dbx 165 Frequency Response Issue

[gg85]

Hey guys, I've been searching all over the internet for some help with this but struggling a bit. My dbx 165 is compressing fine, but I'm getting a low roll-off from about 250Hz down. When I press the bypass switch the signal sounds normal to me but when I engage the compressor I lose bottom end. Voltages look good, and I've also swapped out the output mute FET's in case they were causing any issues, but the problem is the same.

Does this sound like a VCA issue? I don't have one on hand to swap out so I thought to ask for some advice on it before I spend the cash and wait for a new VCA to arrive.

Thanks!

George

 

[PRR]

> Does this sound like a VCA issue?

No.

 

[mjrippe]

Replace any electrolytic caps in the signal path.  LF loss is a sign of failing caps.

 

[fazer]

also a 165 has a detector input on the back that is balanced and has jumpers from the input.  You may have one leg lifted on the input or detector input, which will roll off all  bass.  usually higher than 250 however.  Check wiring in back on the Input.  The output can work unbalance but check it also.

 

[JohnRoberts]

+1 frequency response of the side chain can appear like a path frequency response error, but to over compress bass would require boosted bass in the side chain which is unlikely,

VCA is probably cap coupled. Check that capacitor.

JR

 

[gg85]

Thanks so much guys. Gonna get it on the bench in about  an hour. I'll let you know how I go!

 

[Gene Pink]

Thanks so much guys. Gonna get it on the bench in about  an hour. I'll let you know how I go!

If you have a signal generator that does square waves, and a 'scope, put a 60Hz square wave into the input at a moderate level.

Use the 'scope probe to look at each side of every capacitor in the signal path, any significant waveform difference from one leg of a cap to the other, it is rolling off lows, replace it. Keep testing, it is likely not the only one where some of the uF's have evaporated away.

The exception being any high-pass filters that are supposed to do that. These are easy to spot, they generally just change the angle of the horizontal part of the square wave, if the filter freq is a good amount lower than the sq wave test signal.

Of course, ideally just replace them all, if the thing is old.

Good luck with it.

Gene