Build Your Own Clone Message Board

This is my first pedal build and its been a blast. I'm learning a ton and REALLY enjoying myself. Thanks for all the great info guys!

Here's a link so you can see the required pics of the pcb and hardware: https://drive.google.com/drive/folders/ ... sp=sharing

After the final install into the enclosure, I plugged in my guitar/amp and started trying to bias it I started with the trim pot in the middle (12o'clock) but there was serious distortion. In fact, I found that turning the trim pot anything past 9 o'clock did not change the voltage much at all but created distortion. I also found that the trim pot makes a lot of noise like a very old dirty pot as it spins, and will cut the entire signal at certain places like it has bad contact areas. It's been a very touchy process. The highest voltage I could get metered with or without distortion was 1.44 volts although I can't get it to that voltage now. On average, it meters at 1.2ish across the board no matter where I turn the pot above 8 (7 o'clock being 'off' and the lowest, 5 o'clock being the highest). 1.35 volts is where it's sitting at the moment with the pot at 8:30ish, not even a quarter engaged. The suggested is 1.5-1.7 volts. I've found that if I have the output and blend knobs fully engaged, It's a little below unity gain and thats surprising to me. I can only conclude that maybe the trim pot is bad? Every other compressor I've used can still reach above unity gain at the fullest compression settings.

To be clear, EVERYTHING works. LED, in/out/, footswitch, bypass, battery and/or power supply. And it's pretty quiet. In fact I love the subtlety of the peddle. My boss CS-3 is still pretty obvious even on the lowest compression settings which annoys me from time to time. I'm just wondering if I can switch out the bias trim pot and get it up to 1.5-1.7 volts. Will the gain at full blend be at least unity or above?

Or, have I potentially messed up something else along the way? I've double and quadruple checked everything at this point and can't find any weak solder joints or misplaced parts :/ Thanks you guys!

Unless you substituted another JFET with a different pinout, you have Q1 installed backwards:

_________________
“My favorite programming language is SOLDER” - Bob Pease (RIP)

My Website * My Musical Gear * My DIY Pedals: Pg.1 - Pg.2

It's so obvious now that you've pointed it out! I'll realign it tonight. Thanks for taking the time to look at it for me.

HTH!

I don't know your level of soldering experience, so apologies in advance if you're already aware of this: De-soldering components with 3 or more attachment points gets a little tricky because you can't just sequentially apply the "heat & lift" method to one side and then the other, as you would with a 2-lead component. I find the combination of a "solder sucker" and good quality de-soldering braid to be effective in cleaning out the solder joints enough to free the leads for safe removal from the PCB. Care and patience is the key to this process--avoid forcing the removal at any point, as this is a good way to damage an eyelet or break a board trace.

_________________
“My favorite programming language is SOLDER” - Bob Pease (RIP)

My Website * My Musical Gear * My DIY Pedals: Pg.1 - Pg.2

Well, I'm thoroughly confused now. I was able to get Q1 switched back around the right way. I plugged in and everything works as before. There is no longer any distortion or cut outs when adjusting the bias trim pot. However, I can't get it to read above 0.4 volts. At one moment I saw the volts read 1.69. Oddly as I turned the trim pot, it didn't change. Then it was reading in the 1.5's. Then the 1.7's. I put it back together and played. Metered again and the voltage was below 0.1. It's all over the place but no change in sound.

In fact I can't here any difference when I turn the bias pot from all the way down to all the way up. I also no longer hear any compression. I've been testing it with an overdrive pedal to listen for the sustain. Before, there was clearly a bump in sustain. Now it's like a clean boost. A slight color change in tone but no obvious compression or sustain no matter where I turn the level and blend. I also can only turn the blend 3/4's of the way up before it drops below unity gain. If I turn level and blend all the way up, its WAY below unity. As in unusable.

I opened it up and reflowed solders all over the pcb and looked for bridges. I can only find one suspect but it's in line so I'm pretty sure it doesn't matter. Based on your chart it's between R8 and R22

After tearing it apart and putting it back together so many times, I'm not thrilled with the wiring between the board and some of the hardware. Particularly the power jack, input jack, and output jack (Footswitch still looks great). I think I'll desolder those and maybe start fresh with new wires. The joints have been bent a lot so maybe they could be suspect?

Yeah, the bridge between R8 and R22 is no problem--they're already connected.

Two things on the bias issue:

1) I very much doubt that this is a factor, but I have to ask: Are you sure you're taking the voltage reading correctly? Meter set to DC voltage, 20VDC range if it's not an auto-ranging meter, black probe on ground and red probe to the test point. And there must be a cable inserted into the input jack.

2) Assuming the readings were taken properly, what you describe suggests that you may have a bad trimpot. Try removing it and temporarily soldering a 4.7K resistor across the two eyelets that you didn't use to mount the trimmer. See what the Q2 source bias voltage is then, and how the the pedal sounds & behaves.

_________________
“My favorite programming language is SOLDER” - Bob Pease (RIP)

My Website * My Musical Gear * My DIY Pedals: Pg.1 - Pg.2

You were right about one thing. I had it on AC not DC. My meter broke a while back and just purchased this one. Got in a hurry and didn't look closely :/ Just checked the board again at the test point (and grounded) and it shows up as flat zero. Checked voltage randomly around the board just to make sure the meter was reading and it was.

I'll yank the bias pot tonight...carefully lol. I think I have a 4.7k. Thanks for the advice on how to remove parts with 3 leads, really helped. I might even have another trim pot. I'll check it to make sure it's the right kind

I just had a thought. The level pot works as intended. The Blend pot works like a volume knob in reverse and there is no compression effect. If I'm getting it right, the blend pot has 2 signals coming into it, an untouched signal, and a compressed signal. At 50% it should be letting through both equally. 0% is the uncompressed signal only. 100% is the compressed signal only. My thought is that the compressed signal is not making its way to the blend pot. Its stopped somewhere back down the line, OR so tiny as to be basically unheard. Been checking out the schematic. May try to backtrack from the Blend pot and see what I find.

That's sound reasoning and makes me suspect the JFET. But let's take it a step at a time and see if the resistor instead of the trim pot gets you somewhere first.

Alright. Finally got some parts in and was able to try a 4.6k resistor. When I checked the bias point, it showed up as 0. I checked around the board and definitely had voltage going through. What do I do next?