to Rod Elliot's fet srpp here note the power supply voltage.


http://sound.westhost.com/valves/preamps.html


Thanks Cozy I'm glad you like it enough to experiment with it.
The wife's not home till late tomorrow so I'll crank my amp a BIT and see how I like it then.

"It's not over until the drive sings"

I've been busy trying different things with the tone stack, and wound up with a modified SWTC-3. I think with these values it gives a good even response across its range.

This thing is sounding good, but still needs some work, it swells with higher gain settings. I tried down to 100K drive pot, which helped quite a bit, but there must be a better way.

This is the current circuit on my breadboard:

(http://i1362.photobucket.com/albums/r688/russrutledge/Shaka%20SRPP/DSCN2605_zpsiaybaziy.jpg)

Its easy. Add a cap at the output over a resistor to ground- mine has 100nF over 10K. Louder, takes care of the swell, it sounds good as is, lots of components you can tweak to get your own sound if you don't like it as drawn above.

Godam Cozy.
I never heard the hum on the test amp. It's there on a bigger amp though.
This could be a big headache.
How can it be that were getting this 60hz hum kinda sound.
I tried a B250k for gain and liked it.

QuoteBugger me  :( look what I just found thanks DA

http://www.diystompboxes.com/analogalchemy/old/ccsdrive.gif

thanks DA :)

mac

I like the 250K drive pot better too. I find the hum really distracting at higher gain settings with the 500K, less so with the 250K, the 100K just doesn't have quite enough grit on tap. Now, how are we gonna reduce the 60 cycle and still have gobs of gain?

High pass filter to get rid of the hum?

Tried the CCS last night with my daughter it was a fun little project to breadboard. It wasn't fantastic but could be improved with a few tweaks. I will probably remove the diodes and retest.  Had lots of gain but it didn't clean up well on low guitar volume. 

I replaced the 100n at U1a pin 1 with 56n, followed by 47R to ground, which got rid of most of the hum. And a lot of the volume. Tone was ice picky, very little bass, so I replaced quite a few things to see how much could be brought back. These were replaced:
1) the 33n feeding Q2-G with 100n
2) tone circuit components: replaced the 33K with 22K, 1n5 with 10n, and 22n with 33n. More usable now, but theres room for improvement.
3) the 500K gain pot with 1M.
4) 25K volume pot with 50K.

In total, these brought back a lot of the volume and tone, although theres still room for improvement. The hum is greatly reduced, so yes it was worth it.

I'll leave the 100 nf in and see if I can find a 20_30 ohm resistor for the hum filter.
Thanks again for the help. I'll try some more of your mods.

I'll post up some other links for you Mac

Heres the rub the hum must be introduced in the mini booster because it tried the high pass filter at output of the op amp, between the 100k trimmer and mini booster, and just before the tone stack. The only one that lessened it was the last and it sucked the life out of the pedal. All the output volume is gone.
Time for me to rethink.

I also moved the high pass to the beginning of the tone stack, reasoning that the harmonic generation in the SRPP was important. The trouble with the first location is this circuit turned into a great overdrive or treble booster, but killed a lot of what this pedal is about. Moving the high pass to the the tone side got it back, a great sound like the original without the 60 cycle hum, but almost no volume. Even with the 50K volume pot. I'll try a 100K there, but theres a better solution, we just have to find it.

So you think that the srpp does add character to the sounds of the pedal. Good.
Is this hum caused by DC getting out from the Srpp?
I would find this a little strange since the Srpp is dc decoupled by the 100nf into the tonestack.

So now im wondering if I should use a tl074 buffer the srpp output , (hum filter) and make two active notch filters ala thunderbird and a buffer or make up stage just before the output pot.

Thunderbird notch filters seern here just before the output

http://runoffgroove.com/thunderbird.html

Hut hum. Just tested the DC voltages either side of the tonestack decouplng cap.
4.5v going in 0 v dc coming out.
Conclusion The dc from the srpp is not causing the hum. The cap is doing what its supposed to. Where is this hum coming from?

Maybe this is a dumb thought but could you be getting that hum from your diodes?
All diodes exhibit a photoelectric effect but many are covered in black plastic to prevent this. The 1n34a is a glass body diode.  Try blocking all light to the diodes and see if your hum goes away.

No dice Whisky Tried it. Thanks for the thought though.

I thought the hum was 60 cycle, wiring on the breadboard picking it up and the high gain circuit amplifying. The high-pass kills it in the 2 locations I tried. The next step is to try the high-pass after the SRPP, then go into the second op-amp, then (as PRR says) do more pruning with the tone circuit.

