Help with Death by Octaver (DBA Octave Clang clone)

[neiltheseal]

Hello again. I seem to be making incremental progress on my pedals but I am back for more guidance. This forum has helped me fix my last three pedals and I now have seven under my belt.

I have just put together a Death by Octaver from PCB Guitar Mania. I like the sound it makes but there are clearly a couple of issues.

The first issue is that the tone knob seems to work backwards almost. When turned to the left the volume is quite loud and when to the right it is far quieter. Below is a video.

https://www.youtube.com/shorts/IGOUKk78CjI

The second issue is that when I roll the gain knob down I seem to get this strange feedback noise. Below is a video of the pedal so you can see what I mean. The feedback is particularly noticeable at the end.

https://youtu.be/mPF6f8e04tA

Does anybody know what might be the cause of these issues?

***I did install C3 backwards twice in a row and had to remove it, breaking the metal rings on the PCB. I connected the legs of a 4.7uf capacitor to pin 6 of the IC and pin 1 of the transformer***

You can see both sides of the PCB below and an audio trace I did. I have since reflowed solder after the audio trace.

https://imgur.com/gallery/UM1vGEQ

The build docs are on the link below on page 5

https://pcbguitarmania.com/.../Death-by-Octaver-Building...

Thanks in advance!

[neiltheseal]

I asked this question on the pcb guitar mania group and someone suggested the transformer should be flipped the other way to what is shown on the board. I have p on the bottom and a on top.

The build docs on the pedal below are similar but the transformer is backwards to the one on bought. This has the transformer in the same direction as the tychobrache Octavia.

https://moonnelectronics.bigcartel.com/product/kronk-and-the-octave?fbclid=IwAR2baA-L-1F6P-hJO6Qc174YHiWou6qluGMJ_bHoS1Aeh6-7j6fLMlE0xFc

Thoughts?

[mauman]

I asked this question on the pcb guitar mania group and someone suggested the transformer should be flipped the other way to what is shown on the board. I have p on the bottom and a on top.

The build docs on the pedal below are similar but the transformer is backwards to the one on bought. This has the transformer in the same direction as the tychobrache Octavia.
https://moonnelectronics.bigcartel.com/product/kronk-and-the-octave?fbclid=IwAR2baA-L-1F6P-hJO6Qc174YHiWou6qluGMJ_bHoS1Aeh6-7j6fLMlE0xFc
Thoughts?

The original Octavia has the transformer flipped from the way your build doc and schematic show it.  Moon's PCB and build doc match yours, but the notes in his build doc say that's wrong, and to flip it to match the Octavia, with the primary (higher resistance) side toward the Ge diodes.  That makes it a step-up rather than a step-down transformer.   

[mauman]

The first issue is that the tone knob seems to work backwards almost. When turned to the left the volume is quite loud and when to the right it is far quieter.

The Tone knob is actually a "Low Cut" control that cuts bass when turned clockwise.  It's quieter clockwise because you're removing bass, which decreases the total signal power coming into the op amp.  To match the original Octavia value, Tone pot should be fully CCW (most bass.)   

[mauman]

The second issue is that when I roll the gain knob down I seem to get this strange feedback noise. Below is a video of the pedal so you can see what I mean. The feedback is particularly noticeable at the end.

That noise is from another electronic device nearby, it could be your cell phone, a power supply or another pedal.  I predict it will go away when you box up the PCB, a metal enclosure will help shield that kind of noise. 

[neiltheseal]

I asked this question on the pcb guitar mania group and someone suggested the transformer should be flipped the other way to what is shown on the board. I have p on the bottom and a on top.

The build docs on the pedal below are similar but the transformer is backwards to the one on bought. This has the transformer in the same direction as the tychobrache Octavia.
https://moonnelectronics.bigcartel.com/product/kronk-and-the-octave?fbclid=IwAR2baA-L-1F6P-hJO6Qc174YHiWou6qluGMJ_bHoS1Aeh6-7j6fLMlE0xFc
Thoughts?

The original Octavia has the transformer flipped from the way your build doc and schematic show it.  Moon's PCB and build doc match yours, but the notes in his build doc say that's wrong, and to flip it to match the Octavia, with the primary (higher resistance) side toward the Ge diodes.  That makes it a step-up rather than a step-down transformer.   

Do you think it's worth de soldering the transformer and flipping it to match the moon and Octavia?

[neiltheseal]

I asked this question on the pcb guitar mania group and someone suggested the transformer should be flipped the other way to what is shown on the board. I have p on the bottom and a on top.

The build docs on the pedal below are similar but the transformer is backwards to the one on bought. This has the transformer in the same direction as the tychobrache Octavia.
https://moonnelectronics.bigcartel.com/product/kronk-and-the-octave?fbclid=IwAR2baA-L-1F6P-hJO6Qc174YHiWou6qluGMJ_bHoS1Aeh6-7j6fLMlE0xFc
Thoughts?

The original Octavia has the transformer flipped from the way your build doc and schematic show it.  Moon's PCB and build doc match yours, but the notes in his build doc say that's wrong, and to flip it to match the Octavia, with the primary (higher resistance) side toward the Ge diodes.  That makes it a step-up rather than a step-down transformer.   

Here is the data sheet. I used a 42tmoo2 which seems to have more impedance/resistance on the primary side.

Am I right in saying this reduces the voltage and therefore reduces volume? So if I flip it there's more voltage, gain and volume?

https://au.mouser.com/datasheet/2/449/XC-600134-1212477.pdf

[mauman]

Right, for a signal going from the primary with more turns (higher inductance & resistance) toward the secondary with fewer turns (lower inductance & resistance) you're stepping down the voltage (level/volume.)  Flip the primary toward the output, and you'll be stepping up your output signal level/voltage/volume.  It shouldn't change the waveform much, so the sound will be about the same, just louder. It's not easy to desolder a transformer (or IC with multiple pins) without destroying either the PCB or the part;  if it were me I'd just make a note for the next time I built one of these and leave this one as-is.   

[neiltheseal]

Thanks again for your help. I've decided to leave it as is and boxed it up. Will remember next time I see a transformer to check other schematics for best orientation.

You were right, the feedback is gone now it's in the enclosure. It sounds quite good actually except when the gain is turned down low. I just won't do that