DDA Q Series console modification/ Referb!

[berkleystudios]

Hello everyone, Its time for another crazy DIY studio investment....


I have a 16 Channel DDA Q-Series console and am in the stages of planning  massive upgrade(s)/ modification(s) on it. the thought of selling it had breifly crossed my mind but I would rather turn it into and even more badass desk.

planned upgrades 

DONE1) Beef up/ recap the PSU -> still needing to Recap with higher quality Caps due to age. It is not an excessively hot PSU

2) revise the monitor circuit -> upgrading op amps, recaping, adding bypass caps. another thread has developed where I am asking help on this topic

3) possibly replace summing circuit with CAPI ACA. -> will not fit, nor will it really accomplish what I want.

4) Jensens on the Mic inputs Using this pretty much solely as a line in mixing console so this does nothing for me.

5) recap all channel strips and master section -> still needing to be done.

6) possibly rechip the 5523 with NOS  Phillips 5532? Not necessary. 

Im sure that is all for right now...
But I have a few questions about each of the steps, most are just for reassurance, other I just dont have a clue haha....

I will link the standard schematics and later upload my planned revisions.

1) Its about time for a recap so starting would like to start the PSU. I have read snips on GS of people upgrading the local PSU caps but they did not go into much detail. I plan on possibly having 2 GAR1731's on my mix bus in the ACA, the voltage should be fine but I am wondering if it will draw too much. even If I dont add them, I have heard there is a sonic improvement to the desk via a PSU upgrade, If there is anything else I should think about changing in the PSU I am all ears.

2)This is one of those parts I am really lost. The Monitor section is amplified by a TL074N.  I would like to completely  remove this amp circuit and replace it with something as clean as possible. I plan on having an ELMA 2x24 10k rotary switch as my main attenuator.  any suggestions on a super clean and flat monitoring circuit?

3) ***Redrawing schematic**** I am currently trying to redraw the schematic to have the ACA in the master section, Really the goal is to get rid of the stock EBOs... I have heard of people on GS saying they had LL5402's on them, and the manual does say there was a factory option to have them, but I dont see where on the schematic.

4) This one is really simple, This console had the option of having Neutrik NTM1 transformers on the in, but I hear they arent that great. I would instead like to have Jensen JT-MB-C's not a direct replacement but they should still work right? Im not over looking something obvious?
http://www.jensen-transformers.com/datashts/mbc.pdf
http://www.neutrik.us/en-us/accessoires/transformers/ntm1

5) No real questions here, planning on recapping with Panasonic FMs... but open to suggestions.

6) Is it worth rechipping to the NOS phillips?  Really big PITA sense all the ICs are soldered, but I would do a labor of love if it was truly worth it.

Stock Schematics
http://www.ddaconsoles.com/pdf/schematics/q-series-schematics.pdf

Thats all for now folks! still in planning mode, will hopefully have some modded schemos soon

-Adam

 

[jensenmann]

1) The PSU sits in the audiopath because it provides a path to ground. That´s why you want it to be as low Z as possible. Recapping helps as long as the new caps have an lower ESR than the old ones. That´s mostly the case if you buy newer products. Renew the thermal grease all over the place. "Beefing up" is somewhat unspecific. That´s GS language without a meaningful content. When you pull close to the maximum current out of your PSU then it gets very hot quickly. Overloading it slightly will lead to thermal shutdown of the circuit (hopefully). So if you want to "beef up" your PSU, then the first thing to look at is how to get the increased thermal load out of the PSU. That´s necessary in case you do things with your desk which demands more current. But first I´d check how far the PSU is from it´s limits. Very often console manufacturers sold the same PSUs for smaller and larger frame desks. With your 16ch desk chances are high that it´s far from it´s limits.

2) Recap your master, increase all coupling caps as far as space permits, add bypasscaps (0,1uF) parallel to each electrolytic, replace your TL074s with TLE2074, solder a 0,1uF cap between B+ and B- directly at the pins/socket of the new chips. Check with a squarewave signal and scope for oscillations.

3) Real estate seems to be the limiting factor to install the CAPI thingy....

4) Is there any technical reason, why you want all that iron added? What is wrong with the original circuits? Neutriks indeed distort at higher signal levels. But check it out if this is relevant for you before you settle on a mechanical nightmare to install these Jensens.

5) see 2)

6) I could hear no difference between all those 5532 variants when I checked them next to another. You can measure a difference, though. But if you add transformers to your desk I bet lowest possible distortion is not your goal anyway.

 

[mdainsd]

Keep us updated in this thread please!

Ive got a 40 channel QII. I love mine and hardly ever hear of anyone with one. Done only minor stuff so far cause each project is times 40 or more.

Wonder if they do share a common P/S? Mine runs for days cucumber cool.

 

[berkleystudios]

Recapping the PSU and cleaning everything. With the console being almost 25 years old, should I try to re apply the thermal paste to all the VRegs?

 

[MHanson]

1) The PSU ... Renew the thermal grease all over the place. ...

 

[Brian Roth]

Clean off all of the dregs first....

 

[berkleystudios]

Ahh I looked over that little nugget. Thanks

 

[berkleystudios]

Okay so I have recapped the master section and power supply.


The master section is working great after the recap and bypass caps were added. Super happy with that, will play with rechiping it soon.


I am having a funny issue with the power supply though, it puts out the correct voltage, but only after about 15 min of "warming up". Very odd. What Spec did I over look?

 

[Rob Flinn]

I had to fix  DDA PSU.  Not sure of the desk model, but it had parallel transistors feeding each rail which were connected together via the pcb.  This connection went slightly  resistive which caused the rails to drop out.  The cure was to connect the transistors together with some heavy duty cable to lower the resistance between them. 

