Aion Comet Troubleshooting (Boss DS-1 clone)

[davidvern]

I recently completed an Aion Comet (Boss Ds-1 clone). The volume and tone knobs are working as intended but the distortion when pushed to the 2 o'clock to 5 o'clock range sounds like a very harsh fuzz with almost no sustain (like a noise gate with a super high threshold, palm mutes just cut out). I followed the parts list from the official documentation https://www.dropbox.com/s/k3d93su9d48k8cd/aion-comet-ds1-documentation.pdf?dl=1 with Mods 1 & 2 using an OPA2134 for the op-amp. Clipping diodes used are 3mm green LEDs and 1N914 and BAT41s in series.

Voltages are as follows, power supply is from a wallwart at 9.75V.
IC
Pin1: 5.31V
Pin2: 4.88V
Pin3: 4.88V
Pin4: 0V
Pin5: 4.82V
Pin6: 4.88V
Pin7: 4.88V
Pin8: 9.75V

Transistor Voltages
Q1
C: 9.75V
B: 4.44V
E: 4.07V

Q2
C: 3.38V
B: 0.59V
E: 0.02V

Q3
C: 9.75V
B: 4.03V
E: 3.82V

Diodes
D1
A: 0V
C: 9.74V

D2 A: 4.88V
C: 4.86V

D3 A: 4.57V
C: 4.86V

D4 A: 4.88V
C: 4.88V

D5 A:4.88V
C: 4.88V

D6 A:0V
C: 4.28V

Using an audio probe to check different parts of the circuit, the harsh fizzy sound start from Pins 1 and 2 of the op-amp which I understand to be the second stage of the op-amp. I have switched it out with a spare OPA2134 and a TL072 from another build and the effect was the same. Pictures of actual PCB can be found at https://imgur.com/a/ffNTHB2.

[davidvern]

I have done more troubleshooting and seem to have a short across the pull down resistor. I find there is continuity from IN to the start of R1 and across the pull down resistor RPD. Once i hooked it up, the pedal functions as before. I've looked over the PCB and can't find the solder bridge for the life of me...

Could this the cause of the problems above? Also is it expected for there to be output from the pedal in this state?

[PRR]

Welcome.

Are you poking R1 with the input jack connected? We often wire input jacks "shorting", to short-out "RPD" when nothing is plugged into the jack. Stick a dummy plug or slim pencil in the jack and try again.

"Continuity" is for trailer-light checks, or very initial wire checks. In electronics it matters 1 Ohm 100 Ohms 1K Ohms, so it is best to observe the numbers. "Continuity" has some threshold beep/no-beep but different on every meter. If not showing numbers on "Continuity" mode, use Ohms mode.

[davidvern]

Plugged in some jacks and tried again. Measured 0.5 ohms across RPD same as without the jacks. I noticed this issue when trying to double check that I had the right resistor values to solve my other issue above.

Sorry, was an idiot. Forgot to engage the footswitch as well. With the foot switch I get about 2.2Mohms across RPD.

[davidvern]

Have done further trouble shooting, replaced R4 and R7 with the mod shown here: http://www.muzique.com/news/fat-mod-for-the-boss-ds-1/ to see if the transistor boost was too excessive.

Gain was much lower but the sustain was still cutting out past a certain distortion knob setting.

Are there any reference voltages available online for this or similar ds1 pedal to see where I should be checking.

[ElectricDruid]

Q2 looks suspicious to me.

The emitter is basically grounded, so that's fair enough, but the base is just a diode-drop above the emitter. That suggests to me that it isn't biased properly, which would give the "gated" symptoms you're seeing.

I'd double/triple check the components around Q2.

HTH,
Tom

[Slowpoke101]

I agree with Electric Druid. Q2 really looks odd but my question for you actually is associated with Q2.
Check the values of C3 and C5. The two capacitors that you have there appear somewhat large for a capacitor that should be somewhere between 100pF and 270pF.
Also check the polarity of C7, it looks like a tantalum cap from your picture.