I tried the filter after the srpp (my case the mini booster) I guess it might work with differant values but putting a 27ohm after the 100nf decoupling cap didnt do it for me.
I think the resistor is so small its letting all my signal go to ground. Maybe scaling it up mght work better.

The SRPP is not going to have great power supply rejection. Try the usual tricks with a small resistor in series with the supply and a big cap to ground on the circuit side of this.

I already have power filtering caps and am using a half of an op amp for v bias.
I'll try another cap closer to the srpp and a series resistor. meanwhile ill try it with a battery.

Rich,

- try an independent Vref for the SRPP,
- add a cap between the SRPP trimmer and the diodes/mosfets,
- another breadboard, or undo and start over.

mac

Here's the schematic I'm using

http://www.muzique.com/schem/shaka5.gif

The mini booster has its own v bias (2x 1M)
I'll try some of those it's still on the breadboard. (and on perfboard too)
I did change some decoupling cap, and some values in the tone stack but the rest is stock.

>I already have power filtering caps and am using a half of an op amp for v bias.
I would share your buffer v bias with the SRPP, it will be quieter than your 2 x 1M option.

>I'll try another cap closer to the srpp and a series resistor. meanwhile ill try it with a battery.
The series resistor can make a big difference. If it helps, but isn't perfect, you can always add 2 resistors with a cap in between. Just watch the voltage drop. You can tap off the supply before these for the op-amp to help with headroom there too.

Heres what I wound up with. By paying attention to the ground wires on the breadboard, the hum was substantially reduced. I think it will be fine once its in an enclosure.

(http://i1362.photobucket.com/albums/r688/russrutledge/Shaka%20SRPP/DSCN2609_zps3ar4riee.jpg)

Some SRPP stuff for you guys


http://www.ecircuitcenter.com/Circuits/pushpull/pushpull.htm


http://www.allaboutcircuits.com/textbook/experiments/chpt-6/class-b-audio-amplifier/


http://www.tubecad.com/2014/05/blog0291.htm


http://sound.westhost.com/valves/preamps.html

http://www.muzique.com/news/images2/mosfet2.gif

http://www.muzique.com/news/superhot-mosfet-boost/

http://www.tubecad.com/2005/February/blog0037.htm


http://champ.chips.jp/sonota3/booster2.html

http://www.geofex.com/Article_Folders/jfetdoub/mudoubler.htm

This too

http://www.muzique.com/amz/mini.htm

And here's an example of where I got the inverting/non inverting output theory from the like


http://www.diyaudio.com/media/files/articles/ampcamp1/ampcamp1_simple1_350.png

Quote from: Cozybuilder on June 18, 2015, 04:09:14 PM
Heres what I wound up with. By paying attention to the ground wires on the breadboard, the hum was substantially reduced. I think it will be fine once its in an enclosure.

(http://i1362.photobucket.com/albums/r688/russrutledge/Shaka%20SRPP/DSCN2609_zps3ar4riee.jpg)

Suggestion: to get a little more compression and extra harmonics replace de 1k resistors at the sources of the minibooster by 1.8k resistors.

Cheers.

Quote from: aron on June 11, 2015, 08:59:55 PM
Very nice! It's been a while since I fired up my Shaka 3 - still have it. I use a lot less distortion now so will be interesting what the next "shaka" will sound like.

The Shaka HV (the op-amp part) is great to overdrive anything. Simple and very effective.

TCA- They did just what you said, very worthwhile mod.

Rich- Good reading suggestions, thank you.

Yes, I still use a variation of it all these years.

Quote from: tca on June 19, 2015, 06:39:27 PM

Quote from: aron on June 11, 2015, 08:59:55 PM
Very nice! It's been a while since I fired up my Shaka 3 - still have it. I use a lot less distortion now so will be interesting what the next "shaka" will sound like.

The Shaka HV (the op-amp part) is great to overdrive anything. Simple and very effective.

I'm still working on this currantly experimenting with post distortion eq.

