Problem with API 525 compressor - Please help!

[stefansko]

Dear Gearslutz,

I just got a lunchbox with an API 512c pre followed by a 560 equalizer and a 525 compressor. Now, I know that many of you out there have these units in use, so I think you're able to help me.

The problem:
I can produce a super clean signal with the preamp alone or together with the EQ, but when I switch on the 525 (2:1 setting) the signal becomes noisy/distorted, even at very moderate settings. I had the 525 replaced but the new one obviously has the same noise issue, it's freaking me out!

Is it generally possible that the 525 can't handle the output level of the 512c pre even though the signal is ultra clean, with absolutely no audible preamp distortion and the VU meter never above zero? I mean is it possible that units of the same brand, even of API, aren't matched to each other in terms of signal level?


I checked all cables and stuff, of course. The longer relase time produces less distortion but the sound's still not clean.
Sure, I'm new to the lunchbox thing but this can't be it, right? So, what do you think, where's the problem? Would anyone be as kind as to test their 525 with the settings I used?

THANKS!!!

[A LaMere]

I don't have one here to test... but if you're taking a tele signal and passing it through the different outputs of different pickups may or may not have the same effect...

In my experience the 525 always reacts this way when hit HARD.... you can't really crush things with them like you can't other comps... that's been my experience anyways.... they kind of pop or distort when you try to crush things... they have to be used in kind of a more mellow way.

It simply sounds to me by these tracks that you are hitting the 525 too hard... ??

Hope this helps,

[stefansko]

Thanks for your reply!

I don't think I'm hitting the 525 too hard, I don't even get a clean sound out of it when I turn the gain of the 512c fully down and the VU moves between -12 to -6!

To me it seems that the 525 somehow is just not made to handle electric guitar, it might be great for vocals and other stuff, though.

Even when I use the pad on the preamp and set the gain so that the sound is pure and the VU not even touches -12 (!) the 525 distorts. And this, as I said, even at very very moderate settings, the gain reduction never being higher than 4. This is not good.

S.

[johnnyjellybean]

I don't know why?.......... I POUND mine and it never distorts. The pre distorts before the 525

[Jack Pettit]

The Telecaster humbucker is a crazy hot pickup so that's part of the problem.
I think that while that low Z input is really cool for bass and the 525 will be very cool for that, I wouldn't use it for a guitar amp.

[Ollie]

Turn the pre volume down so it is lower going into the comp, then use the makeup gain on the comp to get the level you need.

[stefansko]

Originally Posted by Jack Pettit

The Telecaster humbucker is a crazy hot pickup so that's part of the problem.
I think that while that low Z input is really cool for bass and the 525 will be very cool for that, I wouldn't use it for a guitar amp.

Thanks for your post. In general I wouldn't go directly into the preamp with the guitar, just did it for the demo files. But: I had the same issue with a miked amp.

[stefansko]

Originally Posted by Ollie

Turn the pre volume down so it is lower going into the comp, then use the makeup gain on the comp to get the level you need.

I did all that, of course. I can turn turn the pre fully down (VU meter at -12) and still get no clean sound from the comp, ain't that crazy?

Could it have to do with the output of the comp feeding its input?

[Jack Pettit]

Something is wrong, I use that setup all the time with no problems.
I'm gessing you have checked the cables, and made sure the module is seated properly.
I don't have anything more.

[stefansko]

Sure, I did check the cables. The crazy thing is that I had the comp replaced and the new one has the same problem. I'm at a loss.

[Doc Mixwell]

A couple of things I would try so as to rule out possible problems

Take ALL the modules out of the Frame,

Put back the 525, in the same slot, Power up the box/Module, try and feed a similar signal from your GTR [from another preamp that's not in the same frame; you want this thing in there in solo]

If the same problem occurs, then take the 525 out and place another module in the same position and check it to see if it works correctly.

Another test, would be to leave everything out and try the 525 in other slots to rule out the slot as the problem. It does seem unlikely that when you had the unit replaced, it offered the same problem. To my ears...it sounds like its either just overloading, or it has a problem, possibly a 2520 op-amp going south.

Also, have you noticed where the distortion in occurring? Threshold control, ceiling, or output gain. I would push the ceiling all the way UP, and run your pre the way you always do, and adjust the threshold to how much gain you're giving the thing. Get about 4 DB rocking in gain circuit.

"The “Ceiling” fine-tune function, which simultaneously modifies both threshold and make-up gain for precise changes in compression without changes in output level"

There should be no breakup.

[stefansko]

alright, thanks, I did what you proposed.
Taking out all units didn't have any effect, nor did the changing of slots or the use of an external preamp. The distortion depends mostly on the threshold, and to a certain degree on the release time (longest release produces the least distortion but still no clean sound).
What do you mean by overloading? I mean, that's exactly what I don't understand: how can you have a super clean signal from the pre with a harmless output level and when you switch on the compressor the signal gets distorted? Isn't a 525 built exactly to be fed by a 512's signal?
Someone suspected there might be some falsely set jumpers in the lunchbox and/or the compressor that I should check, but I couldn't find any information on that at all. I'm still at a loss. I ordered a second pre and comp (Biz and Action) and will do some more testing with them soon. But so far I'm still at a loss.

[toolstudio]

Hi,

that doesn't sound right. I have a pair of vintage ones which aren't exactly clean, but they
don't distort that way.

As you replaced the 525 with a new one and it is still the same, so I guess either both have a
problem, or it is a gain staging thing.