In this instance there were 2 PSU 's for the desk, one for the audio rails & another which from memory was +&- 22v for the logic.  One PSU connected through the other so there was just one cable to the console. Although they were different voltages I think they were the samecircuit. 

Not sure if this relates to you PSU's but it looked like it had happened on the other PSU at some point.

 

[abbey road d enfer]

1) The PSU sits in the audiopath because it provides a path to ground. That´s why you want it to be as low Z as possible.

I would agree with you most of the times, but in the specific case of the Q series and , the PSU rails are distributed via a string of 10 ohm protection resistors, which makes the subject of the PSU's impedance moot.
Indeed, what is "in the signal path" is the 100uF decoupling caps. And the local decoupling caps that are blatantly missing from the schemo. Maybe because they just don't simply exist...?

 

[berkleystudios]

Well The PSU has seemed to fix itself, guess it just needed to fully warm up once.  Putting out the correct Voltages all around and pretty instantly like it used to do . Its a pretty heavy duty PSU so I think all I will do to it is the recap.


the balance of my monitor outs still seems to be an issue. after the recap it seemed to get better, it used to be roughly 10db of difference, with raised the noise floor considerably when the adjustments where made on my focals to compensate. it has dropped to just a few db. possibly 3-4db off, which is driving me bonkers. I have tried so many times to fix this issue that its driving me through a wall. I would like to start chip swapping to see if I can drop the noise floor of the monitor section, But until this is figured out it will just keep causing me headaches.

I also ordered a few of the Bourns pro series  100mm faders. what are yall thoughts on them. the are a few CM shorter that the Alps ill be replacing, but they seem smother than a babies bum, Even the Fiancee picked them out in a blind feel test and said those were the faders i needed to have in the console. at about $280 plus shipping they arent a really a tremendously costly investment, compared to other options, but the alps faders arent causing me any issues at the moment either. My real worry is if they will last, and if anyone has had any issues with the Bourns faders. Their pots have always been a component I could count on.

 

[Rob Flinn]

The problem you are describing which you seem to indicate is intermittant is very similar to one I had with an AMR24 PSU.    In this case the rails were collapsing sometimes.

If your PSU is the same as the one for the AMR 24 which uses two PN2955 & two  2n3055 pass transistors in parallel for the respective + & - rails I would advise doing what I suggested earlier in the thread.  The case connections of these transistors are just made through the circuit board by bolts.  You could check whether there is any resistance between the parallel pairs (with the exception of the bases which are not directly paralleled but fed with 10R resistors).  Even a fraction of an ohm can cause problems because of the high current draw.  Because the tracks can be heated by the transistors the bolted connections can change.  Use some hefty wire to ensure their low resistance.

If you have a different PSU please ignore the above ...

 

[berkleystudios]

2) Recap your master, increase all coupling caps as far as space permits, add bypasscaps (0,1uF) parallel to each electrolytic, replace your TL074s with TLE2074, solder a 0,1uF cap between B+ and B- directly at the pins/socket of the new chips. Check with a squarewave signal and scope for oscillations.

Do you mean the Vcc pins? 

 

[abbey road d enfer]

the balance of my monitor outs still seems to be an issue. after the recap it seemed to get better, it used to be roughly 10db of difference, with raised the noise floor considerably when the adjustments where made on my focals to compensate. it has dropped to just a few db. possibly 3-4db off, which is driving me bonkers. I have tried so many times to fix this issue that its driving me through a wall.

Well, you didn't mention that before...it indicates something's definitely wrong, could be just about anything, from a dirty connector to a leaky cap.

I would like to start chip swapping to see if I can drop the noise floor of the monitor section,

Chip swapping is the last thing to do; you must find the real culprit. 3-4 dB difference judt does not put the indicator on opamps. There is something wrong in the signal path or in the NFB loop. You must use the standard fault-tracing MO, follow the signal and locate where the difference occurs. It's better done with an oscilloscope, but if you don't have access to one, you can use any small amp and follow the signal with a DIY probe, just a 10k resistor in series with a 0.1uF cap. Connect the ground of the amp to the ground of the DUT, the 10k to the amp's input and probe the DUT with the 0.1uF. Make sure the amp is not turned too loud.

I also ordered a few of the Bourns pro series  100mm faders. what are yall thoughts on them. the are a few CM shorter that the Alps ill be replacing, but they seem smother than a babies bum, Even the Fiancee picked them out in a blind feel test and said those were the faders i needed to have in the console. at about $280 plus shipping they arent a really a tremendously costly investment, compared to other options, but the alps faders arent causing me any issues at the moment either. My real worry is if they will last, and if anyone has had any issues with the Bourns faders. Their pots have always been a component I could count on.

I'm not familiar with Bourns faders. Specs show they are not Conductive Plastic, so unless they have made a significant improvement in the technology, they should not be very different than the usual suspects Alps, Panasonic, Noble...
I guess the difference you noted is due to the "newness" factor. Anyway, they look like a good choice. Where did you order them?

 

[berkleystudios]

The balance issue ended up being a broken connection in a connector.

Now that that has been resolved I have re-chipped the master section with TLE2074s for the TL074s, OP275s for the TLO72s, and OPA134s for TL071s.

Super happy with the results. No oscillations, or any issues. Extremely clean and I feel like I have increased the headroom a fair amount.

I definitely notice the monitoring pot seems to be tracking better. I noticed before the recap and re-chip, that at low levels it would output slightly higher on one monitor than the other (prior to the connection issue, I assume that happened from me taking the module out and installing it an insane amount over the past month). It is really hard to find any noticeable difference now.


I ordered the faders from DigiKey. I will probably hold off on the new faders for now, as my tax refund funds are starting to dry up the input channel recap continues. I do not think I will be re-chipping them right now.