pucho812

api 550a weirdness console vs rack
« on: September 14, 2011, 06:07:01 PM »
this one has me p[uzzled. I got an original API 550A that was pulled from an API console( Vintage custom) because when the eq is plugged in, the corresponding channel has audible distortion. Without the eq the channel sounds good and if I patch around the eq audio is good.  Yet I can't duplicate the distortion other then having the eq in the console. If I take the eq and use it in an API 500 series rack, it works flawlessly and sounds good. More over if I move the eq around to a different channel, the distortion follows the eq.

Is there a difference in pinouts between vintage console and  500 series rack?
You tell me whar a man gits his corn pone, en I'll tell you what his 'pinions is.


horvitz

Re: api 550a weirdness console vs rack
« Reply #1 on: September 14, 2011, 06:25:55 PM »
-2 vs. +4 inputs?  Pins 9 and 10..

pucho812

Re: api 550a weirdness console vs rack
« Reply #2 on: September 14, 2011, 06:29:28 PM »
Oh that's possible.  ;) thanks
You tell me whar a man gits his corn pone, en I'll tell you what his 'pinions is.

horvitz

Re: api 550a weirdness console vs rack
« Reply #3 on: September 14, 2011, 06:36:56 PM »
Oh and for whatever it's worth, I have a vintage A here that came with its R2 (7.5k right in back of the input goes to gnd - see the schem in our tech docs section) floating loose.  It just wasn't soldered in on one end.  If I knocked it just wrong, I would get lots of gain and overdrive the first 2520.  I can't imagine that's a common thing but you know, if it happened once..

pucho812

Re: api 550a weirdness console vs rack
« Reply #4 on: September 14, 2011, 06:41:14 PM »
Oh and for whatever it's worth, I have a vintage A here that came with its R2 (7.5k right in back of the input goes to gnd - see the schem in our tech docs section) floating loose.  It just wasn't soldered in on one end.  If I knocked it just wrong, I would get lots of gain and overdrive the first 2520.  I can't imagine that's a common thing but you know, if it happened once..

thanks. update compared the distorted eq with a non distorted one. The distorted one is missing a ceramic cap that seems tied into pin 9/10
You tell me whar a man gits his corn pone, en I'll tell you what his 'pinions is.

horvitz

Re: api 550a weirdness console vs rack
« Reply #5 on: September 14, 2011, 06:47:30 PM »
Interesting.  I've got two schems here.  The one that shows that cap that I think you're talking about (47p sitting parallel to the R2 I mentioned before) I believe to be an older schematic.  The newer doesn't have that anymore.  Doesn't explain your distortion really, but probably you're just looking at different revs of the unit.

pucho812

Re: api 550a weirdness console vs rack
« Reply #6 on: September 14, 2011, 09:51:03 PM »
Probably... this eq rev has a 39pF cap and the distorted one doesn't... both eq's are from the same year so hmmmmm. But yes doesn't explain the distortion.  see when I ran it in the 500 series rack, It was in a studio and was ran at +4. In the console should be the same. and wiring on that end looks to be the same as a good eq
« Last Edit: September 14, 2011, 10:16:55 PM by pucho812 »
You tell me whar a man gits his corn pone, en I'll tell you what his 'pinions is.

jsteiger

Re: api 550a weirdness console vs rack
« Reply #7 on: September 15, 2011, 12:14:04 AM »
In a "typical" old API console, the EQ module is feeding the channel fader which was usually 600 ohms. Probably not the same or similar load while in the rack? Still doesn't answer you question but I have seen some 2503's with very high ringing when not terminated with a 600 ohm load. Not Ed's, I should say only some older vintage ones.
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pucho812

Re: api 550a weirdness console vs rack
« Reply #8 on: September 15, 2011, 12:43:06 AM »
In a "typical" old API console, the EQ module is feeding the channel fader which was usually 600 ohms. Probably not the same or similar load while in the rack? Still doesn't answer you question but I have seen some 2503's with very high ringing when not terminated with a 600 ohm load. Not Ed's, I should say only some older vintage ones.

Interesting. Console does have gml faders. on the inputs.  but  it only does it with this one eq. so there has to be something  different or broken then the others eq's. Other notes is this eq was recapped back in the day and the person who did it destroyed solder pads and such so who knows. Still working on it.
You tell me whar a man gits his corn pone, en I'll tell you what his 'pinions is.

pucho812

Re: api 550a weirdness console vs rack
« Reply #9 on: September 15, 2011, 12:43:59 AM »
oh yeah and thanks for the tips guys...
You tell me whar a man gits his corn pone, en I'll tell you what his 'pinions is.


jsteiger

Re: api 550a weirdness console vs rack
« Reply #10 on: September 15, 2011, 10:26:30 AM »
Pucho, I remember Dale Manquen telling me that they made some mod's to the O'Henry console when they put in the automation. He didn't recall the details exactly but we gathered that it was to replicate the 600 ohm load provided by the old API faders. The desk you are working on could have a similar mod?

It may be worth a shot to terminate that module while it's in a rack to see what happens. Maybe the 2nd opamp is about to take a crap.
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CAPI is not affiliated with, endorsed by, or sponsored by API.

pucho812

Re: api 550a weirdness console vs rack
« Reply #11 on: September 15, 2011, 11:09:32 AM »
Possible. The joys of having a desk sans any documentation.  One of the original techs who installed the console is coming out today for a tutoring session. I'll grab all info I can.
You tell me whar a man gits his corn pone, en I'll tell you what his 'pinions is.

pucho812

Re: api 550a weirdness console vs rack
« Reply #12 on: September 16, 2011, 07:38:50 PM »
eq fixed. Faulty caps and a failing op amp. all console problems are all fixed and just in time to find a box full of what appears to be documentation and schematics and so forth.... DIY is going to have a field day when I get those all scanned in and ready for viewing.

You tell me whar a man gits his corn pone, en I'll tell you what his 'pinions is.


 

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