Depot Fuzz (EQD Terminal Fuzz)

Getting back to the 4n7 vs 47n, I simulated the circuit in partsim.com (an online SPICE simulator). I set fuzz, treble, volume to some fixed values and I played with the value of C3. With C3 at 4.7n, the frequency response has two "humps" around 250Hz and 3.9kHz, with gain around 17dB and 14dB respectively, and a -3dB notch around 1.2kHz. There is also a low frequency cutoff around 16Hz (-6dB). With C3 at 47n, the 250Hz hump becomes almost 36dB, the 3.9kHz hump 16dB, the notch +6dB and the cutoff goes down lower than 10Hz. So that explains the increased "humph" and gain when using the higher value cap. But the 4.7n gives an interesting frequency response. Is anybody able to compare to an original model to figure out how it's supposed to sound like? Happy to share the simulation to those interested (it's always possible that I made a mistake).
 
Disclaimer: SPICE simulations use small signal models, so they work fine for bandwidth and frequency response but they probably don't work as well for non linear gain/distortion. That's just to say that the 36dB boost that the simulation spits out is likely not the actual value you would measure in real life as the non linearity of the transistors might kick in before getting to that level of gain, and saturate/compress the signal.
 
I pulled them all out and put them back in according to the BOM and now it doesn't work at all, so I think your right.
The current build doc is dated 2/16/21, so make sure you're using the right doc for your board. I have the old doc too and R11 is definitely 47k. It's part of the bias network to the last transistor and putting a 1M there would definitely make it not work.
 
Getting back to the 4n7 vs 47n,
FWIW, if you look at the most recent build doc, the boss here quietly changed C3 to 47n. I don't know if he got it verified somewhere else or what. I hope he reaches out to those who purchased the previous board to let them know about the change, as it is significant.
 
Yeah I noticed the BOM. But I tried both values anyway. The more I think about it the more 47n seems to make sense.
 
Let me see, 471 = 47pf, 473 = 47nf, 474 = 470nf, Oh wait a sec, 472 = 4n7 which is also 4.7nf!
Confirmed, your right, 472 = 4.7nf which is also known as 4n7 !!!
 
This is why there was confusion about the proper transistor part number. The original tracer marked the transistor 2N222A which doesn't seem to exist. The TO-92 2N2222A and PN2222A were the incorrect pinout.

P2N2222A (CBE) is the correct part / pinout.

The pinout is marked directly on the Depot PCB to avoid confusion.
 
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I think I spotted the issue with the BOM/build document (based on a board received this month, May 2021, and the build document revised 3/30/21) that was previously brought up. The diagram at the very top of the build document is the problem -- it doesn't line up with the schematic or the silkscreen.

I haven't double-checked every resistor, but it looks like R1 was mistakenly labeled as R11, and then R2-11 were labeled R1-10 instead.

Looking at the PCB and the schematic together cleared it up -- R1 is a 1M resistor connecting the input jack and two of the legs of the FUZZ pot to ground, and physically speaking it is located right above R100 (the LED resistor). The board diagram has the same resistor labeled R11 (which would be a 47k resistor).

I also checked R2 and R11 (according to the schematic) and they line up with the silk, not the board diagram at the top of the build document.

I'm competent enough with reading circuit diagrams but I 100% could have made a mistake, let me know. I'd love to figure out if I need to make any changes before I actually build it, but maybe I should try breadboarding it first at this point.
 
So I'm planning on building this and have read through this whole thread. While I'm glad this all got sorted, I'm left with 2 questions:

1) Can a 2N2222A be used instead of a P2N2222A (but with the orientation reversed)?
2) Going back to the OP's question...is there a preferred hfe range for the transistors in this circuit?
 
So I'm planning on building this and have read through this whole thread. While I'm glad this all got sorted, I'm left with 2 questions:

1) Can a 2N2222A be used instead of a P2N2222A (but with the orientation reversed)?
2) Going back to the OP's question...is there a preferred hfe range for the transistors in this circuit?
I’d also say socket C3; even though the original uses a 4.7nF cap, I’d venture a few of us in this thread definitely prefer the sound and gain with a 47nF.
 
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Just finished the build and have to say the 4.7nF is really weak. Even the gain structure is affected by C3. I tried a few caps and settled on a 18nF I had handy. The 47n was too much for my taste. Thanks to this thread it was a breeze with regards to the transistor alternates pinouts. Thank you all! 🙏
 
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