Chop Shop (Barbershop)

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caiofilipini

Well-known member
One more build that had been sitting in the queue for far too long and I finally wrapped it up tonight: the Chop Shop. Sounds great! I tend to like discrete overdrives more than opamp-based ones, and this one confirms it. Went with another Gørva enclosure, but decided to use a bare one to sort of match the Fairfield look, including the knobs. On the downside, I had the stupid idea of labeling the controls with a Sharpie. It looks terrible. Oh well, at least it sounds great!

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PXL_20211003_031747273.jpg

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Can you get those knobs at Tayda??

I am considering this as a 1st build. Just not sure if Pedalpcb is shipping to Aus currently since USPS stopped service here.
 
fig said:
Very nice! How's that sag control? Oh, and what is between the 3PDT lugs please?
Click to expand...
Thanks, Tim!

The sag control is very subtle. It seems to have some effect on the high end content, at least in my build and rig. But it's fun.
I used clipped leads from carbon comp resistors and diodes (the thicker ones) as jumpers on the 3PDT.
 
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Question since you find the sag control to be subtle. (I find it to increase the distortion quite a bit). Where did you source your jfets? Did you check the drain voltages?
 
phi1 said:
Question since you find the sag control to be subtle. (I find it to increase the distortion quite a bit). Where did you source your jfets? Did you check the drain voltages?
Click to expand...

I did check the drain voltages, they're somewhere between 4V and 4.5V on both. I tend to run my amp fairly hot, though, so maybe the effects aren't as pronounced?
 
Ah, and my J201s are a mix between Mouser (InterFET), GuitarPCB (Fairchild) and Pedal Hacker (Fairchild).
The ones that brought the drain voltages to the 4V range were the ones from ON Semi, all the Fairchild ones had significantly lower Vgs(off).
 
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see how much variation in voltage you are are getting on your transistors at each range of the sag control. I don't think the effect should be subtle when you dial it down, but maybe this sag control is intended to be limited in this build
 
@caiofilipini If I’m not mistaken, drain voltage should be around 6V. You can always replace the drain resistors with 10k or 20k trimmers to dial it in. I found it helped with the Sag.
You can also use a B5K for the Sag to give it a bit more range, but biasing is key IMO.
 
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You all just made me realize the position of the Sag pot should be taken into consideration when biasing. It looks like fully CCW, whatever comes through the power supply is provided to the circuit. As you turn the Sag control CW, it lowers the current going into the circuit. Which means I should probably have it set fully CCW when biasing, correct?
 
Sooooo, turns out you were all correct and I'm stupid. I turned Sag fully CCW, swapped the J201s that were there for a pair that biased right around 6V, and now the Sag control really makes a difference.

I recorded a quick clip demonstrating it. It starts with the bypass sound (guitar straight into amp), then the ChopShop with the Drive control almost dimed and Sag fully CCW. I move my way CW until it's dimed, then move my way back CCW:

https://soundcloud.com/white-mockingbird%2Fchopshop-sag-demo

Thanks to @fig for asking the right question, and to @phi1, @zgrav and @SYLV9ST9R for pointing me in the right direction. Love how it sounds even more now!
 
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