D*A*M - Fleshhead  [traced]

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phibes
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Post by phibes »

Electric Warrior wrote:
phibes wrote:Not 100% percent but this is how it looks from the gut shots on the net. Buddy above said it sounds good so what the hell. Go nuts!
That looks great. What software did you use to draw the schematic?
Copy and pasted stuff off fuzzcentral and shifted things around in paint. I just downloaded ExpressSCHc via sounsonics recommendation in another thread and I love it. Maybe I'll redraw it for more sex appeal.

Transistor recommendations would be to use what you would in a MKII.

I'd throw in for the wide board, I'm running low.
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Post by neoflox »

Thanks for the layout Phibes. Works great. Best sounding thing I ever build. Props to DAM.

Transistors used: AC128 (Q1: 85hFe, Q2: 75hFe, Q3: 105hFe)

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Post by greenskull »

Thanks for sharing this! Just slapped this on the breadboard and liked it better than the Burns Buzzaround circuit I played around right before. Only thing I might change is making the 10k resistor going to ground between input cap and base of Q1 a bit higher. Raising it back up to the Tonebender 100k value gives you the incredible sustain you would expect. Something in between might be a good idea.
Also what's the official verdict on the one resistor: 470 or 820 ohms? Either sound about the same to my ears. :thumbsup
fuck smooth tone, fuck eric johnson - Seiche

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Post by phibes »

820R will be a tad louder. Personally I would use 1K.
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Post by Kollaps »

I could use some help figuring out what I'm doing wrong.

Symptoms:
Picking up tons of rf, even when boxed and closed
Fuzz is horrifically gated and, well, shitty sounding (sounds like a large bee farting)

Details:
Both R1 and R4 are 820ohms
I'm using phibes layout
The transistors I'm using are good and within the gain ranges

Here's the weird thing: when I press down on the first transistor while connecting it's collector and base with my thumb, I get a beautiful, sustaining fuzz with minimal noise and no rf.  In short, the problem disappears as soon as I sandwich Q1 between my thumb and index finger.

Anyone have any ideas whats wrong or remedies for this? 

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Post by Kollaps »

I should also note that I've switched positions of q1 and q2 with identical results. I've also used the filtered power option, all transistors read 0 leakage according to my Peak meter, I've resoldered the board in case of bad joints, and checked for solder bridges.

Don't know how much of that is useful for this situation, but there you have it.

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Post by phibes »

What transistors are you using exactly? I wouldn't recommend zero leakage. You need leakage to help the bias. Sounds like the problems elsewhere. Triple check everything. It's probably something simple.
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Kollaps
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Post by Kollaps »

Nte126As--they are the equivalent to oc75s. I have some nte102As (oc81d) equivalents, but they are pretty leaky--as in .15mA and .21mA on the peak meter.

Could it be R4? It's strange--people say not to handle GE trannies, but despite handling these things ad nauseum, they read exactly the same on the Peak each time for hFe and for leakage. :scratch:

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Post by Kollaps »

Triple and quadruple checked--Im gonna see about reboarding it today and hopefully that'll work, but if not, any other guesses?

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Post by Kollaps »

Okay, I'm pretty sure it's a biasing issue. The tone control on the guitar does squat with it, and the effect has no audible level soon as the volume control is turned below 8 on the guitar as well. I've heard the 8.2k resistor is a good place to adjust the biasing--how big should the trim pot be? 20k seems to be a popular choice, but I don't have any of those on hand--would a 10k or 30k suffice?

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Post by phibes »

Drop the 47K on Q2's collector / Q3's base for a 100K trimmer. Also try some transistors that have some leakage.

Any photos of your build?
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Kollaps
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Post by Kollaps »

I'll take some photos if the suggestions you mentioned don't work out, only because most of the project was done using spare parts (ie an enclosure that was kinda mangled and too small, some enclosed jacks that were on sale, a toggle 3pdt switch instead of a pushbutton, etc) and I'm hoping to replace them along the way. The wiring is very tidy though, and the connections are very solid--suprising considering the limitations of the enclosure.

I'll let you know how those recommendations work out though--what voltage should I be shooting for using the trimmer? 4.5? And should I still be using it between q2 and q3 even though the issue is resolved by pressing q1?

Thanks for the help, phibes!

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Post by phibes »

The whole thing with touching the transistors is beyond me. The trimmer will take care of the bias if that's going wrong. You'll probably want to shoot for 6-7v on Q3's Collector but most important, let your ears make the final position and then mark down the sweet spot for future reference. Especially with the low leakage transistors. You might be real surprised at the number you'll see on the sweet spot!

