Aquaboy (latest version) distortion

[gordo]

I don't recall how prominent the input distortion was on the original but I'm getting a "gggkkkk" on low notes if I hit them with any force on a fairly low output Strat.  This is right on the first repeat.  I've fiddled with the trimmers but can't seem to dial it out.  Is this an issue with the 571?  I have a few of them here and they all seem to sound a bit different but still the same problem.  The worst is a new Cool Audio from Smallbear.  The best is an NE571 oldie.  The output is unity so there's no gain going on.  Pedal itself seems to work fine with or without the mod board.  15v doesn't seem to make a whole bunch of difference.

Any opinions?

[madbean]

What you are describing is a pretty typical problem when using companders to reduce noise from BBDs. The compressor portion of the 570 has a limit to how well it can respond to fast/loud dynamics at the input signal and maintain a consistently smooth output. Upping the voltage supply does not alter this limitation (AFAIK). And, it may be your 570 simply has better tolerances than the 571 so it is more responsive.

However, you can experiment to see if you can attain a better response. Socket C10 and try 100n or 470n there. This will shift the balance between "response" and "ripple". Here is a great explanation: http://electricdruid.net/noise-reduction-with-companders/

One thing I've bee meaning to try for a long time is using a different method of compression in an analog delay (like optical or OTA based) and just use the 570 for expansion and noise suppression. I don't know if anyone has ever done that.

[alanp]

Brian, another method I've seen is the LTC1063 filter IC, with the clock of the filter rising as the delay clock increases also. (This was with a PT2395.)

[gordo]

Is there an audible difference between the 570 and 571?  Seems all I have here is 571's.  I'll work with C10 when I can get more bench time.  I like the Mod board addition.  Puts it into DMM territory.  I went with the trimmers figuring it would be mostly set and forget.  I'm sure I'll change my mind once the box is finished.

Thanks for the response!

[Stomptown]

Well this post couldn't have come at a better time. I just came across the same noise while building a multi with a 2010 Aquaboy.  I swapped out that cap for a 470n and the gggkkk sound went away completely. It's definitely worth experimenting with that cap.  Thanks for the suggestion Brian!

[gordo]

I picked up a few NE570N's this week and it made quite a difference.  I believe my 571's are legit.  With the 571 I was able to get a decent sound using a 47n for C10 but the delay line sounded pretty lifeless.  With the 570 I went back to 220n and there was a tiny bit of "gggkkk".  Dropping it to 100n the noise is all but gone.  I really have to mash the strings to get it to distort.

So I think I'm safe to box this one up, I still need to go thru the calibration process again but as far as I'm concerned this is fixed.

Did I mention how cool it sounds?

Oh, and thanks for killing off the political thread.  I come here to get away from that crap.

[gordo]

I forgot to mention: got the 570's on eBay from Component Traders, LLC.  $4 each and shipping.  Pretty reasonable and I believe they're real Signetics.