Most obvious mod to an ADA8000 - 25-pin D connectors

[pvision]

I've read lots of threads on the ADA8000, most of which make some kind of sense.  I am amazed that no-one's pointed out the most obvious problem - the inputs are on the front and the outputs on the back!

So, to my mind, the most obvious mod would be a pair of 25-pin D connectors on the back connected to the ins & outs

Has anyone done this?

Nick Froome

 

[mingus2112]

I haven't tried this, but it's a great idea.  I've got a SM Pro PR8 that I had "modified" years ago by Black Lion and that's my biggest pet peeve - inputs on the front!

 

[bruce0]

Well DB25 would be nice, as long as all you want is a to turn it into a converter.

You would have to do a new back panel, or cut the old back panel and screw on an overlay panel, because the current one is full.  So you would have to remove some of the board mounted XLR outputs and have both the inputs and outputs on DB25.

No mount screws on the rear end of the PCB, entirely supported by the connectors, maybe just insulating spacers or find a place for a standoff.

It would NOT be good to try to squeeze the DB25's in near the power connector, you can see in the pictures that you would interfere with the 5V regulators, and it would put signal very near power. 

While you are cutting the back panel you could drill and vent the area near the  (notoriously hot) 5V regulators, which would not be such a bad thing either.

As delivered the channel 8 end is noisier (Thus the extra shielding I taped in there in the pictures, I should have twisted the signal leads and rewired the connectors).  I think this is radiated interference from the PSU being picked up by the gain stage.

The front panel PCB is glued in there, I never got it out, don't know how hard that would be.

Circuit issues...  More difficult if you want to leave the front panel inputs in place ( the gain stage and phantom power circuit is in the front panel PCB) you would have to do some switching, or wire directly on to the front panel circuit board (if you could get it out of there). This is because the output of the gain stage output is low impedance, and I think would present very low impedance (500 ohms or less) to the DB25 inputs and possibly fight with them too.  Not too sure about that.

The easier way to just make it a converter.  No phantom power.  No mic gain stage. You could just disconnect the front panel inputs at the pin headers (but leave the 2 LED signal and clip indicator wires).  The 5 pin connectors on the board carry 3 pins of signal and 2 pins of 5V red/green LED and Signal indicator driven by the LM339 comparators.

So you could take out the gain stage (some folks say that it would be an improvement, but general consensus is that the gain stage is not so bad), and run those 3 wires from the connector to your DB25 (twist them), and you would:

1) Retain functioning green signal and red clip indicators.
2) Permanently disable the front panel connections.
3) Get a high impedance input directly to the TL074 (balanced) stage Note: You may want a rectifier bridge to the rails for static/phantom goof protection, and you may want to cap couple it to deal with dc on the inputs.  The existing front panel pcb has the caps (for phantom) but not the bridge, but the TL074 may be more sensitive.
4) A side benefit is that you would be routing twisted wires away from the power and the gain would be external unaffected by the ADA8000 PSU.  So the noise floor should drop some, at least on channel 7 and 8.

If you went that way, I think you could replace the whole front panel too.  Just 8 red/green LED's and the master lock indicator led (circuitry appears to be on the main board, just the LED on the front PCB).  (From a quick look at the schematic)

You could test most of this by pulling the top off, and connecting directly to one of the pin headers in the picture (they are hot glued down) and seeing how it worked.  Pins 4 and 5 are the red/green indicator.  There are nice complete schematics around for this thing.

Ian has some DB25 summing boards that would work for easily wiring up the connection either solder to pad or with a pin header (rather than directly crimping to the DB25, which in my opinion just asks for getting some pin phase inverted)

Here is the inside, from a long time ago:

Back of the front panel PCB, glued in.

 

[pvision]

I bought a broken ADA8000 today so will butcher that one.  I plan to remove the XLR output sockets, blank off the back panel and fit a pair of D-connectors

The front panel has 5 wires to each channel plus a multiway to the phantom switch and the sample rate indicators.  Each channel has two LEDs so it's reasonable to assume the 5 wires are +ve, -ve, earth and two lives for the LEDs. 

