Anyone familiar with the Symetrix SX (208)?

johnpitcairn · 25th March 2005

I have recently acquired a used Symetrix SX208 stereo compressor, which seems like it might sound quite nice for the price. Beefy, but not distorted. The unit is not, however, in the advertised condition. "Works perfectly" - yeah, right.

At the very least, I'll need to clean/replace pots. Feh.

More annoyingly, the three threshold under/equal/over LEDs seem to be injecting low-level background buzz/hiss into the audio circuit when they switch. If there's a little jittering involved, that makes it worse.

Is this a known issue with these units? Given they were aimed at broadcast applications, I wouldn't think so. Or might the LEDs just need replacing? The "gain reduction" LEDs do not seem to inject any noise.

I can probably live with just disabling the LEDs, if it's the LED itself causing the noise (ie not some part of the supporting circuit). The gain reduction LEDs and my ears provide sufficient feedback - but if salvaging the threshold indicators is possible, I'd like to attempt that.

Any advice appreciated.

John Pitcairn

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**Tim Farrant** · 28th March 2005

Hey John,

I am not familiar with the Sx208, but the interference you speak of could be caused by poor earthing somewhere, ie, bad connections or broken wiring. Or the power supply might be in need of some attention. The circuit driving the leds might have lost it's power supply bypassing and is oscillating when switching the leds. This might be a LM339 quad comparator chip singing away to itself. Have you got any schematics for this unit? Have you got a scope you can hang onto the led legs and take a look?

Tim.

johnpitcairn · 29th March 2005

Quote:

Originally Posted by Tim Farrant

The circuit driving the leds might have lost it's power supply bypassing and is oscillating when switching the leds. This might be a LM339 quad comparator chip singing away to itself. Have you got any schematics for this unit?

Thanks for the reply Tim. Found a schematic on the Symetrix website, bless 'em. There's a LM339 running the 5 gain reduction LEDs, but these don't seem to be noisy.

The chip driving the three threshold LEDs is a 4560 (not socketed), pins 2 and 6 grounding through C20 (.056 mylar). Might replacing C20 be a good (and easy) place to start?

Pots have cleaned up nicely, Cailube to the rescue...

Quote:

Have you got a scope you can hang onto the led legs and take a look?

No, afraid not.

John Pitcairn

**Tim Farrant** · 31st March 2005

If you wan to send me the circuit, I could take and look and give you some more advice.

Cheers
Tim.

johnpitcairn · 31st March 2005

Quote:

Originally Posted by Tim Farrant

If you wan to send me the circuit, I could take and look and give you some more advice.

Many thanks Tim - I'll email it to the hq address at Buzz.

John Pitcairn

ulysses · 19th April 2005

If it's any help, I have an SX208 (as well as several other 200 series devices) and I like it. I used to use it a lot on the mixbus or on other stereo feeds. It's a good clean design based on the 2150 VCA and they keep the signal path short an clean. Anyway, I think it's worth fixing up and using even if it isn't worth a whole lot on the used market. I have a lot of respect for Symetrix because they have good designs and they aren't afraid to make their schematics available to their users.

25th March 2005	#1
johnpitcairn Gear interested Join Date: Apr 2004 Posts: 13 Thread Starter	Anyone familiar with the Symetrix SX (208)? I have recently acquired a used Symetrix SX208 stereo compressor, which seems like it might sound quite nice for the price. Beefy, but not distorted. The unit is not, however, in the advertised condition. "Works perfectly" - yeah, right. At the very least, I'll need to clean/replace pots. Feh. More annoyingly, the three threshold under/equal/over LEDs seem to be injecting low-level background buzz/hiss into the audio circuit when they switch. If there's a little jittering involved, that makes it worse. Is this a known issue with these units? Given they were aimed at broadcast applications, I wouldn't think so. Or might the LEDs just need replacing? The "gain reduction" LEDs do not seem to inject any noise. I can probably live with just disabling the LEDs, if it's the LED itself causing the noise (ie not some part of the supporting circuit). The gain reduction LEDs and my ears provide sufficient feedback - but if salvaging the threshold indicators is possible, I'd like to attempt that. Any advice appreciated. John Pitcairn ----------------------------------------------------------------- LC Xview software LC display, LC Xmu Logic Control emulation, Logic environments & stuff: http://www.opuslocus.com -----------------------------------------------------------------

28th March 2005	#2
Tim Farrant Moderator Join Date: Jun 2002 Location: New Zealand Posts: 2,309	Hey John, I am not familiar with the Sx208, but the interference you speak of could be caused by poor earthing somewhere, ie, bad connections or broken wiring. Or the power supply might be in need of some attention. The circuit driving the leds might have lost it's power supply bypassing and is oscillating when switching the leds. This might be a LM339 quad comparator chip singing away to itself. Have you got any schematics for this unit? Have you got a scope you can hang onto the led legs and take a look? Tim. __________________ "Come on, make my day" Dirty Harry (Clint Eastwood) Visit Buzz Audio

19th April 2005	#6
ulysses Lives for gear Join Date: Mar 2003 Location: Minneapolis and Wiesbaden Posts: 1,429	If it's any help, I have an SX208 (as well as several other 200 series devices) and I like it. I used to use it a lot on the mixbus or on other stereo feeds. It's a good clean design based on the 2150 VCA and they keep the signal path short an clean. Anyway, I think it's worth fixing up and using even if it isn't worth a whole lot on the used market. I have a lot of respect for Symetrix because they have good designs and they aren't afraid to make their schematics available to their users. __________________ Justin Ulysses Morse Roll Music Systems Minneapolis, MN Put a bottle of juice in your Lunchbox.

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31st March 2005	#4
Tim Farrant Moderator Join Date: Jun 2002 Location: New Zealand Posts: 2,309	If you wan to send me the circuit, I could take and look and give you some more advice. Cheers Tim.