[BUILD] STA LEVEL PCB OFFICIAL BUILD & HELP THREAD

[Bassniac]

Hi folks.
Finally solved my PSU problems, Voltages seem to be good but.
When Compressing Vocals / Bass / Guitars I am getting ugly Distortion Humps on low Compressions levels in all 3 Modes. Everything despite slowest release seems to be useless.

So. How do I configure the meter properly? Maybe I am compressing more than the meter shows me?
How is Bias calibrated correctly ( yes I did the listening method, but compression seems to be cleaner when the hum is louder).

I am using the Sowters, input Tx configured in 1:8

 

[bernbrue]

Hi,
When using a sowter 1:8 input transformer the input pad is mandatory. In case you haven't installed the input pad I would configure the input tx as 1:4 instead. Your distortion is most likely  in the first tube stage. What are you using, 6386 or 2x 6BA6?  Bias configuration, setting threshold, banlancing tubes etc. is described in the first posts of this thread and in the original manual. There is a meter trimmer for setting the meter to zero.
Bernd

 

[Bassniac]

Hi Bernd.
I am using 2 6BA6 tubes and all the pads are installed. I calibrated BIAS and the meter according to the manual and your posts, So far so good.
But pulling off the 6AL5 removes the previously described distortion artifacts. I can still distort my unit by cranking the input... (as I should be able to). Most of the artifacts happen between 5 and 10 dB Gain reduction. While compressing more they seem to be less strong.
Cheers

 

[bernbrue]

Ok, then your mistake/error can only be found on the frontpanel pcbs. Check the wiring. Also test another 6AL5 tube.
Bernd

 

[bernbrue]

On the control boards there are three wire bridges to be soldered in. When breaking the control board because of a different frontpanel design you need to use some longer wires.
Bernd

 

[Bassniac]

Double checked the control boards component values. Reheated everything. Cleaned everything again. Still the same problem.

https://www.dropbox.com/s/13lando1ieybied/IMG_0002.JPG?dl=0
https://www.dropbox.com/s/5zllunompw7w5ss/IMG_0003.JPG?dl=0

And a Video
https://www.dropbox.com/s/cjoozroqfd1b9tu/IMG_0004.MOV?dl=0

And another one that shows the problem a little better.
https://www.dropbox.com/s/wki2iomh7vq559x/IMG_0005.MOV?dl=0

And the Tube was replaced by another one.

I made one more obervation. In the Fastest Release Setting the Release seems to be nearly infinite.
EDITED:  Solved - one Position too much on the Lorlin Switch.

 

[mysticmerlin]

Ok, I've got both units up and running. They both sound great and quiet.
One compresses more than the other and I have to figure out why the threshold is different .
I am going to lift the large resistors R3 , R23S and D1-D4 off the PCB because of heat.
Now I have to find  the issue with V+ for the bypass relays. 
Should I use the V+ Ground jumper so that this Voltage is referenced to ground?

 

[Bassniac]

Message #293 helped me with my PSU Problems... Make sure that all the voltage regulators are isolated with the ISO Kits. Important!!!

 

[Bassniac]

My distortion problem - Video still exists, any thoughts?

 

[bernbrue]

1) Did you verify that the two control pcb are connected with each other? You need to set wire bridges between the two boards.
2) Have you already done the calibration/balancing of the tubes?
3) Measure the amp without the 6AL5 tube using RMAA software. Is your distortion still there?
4) Did you set the Lorlin switches correctly?
5) I would wire the sowter transformer 1:4 and leave out the input pad.

Cheers
Bernd

 

[Bassniac]

Hey Bernd. I did continuity Checks on the two boards. The Switches behave absolutely correctly. Optically the Release is fine. There is absolutely no distortion without the sidechain Tube installed (intact the STA Level seems to be a very nice Mic/Lineamp when not compressing). I calibrated the unit properly.  Checked all the testing points .

A 92V
B 0V
C 1,1V
D 0,6V
E 1,3V
F 0V
G 77V
H 130V
I 177V
J 0,1V
K 2,51V
L 2,51V
M 0V
N 177V
O 314V
P 5mV
Q 8mV
R 313V
S 209V
T 24V

I attached pictures of my control board and two videos of the discibed and unwanted behavior of my unit in post #345. Have a look at the please.
Removing the pad and wiring the tranny for 1:4 could be a next step, but without any general distortion, disabling the control circuit by pulling the tube, would that make any difference?