If that's the case, and the front panel passes a balanced signal to the main PCB, I could run the input D-conector direct to the main board and lose the mic input & gain trim. There are some diodes on the front board so they may be voltage limiters for the inputs.  I'll work it out using the schematic

I could just snip the +48 Volt wire but as the "new" one I've bought won't power up it probably has a dead power supply. I may scratch the +48 volt part of the PSU entirely

I might do a blanking panel for the front as well and just drill holes for the sig & clip LEDs

BTW I typed this as the post above was being posted so we echo each other a bit!

Nick Froome

 

[bruce0]

Nick:

I like it!

Usually the dead ones burned up the 5V regulators or the transformer.  All or most of the LED's, and the digital stuff of course, are powered by the 5V.  Behringer originally engineered this with a crazy amount of voltage drop forced on the 5V regulators for anyone in the US (wasn't as bad on 220vac).  There is a lot of commentary on the net about it, I won't duplicate it.

Let us know how you proceed.  I only use mine as a converter anyway, and I prefer DB25 connections.

 

[pvision]

OK, broken ADA8000 landed today.  Fuse has popped.  The fuse blows when the transformer is plugged into the circuit board, but doesn't when the transformer outputs are unplugged from the board

Voltages from the transformer are

brown

yellow
  |  44.8 V
yellow

grey
  |  61.8 V
grey

orange
  |  13.85 V
orange

So it looks like the transformer is OK and there's a fault on the board.  Time to locate a schematic!

Nick Froome

 

[PRR]

> Time to locate a schematic!

Why? You know where the PT leads go. Rectifier. Big cap(s). Regulators.

You could even insert say 100 Ohms 1/2W resistors in each secondary circuit, see which resistors smoke and which regulators act happy.

 

[pvision]

> Time to locate a schematic!

Why? You know where the PT leads go. Rectifier. Big cap(s). Regulators.

You could even insert say 100 Ohms 1/2W resistors in each secondary circuit, see which resistors smoke and which regulators act happy.

You're right of course.  A schematic doesn't really add anything except opportunities to waste time looking at details I don't understand, something I've done a lot of today

I'll pull some regulators tomorrow and start testing

Nick Froome

 

[bruce0]

They drop that 13V down to 5V I think!... and a lot of it too... (there are 3 regulators for 5V).  I am thinking those burn up first if the trafo is good.

I think they use the 40V to make +/- 17 and the 60V to make 48V Phantom... but the current is low on those, so the drop is no big deal... but the 13.85V down to 5V ... that is just... well... stupid!

But I think a schematic might help! I am only allowed one attachment, so two posts.

Here is the IO/PSU

take a look at IC1 IC2 and IC7... do they look a little toasty?

Are you in Europe or US? If you don't want to update your profile maybe you could just say "120VAC or 220VAC" instead of a country.

Anyway, I think you can strap these for different line voltages... and people have all sorts of creative ways to try to get the transformers down to reasonable voltages... or just replace the regs and solder on little brass heatsinks, maybe vent the case a little. The 5V regs in a "properly functioning" unit will burn your fingers.

Here is a link to the guys with the autotransformers and light bulbs in series with their ADA8000's http://groupdiy.com/index.php?topic=20591.0 and one guys with an external psu that runs a few.  I have always been of the "a little here... a little there" school.  Put a hi-watt low value resistor in series with the secondary and solder pennies or something to the regulators (that have to stick perpendicular to fit because of they way the are placed) and drill a couple of cooling holes in the case, and maybe your ada will survive.

 

[bruce0]

channels 1 and 2

 

[pvision]

Thanks, those PSU diagrams will make it a lot easier

I am 240 Volt…

Nick Froome

 

[bruce0]

My understanding from those other threads (lots of them) was that the 240V folks fared better on the 5V problem because they didn't have to drop as much voltage (or maybe it was  half of 220 was better than 120).

Good luck.

 

[pvision]

A bit of progress today: I've listed out all the parts to recap the power supply & replace all the regulators.  It's about £7-worth of parts from Farnell

One input mod that is floating around is this one:

The values of the components are those from the front panel PCB and the transistor section of the preamp is bypassed. If I ditch the front panel PCB altogether, any suggestions for the input circuitry?  I am looking at non-polarised capacitors and want to buy an appropriate value

Nick Froome

 

[bruce0]

Suggetion:

Save a bit of time and money... If you plan on replacing ALL the regulators anyway, and you don't plan on testing anything, then I would suggest that you take out (snip) the 3 5V regulators, and plug it in and see if the fuse still blows.  If it doesn't, you can reduce the stuff you replacing (less desoldering, less risk of damaging the board, less parts, less time) to just the regulators.

