# Depot Fuzz (EQD Terminal Fuzz)



## Kroars (Nov 1, 2020)

Hello,

Is there a preferred hfe range for the two 2n2222’s and one 2n3904?
Thanks!


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## stevtron (Nov 4, 2020)

On my PCB is it printed as 2N222A not 2N2222 , it`s a missprint I guess - right ?


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## Robert (Nov 4, 2020)

The person who traced the board listed 2N222A not 2N2222A.  They were in a TO-92 package and the pinout was backwards compared to a 2N2222A....  

So, they are listed as traced, 2N222A and the pinout is printed on the board because of the uncertainty.

I had no luck finding a "2N222A" so I used 2N2222A installed backwards for prototyping and it worked great.   
 This will be noted in the build docs.


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## stevtron (Nov 4, 2020)

Perfect ! Thanx for the explanation !


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## DigitalZombie (Nov 9, 2020)

I noticed what might be a couple errors with the Schem/BOM. The Depot/Terminal is basically the Shin Ei Companion With Booster from GGG with the addition of a "Voice" control in the notch filter (which running though the Tone Stack Calculator on the web doesn't seem to do all that much). I believe C3 should be 47n, not 4n7. Also C9 is flipped from how it looks on the GGG schem, but I'm uncertain how much impact this will have. I don't have Terminal in front of me to trace but I'm suspicious that EQD would bother to make those changes.


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## Robert (Nov 9, 2020)

The circuit was traced from the photos in this thread on FSB.    The capacitor in question was listed as 472, so unless that was an error it's correct.

I've built it and the Voice control definitely works.


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## DigitalZombie (Nov 9, 2020)

I still have a hunch that 472 is an error. You can't read the marking in the photos provided, but you can see the massive physical difference compared the the 222 next to it. Just a hunch, though.


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## chongmagic (Nov 13, 2020)

Here is the plastic version of the transistor on Small Bear.






						Transistor ATP2222A
					

Small Bear Electronics DIY Parts




					smallbear-electronics.mybigcommerce.com


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## Chuck D. Bones (Nov 13, 2020)

I look forward to seeing the schematic.


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## Jimbaaaab (Nov 20, 2020)

Robert said:


> The person who traced the board listed 2N222A not 2N2222A.  They were in a TO-92 package and the pinout was backwards compared to a 2N2222A....
> 
> So, they are listed as traced, 2N222A and the pinout is printed on the board because of the uncertainty.
> 
> ...


When you say ‘installed backwards’, do you mean the leg closest to the little tab on the component should be in the collector hole on the PCb and not the emitter? I just completed the build and it doesn’t sound even close to the Terminal, so I must have made a mistake. Thx in advance.


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## ferdinandstrat (Feb 9, 2021)

Robert said:


> The circuit was traced from the photos in this thread on FSB.    The capacitor in question was listed as 472, so unless that was an error it's correct.
> 
> I've built it and the Voice control definitely works.



Hey dude, I built the pedal with the 4n7 and it just sounded off, weak and lacking gain all around. Switched the 4n7 to 47nF like DigitalZombie suggested and pedal was brought to life


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## giovanni (Feb 11, 2021)

This is one of my next builds, I would like to make sure I get it right. I’m also not sure I understand how to install the 2N2222A. The folks at Smallbear didn’t mention a different pin out?
Thank you!


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## giovanni (Feb 12, 2021)

I actually looked at the board again and it is clearly labeled. Shouldn’t be a problem. Any more thoughts about C3?


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## manfesto (Feb 16, 2021)

DigitalZombie said:


> I still have a hunch that 472 is an error. You can't read the marking in the photos provided, but you can see the massive physical difference compared the the 222 next to it. Just a hunch, though.


Gonna +1 this, I also think the OG Terminal may have a 47nF and not a 4.7 - I had a Depot Fuzz I never boxed because it was lacking in gain and body until about 9 or 10 on the “Fuzz” knob (tried with metal can 2N2222s and flipped plastic 2N2222s, same results), but after reading @ferdinandstrat ‘s post I tried it with a 47nF and all of a sudden it’s gainier and properly thick and what I was expecting this thing to sound like based on the demos.

