D-AOC PCBs - the building and help Thread

[Jonkan]

Any ideas for simple M/S encoding/decoding? MS option would be very nice to have imo.
/J

 

[Script]

Better to build a dedicated box for MS encode/decode than add into this one (little space). Several options around on this forum.

 

[Hobbyist]

Hi,

After testing and debugging the last details, I just can't get rid of my problem with the right channel.. When I pass audio, the frequency response behaves like a 10k High Pass filter .. when I slowly increase the input and output gain, It pops into a "normal" behaviour. but after 10 to 40 minutes, it start to distort and get back to the High Pass "modus". especially with low gain signals.
I measured all the voltages and they are the same on both channels, switched the input and output tubes from the channels,
tried different cables (you never know), without bypass pcb.. ect. No results so far to find the cause of this problem.

Someone familiar with this?
I'm using 5814wa tubes for in and out, could they maybe the reason of this problem? or a broken capacitor?
Would be awesome to get a key where to check next.

EDIT:
Well, i'm not a specialist but it's fixed by accident! Seems like the problem occurred because of bad Grounding.... Learning everyday..

 

[kml23956]

The Vactrols have been the reason I have not built this yet. This guy is blowing out Perkin Elmer original one.  If you are looking for them here they are: https://www.pedalpartsandkits.com/vtl5c4-2/

 

[[silent:arts]]

Thanks for the link  8)

 

[Jonkan]

for the Meter:
the circuit is taken from the LA2A
(which uses a VU Meter)
btw, there is a 3K9 resistor needed in series with the VU which is not on the PCB
(since I wanted to have a switchable "Gain Reduction" / Output VU)

some comments from Keith:
http://www.groupdiy.com/index.php?topic=25646

and how to calibrate it:
http://www.groupdiy.com/index.php?topic=23253.msg276178#msg276178
(R25 = R126 & R226 in the D-AOC)

My unit is finally finished, except for meter calibration. Im wondering is a 3.9k series resistor correct? Isnt this resistor normally 3.6k? The reason im wondering is that i have 3.9k resistors in series with my meters and when i measure 1.228volts (+4dBu) on my output of the compressor the meter doesnt go up to zero when i switch to VU mode (with no load at the output atm, should I connect a 600ohm resistor across the outout for proper loading?)

Thanks!
/J

 

[[silent:arts]]

The value depends on your meter, and the level you want to have your 0VU at.

If 3K6 gives your Meter 0VU @ +4dBu use 3K6.

+6dBu is what we use in Germany and where the 3K9 may come from.

 

[Jonkan]

ok, I understand, thank you!

The meter position is changing depending on what I connect the output to,for instance if I connect to my soundcard the meters goes up quite a bit. Should I calibrate with a 600ohm load across the output xlr pins 2-3?
/J

 

[[silent:arts]]

Calibrate it to your normal standard environment, or your taste.
It makes no sense calibrating it to a 600R load if you don't connect it to a 600R load in your daily use.
It is just a VU meter. You decide where it should show 0VU.

 

[Jonkan]

Ok, It seems im not finished after all. After trying to calibrate the meter gain reduction, the meter on one channel refuses to stay still anymore. Its pulsing up and down, and it seems to have something to do with the neon light? I have a 100k trimpot instead of r126 r226.

It stays at 0 dB gain reduction for a second, the all of a sudden moves a tiny bit, then back up. Changing the r126 trimpot affects the tempo of the pulsing it seems.

change the neon light on the affected channel? use 1n5371 instead?

attaching a motivational shot of the unit

/J

 

[Jonkan]

It was the lamp!
managed to melt the isolation a tiny bit on a cable and one of the nearby wima caps while replacing it. Dont think it matters except it hurts my ocd, but at least now its working!

/J

 

[Jonkan]

And.... there the meter pulsing comes back Any ideas? I swapped the neon and it worked for a few minutes again. Only a problem on one channel, audio is ok ( though havent checked with a scope or anything)

/J

 

[Jonkan]

So I swapped the neon lights for the zener diodes in the meter circuit. Now the meters are stable and working properly, but both channels has a big HUM instead! *fail*

Any ideas why? and how to fix it? The meters werent stable with neon lamps, but audio was working perfectly.

Both channels are still working correctly and compresses, gains are working etc, except for this hum that is making me want to tear my hair out and sell this project for a loss and some broken self esteem.

Any help is greatly appreciated, im about to give up on this...
/J

 

[dagoose]

So I swapped the neon lights for the zener diodes in the meter circuit. Now the meters are stable and working properly, but both channels has a big HUM instead! *fail*

Any ideas why? and how to fix it? The meters werent stable with neon lamps, but audio was working perfectly.

Both channels are still working correctly and compresses, gains are working etc, except for this hum that is making me want to tear my hair out and sell this project for a loss and some broken self esteem.

Any help is greatly appreciated, im about to give up on this...
/J

I had the same issue with the neon lamps. I simply swapped it with another one and all was fine. I still have a couple of 'm left just in case, I bought them back then in a set of 10 I think.
Please give it another try, it;s a great comp!

 

[Jonkan]

Thanks for the encouragement! I just dont know where to start... I tested all the voltages and been moving the toroid around, changing grounding...

Could just changing the neon lights to the zener diodes have caused this hum??

It was working perfectly before except for the meter jumping around a bit before this!

Thanks!
/J

 

[druu]

Try to check your molex connections. I had a couple cause something similar, they’re not the most reliable connection sometimes..

 

[Potato Cakes]

Thanks for the encouragement! I just dont know where to start... I tested all the voltages and been moving the toroid around, changing grounding...

Could just changing the neon lights to the zener diodes have caused this hum??

It was working perfectly before except for the meter jumping around a bit before this!

Thanks!
/J

Is the hum still there if you disconnect the meters? One thing I noticed is the lack of a star ground in your build (unless I can't see it) I would also recommend adhering to the Grounding 101 that Ian Bell wrote on this forum sometime ago. I know you said it was working before you swapped out the neon bulbs, but I'm not sure if that would become the culprit . Dagoose stated he swapped his neon bulbs out and apparently everything was fine.

Thanks!

Paul

 

[Jonkan]

Yup, still hum without meters attached unfortunately.

There is a star ground just next to the IEC btw

It worked perfectly before i changed the neon bulbs with the same grounding config. I also replaced a wima mks-4 cap that i had accidently melted a bit of the insulation on. But its exactly the same kind, should work right? Maybe i should double check so the soldering job is ok there?

Will also reseat all the molex connectors and see if that makes any difference.

Thanks!
/J

 

[Potato Cakes]

Does it hum with the unit bypassed? You could put the neons back in one side or both and see if it goes back to being clean.

Thanks!

Paul

 

[Jonkan]

bypass is clean, but its relay bypass so it makes sense.

I might have snipped the leads when desoldering the neons, so... hard to recycle....

I guess I could always order new neons if I can find any.... Any leads in europe?

/J