JHS Pedals Overdrive Preamp

[jeffwhitfield]

I highly doubt this is a complex circuit so shouldn’t take long to trace. It’s a precursor to the DOD 250. Very interested in seeing what this circuit looks like. Sounds interesting.

JHS Pedals, Kansas City USA— Overdrive Preamp

www.jhspedals.info

 

[jesuscrisp]

Got the pedal today. And...well...it's SMD. All is not lost though. Good news is that most of the circuit can be traced. Only components with no lookups are a handful of capacitors. Even then, most of them look like they might be pretty easy to figure out though a bit of trial and error. I'm gonna trace the circuit, record the values that are readable, and then figure out the rest after setting up a breadboard.

Nice! Now... Does the switch go between silicon and schottky diodes respectively?

 

[jimilee]

Excellent

 

[jeffwhitfield]

Nice! Now... Does the switch go between silicon and schottky diodes respectively?

Yup...most definitely silicon and Schottky's. If I had to guess, probably 1N914 or 1N4148's for the silicon. The Schottky's are probably BAT41's or the like. Germaniums would be better though...1N270 or similar.

 

[phi1]

Is that a 1ohm resistor between D3/D4 and ground? Looks like 01R. I know a series resistor can soften the knee a bit, but would 1ohm do anything?

 

[music6000]

Is that a 1ohm resistor between D3/D4 and ground? Looks like 01R. I know a series resistor can soften the knee a bit, but would 1ohm do anything?

I believe that's 100r!

 

[jimilee]

I saw one of the most recent videos, he uses 1n4001 for the silicon clipping.

 

[jeffwhitfield]

I believe that's 100r!

Yup, 100R.

 

[music6000]

Yup, 100R.

I saw one of the most recent videos, he uses 1n4001 for the silicon clipping.

T4 should be 1N4148's!

 

[jeffwhitfield]

I saw one of the most recent videos, he uses 1n4001 for the silicon clipping.

Ah, good to know!

T4 should be 1N4148's!

True, but this is a bit different circuit. It's quite possible that early versions of the 250 had different clipping diodes.

 

[jesuscrisp]

Ah, good to know!

True, but this is a bit different circuit. It's quite possible that early versions of the 250 had different clipping diodes.

There's a spreadsheet according to which the earliest version documented pre JHS was one with 1N4001s

 

[Feral Feline]

Just wondering aloud: what makes a circuit “different”?

Is not Ford’s Mustang still a Mustang whether all red vs blue with white Shelby stripes?

Whatever level of trim you order one in, it’s still a Mustang, is it not?


How far from the original schematic’s values does a circuit have to go to be thought of as different, a Ford Focus instead of a Mustang? A Chevy vs a Subaru?

Not trying to derail/hijack the thread, even car-folk debate the details!

 

[music6000]

There's a spreadsheet according to which the earliest version documented pre JHS was one with 1N4001s

Did JHS get it wrong?????????????????????/

 

[jesuscrisp]

Did JHS get it wrong?????????????????????/

View attachment 23734 View attachment 23735

This one is the "lost prototype" one. Apparently it had germaniums which JHS used in this as it's the faithful(ish) recreation of the '75 version, the '76 had 1N4001. In the production ones it seems he simulates germanium using schottky + a resistor to soften the knee.

 

[music6000]

This one is the "lost prototype" one. Apparently it had germaniums which JHS used in this as it's the faithful(ish) recreation of the '75 version, the '76 had 1N4001. In the production ones it seems he simulates germanium using schottky + a resistor to soften the knee.

So the production run is purely to Con people & make money at the same time.
I would replace it with Germaniums & 1N4001's on the switch as it would cover what the Overdrive Preamp is suppose to be about!!!.

I'm proud to say I don't own a single JHS pedal, I've built 2 of the PedalPCB versions & they don't impress me at all!!!

 

[jeffwhitfield]

Just wondering aloud: what makes a circuit “different”?

Is not Ford’s Mustang still a Mustang whether all red vs blue with white Shelby stripes?

Whatever level of trim you order one in, it’s still a Mustang, is it not?


How far from the original schematic’s values does a circuit have to go to be thought of as different, a Ford Focus instead of a Mustang? A Chevy vs a Subaru?

Not trying to derail/hijack the thread, even car-folk debate the details!

Think of it as different models of Mustangs. A '76 Mustang is quite different from an '82. They're both Mustangs. Look like Mustangs. Drive like 'em....but look different. Same here.

In this case, the differences could be wildly different or very subtle.

Honestly, this is just an exercise to see just what makes this pedal so different than a standard DOD 250 (early grey version). Based on what I'm seeing in the production version, seems JHS is making some substitutions that even their "throwback" version doesn't use. Basically, they're cheating a bit. Kind of disappointing. The version I would like to end up with would be one much closer to the "throwback" for sure.

 

[music6000]

Yup...most definitely silicon and Schottky's. If I had to guess, probably 1N914 or 1N4148's for the silicon. The Schottky's are probably BAT41's or the like. Germaniums would be better though...1N270 or similar.

View attachment 23729

Maybe this is what it should be :

 

[phi1]

Someone get this info on TGP to get the word out haha. Let people know what they’re actually getting.

Side note, has anyone been successful emulating germanium diodes with schotkey plus series R?

I gave it a try on a klon circuit using bat46 and various values of series R. I wasn’t able to get it satisfyingly close to ge (using 1n34A) to my ears. Curious if anyone else has found a formula that works. On a distortion like the 250 circuit, might be harder to hear a difference.

 

[music6000]

Someone get this info on TGP to get the word out haha. Let people know what they’re actually getting.

Side note, has anyone been successful emulating germanium diodes with schotkey plus series R?

I gave it a try on a klon circuit using bat46 and various values of series R. I wasn’t able to get it satisfyingly close to ge (using 1n34A) to my ears. Curious if anyone else has found a formula that works. On a distortion like the 250 circuit, might be harder to hear a difference.

Apparently Josh has!!! ??????????????????????????????????????????????????????????????????????????????????????????????????

 

[phi1]

Completely different clipping arrangement seems like an overstatement for ge vs silicon diodes.

 

[jeffwhitfield]

Someone get this info on TGP to get the word out haha. Let people know what they’re actually getting.

Side note, has anyone been successful emulating germanium diodes with schotkey plus series R?

I gave it a try on a klon circuit using bat46 and various values of series R. I wasn’t able to get it satisfyingly close to ge (using 1n34A) to my ears. Curious if anyone else has found a formula that works. On a distortion like the 250 circuit, might be harder to hear a difference.

I think the answer to that is the newest Klon KTR's. Apparently, they cracked it. It was revealed that the newest KTR's will have silicon diodes going forward so...only way that's possible while maintaining the same tone and character is with Schottky's, right?