On the breadboard right now
Link to schematic earlier on in the thread
the basic Shaka5 IC1 and clippers (mosfet) right up to and including the 100k trimmer
Whats new
A 1uf decoupling cap after the trimmer.
then an active 3 band EQ based on the TL082 application data sheet (redrawn by RDV with Bias).


see here
IIRC page 9

http://users.ece.gatech.edu/~lanterma/sdiy/datasheets/opamp/TL082.pdf
only differnace is that the oppy is biased with 100k to VB on the non inverting input

Option 2
after the decoupling 1uf
The active EQ from the ROG Thunderbird (might need some tweeking to my taste)


see here
http://runoffgroove.com/thunderbird.html
the final 2 op amps

A lot let noisy than my attempt with the mini booster
Wish me luck
Rich

Did some testing this morning with the tl082 tone control. It sounds awesome and has lost little to none of that greasy mosfet clipping even without the mini booster.
I'd like to change some of the caps/ resistor in the control. If anyone has any advice on how the work out the frequency cut off for the tl082 filter please feel free to advise me.
Thanks
Rich

QuoteA 1uf decoupling cap after the trimmer.
then an active 3 band EQ based on the TL082 application data sheet (redrawn by RDV with Bias).


see here
IIRC page 9

http://users.ece.gatech.edu/~lanterma/sdiy/datasheets/opamp/TL082.pdf
only differnace is that the oppy is biased with 100k to VB on the non inverting input

:)

mac

I think I've found the formulas I need at least to do the TBird filters here

http://www.diystompboxes.com/smfforum/index.php?topic=110210.msg1010097#msg1010097

Rich- Good call on the TL082 tone stack. I tried it in a few different ways, including removing the SRPP, a second chip (blah blah woof woof), and finally decided to simplify and just replace the tone-stack. It really came alive then, the stack as presented below sounds very good, yet I plan to tinker with C & R values a bit and hope to improve the top and mid responses (at least to my tin ear). The 60 cycle hum is reduced significantly compared to the SWTC-V3 that was in there before.

Here is what is on the breadboard now:

(http://i1362.photobucket.com/albums/r688/russrutledge/Shaka%20SRPP/DSCN2632_zpsudlzsht8.jpg)

Russ.
I cut the SRPP from the design as the distortion circuit upto that 33k has enough u mph to drive the stack.
I left in the 100k trimmer from the original design (where you have the 33k)only difference is it is now a pot (level) and tagged on my tone stack after it with a decoupling cap 100f

Thus far
Errata.
R7 100k
R13 3k3
R14 1k8
and the second 1n34a diode on the second mosfet clipper should be above it not below(see Cozybuilders schematic)
Treble pot should be 500k


(http://imagizer.imageshack.com/img912/4502/N7lS7f.jpg)

Hi Guys,

Love what you are doing with the tone stack but your diodes D4 and D4 are in backwards.
You might find it sounds quite a bit smoother if you reverse them. This is because all mosfets have a built in reverse polarity protection diode between the drain and source. This is what you are listening to at the moment.
Try it and see!

Cheers

sorry Q&D schematic you are correct D5 should be above the mosfet not as drawn.
thanks

edit :C10 is probably superflous too

Hi Rich,

What I am suggesting is to simply flip d4 (end for end) and put back in that way, and the same for D5. Try it, you'll like it!

Cheers
G

will do Thanks

sounds like silicone diodes. more gain/volume.

ok,

you have more volume because now you are hearing the mosfet distortion whereas before it was just the 2 diode pairs  in series.
At least now it is built as it was designed!

Cheers

how so sir?

http://www.muzique.com/schem/shaka5.gif

Another thought,

The mosfets have this intrinsic diode in parallel with the drain and source, only backwards, so if your d4 and d5 are backwards they force the signal through the intrinsic mosfet diodes instead of the drain/source junction, which gives you the different sound. I think I need to draw you a picture but I"m new on here and am not sure how....... I have noticed a few places where I have seen this circuit that have these diodes around the wrong way...

You might like to try out the irf510 fets instead of the 2n7000's for a different sound.   :icon_biggrin:

Pretty sure the muzique circuit is wrong too!

It's not rocket science!

In the 2n7000 current flows from drain to source. The intrinsic diode is wired anode to source/cathode to drain, which allows current to flow source to drain, if the drain/source channel is off (ie in a high impedance state).

Where is R.G when you need him!????!!!

http://www.diystompboxes.com/smfforum/index.php?topic=58843.msg458654#msg458654

btw I'm using LRF520s

(http://i12.photobucket.com/albums/a228/graeme58/mosfets_zpsq581q9ef.jpeg) (http://s12.photobucket.com/user/graeme58/media/mosfets_zpsq581q9ef.jpeg.html)

Hope this helps!

