If it's a leaky cap at the input, a 1Meg or 2.2Meg resistor to ground at the input will help discharge it and reduce the pop. You can tie it to ground from the tip lead of the input jack, or the input lug on the 3PDT, mostly anywhere before the first cap at the PCB input.

One of this rock opera's orchestra guitarists posted this somewhere more than 20 years ago. I forgot I had it until the topic came up on another forum. Thought I'd post it here for the record (which is the meaning of the file names: Side 1, Side 2, etc. refer to the 2-disc LP set.)

I think the overall scheme will work, with a few changes. I'd increase the bias resistor R2 from 10k to 1M or so, depending on the bias current requirements of the op amps you select. I'd also add a cap between R3/R13 and the bias supply VA, you don't a DC path there since you're biasing the op amps...

You may have problems with hum if you split the output to two different amps without some sort of isolation. Here is some previous work on that topic, with possible solutions: https://www.freestompboxes.org/viewtopic.php?p=296138 Split the input rather than the output, but it reduces the buffer's in...

Sounds like you have a problem with your ground. Touching the case of Q2 grounds the collector thru you, when it should be grounded thru a 10k resistor already. Pin 1 of the volume pot should already be tied to ground, so grounding it directly shouldn't make any difference. Check your ground bus.

I wonder if its suitable to use a 071 or 741 instead of 4250, as its an unobtanium already.. Either one of these should work OK, just omit the programming resistor R8 and leave the op amp pin 8 floating. I just ran across another substitute for the 4250, though it's also obsolete. If you can locate...

slammer88 wrote: ↑19 Mar 2024, 09:12 I wonder if its suitable to use a 071 or 741 instead of 4250, as its an unobtanium already..

Either one of these should work OK, just omit the programming resistor R8 and leave the op amp pin 8 floating.

Yeah, just decrease the value of R10, that first 15k resistor after the clean buffer IC2.4, to increase the clean signal level. Or increase the value of the corresponding resistor after IC2.1 (R11) to decrease the effect level.

The resolution on the PDS-8000 schematic is poor, but this source says the PDS-2000 is similar: https://falseelectronics.blogspot.com/2 ... -8000.html

So here are both.

Hi Aleksandar, Hi guys. I have a few questions and I need your advice. Can POT 100KC (antilog), LOW and TIGHT be replaced in the following way? Yes, those will work, and will give you approximately 100k antilog for each one. I have a little confusion about the A,B and C pot markings. Is this correct...

For continuity and to assist troubleshooting, here's a thread on this pedal: https://www.freestompboxes.org/viewtopic.php?t=9043 Various posts there include links to the layout, BOM, service manual and schematic. Below is Harald Sabro's redrawn schematic with his notes. I would suspect either the co...

I don't think it should do that. If the output is clipping, I would suspect a transistor. Here's a starting point for schematics, apparently there have been several revisions of the JH-1 across time. viewtopic.php?p=267574

If you have a tone generator and a scope (or true-RMS VOM) you can use a signal to do the same. Inject 60 hz at 1V on the primary, and measure the voltage on the secondaries to get your ratio.

I think you'd need to bypass the pedal completely, since whatever it is, remains in the signal path during the current bypass method. It's a pretty small enclosure, and the bypass switch is mounted on the PCB so that might be tough unless you rehouse it in a larger enclosure to make room for a separ...

Hi, everyone. I would like to ask it's the correct schematic? I am confused about the voltage line (V+) connects to non-inverting input but it should be connected to pin8 accordingly to the datasheet. Welcome to the forum, Eugene! This schematic, like many, doesn't show the V+/V- connections to the...

Good job in finding and fixing this, Johan. For those who didn't see it, it was pretty bad for a day or two. Mike

plush wrote: ↑10 Feb 2024, 10:31 I'd bootstrap vt6 to increase it's input impedance.

How would you select the value for a bootstrap cap here? Is there a rule of thumb, or a formula, or is it just by ear? I've built circuits that use them, but have never added one.

Sounds good! Your bias plan looks interesting with the two 1N4007 diodes. So the bias voltage will be about 1.2 V?

I'm repairing yet another one of these, and this one has a Motorola MC33171P op amp. It's similar to the MC34181, with slightly worse specs, but still plenty good enough for this device. This op amp has a noisy output, but both the 33171 and 34181 are obsolete in PDIP, I will probably get a used one...

I'm curious of someone can explain to me, in as simple of terms as possible what the harmonics switch accomplishes. Thanks. If I'm reading the schematic labels right, the "harmonics" switch (labelled H+ here) puts C28 in series with C27, making an effective capacitance of 69 nF (220 nF + ...