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Old 8th November 2010, 08:02 AM   #1
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Default Studer A-779 caps?

Hi there.
I've got a Studer A-779 mixer, which developed a buzz.
I found one dry joint on a big cap near the PSU, but the buzz was still there.
Upon dissconnecting all the channels, then plugging them in one at a time, i narrowed the fault down to one channel strip board.
this board has about 19 x 100u 16v caps on it, some of which look like they've leaked a bit.
can I get any equivalent capacitor, or would someone be able to recomend me a good one please?
I've found some for 16p each, but i'm a bit worried they might be rubbish, and for the sake of a few quid, i'd rather do it good, if it'll make a difference.
also, should i do all the channels while i'm in there?
any other things it's good to check / change on a 30yr old mixer?
any help much appreciated.
Studer/Revox forum wasn't very helpful.
Ta.

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Old 10th November 2010, 11:04 AM   #2
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You'll have to recap all of the caps in the unit . If they aren't leaking they'll be soon or dryed out. Elna Silmic or Muse would be good choices, but cost more than the 16p. Use 25 volt caps for the 16 volt caps if they fit physicaly and the cost isn't too high. Given the 19 caps a channel there is a bit of work changing 200+ caps. You might want to look at the opamps too if their used for newer ones.
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Old 10th November 2010, 06:11 PM   #3
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Caps on order, cheers.
too late to get your recommendation, i'm afraid.
I got a load of Nichicons in the end.
I hope they're ok.
I could send them back if they're no good?
I was wondering about the op amps, and the VCA's, too.
to be honest, it's not sounding as good as i'd hoped. a bit flat. there's no 3D 'out-of-the-box' going on compared to some other mixers. Is there a more modern op amp & VCA you could recommend? can they just be swapped out? TL072's maybe?

theres loads of RC455P, and one MC 33078p i think, although the writings so gobsmackingly small, i really struggled to read it.

I just noticed a TL052. is that a predecessor of the 072?

Thanks for your help BTW.
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Old 14th November 2010, 10:45 AM   #4
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Quote:
Originally Posted by opus jody View Post
theres loads of RC455P
that should read RC4558 right ? I have good experiences with swapping them for opa2604
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Old 14th November 2010, 11:18 PM   #5
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cool, thanks. i'll check them out.
did you find the sound 'flat' with the old ones in?
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Old 15th November 2010, 09:17 PM   #6
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Quote:
Originally Posted by opus jody View Post
cool, thanks. i'll check them out.
did you find the sound 'flat' with the old ones in?
Well, I can't make any valid judgement yet because I still have to compare the both, pls see my other post about rejuvenating an old korean mixer. I did however swap a NE5532 with a OPA2604 in my musical fidelity v-dac which resulted in a considerably more enjoyable soundstage. Just give it a try, a OPA2604 is just a few euros ...

On a side note, some nice 4558 press over here, ignorance is hiss

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Old 22nd November 2010, 09:14 AM   #7
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Nichiconis is my favorite industrial grade cap - like to use 105c long life low ESR grade. ( likely has steel leads - I prefer muse and silmic because they have non- ferrous leads in the signal path at a minimum - I generally used Blackgates when they were available and that would cost the price of a new car for the 200+ caps you need.

The nichicons will be an improvement on what's there now. The op- amps you have some suggestions for replacements. What about the resistors ? Are they metal or carbon film? This could become a lot of work for a major rebuild. You have no choice about the needing to change the caps as the unit would cease to work soon. Getting better performance would take newer oppamps and resistors - at that point is it better to buy a newer unit ( I prefer to restore old classics, rather that buy new , making I should take up something more productive like smoking or binge drinking)
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Old 22nd November 2010, 10:00 AM   #8
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Hi.
Thanks very much.
I've re-capped the faulty (buzz) board, and am just about to have a go at finding the fault, & replacing the opamps with TL072. then I can do a sound check between that & the other boards, then presumably re-do the other 5 inputs.
I've got a couple of big jobs to do over the next week or so though, so it might be progressing in fits & starts.
I don't think I'm going to do the resistors. It's hard enough getting the caps out without trashing the circuit board tracks.
i'll be putting IC sockets in for the opamps too, in case they need to be changed again.
Oh, and i'm going to build some wooden sides on it too. shame not to really.
Shall I put pics & listening results up as i go? is anyone interested?
cheers, Jody.
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Old 22nd November 2010, 10:19 AM   #9
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Originally Posted by opus jody View Post
It's hard enough getting the caps out without trashing the circuit board tracks.
You are using desolder litze i presume, without it you are pretty much set to destroy your pcb, specially 8pin dips ....

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Old 8th December 2010, 01:22 PM   #10
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All good thanks. I've been snipping all the legs off the op amps, and removing the legs from the board afterwards, individually, then inserting 8 pin DIL IC sockets for the new opamps.
I've replaced all the caps on the channel with a buzz, and replaced all the rc4558/rc4559's, and was pleasantly surprised when it all worked great, and now with no buzz!!! woop woooop.
just the loud noise floor to fix now. probably PSU caps.
so, i've ordered the rest of the caps & opamps for the other 5 channels, and for the master channel, and new caps for the PSU board.
I've got 3 mixers, and one of them has to go.
- a vestax PMC500, which sounds best, but keeps falling apart,
an ecler sclat, which is 2nd on sound, but solid as you like,
and the studer.
I'm really hoping i can get the sound up to spec, if so, then I'll keep it.
awesome engineering quality, and connectivity.

Thanks for all your links & sugestions.
I'm going to order some OPA2604, for checking out.
which ones though?
OPA2604AP
OPA2604AU
OPA2604AUE4
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