Monolithic Fuzz Oracle

[johnk]

yep, both are AC128's (PNP) with just about matching hfe's around 100.

[GSoave]

Hey IvIark, I think that, maybe would be great you put the johnk's layout on your site. Only if he's ok with that, of course. That is a great layout, and probably will help and interest a lot of people, like helped me.

[johnk]

that's fine with me.

[rocket88]

Hey John, or anyone else out there got a question. I finally had time to make this and I ran out of 4.7pf caps. what would be a good substitute? Should I take 2 2.2pf caps and use them together, effectively making it 4.4pf or the next closest cap I have is 10pf. What will changing this cap value do to the gain control?

[johnk]

I put two 10pf caps in series on mine. that makes it 5pf.

[rocket88]

Ahh, thanks. I completely spaced and forgot that running caps parallel halves the capatance.

[johnk]

my bad. actually in series halves it, in parallel doubles it. you could just use a 10pf in place of the 4.7pf one. I really doubt that you could tell the difference at that tiny of a value.

[rocket88]

Oh..... crap. I just built it with 2 10pf wrapped together (parallel?), and the thing is insane. I love it actually, but to say the gain pot is useless is an understatement. Could essentially having a 20pf cap in place of the 4.7pf be causing the problem?

As a side note, I'm waiting for some ac128's to come with ~100hfe like you used, so in the meantime I'm using Russian MP41A with hfe ~80 and it sounds fantastic. Smooth, deep, warm, fuzzy goodness.

[johnk]

that 20p cap (in your case) wouldn't effect the gain at all and the tone very much. it's just a bypass cap for the 470K so it would probably just be a tiny bit brighter.

[rocket88]

Hmmm. It must not really be noticeably brighter, cause there is nothing bright about this monster. With the gain mod, how effective is it now? Any suggestions as to why its not usable?

[johnk]

rocket88 wrote

With the gain mod, how effective is it now? Any suggestions as to why its not usable?

it's a lot better with the gain mod. the way that the original gain control was wired was a poor (and IMO, failed) attempt at simulating the volume control on your guitar's output and it really did almost nothing to control the gain.

[rocket88]

I figured out my problem. I accidentally grabbed a 1K reverse log instead of 1M reverse log. I must have put it in the wrong bin while putting it away. I feel so stupid for not checking that first.

BTW, john i got the GammaRay the other day. I absolutely love it, and proud to have it, especially since I have #3 .

[johnk]

rocket88 wrote

I figured out my problem. I accidentally grabbed a 1K reverse log instead of 1M reverse log. I must have put it in the wrong bin while putting it away. I feel so stupid for not checking that first.

that happens to the best of us.

rocket88 wrote

BTW, john i got the GammaRay the other day. I absolutely love it, and proud to have it, especially since I have #3 .

glad to hear that you dig it. your's was built with three others at the same time. here's a pic of the prototype and #'s 3-6:

[rocket88]

Love the sounds, and growl from it. Nice to see mine with her siblings.

[boratto]

This the best Fuzz i´ve built so far!!!! Oh God, thanks!!!
BUT, i have built the original version (dont´see the MOD GAIN), and really it´s gain is almost unusable.  I will gonna try another one with GAIN MOD.
I notice a bit of low HUM... when using a 9 DC Adaptor. Is there a way to get rid f this?

[rocket88]

The gain mod is totally worth it. Now it can go from sorta overdrivey to full on gnarly fuzz. Definitely one of my favorites. Since it's PNP i just use a 9V battery and have 0 hum. You could take and use the offboard pump to allow you to daisy chain it, and might get rid of the hum. It could also be the power supply itself, I know a few people have that issue due to the power supply. Also, what transistors did you use?

[boratto]

I know my power supply is so so. But i got in my mind, if it can work with crappy power suply, that it will be an unbeatable beast.
In your suggestion, but that way i must change the trannies for NPN?I ve used a MP40 for the low hfe and a sft323. I´ll post a project of a cut on (60 to 100 hz) by trimpot project on requests. Take a look, and gimme a feedback.

[rocket88]

If you want to change it to npn you'll need to do a lot of changes to the layout. You'll need to reverse the polarity of any electrolytics, and the power going to the board will be +9V. To do what I said all you need to do is change the power from the jack. Power from the jack goes to the daughterboard then then -9V from the daughter board to the main board. Also, I would use higher hfe transistors. In mine I have mp41's that are around 90-100hfe, and I know john's are 100hfe.

[squirrels]

I know this is an old thread but I built this one up using the modified gain layout. It fired right up but the switch didn’t work.  I noticed two differences in the layouts. John’s layout uses a 680r resistor while Mark’s uses a 68k. Switch 5 goes to tone 3 on John’s and tone 1 on Mark’s. After swapping the resistor and switch connection it sounds great and works as it should. I’m using an AC125 with around 113 Hfe for Q1 and a 2N404A measuring around 295 for Q2. It sounded pretty good with more of a Fuzz Face set as well but I preferred the higher gain in my build. This ones a beast and the gain mod works great. Thanks John.

[Mulekicker]

I built the main page layout the other day coincidentally and it sounds great. I used 2 Japanese 2sb176's at 136 and 167 hfe. I'm gonna order a higher gain q2 just to see what happens but I love it as is.. I didn't think to check this thread, maybe I'll build John's layout too and compare em.