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Ashly SC-33 Gates - noise problem
Old 24th November 2009
  #1
Here for the gear
 
🎧 10 years
Ashly SC-33 Gates - noise problem

Hi,
This is my first post, so I hope it's in the right forum.
I recently bought an Ashly SC-33 noise gate which has a fault which I suspect might be age related - I'll describe the symptoms and if anyone can shed any light on it, I'd appreciate it.

It is in good working order as far as the gating is concerned, but there is a continuous bubbly fizz sound (like white noise with irregular crackles on top) in the background when the gates are switched in. The crackling is slightly worse in one channel than the other. When the gates are bypassed there is no fizzing sound, just the audio input signal. The fizzing noise is continuous and doesn't change with the operation of the gate (which gates the input audio signal as expected).

I'm guessing that some component(s) have come to the end of their working life (it is 25+ years old). Internally, everything looks in good order. The ICs are socketed and all components look to be easy enough to replace (obviously no surface mount / micro parts) so my soldering skills should be OK if I can just find the faulty part(s). The circuit boards are cushioned by black foam underneath, with more foam stuck to the underside of the removable case top. The foam is not decayed as far as I can tell.

Any ideas? Also any opinions about the SC-33, mods etc...

Kind regards,
Steve
Old 24th November 2009
  #2
Here for the gear
 
🎧 10 years
It's definately a SC-33. It looks exactly like the picture labelled as SG-33 about 3/4 down this page:
Ashly Audio Historic Parade - our back pages
I'm pretty sure that picture is a SC-33 that's been mislabled as a SG-33, because if you click through to the PDF the real SG-33 looks different e.g. all black knobs vrs silver centered knobs.

The SC-33 cut sheet is here:
http://www.ashly.com/images/relics/sc33.pdf

And the fantastic manual is here:
http://mpe.berklee.edu/documents/stu...hly%20SC33.pdf

Regards,
Steve
Old 24th November 2009
  #3
Lives for gear
I'm not comfortable diagnosing problems because I just started getting into modifying equipment, but I would start by replacing all the electrolytic capacitors, especially in the power supply section. If you decide to do that I'd bump up the values in the PSU, at least doubled. Nichicon HE and Panasonic FM series electrolytics seem to be favored. You can also bypass them with WIMA polyprops. That really helped the noise of my DBX 163X's I just re-built.

E-mail Ashly for the schematics. They e-mailed me what they had for my SC-50 that's in the mail and I didn't have to pay.
Old 24th November 2009 | Show parent
  #4
Here for the gear
 
🎧 10 years
Hi upinflames,

I've heard that electrolytics can degrade over time, is this fizzing sound one of the symptoms? I describe it as fizzing because there's more than just noise, there's a continuous hiss with irregular crackles on top, if that makes sense.

When you say bypass with polyprops, are you referring to adding a smaller value capacitor in parallel to the power supply electrolytics? If so, what sort of value / ratio compared to the electroytics?

Cheers,
Steve
Old 24th November 2009 | Show parent
  #5
Lives for gear
Quote:
Originally Posted by SteveJ ➑️
Hi upinflames,

I've heard that electrolytics can degrade over time, is this fizzing sound one of the symptoms? I describe it as fizzing because there's more than just noise, there's a continuous hiss with irregular crackles on top, if that makes sense.

When you say bypass with polyprops, are you referring to adding a smaller value capacitor in parallel to the power supply electrolytics? If so, what sort of value / ratio compared to the electroytics?

Cheers,
Steve
Yes Steve, you got it right. You can just solder if to the back side of the PCB. .1uF is the most common I've seen used, but some use .01uF. .1uF has better low frequency response, .01uF would have better high frequency response.

Bad op-amps also hiss. It might be worth replacing those.

This is probably getting a little costly
Old 27th November 2009 | Show parent
  #6
Gear Head
 
🎧 10 years
i had this problem too once. opened it up and adjusted the vca and its quiet again. might not be the right way but it worked. try opening it up. everything is labeled
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