Still sound good the way we have it. Yes the character changes when the diodes are reversed .
If it's wrong how come nobody else picked it up in the last 15 yrs.
I'm not arguing just wondering.

>If it's wrong how come nobody else picked it up in the last 15 yrs.

It's not wrong, it's just one of several options.

http://www.diystompboxes.com/smfforum/index.php?topic=38581.0
http://www.diystompboxes.com/smfforum/index.php?topic=90474.0

Interesting. I had always assumed we were using the Mosfet internal diode as the clipper.

From the schematic I posted yesterday, a few R & C value changes, the most significant is the coupling cap from the Q2-S, I had 1uF, not 100nF in there, and that makes a huge difference in bass response. I tested down to 100nF, which kills the bass, 470nF brings it right back. In the tone circuit, like you I replaced 11K with 10K in the 3 Bass pot positions, in mid I changed 3K6 to 3K3 both positions, and for treble changed the 4n7 to 3n3, pot to B250K, and added a 330pF bypass to the pot (pins 1 & 3). So far, its sounding like a winner. 5 pots- don't see any way to stuff that in an LB, will have to look at 1590A instead  :icon_mrgreen:

Mosfets as diodes, not the internal diode, have a voltage drop of 1v -3v.
Has anyone compared a mosfet with a fet like mpf102, and leds of different colors?

mac

Yes, I know the Shaka 5 uses the internal diode. I just liked the sound more that way. Yes, I tried a ton of different configurations. I like series diodes the most.

I like it that way too Aron.
Thanks Sam I was looking for those all morning.
Maybe I'll put the diodes on a reverse ing switch and call it boost.
Thanks everyone for the input.
Some good discussion here.

Perhaps you'd like to expand on the series diode some aron. Where? Which? Polarity? Etc thanks

If you like the sound of the internal diode then why would you go to the expense of using the MOSFETS?
A cheaper alternative would be to stick any old diode in there and not bother using the MOSFET.
I don't think that there is anything special about the characteristics of the MOSFET intrinsic diode, but not too sure about that, will need to check.
That is why I suggested that there is a right and wrong way. Of course there is no right and wrong as far as musical taste is concerned!!

Don't get me wrong.
I'm grateful of your input Graemestrat and I'm sure i will put it to use in future.
I'm sure i read somewhere that part of the mosets character comes from the fact that it has a high capacitance compared to most others. Indeed when measured the capacitance was over 1nf on my little chinese tester.
I will probably test your theory and see if any old diode and a 1n34a combination sounds like too.
Every little helps when like me your on a slow learning curve after all I'm no EE. Everything I've learnt about pedals is mostly down to this forum thanks to guys like you willing to share there knowledge and take the time and patience and effort to educate us.
Tip my hat  :icon_cool:

Thanks for the kind words, Rich.

Quote from: Cozybuilder on June 25, 2015, 11:02:45 AM
Interesting. I had always assumed we were using the Mosfet internal diode as the clipper.

From the schematic I posted yesterday, a few R & C value changes, the most significant is the coupling cap from the Q2-S, I had 1uF, not 100nF in there, and that makes a huge difference in bass response. I tested down to 100nF, which kills the bass, 470nF brings it right back. In the tone circuit, like you I replaced 11K with 10K in the 3 Bass pot positions, in mid I changed 3K6 to 3K3 both positions, and for treble changed the 4n7 to 3n3, pot to B250K, and added a 330pF bypass to the pot (pins 1 & 3). So far, its sounding like a winner. 5 pots- don't see any way to stuff that in an LB, will have to look at 1590A instead  :icon_mrgreen:

Thanks Russ I'll try that maybe not in a 1590A though.

> If you like the sound of the internal diode then why would you go to the expense of using the MOSFETS?A cheaper alternative would be to stick any old diode in there and not bother using the MOSFET.


You are probably right. However, remember at the time when I was playing around with this, I didn't know that. I was still purchasing a ton of "matching" transistors from the local store (when I was purchasing the same type over and over).
I just liked the sound and to me, it sounded different than my usual 1n4148 clippers.


As for the series diodes, I use them like the original Shaka Braddah.
http://www.diystompboxes.com/pedals/shaka.JPG (http://www.diystompboxes.com/pedals/shaka.JPG)

Thanks Aron

Thanks Aron,

Please understand that I am not "having a go" at anyone, I just wanted to understand how you came to be using the mosfets if it wasn't for their (to me) interesting sound. (see ROG's many mosfet circuits).