Does the distorting get more when you increase the input knob ?

wolfgang

[stefansko]

yes, the distortion gets more when I increase the threshold/in, everything above 8 o'clock isn't clean anymore, can't be normal.

In the meantime I checked the comp with a Purple Audio Biz preamp and it's doing the same, whereas going into a Purple Audio Action comp from either preamp, the 512c or the Biz, doesn't produce distortion at all, not even when I crank the 512c up rather extremely. So I suspect, too, that the 525 is kind of defective, as strange as this sounds after having it replaced.

Cheers, S.

[toolstudio]

hmmm, so it's after the input amp from the 525. yes, as strange as it sound I guess it's the 525.

Does it get's less when you turn down the output knob ? Maybe it's driving the next in chain (your hd input) into distortion ?

wolfgang

[stefansko]

thanks, but no, turning down the output doesn't make the signal cleaner. Of course I checked if the distortion is coming from my monitoring system before I started this thread.
When the 525 is in "off" position the signal runs through it clean, causing no distortion whatsoever in my monitoring system. Only when I switch it into compression mode it starts to distort, and that already before the gain reduction even reaches 4 on the scale, ridiculous. When I leave the threshold/in fully down there's no distortion, but of course also no compression... It must be the OP amp of the 525 input stage.

[Arturo00]

Originally Posted by stefansko

Dear Gearslutz,

I just got a lunchbox with an API 512c pre followed by a 560 equalizer and a 525 compressor. Now, I know that many of you out there have these units in use, so I think you're able to help me.

The problem:
I can produce a super clean signal with the preamp alone or together with the EQ, but when I switch on the 525 (2:1 setting) the signal becomes noisy/distorted, even at very moderate settings. I had the 525 replaced but the new one obviously has the same noise issue, it's freaking me out!

Is it generally possible that the 525 can't handle the output level of the 512c pre even though the signal is ultra clean, with absolutely no audible preamp distortion and the VU meter never above zero? I mean is it possible that units of the same brand, even of API, aren't matched to each other in terms of signal level?

I made a little demo page for you with a picture of my settings and some audio samples here:
http://www.geschmeido.com/api/api_test.html

I checked all cables and stuff, of course. The longer relase time produces less distortion but the sound's still not clean.
Sure, I'm new to the lunchbox thing but this can't be it, right? So, what do you think, where's the problem? Would anyone be as kind as to test their 525 with the settings I used?

THANKS!!!

Hey there, I have (2) 512c -> 550b -> 525a (vintage) and I was getting crackling and clipping...and i deduced that my issue was output level from the pre. As long as the pre gain stays below 0dB, you should be ok further down the chain.

Anyway, I was going to go as far as replacing the Opamps...but decided to do a *very* thorough examination of the problem. I spent hours and came to the above conclusion. I haven't had a problem since...

[johnnyjellybean]

Originally Posted by Arturo00

Hey there, I have (2) 512c -> 550b -> 525a (vintage) and I was getting crackling and clipping...and i deduced that my issue was input level from the pre. As long as the pre gain stays below 0dB, you should be ok further down the chain.

Anyway, I was going to go as far as replacing the Opamps...but decided to do a *very* thorough examination of the problem. I spent hours and came to the above conclusion. I haven't had a problem since...

That's weird because I have a P-Bass with EMG's which are HOT and I don't hear any clipping even when slamming the 525 to the point of +18db on the 512. The only time I hear clipping is when the 512C is in the red which I figure is the pre clipping and not the 525.

[stefansko]

thanks, that consolidates my theory. From the beginning I couldn't believe that a clean and harmless signal from the 512c becomes distorted when run through the 525, that's just not possible, right?

[Arturo00]

I might also add that my problems (which I'm certain I posted on here a while ago) only ever happened when i had more then 6dB of compression and normally on signals with a lot of attack (ie. guitar pluck, big guitar strum, lead synth, etc)..or at least that's where it was most noticeable.

Johnny, I really don't know either. My studio partner wasn't experiencing any issues...and he said that he doesn't use as much compression as i do. But I thought it was ridiculous for a unit of that caliber to crackle when moderately pushed. I guess in the end it was just that i had too high of an output from the pre...but you don't have those problems. interesting...

Also, I have the vintage comps. Not sure how similar they are to the new ones...

[stefansko]

I even tried with a Shure A15AS inline attenuator after the pre. At first, the sounds stays clean but that's logical because the signal is attenuated so much. However, as soon as the comp starts doing its job (when the gain reduction meter starts moving) I had the crackling again...

[wannaberocker]

I think that the "out ceiling" being set to low is what makes it sound like it is distorted. I wonder if these little circuits can handle that?

I don't own one, so I don't know for sure....

[eamblar]

Hi.

It happens the same to me. how you solved it?.
Thanks!.

[stefansko]

I made an a/b comparison in another studio and found out that my comp wasn't defective at all (embarassing moment...). It's just not as easy to use as I originally thought. As soon as I figured that out I used it accordingly (less IN/Tresh with certain signals) and got great results. It sounds terrific on most everything, even in the off-mode it seems to add a little thickness to the signal, I'd never sell it, it's a great compressor, it just takes some time to get to know it really. Hope that helped.

[Shy]

Yes, this compressor simply requires a pretty low level signal compared to most, or things will distort (especially drums' peaks etc). When the output level of the device that goes into it is set "correctly", results are great.

[eamblar]

ok, thank you.

I will try to do it as you say.