EffectsLayouts also has a 4.7nF on their BoM and schematic, but I’m assuming they’re working from the same FSB trace


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## giovanni (Feb 16, 2021)

If I understand the schematic correctly (the first two stages are both collector feedback biased), the cutoff frequency of the high pass filter coupling the output of the first stage to the next is dominated by R3 and C3. If we pick 4n7 for the cap, this leads to something around 1.5KHz, i.e., most low frequencies are cut off. If we pick 47n, we get a more reasonable 150Hz. So once again, based on my understanding of the circuit, 47n seems to make more sense. Also makes me wonder if an event higher cap would improve the frequency response on electric bass.


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## DigitalZombie (Feb 22, 2021)

giovanni said:


> If I understand the schematic correctly (the first two stages are both collector feedback biased), the cutoff frequency of the high pass filter coupling the output of the first stage to the next is dominated by R3 and C3. If we pick 4n7 for the cap, this leads to something around 1.5KHz, i.e., most low frequencies are cut off. If we pick 47n, we get a more reasonable 150Hz. So once again, based on my understanding of the circuit, 47n seems to make more sense. Also makes me wonder if an event higher cap would improve the frequency response on electric bass.


I played around with the values of different caps quite a bit before boxing one up. Going higher than 47n for C3 didn't really do much. Increasing C5 from 3n3 however made quite the difference. I found a 5n6 to really give it some "umph" but anything larger sounded too boomy. I gave it to a friend to try out and the extra low end sounded great through a Fender but didn't play too well on a AC15. Going to try putting the two different values for C5 on a switch.


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## manfesto (Feb 22, 2021)

Anyone else notice the newest revision of the build doc?


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## peatpatrick (Mar 3, 2021)

I bought this pedal November 2020.  It didn't sound right and I realized the resistor values that were silk screened on the board are different then the values listed in the build document.  Which is correct?   for example  r11 in the build document shows 47k but the board says 1M.


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## giovanni (Mar 3, 2021)

I think the silk screen usually trumps the BOM?


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## peatpatrick (Mar 4, 2021)

giovanni said:


> I think the silk screen usually trumps the BOM?


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.


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## giovanni (Mar 8, 2021)

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).


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## giovanni (Mar 8, 2021)

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.


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## DigitalZombie (Mar 8, 2021)

peatpatrick said:


> 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.


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## DigitalZombie (Mar 8, 2021)

giovanni said:


> 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.


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## Hirti (Mar 8, 2021)

giovanni said:


> I think the silk screen usually trumps the BOM?


I was also wondering that. Pretty much all the resistor values printed on the PCB are different than the one in the BOM. Which values should I use? I bought the PCB in October of last year. @PedalPCB ?


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## giovanni (Mar 8, 2021)

Yeah I noticed the BOM. But I tried both values anyway. The more I think about it the more 47n seems to make sense.


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## Robert (Mar 30, 2021)

Confirmed.

Transistors are P2N2222A and C3 is in fact 4.7nF.


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## music6000 (Mar 30, 2021)

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 !!!


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## music6000 (Mar 30, 2021)

*There are 3 versions ,* *2N2222A TO-92,  P2N2222A TO-92 & 2N2222A TO-18 .*


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## Robert (Mar 30, 2021)

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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## giovanni (Mar 30, 2021)

Glad we figured this out before I started building


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## gasp (May 16, 2021)

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.


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## Robert (May 16, 2021)

Build doc has been updated / corrected.

The only component value that likely doesn't match your silkscreen is C3, which should be 4.7nF.


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## gasp (May 17, 2021)

Robert said:


> Build doc has been updated / corrected.
> 
> The only component value that likely doesn't match your silkscreen is C3, which should be 4.7nF.


Thanks for the quick response!


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## A2K (Jul 31, 2021)

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?


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## music6000 (Jul 31, 2021)

Yep, just flip it!


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## manfesto (Aug 1, 2021)

A2K said:


> 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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## NSJ (Apr 7, 2022)

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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