Also...Did you look at the regulators and see if any have a toasted look to them or the surrounding board?  Any apparent "hot spot" on the board?  Burned or brown looking?  Any burned smell?

Also... Why recapping the PSU... ADA-8000 not all that old, caps probably fine unless you have some other indication (do you see any caps that have goo or brown stuff under them, or have bulging tops)?


The issue with the inputs is I think "either/or"...  Because the output of the front panel transistor gain amp appears to be low impedance I think you can't plug in "between" the front panel and the LT074's.

As far as an input schematic... I think you just posted one.  (i don't know about the 10K resistors, the TL074 has like a gigaohm input impedance or something so I am not sure why they have to be as large as 10k, but I haven't looked at the schematic). 

One other idea, if it was me, I might put a bridge (or 4 diodes) to hold the inputs between the rails, and to stop damage from static, or a goof with plugging in phantom, etc.

Keep me in the loop... I have lots of 500 series preamps now, and I am thinking about turning mine into just the converter... and I like the idea of Db25 Tascam, so I am interested in your progress.

 

[Sleeper]

If you want my 2 cents. I'm on 110v and I did the mod that was posted here years ago. I think it was sssltech.? Works great and never looked back. 

I put right angle trs plugs on my snake/ fan and saved my metalwork for another day. The front panel is really quite manageable this way but it does require an open rack space below to pass these through to the rear of the unit.
I utilize that space below with a shelf that holds a a piece of half-rack wide gear so I haven't sacrificed much room in the rack and I've gained some ventilation.
You can see the leds and use the level control when needed.
Don't overthink it.

 

[s2udio]

If you want my 2 cents. I'm on 110v and I did the mod that was posted here years ago. I think it was sssltech.? Works great and never looked back. 

Keefs mod is the fix !   

Don't overthink it.

Absolutely correct

 

[pvision]

Don't overthink it.

Words to live by!

The ADA8000 lives in a 6U rack with five other pieces of gear, three stereo, two mono.  So there are are no spare rack spaces and the ADA provides the ins & outs for the whole rack.  There's power distribution in the back so it only needs 1 power cable, two Toslink/ADAT cables and (possibly) a Word Clock cable to work

6U racks make the kit portable and not too heavy

I was going to have a patchbay but I think this approach will be simpler & cheaper.  At some point I will upgrade to an SSL Alphalink so using D connectors would make for an easy upgrade

Back to my dead ADA8000: before I pulled anything out I had a quick look round.  The fuses blow instantly with no heat from the regulators… so I check continuity on the socket on the main board.  The plug from the transformer is OK - all the voltages are present.  And - pins 4 & 5 on the socket are dead short.  Turns out C82 is dead short

This was mentioned in another post I saw somewhere - that these caps fail with a dead short.  C82 is a 103 (0.01 uF or 10 nan)

So it looks like the fault with my ADA8000 is a 10-penny capacitor

Nick Froome

 

[s2udio]

Keefs ADA8000 PSU fix thread
http://groupdiy.com/index.php?topic=20591.0;topicseen

 

[pvision]

OK, ADA8000 works again after fitting one new cap.  I've ripped out the XLR outputs, blanked the rear panel and am wiring the D connectors.  I've run the inputs to the back of the front panel jacks to test everything works.  Once it does I'll bypass a couple of input preamps & test the setup before making a final decision on how much of the input to bypass

Next time around I won't desolder the XLRs - I'll chop the pins and solder the wires to the stubs

I'll leave the front panel PCB in place as it has the Sync, Signal & Overload LEDs.  I was going to blank the front panel as well but have decided to leave it as-is.  The easiest way to blank it and get a good finish would be to cover it with a black or silver 1U panel and fit a new mains switch cap

Nick Froome

 

[bruce0]

Congrats on the fix!

Remember to support the back of the PCB somehow.  Someone mentioned that the Optical connectors are very delicate (easy to break off the board), so you don't want them taking any strain.

How did you get the front panel PCB out? (mine was glued in).