D-AOC PCBs - the building and help Thread

220V from Transformers secondary is indeed a bit low. Nevertheless your problem is somewhere else. Vactrols could be the reason but pot wiring as well. Don't care to much about the low voltages. The tubes are quite forgiving.
Bernd

Hi Bernd,

Thanks for your help.
I thought that because of the absence of compression was due to vactrols.
Anyway I had a doubt about the wiring of the stepped attenuators that I used for all controls of threshold, input and output.
I also tried to change the position of the wires, but have not had any results.
Now I have the attenuators connected on PCB in this way:
IN = on first pin (-> R108)
OUT = in the middle
GND = on third pin (ground)
The connection shown above is correct?

The connections shown refer only to the wiring of threshold attenuator.

Hi there,

Channel left is working now.
Bypass PCB is working too.
I continue to investigate on the right channel that is not operational yet.
With the stereo link active and through the VU meters I can see the two channels that work,  but no audio output on right channel.
No audio on right channel in dual mono mode as well.
I also swapped the valves between the two channels without any results.
Vactrols seem to work, then the problem is to be found elsewhere.
More news to follow...

Good news! With a working channel it will be easy to repair the non working channel.

Any mistake you found yourself is a good mistake. You'll learn from it and won't make it again.

Bend

Solved! The problem were the two pins (maybe one) of the molex of the input transformer badly crimped.
I was looking for the problem in the circuit, tubes, vactrols, attenuators, etc... no words!
Today I did some testing and I must say that this compressor is one of the best I've ever heard so far.
A 20-year career spent in recording and mastering studios I had the chance to try a multitude of tube and solid state compressors and it has nothing to envy to those blazoned $$$ on the market nowadays and some old designs from the past yet.
So I want to thank Rowan for the design of this amazing compressor, to Volker for PCBs and helpful advices, to Kubi for mods and all those who have tried before me and gave me the right direction to follow for its build.
And last but not least, I want to thank Bernd for not having made me feel alone in these days on this thread and his useful tips and support
I still have to do a bit of testing, changes and improvements on it, after that I'll post some photos showing what I got.

I wish I had made the post to suggest checking your crimp connections as I had a similar issue with my build although intermittent.

I have bought a proper crimping tool since then and I would advise you do the same, if not already.

Hi Druu,

I had thought of everything except for that trouble.
It's amazing how a small problem can become a headache in researching problems.
However, I am using a good crimping tool, it is not expensive and quality as that of the Molex brand, but it really does its job well. I did not do mine, obviously

Unfortunately my D-AOC recently developed a  problem:  There's significant hum (-60 db on my converters input) present on both channels indeptendent of input or pot settings. It has a very prominent 100hz component (almost 30 db higher than 50 hz). Changing grounding etc. doesn't do anything, everything is transformer balanced. DC Voltages seem to be OK, but I've looked at the B+ with a scope and found +/- 3V of ripple present. 

Otherwise it is working fine. I've got the Kubi advanced mods installed.

What to do? I love this compressor and need to get it back to working fully . Thanks!

living sounds said:

Unfortunately my D-AOC recently developed a  problem:  There's significant hum (-60 db on my converters input) present on both channels indeptendent of input or pot settings. It has a very prominent 100hz component (almost 30 db higher than 50 hz). Changing grounding etc. doesn't do anything, everything is transformer balanced. DC Voltages seem to be OK, but I've looked at the B+ with a scope and found +/- 3V of ripple present. 

Otherwise it is working fine. I've got the Kubi advanced mods installed.

What to do? I love this compressor and need to get it back to working fully . Thanks!

Click to expand...

What does the B+ look like unloaded?  A tech showed me a tip once dealing with ICs simply to desolder/lift the power rail pin and measure the psu rail DC with the scope as it would show any ripple as well.  Dealing with a lot higher voltage but maybe it would help to identify if it is coming from the psu rail maybe regulator is unhappy or something else upstream failed.  Is your room hotter, maybe higher temp wearing on the reg?

MicDaddy said:

What does the B+ look like unloaded?  A tech showed me a tip once dealing with ICs simply to desolder/lift the power rail pin and measure the psu rail DC with the scope as it would show any ripple as well.  Dealing with a lot higher voltage but maybe it would help to identify if it is coming from the psu rail maybe regulator is unhappy or something else upstream failed.  Is your room hotter, maybe higher temp wearing on the reg?

Click to expand...

Thanks MicDaddy! I found out that traces have been burned in the B+ PSU section...

Reconnected them, this lowered the hum but it's still way too high.

This was an early, rather sloppy build of mine, I'll I think I'll order a new PCB...

I've measured continuity between pin 2 and 3  of the TL783. The 3 Zeners and the 1N4004 test OK.

So I guess the regulator is broken?

Hi all,

After completing all tests and had a long burn-in for tubes as well as for audio transformers i confirm the quality of this compressor. I really love it!
Here are a few pictures.

^ wow Unit-8, that is incredible!  I'm about to finish mine and you've given entire new inspirations on what to try to do... care to share what all you have going on?

What is that enclosure on the far right?

What are those switch/pcb assemblies, are they custom or off the shelf available?

Hi MicDaddy,

Thanks for appreciating my work!
The small box on the right you see is an AC / DC - 220v to 5v converter that covers the demand of current required for operation of the 4 relays of bypass.
The toroidal transformer also has an output of 5v as the converter, but with only 0.5A which are not enough to drive all the 4 relays at the same time unfortunately.
All PCBs you see apart the main board, of course were drawn by me and then etched by a company in Italy.
I thought to the PCBs for the 4 switches Elma type 01 (1 pole - 12 positions) to create the resistor networks for the input and output attenuators.
The threshold switches are the Elma type 04 (1 pole - 24 pos)
All the attenuators have a 1 dB step.
To change the slope I used 2 ALPS switches (2 pole - 5 pos - no shorting)
On the red PCB there are mounted 2 pairs of vactrols as the Kubi mod plus one resistor and 3 LEDs that modify the compression slope (Volker mod)
From soft to hard compression I used: position 1) 100K resistor, 2) white LED, 3) blue LED, 4) red LED, 5) 2 pairs of vactrols with one in reverse that work together.
With the use of the resistor as well as the 3 LEDs just one vactrol (no reverse) works.
After trying different resistors and LEDs, with this combination I found the compression curves that work well for me according to my tastes.
I hope this helps.

Got my D-AOC up and running again. The TL783 was the culprit, presumably because of the plastic insulator inlay being faulty and thus having created a short to ground via the heat sink at one point. It might have melted through, as this thing gets pretty hot. Hope it won't happen again...

living sounds said:

Got my D-AOC up and running again.

Click to expand...

Well done! 

Unit-8 said:

Well done! 

Click to expand...

Thanks, couldn't live without my favourite vocal compressor. 

Unit-8 said:

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That's one of the coolest faceplates I've seen here in a while... Where did you get those knobs from?   

Hi Mitsos,

You are welcome! It 's always great to receive compliments after a hard work. 
Knobs are manufactured by the German company Mentor and you can buy them online from Farnell or TME.
Probably you find them also from RS, Mouser or Distrelec, but I'm not sure. Try to take a look.
From the Mentor website you can also download the catalog in pdf format where all the data about them.