Afterlife distortion

[BoxOfSnoo]

Hi folks,

I finally built my afterlife, and crammed it into a 1590a... that was quite a task.

It all seems to be mostly working, very subtly... except I am getting some kind of distortion when playing my bass through it.  It's a high-end staticky type of distortion, I'm not sure where to look to see what is causing it.  It is mostly evident with my bass, higher notes on the guitar don't seem to bring it out as much.

I used a VTL5C3 and replaced R7 with a 50K pot with a 33k resistor in series (I changed that to a 47k, so that when the pot is dialled down it is in stock configuration).

What could be causing the noise?  How can I trace this?  Thanks.

[Boba7]

I never build an Afterlife and I don't play bass, so here's that...

First thing I'd do would be to check again all connections, check if there's no solder bridge anywhere, check the voltages, and finally use an audio probe to find where exactly the noise comes from.

[jimilee]

I used one with my bass and never had any issues. Check your component values and your soldering. I never changed any values for bass.


Sent from my iPhone using Tapatalk

[midwayfair]

Please post voltages and pictures and follow the tech help rules for your post format.

[BoxOfSnoo]

Voltages:

input: 9.45 (Boss PSU)

TL072:
1: 3.76
2: 5.23
3: 2.68
4: 0
5: 4.62
6: 4.62
7: 7.72
8: 9.23



note: R7 is replaced by a pot soldered on the other side of the board.  The pot doesn't seem to make a huge difference so far...



(the connections on the bottom are not bridged)... so hard to get these in focus!

Note: I pulled off a trace on the daughter board so I had to make that ugly little jumper... it's soldered on the other side and anyway, that board seems to work.



I have an active preamp in my bass, plus it seems when I hit the low notes hard I hear the crackle. 

Anything else that might help?

[midwayfair]

Pin 7 looks high, but I'm not sure what might cause that. Does it vary when you twist the threshold pot?

--

Set the comp to max and your threshold pot to 0K.

Measure the resistance across the vactrol's LDR side without playing and after plucking a note.

Turn down your bass. Measure again. Repeat until your volume's almost off.

You should have ~200K when it's at rest and as little as a few KOhms when you're playing a note. If you drive it that low even with the volume on your bass all the way down, there might be something wrong.

You can actually remove the compression from the equation entirely by shorting the two pins of the LDR (like with an alligator clip). If you still get distortion in that circumstance, then it's possible your signal is just too hot for a 9V box.

It's also conceivable, though unusual even with a hot bass signal, that you're distorting the op amp even when the gain is 1x (which is what happens when the vactrol drops below 10K). If that's happening, then you really only have two choices: Play with your bass's volume turned down until you're no longer distorting, or run the circuit on higher voltage.

There might be other things wrong, but this can help narrow down whether the pedal's working at all.

[BoxOfSnoo]

Thanks so much, I will have to test this out when I get a few minutes free.  That's fantastic info.

> Set the comp to max and your threshold pot to 0K.

I presume by this you mean the sensitivity pot - set it to 0k so that the resistance across R7 is back to stock values?

[BoxOfSnoo]

Ok that was a seriously long pause... life interrupts (how rude)    I'm back to tweaking!

(edit, uh let me try that again) I measured across the LDR side and I'm getting nothing that low.  I get ~200K when not playing but it only goes down to 60K or so.  It still has the quiet static overlaid with a strong signal.

Thanks for your patience.

I replaced the diodes, I suspected one was broken, and it was, at least once I removed it... here are the measurements now:

1 - 5.0v
2 - 4.6v
3 - 2v
4 - 0
5 - 4.6v
6 - 4.6v
7 - 2.9v
8 - 9.3v

Pin 7 changed considerably so at least that part helped.