May I recommend breadboarding before constructing for next time when using Germs? :popcorn:
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Post by Kollaps »

Using a 50k I had on hand gets me to about 4.3v, so at least I know for sure that it's was a biasing issue for sure now--I'll run by later and pick up a 100k trim to see if I can get up to that 6-7v. And you're right: on my drag'n'fly, I was quite pleased with the sound of it at about 7.3v, so I guess I'll see how that turns out. Regardless, thanks for the help and heads-up phibes! :thumbsup

I need to build one of those beavis boards, as my breadboard and I have a very tumultuous relationship as things stand right now. Many times I've thought things were cool between us and we were on the same page, only to find out later that it wasn't working out, and that I'd be on my own when I really couldve used it's help. :wink:

Thanks again!

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Post by Whoismarykelly »

phibes wrote:The whole thing with touching the transistors is beyond me. The trimmer will take care of the bias if that's going wrong. You'll probably want to shoot for 6-7v on Q3's Collector but most important, let your ears make the final position and then mark down the sweet spot for future reference. Especially with the low leakage transistors. You might be real surprised at the number you'll see on the sweet spot!

May I recommend breadboarding before constructing for next time when using Germs? :popcorn:
When you touch the transistor your finger heats it up which increases the gain of the device. This can bring it into the ideal range for whatever bias value is in the pedal.

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Post by phibes »

Makes sense!
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Kollaps
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Post by Kollaps »

Whoismarykelly wrote:
phibes wrote:The whole thing with touching the transistors is beyond me. The trimmer will take care of the bias if that's going wrong. You'll probably want to shoot for 6-7v on Q3's Collector but most important, let your ears make the final position and then mark down the sweet spot for future reference. Especially with the low leakage transistors. You might be real surprised at the number you'll see on the sweet spot!

May I recommend breadboarding before constructing for next time when using Germs? :popcorn:
When you touch the transistor your finger heats it up which increases the gain of the device. This can bring it into the ideal range for whatever bias value is in the pedal.
that's what I thought, but I thought the heat transfer would take longer than being instantaneous, and thought the cooldown wouldn't be instant either. Also, when running the Peak meter, I would run tests while holding the trannies and while not holding them, and they'd read the same. [smilie=a_whyme.gif]

Do they really heat and cool that fast??

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Post by DaveKerr »

Kollaps wrote:I've heard the 8.2k resistor is a good place to adjust the biasing--how big should the trim pot be? 20k seems to be a popular choice, but I don't have any of those on hand--would a 10k or 30k suffice?
On this circuit and its cousin the MKII I like to throw a 4K7 or so resister in series with a 5K pot and drill a spot for the extra control.
... multiple LFO waveforms (saw up, saw down, triangle, square); a more flexible envelope with attack/release controls as well as inverted envelope. I am afraid it will have more knobs than the TGP annual convention - frequencycentral

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Post by Whoismarykelly »

Kollaps wrote:
Whoismarykelly wrote:
phibes wrote:The whole thing with touching the transistors is beyond me. The trimmer will take care of the bias if that's going wrong. You'll probably want to shoot for 6-7v on Q3's Collector but most important, let your ears make the final position and then mark down the sweet spot for future reference. Especially with the low leakage transistors. You might be real surprised at the number you'll see on the sweet spot!

May I recommend breadboarding before constructing for next time when using Germs? :popcorn:
When you touch the transistor your finger heats it up which increases the gain of the device. This can bring it into the ideal range for whatever bias value is in the pedal.
that's what I thought, but I thought the heat transfer would take longer than being instantaneous, and thought the cooldown wouldn't be instant either. Also, when running the Peak meter, I would run tests while holding the trannies and while not holding them, and they'd read the same. [smilie=a_whyme.gif]

Do they really heat and cool that fast??
I haven't used the peak but if the values aren't fluctuating when you heat the transistors with your finger either the meter or the transistor is not functioning properly.

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Kollaps
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Post by Kollaps »

Well, sure enough, soon as I try to replace the 50k trim with the 100k, it no longer works again. This thing will be the death of me.

I think I'm gonna give it a rest for a couple days--worked on it for 6 hours yesterday with very limited success. [smilie=a_whyohwhy.gif]

edit: thanks for the insight regarding the peak--I think it's the transistors. I wonder how common it is for the legs to break loose from the housing for the transistor. It would definitely explain a lot.

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