I checked the switches yesterday. They seem to be setup fine. Continuity while switching them between the switch position and the according resistor is fine. Resistors have he correct values. The two Caps are 250Vs, correct capacitance.

 

[bernbrue]

Sorry, just a copy and paste from earlier post, but I recommend to lower the threshold first as described below and then maybe wire the input transformer 1:4. From the video I get the impression that you have to crank up the input pot way too much in order to get compression.

6) A few things to keep in mind when using different input tubes (6386 or 6BA6 combo): 
- with the 6BA6 combo the unit sounds almost the same as with the 6386 tube, but the gain structure and threshold is completely different.
-  First I tested the 6BA6 combo with a 1:4 input transformer, input pad, all values according to original schematic: works fantastic and sounds very good.
- Then I replaced the combo with a single 6386 tube.  I had to crank up the input pot in order to get some slight compression. Not very satisfying.
- So I removed the input pad and lowered the threshold by reducing R32 (24K). I replaced the resistor with a 20K pot plus a 4K7 to ground in order to find the right threshold. Finally ended with around 18K. The unit works fantastic.

 

[hugo]

Sorry, just a copy and paste from earlier post, but I recommend to lower the threshold first as described below and then maybe wire the input transformer 1:4. From the video I get the impression that you have to crank up the input pot way too much in order to get compression.

6) A few things to keep in mind when using different input tubes (6386 or 6BA6 combo): 
- with the 6BA6 combo the unit sounds almost the same as with the 6386 tube, but the gain structure and threshold is completely different.
-  First I tested the 6BA6 combo with a 1:4 input transformer, input pad, all values according to original schematic: works fantastic and sounds very good.
- Then I replaced the combo with a single 6386 tube.  I had to crank up the input pot in order to get some slight compression. Not very satisfying.
- So I removed the input pad and lowered the threshold by reducing R32 (24K). I replaced the resistor with a 20K pot plus a 4K7 to ground in order to find the right threshold. Finally ended with around 18K. The unit works fantastic.

And dont short the middle resistor of Input pad, jumpers only on other resistors..or you will not have any sound entering the circuitry

 

[hugo]

I noticed a high distotion on my unit...
6386 (untested)
input pad is removed
threshold resistor 20k
U-pad followed by T-Pad on the output (recommended by Koslik on this thread)

I have to put output at maximum to have good level, matched with input
input pot at 7", it compress / 9" : usable / 12" : start to distord

Does somebody have an idea, how to solve this ?

Thanks

 

[bernbrue]

Pull out the 6AL5 tube and measure the amp with RMAA (Rightmark Audio Analyser ). With this you can find out if there is a mistake in the amp or in the sidechain. In case the amp hasn’t got any distortion, your 6386 and all other tubes in the amp are fine. The mistake must be somewhere in the sidechain.
See also the comments above about using different input tubes and gain structure.
Bernd

EDIT: it should be clear, that either a pair of 6BA6 or a single 6386 should be used, not all three tubes together!!

 

[gareth33]

My build is coming along nicely, I'm ready to hook up however, one of the 6AQ5's glass has broken, I'm assuming it's better to keep these two tubes as a same brand/model pair?

 

[bernbrue]

For testing you can take any working 6AQ5 you have at hand. When doing final calibration you should have quality tubes.
Cheers
Bernd

 

[Bassniac]

Hello Folks, hello Bernd.

I did everything as suggested to solve my problem, but the Pops on Compression still remain. To clarify the problem I upped an audio file:

https://www.dropbox.com/s/r8tf4o4lkjqwseh/GDIY%20Demo.mp3?dl=0#

Maybe someone has an idea what is going  wrong.

Thanks in advance

 

[Bassniac]

Problem solved. Was a bad resistor in the Sidechain.

 

[dustbro]

I noticed a high distotion on my unit...

I've built a bunch of sta-levels I  the past.  They seem to be picky about their 6v6. Try some different pairs and compare distortion