D-AOC PCBs - the building and help Thread

[Gold]

Looks great. What kind of output transformers are those?

 

[Potato Cakes]

Those are the high nickel version of Ed Anderson's 2503 that Jeff sells. Seems lend a bit of musical weight with much lower distortion than your standard 2503. It's a much more cost effective if you are looking for a high nickel output transformer option and it performs very well, like all the other Ed Anderson windings do.

Thanks!

Paul

 

[Gold]

That looks nice. If I’d had known about them  i would have given them a shot. I could have saved a bundle over the Jensen.

 

[Potato Cakes]

The only thing is that I think a 1:4 option (the 2503 are 1:3) might be a little better in terms of gain, but as I mess with this compressor more I keep reevaluating that statement. As I said before, I think that messing with the value of R125 might give a little more gain but I don't know if there is some other electronic penalty to pay by doing so.

I saw all those Jensen you are using. Must have been a fair amount for them. I bet yours sounds real nice though!

Thanks!

Paul

 

[[silent:arts]]

Your 2503 is the output transformer, right?
Needs to be wired 3:1, not 1:3.

 

[Potato Cakes]

Your 2503 is the output transformer, right?
Needs to be wired 3:1, not 1:3.

I did have it wired 3:1, but I was not getting enough gain through it. I'm using stepped switches for the controls and and used a multimeter to confirm I was getting the correct values for each step I calculated. I swapped it to 1:3 and it seemed to solve my problem. The compressor is very quiet and I suspect if had a bad impedance mismatch I would be getting all kinds of noise.

Thanks!

Paul

 

[[silent:arts]]

There must be something wrong but if it works for you all is fine.

 

[Potato Cakes]

Almost undoubtedly there is something wrong, but I scoured the the board and I couldn't find what the issue was. When I rewired the transformer to 1:3 I was expecting a problem but when it gave me more gain and no noise, I decided to just leave it. As you said, if it works then it works.

Thanks!

Paul

 

[Gold]

The first time I built one I installed the output transformer backwards. I got lovely but unwanted distortion.

If you want to investigate further I’d start by finding unity gain with no compression. Then try to apply some compression. If you want more at that point in the pot rotation increase input. Then adjust output to where you want it.

I’d also measure at the top of the compression pot to see what level the threshold is at.

This way you could at least isolate where the gain error is. Input or output.

 

[Potato Cakes]

I'm definitely not getting distortion, which again I thought would happen with an impedance mismatch. I know the input transformer is correct and I can measure it accordingly and the compression seems kicking in where I would expect it, so I know it's on the output side, but I could seem to find anything wrong prior to the output transformer. I know that at the output connections on the board the signal was quite low, which is when I tried the transformer 1:3, which seemed to work and sound like I hoped it would. At this point it's in the rack. If a problem does develop I will revisit this issue. But as I said, it's working great so I'm just going to roll with the transformer being wired backwards.

Thanks!

Paul

 

[Gold]

I'll just throw this out there. If it sounds clean and you think the issue is in the output section then it sounds like a gain issue. Assuming the tube types are correct I'd look for gain error possibilities. I'm no tube guy but it looks to me like R125 sets the negative feedback for the output section. Maybe that resistor is the wrong value? Or R115 at the input to the Output section.

 

[Potato Cakes]

R125 is where I was looking as the problem area when going over the schematic, but I did not find an error there when I was checking resistor values. Not so say that I didn't miss something, which seems to be a chronic illness of mine. I'm not curious enough at this point to pull it back out and double/triple check since it is working. If it needs service in the future I may look at this issue again. But for now, it's on to the next thing!

Thanks!

Paul

 

[Gold]

I'm somewhat dyslexic. I mix that kind of stuff up all the time. I triple check capacitor values as getting the number of zero's right is a constant battle. I also don't think I've ever had anything work the first time I turn it on.

 

[fragletrollet]

In order to switch between two pairs of vactrols, what kind of switch would I need? Is it enough to switch the + and - of the vactrols?

 

[mrdarwin]

Hi there.
For new  D-AOC builders, and other
I built mine few years ago, and had 1,2 dB difference between two channels when compression engaged.
I rebuilt the unit with stepped pots and bought Xvive vtlc5 from banzai, to make a matched pair for a perfect stereo unit. All I got is a crappy distortion when unit is compressing... so Xvive is not an option. Sounds good with Vactrol vtlc.
If anyone knows where I can source a matched pair or a mod... I have now 0,9 dB between two channels, not so bad?

 

[TillM]

That’s analog.
If you want totally stereo matching, then unfortunately you have to use plugins.

 

[mrdarwin]

That’s analog.
If you want totally stereo matching, then unfortunately you have to use plugins.

My sb4000 is stereo matched
My 33609 is stereo matched
My TG Limiter is stereo matched
My clx 160vu is stereo matched
My pultec with 1073 gain stage is stereo matched
My 33609 is stereo matched.
That's analog too

 

[justinheronmusic]

Does anyone have asource or part number for the PSU transformer?

 

[dagoose]

I still love my d-aoc, use it pretty much everyday. There is one things which has bothered me for some time, the left channel is 0.2dB louder (yes, I know it's nitpicking, but so is mastering by nature). So I was thinking of adding trimmers so that I can calibrate things a bit more precise. What would be a good place to do the actual trimming? I was thinking of using a 10k multitrim in place of R102 (8k2 resistor) which is on in the input. Or a 100k trimmer instead of R115.
What would you do? Or did anyone tried this already?

 

[Holger]

I still love my d-aoc, use it pretty much everyday. There is one things which has bothered me for some time, the left channel is 0.2dB louder (yes, I know it's nitpicking, but so is mastering by nature). So I was thinking of adding trimmers so that I can calibrate things a bit more precise. What would be a good place to do the actual trimming? I was thinking of using a 10k multitrim in place of R102 (8k2 resistor) which is on in the input. Or a 100k trimmer instead of R115.
What would you do? Or did anyone tried this already?

My guess is that you won't get the required accuracy by modding the device. Try Ian's "Neve Trick":take a 1k variable trimmer and put the hot leg of the 600 ohm transformer secondary to pin 1 of the trimmer, take the "wiper" or pin 2 as output and connect the TX 600 ohm secondary cold leg to pin 3. Do that on both L and R and set the trimmer to match gain.