# Carcass Fuzz / DOD Carcosa transistor selection



## MrSage (Dec 18, 2020)

I've been poking around trying to figure out my transistor strategy for the Carcass Fuzz that USPS swears is "currently in transit to the destination."

While I learn a valuable lesson about patience, I thought I'd start a thread to collect some resources on Carcosa transistors.

I few places have mentioned that transistors with high hfe (600+) resulted in unpleasant squealing, and that the sweet spot seemed to be ones with gain around 500 - 550. 









						DOD Carcosa
					

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						DOD Carcosa Fuzz
					

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						Booster, OD, Fuzz, Distortion - DOD Carcosa Fuzz - Verified
					

DOD Carcosa Fuzz - Verified. PedalPCB released a schematic of DOD Carcosa Fuzz over at FSB Couldn't resist to make a layout, will build this tomorrow. Cheers.



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As far as transistor choice, a few of the posts above mentioned that 2n5089s were a little too hot. 

A few alternatives mentioned: 

2N5088
BC109C
BC549C (lower gain; lower noise; not enough distortion)
So here are a few questions:

1) What transistors have people tried in this? What gain ranges have seemed to work best?
2) If I have a handful of transistors with varying gain, is there a recommended order I should put them in? (e.g., lowest to highest gain? vice versa?)

I'm going to socket everything, but wanted to tap into collective wisdom ahead of time.


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## mdc (Dec 19, 2020)

If the circuit is particularly sensitive to transistor specs, your best bet is to get a component tester like a not-_not_-expensive Peak Atlas DCA55 or one of the $20 ebay/amazon boxes, and sort through the NPNs you have on hand to see what works best. 

I like BC549Cs in most circuits where I've tried them and on paper they seem like they'd be a good fit, as would the 2N5089. Most of the 2N5088s I have seem to be more in the 200-400 range. BC109Cs have the added benefit of being metal can so they obviously will sound better because metal can.


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## Robert (Dec 19, 2020)

This is a new layout with improved trace routing compared to the first version.     

I don't believe there have been any reports of oscillation with this version _so far._

I built the prototype with 2N5088's and it worked great with no oscillations.


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## MrSage (Dec 19, 2020)

Thanks! I bought a super cheap multimeter with a transistor tester to sort through the transistors I have laying around... A bunch of super old 2n5088s that have hfe all over the map, including up to ~700 on a few!

Good to know that this layout seems to be pretty solid. 

USPS delivered the PCBs (finally!), but now they've rerouted my Tayda order that has all the 100nF caps I need... back to waiting and planning!


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## mdc (Dec 19, 2020)

The tester on your DMM will give you values that are useful relative to one another but it’s unlikely that you can trust them to the sort of pedal-world standard measurements which you’d get off of a DCA55 or using the RG Keen method. I wouldn’t trust the 700hfe you’re seeing on a DMM to equal 700hfe in pedal-world.


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## MrSage (Jan 12, 2021)

Bumping this back to top.

I fiddled around with a few sets of transistors yesterday, and I was getting oscillation with all of them when I cranked both the Before and After pots. I tried a few sets of 2N5088 and 2N5089 to start out. 

Does anyone know which transistors the production Carcosa uses?
Are they all the same, or are there different transistors / gains for each of the positions?
The only thing I could find in a quick search was Tom Cram saying they were "off the shelf / non-mojo" transistors, and a DOD engineer saying that they started with an FZ-1s on a breadboard... but nothing more detailed than that.



			https://www.thegearpage.net/board/index.php?threads/new-fuzz-pedal-from-digitech-dod-carcosa.1716712/post-22360221
		




			https://www.thegearpage.net/board/index.php?threads/new-fuzz-pedal-from-digitech-dod-carcosa.1716712/post-22415304
		


Looks like the FZ-1s used 2N5088s, which squealed when I tried them (~320 hfe on my cheap multimeter), or BC109C, which I haven't tried yet.

I can obviously turn down Before or After to reduce the oscillation, but since I'm building this for a friend, I'd love for it to behave similarly to the original.

Any suggestions?


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## Nostradoomus (Jan 12, 2021)

Do you have one of the newer revision boards? I had to bin mine which was the first revision. Nothing made it not squeal!


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## MrSage (Jan 12, 2021)

Nostradoomus said:


> Do you have one of the newer revision boards? I had to bin mine which was the first revision. Nothing made it not squeal!


Yep, it's a newer one. Chatting with Mr PCB to see what we can figure out. 

I actually bought a couple of boards, so I might wire up the second one tonight and see if it's doing the same thing.


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## SandyD (Feb 5, 2021)

Hey all,
I'm shopping for parts for the Carcass at the moment and the resistor size isn't mentioned... is it 1/4w? Is there a standard size for pedalPCB boards?
The board hasn't arrived yet so I can't measure. Also never built a single pedal in my life so this will be one of my first! Thanks


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## Nostradoomus (Feb 6, 2021)

Yep. Unless it specifies otherwise in the build doc the standard is 1/4w


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## SandyD (Feb 6, 2021)

Cheers Nostradoomus


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## Were we brave? (Jul 1, 2022)

Nostradoomus said:


> Do you have one of the newer revision boards? I had to bin mine which was the first revision. Nothing made it not squeal!


Did you ever manage to get your early Carcass board to stop squealing? Mine's still in my troubleshooting bin.


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