Hello

I bought a used dbx160A and testest it with noise connected to my RME Fireface. It sounded really dull in the high frequencies so i decided to test it with noise and an analyzer. The resulting measuremts are with "bypass" pressed and non-pressed on the dbx.
I found an rolloff in the high end. Its nearly equally with the 1/4 audio jacks and the xlr jacks.
Is it broken? Do you have any tips?
I attache a jpg.
Thank you so much

Sounds like something is off. Open it up and see if any caps are leaking.

Oh...thx for the tip. I opended it, but couldnt see a leaking cap.

I literally JUST finished one of these tonight. First of all.....dbx needs to get their **** together with these things being so expensive new.
They use some very mediocre parts on a 30+ year old design.

Secondly....I didn't graph mine before and after but it's likely not very broken if at all. These use some really cheap op amps that could certainly be dimming things. Or the VCAs could be adding some distortion or rounding off the highs. What were your settings, were you affecting anything with the compressor circuit? Or were you just passing through with a very high threshold? That matters quite a bit because if you were slamming it a lot of compressors of this style will round off the highs.

There are several mod threads around on the internet. Basically you can replace all your electrolytic caps with high quality ones. Make the big ones by the power transistors like 2200uf or something. The little ones on the other side just need to be low-esr. There's a bunch of 10uf 50v caps in there. Decent audio caps are fine there. I think there's one NP.

The weirdest thing in there are these ancient tl074's which are the 16pin quad versions of the loathed tl072. I recommend socketing these as well and dropping in some tle2074 which is the TI updated version. And really a nice unsung opamp imo. I think one does the side chain but the other does at least one part of the gain/threshold. I never found a schematic just noodled about with the scope. There are trim pots around each vca and the tl074s.

My original problem with the 160a I just finished was there was an actual bad NE5532. Never seen that. It got internally bridged somehow and cooked the previous transformer without burning up the pcb. Pretty odd. Anyway, socket the 8dips as well. 5532 ain't terrible but I'm sure many people on here will have their favorites. The lf363 I swapped with a tle49720 because they're usually pretty stable off the bat.

I may have missed some things because I ended the night with a couple beers but don't worry too much about. These things are pretty low-fi when hit hard. That isn't always so bad. But it can be limiting and disappointing too. All because dbx didn't want to spend an extra $6 on better parts. Oh also, if you ever want to swap vcas the 2180s are pre-trimmed so you can lose a trim pot there. I know Jim Williams has mentioned doing this as he likes clear sailing wherever possible. Good luck!

Final note: I wrote DBX (Harman) about my 160a and their customer service has devolved into pure garbage. The guy told me no one was there any more that knew anything about the 160a or any vintage models....I was like....you still sell these dude! Then I asked where I could find one of the "dbx V1" chips. He sent me a link to google search for "v1 chips". Wow.

Again, good luck!

Oh, that are not so good news.
I think i will buy another one and try it. Couldnt work with the roll off.
Hm....yes, the compressor threshold is at highest point, so it isnt compressing or processing.
Thank you so much for these informations