So I built this up today and get boost, running at 9v, trim set to 4.5. It certainly boosts, but the switches don't do anything. I disconnected the switches so I could swap leads in case my assumption about which pole to connect to the square pad was incorrect. Hopefully I'm just being a dope!
(http://imageshack.com/a/img921/3562/RaWHbh.jpg)
(http://imageshack.com/a/img923/5937/uiH98e.jpg)
Heres mine from Sunday:
(http://music.codydeschenes.com/wp-content/uploads/2016/04/img_0726.jpg)
I am having a bit of issues getting it biased as Q1 is not being happy. I HATE J201's lol
But my Hot switch definitely brightens up the sound considerably. You may have a bridge or the wrong cap for C5... maybe.
Cody
Okay. I've got a something amiss! I'll check the 3n3. I know it's hard to tell from the blurry solder-side pic, but no bridges found. I'll check again tho.
Use your multimeter not your eyes. Measure the resistance across R6. Does it go to 0 when the switch is flipped, and is it 15K when it's not?
Cody: Bias isn't really important here. Anything below 7V and above 3V is fine but will make a difference. Not really sure what could go wrong with the bias on something like this ...
I'm going to drop a criticism into this thread, though. The original used a 2N5457 and a fixed 8.2K drain resistor. The J201 requires a much larger drain resistor, which in turn increases the output impedance of the stage, as much as tripling the resistance seen by the 3n3 (could be even more with a particularly high-gain J201 or a lower bias) and severely lowering the low-pass frequency cutoff. The 15K is actually likely to be less resistance than the value the trimpot is set at, so it doesn't even raise the cutoff by a whole octave, whereas the original raised the cutoff an octave and a half.
I would give serious thought to recalculating the 15K and 3n3 and/or going back to the 2N5457 so that a "flat" treble setting exists. Otherwise, I'd expect the pedal to be much darker than the EP Booster.
Quote from: midwayfair on April 13, 2016, 04:18:49 PM
Use your multimeter not your eyes. Measure the resistance across R6. Does it go to 0 when the switch is flipped, and is it 15K when it's not?
Cody: Bias isn't really important here. Anything below 7V and above 3V is fine but will make a difference. Not really sure what could go wrong with the bias on something like this ...
I'm going to drop a criticism into this thread, though. The original used a 2N5457 and a fixed 8.2K drain resistor. The J201 requires a much larger drain resistor, which in turn increases the output impedance of the stage, as much as tripling the resistance seen by the 3n3 (could be even more with a particularly high-gain J201 or a lower bias) and severely lowering the low-pass frequency cutoff. The 15K is actually likely to be less resistance than the value the trimpot is set at, so it doesn't even raise the cutoff by a whole octave, whereas the original raised the cutoff an octave and a half.
I would give serious thought to recalculating the 15K and 3n3 and/or going back to the 2N5457 so that a "flat" treble setting exists. Otherwise, I'd expect the pedal to be much darker than the EP Booster.
Thanks Jon for the note. I can get it to around 6/7v but not near the 4.5v that I was shooting for (As per the doc). I will need to do some more reading on what your pointing out with the frequency cutoff but it looks to be worth looking into.
Cody
Tried this out and I'm getting overdrive and not a clean boost, and volume is higher than unity even with pot fully CCW. All parts seem to be right. Using a 2n3904 for Q2. Biasing Q1 (tested with normal through hole and smd adapted to a small piece or perf) doesn't help . Anything in particular to look for?