Shaka Braddah III

Started by SoV, October 05, 2012, 10:43:30 AM

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SoV

Hey all,
I'm new to the forum, so forgive me if the answers to this are somewhere already and I haven't found them yet.  I just finished my build of the Shaka Braddah III.  I noticed after I finished that I wired the MOSFET/diode arrangement a little differently than schematics that I found later.  Are there any sound samples out there so I can compare mine?  I haven't had much luck googling.
Mine goes from almost completely clean to heavier overdrive than I'll ever want with a good overall tonality.  However, I feel the overdrive to me seems to be more like a fuzz than what I tend to think of when considering an OD.  It seems to overdrive at the attack of the note and quickly fade away to a clean note as it's held, much like a fuzzface on lower fuzz settings.  Has anyone else found this to be the case with their builds?
Maybe that's the way it's supposed to work, but considering it's a tweaked booster, I was expecting something a little different....IDK
It sounds really cool as is, but like everything else I've built, I wonder if it could sound better.... :icon_wink:
Thanks!

SoV

Re-reading my post, I realized that I didn't really ask what I was intending to ask.  What I am really wondering is if it's worth it to rewire it to what I've seen later or if it will act the same way.  Now, I have it wired so that both diodes go to ground off the MOSFETS.  What I've seen is that one diode goes to ground off the source of the first MOSFET and the other MOSFET goes to the ground through the gate/drain tied together (like the Shaka IV w/mods by Doug Hammond). 
Thank you for any input

Keppy

If I understand you correctly, the way you have it wired gives you symmetrical clipping, whereas the other way will give you asymmetrical clipping (with slightly less headroom on one side of the waveform). This makes a noticeable difference in every circuit I've tried it in, though I've never built a Shaka. IMO, it's worth setting it up the other way just to hear the difference, but you'll want to set it up so you can A/B the two to be confident of what you're hearing and choose your favorite. I don't know if it's what you're looking for, but it should be noticeably different.
"Electrons go where I tell them to go." - wavley

SoV

ah, I usually associate asymmetrical clipping with odd numbers, or mismatched pairs.  How does this occur with an even number?  I don't think I would ever thought of that.  I agree that I've found asymmetrical clipping to be different when testing things.
Thanks for your input.  If I get time, I'll try it out. 

Keppy

Well, I might be misunderstanding you. The common MOSFET-germanium setup I've seen has a single diode wired to one of the MOSFETs for asymmetrical clipping, and I thought that's what your were asking about. It would help if you could draw a diagram.
"Electrons go where I tell them to go." - wavley

aron

> It seems to overdrive at the attack of the note and quickly fade away to a clean note as it's held, much like a fuzzface on lower fuzz settings.  Has anyone else found this to be the case with their builds?

It shouldn't sound like that. It sounds like something is mis-biased.

SoV

Hey Aron
Thanks for reply.  Maybe quickly wasn't quite the right word, but there does seem too be more overdrive on the attack.  Do you have voltage reading I can check?

SoV

How do I insert the image of the drawing I made to show how I wired the mosfets?  I can't figure it out    :icon_redface:

aron

The op amp part is totally standard. VR should be 1/2 V+. After that the FET minibooster is self biasing as well. Check your drain measurement on the bottom FET of the minibooster and your VR voltage.

aron

BTW: the SB3 is an old design. My newest and most used pedal ever is based off the Shaka HV. It's the best sound I've gotten and I use it on my analog pedal boards.

aron

I should add that I suppose if I were to fool around with the SB3 again, I would probably revoice it a little with my current setup.

SoV

Thanks Aron,
I'm gone for the weekend so I won't have time to check anything, but hopefully I can on Sunday night.  I'll post them then.
BTW, do you have a mental picture of what I was trying to explain about the way I wired the MOSFET/diode arrangement?  I have a drawing scanned in, but don't know how to post that....

SoV

Sorry this took so long.  It ended up being a really busy couple weeks.
This is what I have for voltages on the TL071 from pin 1 to 8 with a brand new battery at 9.74V:

.15
4.75
4.54
0
.15
4.75
9.49
0

for Q1 and Q2 respectively:

G: 0.0
S: .17
D: 4.99

G:  4.47
S:  4.96
D:  9.4