DDA S Series Mixer

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tchgtr

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    I just acquired one of these for not very much from a local Craigslist sale. There isn't a lot of info on the web about them, so I thought I'd start a thread here and see what happens. Fortunately, this one came with the manual and schematics.

      This is a UK-made mixer from around 1990. The designers went on to Midas and Audient. The S Series is designed for live work, according to the DDA website (ddaconsoles.com), but I'm finding that it works and sounds great in my home studio. The one I have is a 24-channel version, but it's in a frame that can hold 32 channels, so the search is on for more channel strips. Schematics can be found at the website, but I will post some here for convenience.

PSU
      The biggest problem with the mixer was the power supply. I took a chance on it when purchasing, as the PSU was obviously fluctuating quite a bit when I first examined the board. Meters were swinging about and the V+ and V- indicators on the PSU would go on and off. P48 seemed solid. First thing I did was recap the PSU.
  Opening it up, I found one 12,000uf  and one 10,000uf cap in the +- section of the supply. I'm no genius, but this seems to me to be asking for trouble, since we want the +- voltages to be consistent. The schemo calls for 10,000u in this place, but good ole' All Electronics had some 15,000uf Panasonics in stock, and in they went, as well as replacing all electrolytics in there with slightly larger values.
  However, the voltages were still fluctuating wildly, and it took some more poking and prodding to discover that the problem was merely that the 2N3055/PN3055 transistors were not bolted down to their heat sinks properly. Perhaps the insulation between them and the heat sinks had shrunk over time. It was amazing to me that a light tightening of the nuts immediately solved the PSU problems, and ever since it has been rock solid.
    It has a fan, which was not working, so I vacuumed it out and sprayed it with contact cleaner. Sure enough, with some coaxing it slowly started to rotate and get up to speed. Seems reliable now. I'm glad, because it was glued in place at the factory, and was going to be quite an ordeal to get loose. I imagine I will have to do this at some point in time...
  Voltages are now @ + and - 17.3V. All good, except P48 is up around 51V!

MASTER CHANNELS
  The obvious problems I found were that the left side of the headphones was much quieter than the right, and the Monitor output was strangely putting out mono on one side (into both channels!).
    The schematics were a time saver here. A simple recap of the phones amp fixed the headphones imbalance, and for some reason the wiring from the Monitor out XLR jacks to the card connectors was all wrong. Mix out was OK, and I can't imagine why someone wired the Monitor out the way it was. Once these items were fixed, the Master channels were working fine, and I have since replaced the electrolytics with Panasonic FCs, using stock values everywhere, except in the signal path coupling between stages, where I upped the values to 220uf.
    No bypass caps on the signal path yet, but thinking about trying it. I like the balance on the mixer now and the high end is present, but not strident, so I'm leaving it alone for the moment.

GROUP CHANNELS
    The groups had few problems, other than dirty faders. They have now been recapped, again with 220uf in any stage coupling caps. The schematic calls for 68uf in most coupling caps, but the original coupling caps in the board were mostly 100uf.
    However, these caps had some discrepancies from the schematics.
    C31 was 22uf on all 4 group channels, but the schemo called for 100uf. I installed 100uf.
    In the group and master channels, there are sections labeled EBO 1, 2, 3,...etc.. I assume this means Electronically Balanced Output. On the group channels one cap in EBO 1 (going to the Matrix 1 output) was consistently backwards from the PCB printing as well as the other 3 caps in the EBO section. on all 4 cards. This was perplexing, to say the least. I ended up matching the other caps polarity and PCB labeling, and so far everything seems fine. I'm using Matrix 1 as a send for parallel drum compression, and it works.

INPUT CHANNELS
    All 24 input channels are working great. So far 16 have been recapped with 220uf for coupling between stages. Most mic input caps were 33uf or 47uf axials. I replaced with 47uf radials. I left the line inputs at 100uf as they came with the board, tho I tried 220uf on a few.
    The improvement is noticeable when comparing two-channel material between new and old caps.
    I removed and jumpered C36, as it seemed redundant to me, and so far I'm not hearing any noise or clicking from the EQ switch, which is the only reason I can see for that cap being there.
  Another interesting thing about the input PCBs is the option of an input transformer in the mic pre, but no one on the net seems to be able to find any info about what transformer might be used. There is some discussion of it in a GroupDIY thread (http://groupdiy.com/index.php?topic=30240.msg366794#msg366794). Naturally, this is something I would like to try, at least on a few channels, though I am mainly using the board for mixing, and using the line inputs at this point in time.

AUX/FOLDBACK MASTERS

  There are 4 AUX and 4 FB sends from each input channel (and 4 FB sends from the Group channels), and there are two channel strips on the board to control these. This is a nice feature, especially since each send has it's ow EQ, as do the returns on the group channels. All have been recapped.

METERS
  All 6 SIFAM meters seem to work, but the R output meter does not rest fully at 0, nor can it be adjusted there.
  The manual mentions changing the bulbs in them, but gives incomplete instructions. None light up on this board, but when I try to open them up, I'm afraid of damaging them, as they don't come apart easily, so I've left them alone until I have a better idea or maybe find some info in the archives. I see on the web that other folks have pondered this also.

