[SOLVED]Troubleshooting another Aion L5

[njmattes]

My first post here at Mad Bean Pedals. Please be gentle

So I finally got all the pieces and parts to box up the Aion L5 I built a while back, and I'm running into some trouble that I just can't sort on my own.

When I first plugged the board in to calibrate the Distortion, the highest voltage I could get from pin 6 on IC10 was 2.9VAC. So I checked the voltage on PCB OUT and was unable to get any sort of stable reading. So I put my thinking cap on and tried to jump start my brain.

Running a 1kHz sinewave into the input and listening with an audio probe, I get reasonable output until QX2. The signal from the emitter of QX2 is just a buzz, all the way to the output jack. I've tried a few 2N5088s for QX2, and the problem is the same even when I swap QX1 and QX2. Also, the voltages on my transistors are all over the place compared to the list of voltages on the Google Sheet that Kevin made. Below my values are all in VDC and his values are in parentheses.

Q1_1: 14.96 (V+)
Q1_2: 0.10 (.02)
Q1_3: -0.01 (-0.02)

Q2 checks out perfectly

Q3_1: -14.84 (-15.19)
Q3_2: -14.10 (-14.44)
Q3_3: can't get a stable reading on my DMM (-0.32)

QX1_1: 9.08 (0.4)
QX1_2: 1.59 (0.9)
QX1_3: 14.96 (14.66)

QX2_1: 14.96 (-0.22)
QX2_2: 9.08 (0.4)
QX2_3: 14.96 (13.21)

I've pulled R68, R70, and R74. They all checked out but I replaced them all anyway. I've socketed RX1 and RX2 and those check out on the DMM as well.

I'm using CA3080s fram Smallbear, an OPA134 in place of the LF356, and NE5532s in place of the RC4558s. All the voltages on the ICs check out OK.

I'm terrible about cleaning up rosin, but I've been over the board and I'm 98% certain I don't have any solder bridges. If anyone has any ideas about what I might check next, I'd greatly appreciate it.

[njmattes]

Turns out I have a short to V+ on the net between R74, RX2, C35, and QX2.E. Which seems not right to me. However I pulled some of the pots so I could see the backside of the board; cleaned it up with some isopropyl; didn;t see any bridges but pulled R74, R68, R70 anyway; cleaned the board up a bit and replaced them; and still the same situation. It's late here so perhaps tomorrow a clearer head will prevail.

[Scruffie]

Can you link to the schematic please.

[njmattes]

Hi Scruffie. The schematic is here, pages 9 and 10. https://www.dropbox.com/s/dnizjzbetec84gu/aion-l5-preamp-documentation.pdf?dl=1

Turns out that if remove the solder form pin 7 of IC 10, or from the socket at any rate, the short to V+ disappears. I'm not overjoyed at my 'fix' because it seems like a very dry connection now. But it addresses most of the problems I was having—I can finally get 4.4VAC on pin 6 of IC 10, and the pedal produces sound. Huzzah!

I'm left with some weirdness in the compressor. This thread at diystompboxes (https://www.diystompboxes.com/smfforum/index.php?topic=113954.0) is interesting, nonetheless I haven't been able to completely sort things. The voltage on Q3_3 is still too squirrelly to read. And I can't get close to 1.2VAC on my output in order to calibrate the compressor. I'm getting in the range of 0.250–0.300V.

And if I turn the Limit knob all the way counterclockwise—between say 7 and 8 o'clock—I just get some fuzzy chirping. My understanding is that setting the knob to 0 is maximum compressionm and 10 is minimum—but my hunch is that it shouldn't sound like a mess. Or am I misunderstanfing how this works?

[njmattes]

Realized I didn't inlude a photo of my work either, which is now attached.

I don't understand the compressor circuit—but would a bad D4 or D5 cause it to emit a glitchy chirping sound when the limiter kicked in?

[Scruffie]

IC12/Q2 is your envelope detecty business, IC11 is acting like a resistor dividing the signal around the J-FET buffer.

Does the 'chirping' sound a little like a fuzzy octave up?

Envelope ripple can sometimes sound like distortion, I've not tried the circuit so don't know how it responds.

[njmattes]

Thanks Scruffie. I still can't say I understand it, but at least now it seems possible to comprehend.

In other news, I can no longer replicate the chirping. I plugged the pedal back in to see if it indeed sounded like an octave up fuzz—and it sounds perfectly fine. So I'm gonna go enjoy this beast!