While I was thinking about all of this I came to realise that I really like the enthusiasm of you guys, it inspires me to do more than I normally would and that can only be a good thing, so thanks for that.

The other thing I should mention is that I come from an engineering background where "design reviews" are the norm. In these we are expected to "nit pick" each others' designs in order to come up with the best design. So that is the mindset from where I am coming....I am not trying to be negative as such. hope you understand.

Cheers,
Graeme

No thank you for the clarification and explanation.
I learnt something and will try it.
I guess it was the Right/Wrong thing that threw me. No offense taken or given.
We are all sonic travellers on the road to tone.
Rich

Thanks Rich.

Oh yes, no offense taken. When the Shaka 3 came along, Jack was helping and feeding me all sorts of designs which I would try. He had a lot of ideas and I was ready and willing to try them. I never even knew about the "internal diode" at that time. I just connected things up and if I liked the sound, I went with it.

I see what you mean now Aron. Although i though for a while you were litterally using a series diode in the signal path not NFB style.
I have seen series diodes suggested by Jack in his clipping article.

QuoteI'm sure i read somewhere that part of the mosets character comes from the fact that it has a high capacitance compared to most others. Indeed when measured the capacitance was over 1nf on my little chinese tester.

Unused leaky germs, like bad ACxxx, have high internal capacitance too.
Or maybe a cap across the diodes, like in the Dist+.

mac

Really I never knew that Mac. Sweet bit of info.
I have lots of ac153 with low gain so that maybe an option.
I'll take a look at the dist+ too although I feel sure I must have already made one as a debutant.
Cheers guys

Edit: I see what you mean about the cap in parallel with the diodes in the dist +.
A similar thing is already used in the Shaka 5 too and the cap size does make a difference.
Note that Aron uses a 220pf and I'm using a 10nf.

Hopefully sometime this weekend I'll get to do a bit more.

Talking about caps, just an idea:


-----|<-----|<----- gnd
         |
-----||-----||----- gnd


----->|----->|----- gnd
         |
-----||-----||----- gnd



mac

I m having a high pitched squealing when the treble if flat out with this .
I tried a low pass filter 750 Hz Fc on the output I didn't fix it
Need some help and inspiring .
Thanks
https://http://imagizer.imageshack.com/img910/5274/19zyMT.jpg



(http://imagizer.imageshack.com/img910/5274/19zyMT.jpg)

I should add that if I reduce the gain (level pot) the noise goes and that there's a point in turning the level pot where it goes quite.

that schematic looks funny to me. So unhorizontallined.

Sorry the image didn't work

Here's a new one

(http://imagizer.imageshack.com/img537/4530/DcBMVt.jpg)

https://http://imagizer.imageshack.com/img537/4530/DcBMVt.jpg

A cap (maybe 100p) from output to (-) input of IC2B might fix the squeal. If not, I don't think it is causing the squeal, but R15 (and R 1) aren't helping, and I would jumper those.
If the squeal gets worse as you turn up the level then a cap across the level pot would be a good idea - 330p to 1n would be a good place to start.

Cheers Sam I'll try some of that. :)

Layout and wiring could be a cause of the squealing. 
Also a DPDT, 3PDT switch can bring the input and output too close together with some high gain circuits

Thanks Gus
I'll post up the layout although, I always try to keep good input and output seperated as you point out the switch could be an issue.
I'll report back
cheers guys

No Luck yet guys although I still have some of those bits to do.
I got to thinking and wondered what anyone thinks of the idea of moving the active tonestack between IC1B output cap  and The clippers.
I'll probably make the IC1B output decoupling cap  470nf while im at it.
I remembered reading some post talking about predistortion eq or have I got this wrong?
Cheers
Rich

I tried all the fixs Sam but to no avail.
Its sorted now. Note. I used an active James tonestack from boss FA1
I changed the NFB resistor in IC2b to 1k8.
How did  I arrive at this I kept turning the old level pot up until it started to squeel which was around the 2k mark. So I figured err on the side of caution and use he next value down i could think of.
Strange though since I'm using a R in of 10k. i thought the least value i would have to use would be a 10k (to make a straight buffer with a gain of 1) since I thought that op amps cannot attenuate. Don't ask me why I thought I rad it somewhere. So I found this a little confusing.
It all works now I just have to test it with the big rig then hopefully tidy up the board. Its had a bit of  bashing with all the mods i've been doing.
Thanks for the help guys. I'll post up a schematic once I'm done.
Rich

 I am using a half of an op amp for v bias.