Please help with Bixonic Expandora

[Highsmith]

Hi there, I’m having an awful time getting this Expandora to work. Any help is appreciated! This is the first time I’ve measured voltages and used an audio probe…please excuse my ignorance.

I checked for continuity on the back, no bridges I’m pretty sure.

I should mention that through a clean amp, I can turn the white noise up and down with the volume control, and the tone appears to be changing the tone of the white noise. No guitar signal will pass though.

Also, when I randomly press my fingers on the back, guitar signal will pass.

My first attempt at the audio probe reveals sound at the input, and in between Gain 1 and +9 V only. I can’t find sound anywhere else. This leads me to believe my problem is at the start, no?

Thanks again….Highsmith

2N3906:
E = .922 V
B = 3.17 V
C = 00.5 MV

JRC 4558D:

1 3.17 V
2 60 MV
3 29.4 MV
4 00.7 MV
5 6.60 V
6 3.75 V
7 5.5 MV
8 .538 V

LM308N (below JRC 4558D):

1 3.87 V
2 00.1 MV
3 .536 V
4 00.6 MV
5 5.14 V
6 7.31 V
7 00.1 MV
8 000 MV

H11F3:

1 7.31 V
2 6.14 V
3 00.1 MV
4 00.1 MV
5 000 MV
6 000 MV

LM308N:

1 3.9 V
2 00.1 MV
3 01.3 MV
4 00.9 MV
5 5.18 V
6 7.31 V
7 000 MV
8 000 MV

H

[Travis]

You seem to be numbering the IC pins incorrectly

It should be like this where the numbers go in a U shape

1   8
2   7
3   6
4   5

If you could repost the voltages with that pin numbering, it will be easier to help you. It would be helpful to have a more straight-on photo of the top and bottom of the board as well.

The voltages are indicating a problem though

[Travis]

Edit for some reason I didn’t see the photo of the bottom of the board.

Not offense but you need to work on your soldering technique. Make sure your iron is hot enough. When you solder a joint, first put a tiny bit of solder on the tip of your iron. Then touch the tip of your iron to both the copper on the board as well as the component leg being soldered at the same time.

I can tell by looking at the board that you are not touching your iron to the copper and the component leg at the same time, and I can see where the solder is dripped over the leg but not flowing onto the leg correctly every time

Touch the iron to both parts at the same time so that they are both heated and solder will flow onto both surfaces creating the joint.

Only apply the minimum amount of solder necessary. When you flood the whole back of the board with solder, you can’t see the joints and increase the chances of shorts

With so much solder especially you will absolutely need to run a knife or small file or something to clear out the space between the strips. There is a lot of flux and possibly bits of solder between the strips which could cause a problem

[Highsmith]

Ha, no offense taken. Thanks for the help.

 I reflowed the back and check for continuity again. I know it looks like a lot of things are touching, but they aren't.  New pix on the bottom.

E = .922 v
B = 3.17 v
C = 00.6 mv

4588:
1 3.17 v
2 60 mv
3 29.2 mv
4 00.6 mv
5 .539 v
6 5.4 mv
7 3.75 v
8 6.60 v

308 below 4588:
1 3.88 v
2 00.1 mv
3 .537 v
4 00.5 mv
5 000
6 000
7 7.31 v
8 5.15 v

opto:
1 7.31 v
2 6.00 v
3 000
4 000
5 000
6 000

the other 308:
1 3.9 v
2 000
3 1.3 mv
4 00.5 mv
5 00.1 mv
6 000
7 7.31 v
8 5.18 v

[Travis]

Here comes a way delayed reply

Your voltages are funky. You don’t have ground where you should and the supply voltages are wrong. I’m having a hell of a time spotting the actual problem though.

I would really carefully check everything associated with 9V and ground first. Resistor values, component placement, cuts, etc. something is wrong there

[Travis]

Before you put too much effort into debugging this, do you know if the layout is verified?

I just noticed that in typical John K fashion he copied an existing Sabrotone layout. When I look at the Sabrotone page there is talk of errors

[Highsmith]

Thanks for taking the time to reply Travis!

I got the layout from the Verified section of the Contributions sub-forum here. I think I'm done futzing with it.

Since this failure, I ordered a pcb from Fuzz Dog and I wired it up yesterday using the pots from this build. It worked like a charm with a H11f3,  NTE2370, Toshiba 1S1588 diodes.

I have an original one which I'll be comparing the pcb to soon at volume.

The original feels somewhat delicate, which is why I'll be using this live.

The original appears to have 2 transistors, whereas all the layouts & pcbs only have 1. What's up with that?

[Travis]

Very cool! I’d love to hear how you think it compares to the original

The original used a transistor in the bypass switching. It wasn’t in the audio path so most people now use the more common true bypass switching with a 3PDT