[BUILD] STA LEVEL PCB OFFICIAL BUILD & HELP THREAD

[groselicain]

Stupid mistake on my part. I wasn't paying attention. It all appears correct now. However, now that I have everything running correctly at the PSU, I just hooked it up to calibrate and noticed I'm not getting any output. I'm going to wait until I have the new meters in to replace the wrong one I had before—then I'll see if the unit is getting anything on input. I think it has something to do with the output, however, as even pushing the momentary switch to set the bias isn't producing any noise.

I'll update you when I have the new meter. Thank you again Bernd for working with me—you're much too kind.

 

[prepanic]

Hi, how did you fix the phase invert on the outputs?

I changed the hot and cold pin at the output. Any other ideas?

 

[bernbrue]

I have no inverted phase on the output.
Bernd

 

[prepanic]

Ok, that´s strange.

Did you try it with a parallel signal?

My output is inverted.

Isn´t it right?

In my opinion the first tube stage make a 180° Degree Phas Shift, the second stage too.

But the output Transformer get the same signal as the feedback from the EL90 Tubes.

Ans this signal is phase inverted to the second stage.

So i get an phase inverted singal at the output!

 

[bernbrue]

Hi Patrick,
Test your unit with Rightmark Audio Analyser (RMMA). Besides frequency response and other useful tests it checks the phase/polarity of your compressor. I'm quite shure that a wiring mistake (input or output transformer) is the reason for your phase inversion.

http://audio.rightmark.org/download.shtml

Your should pull the 6AL5 tube before testing.
Bernd

 

[groselicain]

Big edit: After all my other posts today, I decided to delete them and report that my relays were the issue with no input or output. I've removed that board temporarily to figure out what their deal is, but until then I'm passing audio just fine and I've sorted wiring to have as much isolation from the PSU as possible. I also used the SPST to set the bias, and I have a really close to no-noise unit.

I have but one last—I promise, this should be all—question. I'm experiencing almost no headroom on the input, and I'm getting quite a bit of distortion. As such, by the time I get the needle moving it's just unreasonably distorted. Any ideas?

Thanks so, so much for all of your patience and help.

 

[bernbrue]

Hi,
With the Input pot you should be able to completely shut down the signal (ccw) whereas the output pot is just a variable output pad. You can't shut down the signal completely with the output pot, even when it's turned completely counter clock wise.

Bias voltage of 25V is mentioned in the manual but in fact a voltage of about 18V is preferable. By lowering the voltage compression sets in earlier.
Tweaking bias voltage is described earlier in this help thread. Will come back to you later.
Bernd

 

[groselicain]

Bernd,

    So you think this distortion is related to Bias? Which test points relate to bias—the ones by the 6AL5? Also, should I be concerned that one of the EL90s doesn't appear to be heating or glowing? I've switched them back and forth and the one closest to the 6AL5 never seems to heat while the one closest to the 12AT7 is quite hot. Is this normal?

Cody

 

[bernbrue]

Hi Cody,
No, that's not normal. Check your heater wiring especially around the not glowing EL90. Pull the 6AL5 tube and measure the amp with RMAA (download link a few posts above). Which output transformer do you use?
Cheers
Bernd

 

[groselicain]

Bernd,

    I used the same Edcor you used. I'll check the heaters momentarily and get back to you.

EDIT: I've checked the heaters, and now all tubes are glowing equally well. However, I'm still getting the same distortion if I push the input gain even past 12 o'clock. I'm giving very little preamplifier signal on input as well, so there's no way I'm somehow clipping the input. Any ideas?

 

[bernbrue]

Input pad? Which input transformer? Which input tube? 6386 or 2x 6BA6? Input pot wiring correct?
Are you shure you're clipping the input? The Sta level has an extremely hot output level. Could it be that your mixer/sound card is clipping?

Bernd

 

[groselicain]

I'm using all the resistors on the pad since I'm using the Sowter 9062 input transformer. Input tube is a 6386, and the pot is wired exactly as the wiring guide. I'm definitely not clipping the converters, as my meters are registering way below zero. The clipping is somewhere in this unit.

 

[bernbrue]

Is the clipping still there when you pull out the 6AL5? Please use RMAA to check levels, distortion, frequency response et al.
Bernd

 

[groselicain]

Bernd,

Yes, the distortion is there regardless. I've attached the readout from RMAA.

 

[bernbrue]

Oh, there is something very strange going on.
1) verify that you used the correct values for C1-6
2) bad tubes?
3) wiring of the output transformer could be wrong.

What did you do with the not used wires of the Edcor output tx? The color code of the Sowter output transformer in the wiring guide is NOT suitable for the Edcor output transformer. Be careful! High Voltage!
Please post a picture of your build.
Bernd

 

[groselicain]

Bernd,

    I gathered as much, haha! In order,
[list type=decimal]
[*]C1-6 are all 1000uf 25V, as listed in the BOM.
[*]The tubes were all NOS purchased at once from TubeDepot.com.
[*]I wired the output transformer as it appeared in your pictures. White to GRN, Black to BLK, Blue to BLU, Red to RED, and Brown to BRN. The two unused wires—White and blue, and white and brown—are disconnected and taped off.
[/list]

Here's pictures of the build.

 

[bernbrue]

A few observation/questions

1) What kind of pcb is right behind the power switch? Looks frightening. Oh, this pcb is meant to be a power transformer primary selector and switches between 115V + 115V = 230V (European countries) and 2x115V in parallel (USA et al).  Powertransformer primary needs to be hardwired to this pcb. It has nothing to do with the power switch.

2) input and output pot wiring can cause a short. Lots of solder lead around.
3) At least one voltage regulator is not isolated from ground./chassis. The plastic isolation washer must be between the back of the regulator and the heat sink. Check the others as well.
4) double check the values of C1s - C6s on the mainboard.
5) double check the wiring of the output and input transformer
6) .........

I'm quite shure that either there is a wiring mistake or a wrong/broken/dead component in your build.
Bernd

 

[j.frad]

I'm close to finishing my unit here,
R3 is burning up too, even with 1K.
I hear something buzzing in the power supply, could it be R3?
Also I the bias procedure doesn't seem to work, the buss doesn't change when turning the trimpot...

Also testpoints  A,G and H read full B+ voltages, 310V... I find out why.

 

[j.frad]

Hmmm  ok
voltages settle after 20sec or so, but R3 still smokes a little bit...
The Bias trim pot doesn't change the hum level at all though.

Edit:
I read 420V after the retifier and 330V after R3.

I used edcor input transformer (wsm600/15k) for now, had to bypass the input pad to get the unit to compress and used Avdos output pads.
The unit's audio is quiet but distorts with modes 2 and 3.
The release switch behaves strangely, the shortest release in in the middle of the range.

 

[bernbrue]

Hi,
your voltages are quite high. Try to bring them down. Maybe use one of these resistors and bolt it to chassis.

This compressor (and the real one as well) is prone to distortion in double and triple mode  when fed with bass heavy signals. Sometimes a bad rectifier tube (6AL5) can lead to distortion as well. Pull out this tube and measure the amp only. Concerning strange release setting, please check the wiring of the backpanel pcb and check the values of the resistors 1-6 on the recovery pcb. I think you didn't put them in in the right order.
Cheers
Bernd