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DDA Q console: recapping, modding and fader replacement
Old 16th January 2020
  #1
DDA Q console: recapping, modding and fader replacement

Hey fellas.

This is my first post on the Geekslutz section and I'm just a humble recording engineer who barely knows how to use a voltmeter, let alone read a diagram, so be gentle please

I run a lovely DDA Q which along with a 2" tape machine is the heart of my studio. And while my MTR-90 is almost like new, the DDA need some love. Especially with headroom, where it seems to sound "exhausted" if I'm not very careful with gainstaging. I got a torrent of questions, so for the sake of your sanity I'm gonna list them in each their section although some of them are connected.

Would be grateful if you can give me a bit of advice.
My plan is to have an experienced guy drop by and doing the master section as its more risky and trickier than the individual channels. After that I'll try and gain the courage to recap a few channels myself as well as changing some faders that are too scratchy and have been bugging me for a while.

1. Where in Europe do I buy Panasonic FM caps or something equally good?

Which values do I need for the master section and while I'm at it the channel strips? For the master I'd love to do the bypass cap thing, that is said to improve the sound a fair deal.
The schematics is here: http://ddaconsoles.com/pdf/schematic...schematics.pdf
And here's a thread on GroupDIY that discuss the mod: https://groupdiy.com/index.php?topic=57729.0


2. Which faders do I need?

The originals are Alps and says 006K - 10 KA.
I suppose they come in different sizes. Any way to make sure I get some that would fit?

3. What about the transformer option?

Where are they supposed to sit? They're for the mic inputs and if I proceed with this it's just gonna be for two channels in the first place. I find myself using an ancient Yamaha live desk as a pre for vocals and I suppose trafos in the DDA could get it closer to this sound although more hifi and more convinient to use.
According to David Dearden it's built to accomodate a 1:1 Neutrik NTM1. Is there room for it on the channel cards? I'm struggle to figure out how?
Old 17th January 2020
  #2
First thing you should do is recap the power supply. This might be the source of your headroom problems. Too many channels get going and the PSU can't keep them properly powered. Could be why you have scratchy faders also.
If the PSU has never been recapped, this makes it even more important.
I suspect Digikey will ship Panasonic caps to you. Might not be the case (don't know where you are), but check them out.
Forget about the transformers, or just try them on a few channels to see what you think. The posts I saw about them did not speak highly of them sound-wise. Their main purpose is decoupling mics in noisy environments. On my S Series, there is a space on the input channel PCBs ready to accept them. But this should be the least of your concerns. Recapping the channels will give you better results, if it has never been done, and you might try bypass caps on a few to see what you think.
Bypass caps are easy and worthwhile on the output section. Did that to mine and loved it. Lots of info online about which ones to use.
Can't help you with the faders. I dismantled and hand-cleaned all of mine, and they seem to be doing OK. Not recommended.
My only recommendation is replace all coupling caps with 220uf caps to keep the low end happy and in phase. Worked like a charm on mine.
Get a nice temp-controlled soldering iron and look at tutorials online about reading schematics. It's not that hard... understanding them is what's difficult.
Great boards, but keep it under your hat!
Old 18th January 2020
  #3
Quote:
Originally Posted by tchgtr View Post
First thing you should do is recap the power supply. This might be the source of your headroom problems. Too many channels get going and the PSU can't keep them properly powered. Could be why you have scratchy faders also.
If the PSU has never been recapped, this makes it even more important.
I suspect Digikey will ship Panasonic caps to you. Might not be the case (don't know where you are), but check them out.
Forget about the transformers, or just try them on a few channels to see what you think. The posts I saw about them did not speak highly of them sound-wise. Their main purpose is decoupling mics in noisy environments. On my S Series, there is a space on the input channel PCBs ready to accept them. But this should be the least of your concerns. Recapping the channels will give you better results, if it has never been done, and you might try bypass caps on a few to see what you think.
Bypass caps are easy and worthwhile on the output section. Did that to mine and loved it. Lots of info online about which ones to use.
Can't help you with the faders. I dismantled and hand-cleaned all of mine, and they seem to be doing OK. Not recommended.
My only recommendation is replace all coupling caps with 220uf caps to keep the low end happy and in phase. Worked like a charm on mine.
Get a nice temp-controlled soldering iron and look at tutorials online about reading schematics. It's not that hard... understanding them is what's difficult.
Great boards, but keep it under your hat!
My hat ain't big enough to hold a console... otherwise I would sure hide my spare Q-series there.

All sillyness aside, thanks for a great and encouraging post... will definitely check out Digikey first thing tomorrow. Still not really sure what caps to order though, would you happen to know? Gonna ask the tech that have done some repairs to it throughout the years including recapping a channel and going through the PSU. When we got it five years ago the PSU was moody and we had it fixed and modified including a fan and some other mods suggested by a very DDA-loving user on Homerecording.
Wouldn't think it got bad again after such a short while?

Been cleaning the faders to my best ability and while a lot of chain smoking is taking place over the desk while tracking I keep the desk pretty clean. The headroom issues didn't start occuring till I went from a Fostex G16 running minus 10 to my current Otari. Some of my issues comes from me having to get used to the lack of transient response of VU's compared to LEDS with peak readings on the G16, some of them coming from the Otari accidentially being calibrated two DB too hot for a while which is now taken care of. And it got better. But there's still a few busy songs were the transients seem good when I solo the track, but in the mix it turns overcooked. I managed to calibrate the subgroups to be within spec but I can't turn the master input down from their current level which is a hair above 1.226v. Would like to try taking it to 0.775V (0 DB) to make it a better match for the PR99 that'll be replacing a B77 (RIP dear record amplifier) in a few days.

It has a lot of trimpots and while I managed to set the meters well enough, I struggle to make sense of the rest but I assume that those that might affect the internal gain structure could be the key to solve this headache?

It also seems to help to only use the sub groups sparingly.

A lot of info and a lot of confusion, hope it all made sense somehow.
Old 18th January 2020
  #4
Talk to the guys that worked on the PSU and see if they replaced the caps. If it's not being moody any more, they might have taken care of that. If those caps have never been replaced on a 30yo PSU or board, they should be. Almost any new cap of the same value will be much better. I used Panasonc FM or FC from Digikey for most replacements, tho I went with slightly higher value filtering caps in my PSU, which a local supply store had in stock.
Bypass caps on the output module will help you hear the transients much better, and I highly recommend the 220uf caps on all coupling caps (the ones that pass signal).
My other best advice is to ignore any ideas about replacing ICs. This is not to say that advantages can't be had there, but I'd restore the mixer to it's original state first, before opening that can of worms.
Having restored a few mixers, I know the temptation of trying to do everything at once while you have it apart, but one of the beauties of the DDA is that it's modular, and you can still use it as you work on channels, unless you are working on the outputs.
From what you say, it sounds like you are using it a lot, and getting along with it.

Years ago, someone had a comprehensive website regarding their research into restoring a Soundcraft Ghost, which is similar in basic design to the DDA. Unfortunately can't find it now, but it would be useful if it still exists.

Here is my groupDIY thread about restoring my S Series
https://groupdiy.com/index.php?topic=53911.0
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