OTHER WORK

  All knobs and fader knobs were removed and cleaned with a gentle mix of water and hand soap.
  All (ALPS) faders were removed, dismantled, and had years of sound tech grunge and hair painstakingly cleaned out. The rails were then lubricated with silicone oil after being cleaned and blown out.
  Armrest was cleaned and treated with Armor All. It's in amazingly good condition with only one small tear.
    There are two DIY channels on the board that seem to have been for injecting two-channel info into the main mix. I have disconnected them, but they nicely have P&G faders, which I have cleaned and might put on the Master channels.

CONCLUSIONS
    I got this board for $150, which is amazing to me, but it's a good thing I could solve it's problems The sound is a big improvement over the modded Studiomaster Mixdown I have been using, though the design and age of the two mixers is similar. It's full of TL072/74 and 5532/4 chips, which are soldered to the PCBs so I don't have any plans to swap chips at the moment, based on my experience with the Studiomasters (I've restored three of them), which seemed to benefit more from cap replacement and bypass caps than any chip swaps.
    The DDA sounds more transparent and less beefy than the SMs, and the EQs seem very nice with good film caps already in place. They are a pleasure to use, and I don't feel the need for cap upgrades, which were a big improvement to the SMs.
    The board is a pleasure to work on compared to the SMs, since all channels can be easily removed, instead of the need to dismantle the whole mixer to work on it. 
    There are no direct outs on the DDA, but I have lots of pres in the studio so I don't plan on using the board for mic inputs, but the pres do sound good after the recap.
    Each channel has FX send and return, but they are unbalanced, which is fine for my current studio set up. I now have them hooked up to a patch bay, and the mixer interacts well with all my compression and FX so far.
    There are various arguments online as to the quality of these mixers related to other DDA models, but a quick look at the schematics shows me that basically they are all modeled after the same design, especially the S, M, Q, and D series. Routing and flexibility is different from model to model, but the basic design of each segment of the mixers seem to be based on the same circuits.
  My manual came in what appears to be the original DDA notebook cover, and has a page indicating 1990 prices for the various models and options. This mixer was just over 13K USD at the time.
   
QUESTIONS/COMMENTS?

  1. Can anybody suggest a mic input transformer to try? The PCB cards show it replacing two axial caps (33uf in some of my channels and 47uf in others).
In the GroupDIY thread, someone mentions trying the Neutrik NT4, but says it doesn't work. Schematics show all models of this era DDA having the transformer option, and it's hard to believe they would use a different transformer for each model. Any info here would be gratefully accepted from anyone ho's opened up their S, M, Q, or D series mixer.
  2. Snatchman, are you still around? You started an S Series thread in GroupDIY, but didn't follow up, as far as I can find. Any more info you might have discovered would be a welcome addition here.
  3. Glad to hear from anyone who has experience with the mixers or sees errors with any of the info above. I'm here to learn, and always grateful for any added knowledge from the folks here on this wonderful forum.
 
 

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ruffrecords

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Just a quick note on the phantom voltage. The spec says it should be 48V plus or minus 4 volts so 51V is actually within spec and being a little on the high side is probably better than being low.

Cheers

Ian
 

tchgtr

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Thanks Ian,
    That was one of the things that worried me, so I appreciate the response. I tried one of my more disposable DIY P48 mics and it sounded fine, so I tried some others, and they all sound great thru these pres.
  Liking this UK product very much!
 

David Dearden

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The correct transformer for the DDA S Series console is the 1:1 ratio Neutrik NTM1. The NT4 is an unscreened transformer with 1:4 ratio and is not suitable.

Well done for bringing the console back to life! To see how others approached this situation search You Tube for "Requiem for a console"

David
 

tchgtr

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Grateful for the info David, and honored by the response.
Mixed my third tune on it today and it just gets better and better as I become acquainted with the desk.
Cheers!
 

tchgtr

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...and as for the "Requiem for a Console" video...
Egad! We have what's called the "six-inch service drop" here in the US, but that's ridiculous, and offends every DIY instinct I have. :)
All I can think of is how much I'd like to have some of those knobs, Alps faders, and other goodies.
Hopefully they purchased an Audient or Midas console to replace that one.
 

helterbelter

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well..... that video......no words for that.

The DDA is a fantastic console, period. Since a few years I own a 16ch SSL mixer. But I still have my M series desk, (although i have cut it down from 16 to 8 channels.) I still love that mixer. great sound.
 

3nity

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That video is disgusting.
Congrats on the console tchgtr.
Makes me feel all stupid when i sold my 2 Amek Einstein!

Right now in the city theres an Interface for around 1k...

Congrats
 

tchgtr

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  Thanks for reading and commenting 3nity and helterbelter. The more I work with this mixer the happier I get.
    I think we're all in agreement about that video, but it's quite amusing that Mr. Dearden is the one who posted it.
  Here is a schematic of the input channel.
    I still don't seem to be experiencing any problems from bypassing C36 on all channels, and am curious about 2 other things.

