Chop Shop

[szukalski]

The latest off the line and one of the more rewarding so far from a build perspective.

Getting it into the 1590B was tricky, a few lessons learned.

What was so rewarding was biasing.

Shout-outs to @bowanderror for this guide to calculating the resistor value, and to @music6000 for helping with the right JFET measurements.

Luckily, I had a selection of J201s, all the ones from GuitarPCB measured 300-400uA, but I had a quartet from Banzai which hit the right spots.

I used a B10K as the Sag pot, but it really cuts the volume after half-way, up to there it works as expected so nothing to worry about.

 

[Mentaltossflycoon]

Love the chopshop.

 

[szukalski]

Love the chopshop.

I'm really feeling the low-gain and boost pedals. I have a Duocast set for low-gain, and a Dragon's Breath Boost, between the three of them I am smiling widely.

I have a feeling there are a lot more to come.

 

[jwyles90]

The latest off the line and one of the more rewarding so far from a build perspective.

Getting it into the 1590B was tricky, a few lessons learned.

What was so rewarding was biasing.

Shout-outs to @bowanderror for this guide to calculating the resistor value, and to @music6000 for helping with the right JFET measurements.

Luckily, I had a selection of J201s, all the ones from GuitarPCB measured 300-400uA, but I had a quartet from Banzai which hit the right spots.

I used a B10K as the Sag pot, but it really cuts the volume after half-way, up to there it works as expected so nothing to worry about.

Nice build! I’ve got one of these waiting in my drawer, and didn’t really think about the jfet values till just now since there’s no internal trimpot for biasing them. If I’m understanding that guide correctly, did you basically just mix and match from your JFETs until they both were around 6v at the drain?

 

[szukalski]

Following this advice, I measured by J201s and choose 2 in that range (I had one at 780uA and the other at 550uA).

Then I calculated the resistor value I needed for 6.6v at the drain using this guide.

 

[jwyles90]

Following this advice, I measured by J201s and choose 2 in that range (I had one at 780uA and the other at 550uA).

Then I calculated the resistor value I needed for 6.6v at the drain using this guide.

Awesome, thanks! So did you have to resolder the correct value resistor into it? I'm trying to wrap my head around the order of operations for all of that to make the build a little easier in the long run. Ideally, I'd like to just socket the JFETs and cross my fingers that I have some that will be close enough right off the bat, but that's almost never the case haha.

 

[szukalski]

I used some SIP-1 sockets so I could swap resistors out. Same with the J201s, I had a few I tested with and each time I changed J201 then I’d change resistor. If your J201 is specced right then you probably don’t need to swap around unless you like tinkering.

 

[szukalski]

Update on this build, I was never satisfied with the sound and it didn't excite me the same way that it has others.

I never got much distortion from it (almost none) and the sag would cut volume at around 35%.

After my recent experience with through-hole J201s not being up to spec, I rebuilt this with MMBFJ201 and used 20K trimmer pots for the drain resistors. After biasing to 6.6V, it does everything from the demos. Sag is functional the entire range, drive is awesome.

Moral of the story, can't trust through-hole J201 anymore. The ones I have had from all sources have let me down..

 

[MichaelW]

Update on this build, I was never satisfied with the sound and it didn't excite me the same way that it has others.

I never got much distortion from it (almost none) and the sag would cut volume at around 35%.

After my recent experience with through-hole J201s not being up to spec, I rebuilt this with MMBFJ201 and used 20K trimmer pots for the drain resistors. After biasing to 6.6V, it does everything from the demos. Sag is functional the entire range, drive is awesome.

Moral of the story, can't trust through-hole J201 anymore. The ones I have had from all sources have let me down..

Ok now you have my wanting to mod mine...hhahaha. You used 20k trimmers on R4 and R8?

 

[szukalski]

Ok now you have my wanting to mod mine...hhahaha. You used 20k trimmers on R4 and R8?

R5 & R9 I think. 8K2 and 9K1.

 

[szukalski]

Ok now you have my wanting to mod mine...hhahaha. You used 20k trimmers on R4 and R8?

You have the new board revision with trimmers already? That’s the mod.. I just had an older revision without them.

 

[MichaelW]

You have the new board revision with trimmers already? That’s the mod.. I just had an older revision without them.

Duhh.....yah I forgot about that. I guess I need to go read my own build report to see what I biased it to....I don't think it was 6.6v. I need to revisit this pedal, there was some elements that I really liked about it and some I didn't.

 

[szukalski]

The designer said around 2/3 voltage, so 6.6V. I assume this would be at 0 SAG, since that is supposed to simulate voltage starvation I guess it’s lowering the voltage to the J201s but I haven’t tested that.

@MichaelW