1. The schematic shows a direct out, but there are none on the mixer. If I decide I like the pres enough, I suppose I could rig a direct out for a few channels by using the connections on the back of the board to the non-existent channels 25-32, but I hope to eventually find at least two more channel strips.
    I suppose the FX send on each channel could be used as an output. It's even earlier in the signal path, so maybe I'll try that.

2. A previous owner has penciled in a bypass around C43 (right before the direct out) - or maybe it's an unintentional smudge.

The Neutrik NTM1s are about $40-50 each so putting them on all channels would be fairly expensive, but having two as pres could be just the thing.

 

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helterbelter

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Hi,

Regarding direct outs : You could split the insert send (or tap it off and add a balancing driver like a BB DRV134 or an AD SSM type ( I used SSLTechs driverpcb's for this, but you can easily make these on veroboard).
Or, in case you won't use all the auxes, you could use one of the prefader Aux send pots. Remove the 10k resistor after the pot, and again add a driver connected to the taper of the pot. This way you have a gain control for the direct out, and, the PCB of the channelstrip already has links provided for pre or postinsert. However, this way, the direct out will be post EQ in case the eq is enabled. I think you could link the auxpot to the pole of the low cut switch via a blocking cap (68uF is what is usually used in the circuit) , then it's pre-eq/pre insert direct out, and post lowcut/phaseswitch.

Oh, C36....It's a DC blocking cap. Why would you want to bypass it ? It's there for a purpose. Now you're also parallelling R69 and R51 to ground.

C43, again a DC blocking cap. it looks to me it's there for hot plugging of the direct out.. Don't take it out in case you use the direct out on that position.



 

tchgtr

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Thanks Helterbelter,
  I erroneously assumed that C14 (or 16, or 19) would do the job of C36, or if the EQ was engaged, C37. I think I understand what you say about R51 and R69, so I will start putting those back in the circuit.
  Also appreciate your suggestions about installing in a direct out. I have a few nice pres, so still just thinking about it.
Here is the schematic for the PSU.

usekgb- That first video looks like the Tea Party caught the mixer coming across the border. With the price of ammo these days, they could have recapped that thing, and bought beer, too :) 
 

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usekgb

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They had to destroy the mixer to get it out of rental inventory.  Tax reasons mostly.  Kinda sad, really.  I would have happily bought a few channels from them.
 

helterbelter

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Seeing mixing consoles demolished always aches.... Please stop posting them , haha.


Regarding the direct out : well, if you're not sure you'll be using direct outputs a lot, you can always use the insert send as direct out. I used these on my DDA as well for that purpose, I didn't feel the need to change that (amount of labour vs benefit).

By the way, and I think you must have read this before on this forum : if you want to upgrade the sound quality, you should change the TL072 (IC 1) to OPA 2604. Not many opamp "upgrades" are worth it (usually the sound only gets "hyped", but not better useable), but this one is really worth it. Half of IC1 is used for the line input, the other half is used as part of the micpre.

(I have tried other opamps for the EQ and the fader as well, but the 74's are doing their job very well, and a 5534 is already one of the best opamps around. If not THE best for mixing purposes.)
 

tchgtr

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Thanks Helterbelter,
  I saw those channels on E-bay, but they don't show up on the U.S. version any more. I will wait and see if something nearby arises.
There is a S-Series PSU up there (also from the Netherlands), but fortunately mine is working well.
  I have the FX send/return coming into a patch bay, so, like you, I will use that for the moment to try the pres for recording. P48 mics sound really good, probably due in part to the strong voltage the board puts out.
  The first mixes I have done are a bit bright (likely due to my mix habits with the Studiomasters, and the NS-10s I'm using), but it's very gratifying how clean the highs are, and I'm sure I can make them sound just right with a bit more work.
  Happy Thanksgiving everyone!
 

jrowell

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Actually working on one of these right now.

PM me and I will give you my contact, if you can send me all the schems I will tell you how to deal with the meters.

The four meters on the one I have are wired in series. The left and right are in a series pair on their own.

The meters have two internal bulbs also wired in series.

So one bad bulb can knock down all the 4 meters.

Find which meter is open from resistance measurements.

To remove the meter bezel to get at the lightbulbs in front behind the meter glass, heat it gently with a heatgun on low or a gentle application of a hair dryer.

This will make it possible to remove the bezel without prying or breaking it.

Sifam didn't make this series of meters for that long and I can see why.

Replacements are basically unavailable so take your time.

PM me and get me those schematics and I will look up the bulb specs for you tomorrow at the shop.

Might as well replace them all while you are in there or you will be back in sooner than later.

Really the only PITA area on these desks. But a pretty big PITA.

James Rowell

Owner / Head Technician
Sound Service Electronics
www.ssevintageaudio.com
www.facebook.com/ssevintageaudio
 
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Hello,

I would like to know if the insert send (jack output) could be used like a direct out (not cutting the signal path) ?
If there is a direct out on the board it might be possible to wire it to a female jack socket added on the back of the desk ?

Thanks a lot.
 

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