[BUILD] STA LEVEL PCB OFFICIAL BUILD & HELP THREAD

[techineer]

I need to know if the input pad is installed, which input transformer was used and what the voltages are at the dedicated test points. The other aspects you mentioned are basically right or have already been discussed before.
Best
Bernd

Input pad is installed. Input transformer is the Sowter 9062E, output transformer is a blue Edcor (no visible part number). 

Testing with a 400 Hz sine wave input across pins 2&3 (L&R) of the input connector, with the input level control at maximum, compression just begins to move the needle at about 60 mV RMS.  At that level, the output is minimum 1VRMS, and up to 6.2V RMS at max.  Seems awfully hot for any line level signal.

No-signal DC voltages with respect to ground are:

+V  4.1V
B+ 323V
F+ 6.3V
BS 99.7v
A - 70.2V
B - 0v
C - 1.33v
D - 0.68v
E - 1.33v
F  - 0v
G - 69v
H - 119v
I - 177v
J - 0v
K - 2.65V
L - 2.49v
M - 0v
N - 186v
O - 316v
P - 0v
Q - 0v
R - 318v
S - 221v
T  - 24.6v

(Any reading less than 0.1V was considered to be 0V.)

So, my question is,  is this normal operation for this unit?

 

[bernbrue]

Hi,
Can you check how the Sowter input tx has been wired , 1:4 or 1:8 ?
You can  either  remove the input pad or  bring down the bias voltage (25V ->18-20V).  You will need to install another output pad (10-15 dB) after the already existing to bring down the output level.

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.

Bernd

 

[techineer]

Hi,
Can you check how the Sowter input tx has been wired , 1:4 or 1:8 ?
You can  either  remove the input pad or  bring down the bias voltage (25V ->18-20V).  You will need to install another output pad (10-15 dB) after the already existing to bring down the output level.

He used the Pink and Grey primary leads and the Red and Yellow secondary leads, (Blue and violet connected together)  so I think that is 1:8.    Based on my input readings, the input sensitivity is probably OK, as a .775V RMS signal input brings the meter needle back to 75 uA /200 at full rotation of the input pot.  The output level is just excessive, so an additional pad on the output is probably the way to go if desired.

 

[bernbrue]

http://www.nu9n.com/tpad-calculator.html

I think I went for a 15 dB  H-pad. You can connect it to the "audio out"  screw terminal.
Cheers
Bernd

 

[Mulmany]

What is the rough parts cost, USD, for this build?

Thanks

 

[bernbrue]

500-700 USD depending on the choice of components/transformers/case.
Bernd

 

[Mulmany]

Thanks.

 

[pzjones]

Hello everyone.  I have completed my Sta Level using Steves case which I picked up from him a couple of weeks ago. It was a pleasure meeting you Steve and thanks for the case which is excellent. I am not quite sure how to get photos into my post but have attached a quick pic as a file attachment. if you are starting a build with Steves case you might want to make sure you are using 5mm standoffs as things get a bit tight in the power supply area with anything longer. Also the relay board can get a bit close to Vi with 10mm standoffs. I have measured voltages on the board and all seems within spec although I have to do it again properly now that all is connected. I am guessing a bit with the three gang attenuator pot but will experiment a bit. If anyone has any ideas I would love to hear. Steve has sent me a copy of it being used on the input of an1176 which will help. If i come across any problems (likely) i will try to run them past you guys. Hope all of your builds go well. PZJ

 

[bernbrue]

Nice!
Bernd

 

[pzjones]

Well testing has gone well I have balanced the valves and calibrated the meter. I was getting a short oscillation with the input pot at about three quarters on but this has gone since I have balanced the valves . I have wired the three gang output pot the way I thought it should be and it seems to work ok. The input is nice and clean and the unit is very quiet for a valve unit.
I am going to shield the screen  wires from the input pot as they are V sensitive. I am waiting for some 5mm standoffs to arrive which I will use on the PSU and bias boards as well as the Relay board which is working fine now that I have wired it correctly (idiot). I have taken a supply from the heater supply with an appropriate resistor to the Meter LED to give it a fairly faint light. All the voltages are looking good and I can post them here if anyone is interested. Thats about it I cannot think of any other problems so far. Thanks Bernd for the boards and all the work you have put into the project. Thank you Steve for a great case. I look forward to putting it to use. I have used Sowter TX,s, the 9185s on the output and the 9062e on the input wired as per the excellent wiring guide. I used Steve's power tx and the voltages were spot on.

 

[bernbrue]

Well, that's the way it should go! Congratulations! Zayance has done a great job as well!
Cheers
Bernd

 

[pzjones]

Yes sorry thanks to Zayance also. 

 

[hugo]

Hi all,
I am starting this build, and would like to know which wires would need to be shielded..
Kind regards,
Hugo

 

[bernbrue]

Hi Hugo,
I didn't use any shielded wire in my build. Check the measurement PDF, it's very quite. If you want to use shielded wires, use them for the pots.
Bernd

 

[hugo]

Hi Hugo,
I didn't use any shielded wire in my build. Check the measurement PDF, it's very quite. If you want to use shielded wires, use them for the pots.
Bernd

Thank you very much for the support.

 

[mysticmerlin]

Hi, I'm a puzzled with the V+ . I'm getting 5.6V DC at the input of the LM317T regulator on both my units . I have 5.2 v AC from the transformer, so normally I should be getting around 7v DC at the input of the regulator. So at the end I get something around 3.6V volts DC max for the relays which is not enough to close them. I have jumpered R8

Any ideas ?
Thanks

 

[pzjones]

Hi Mystic. I have just checked the volts at my relay board and I am getting 3.7V across the switch terminals and the relays are switching OK. do you have the relays powered in series or Parallel? (Jumper the two pads marked -//  and    +//  on the relay board) then make the supply switchable.. which is what I have done. Hope this helps.

PZJ

 

[StefanAC]

Same here.  I got 3.7V DC at the terminal and wired the relay coils in parallel. Everything is working as it should.

 

[mysticmerlin]

Thank you for your help. I will check the relays again, at the moment I have removed them and I'm getting a distorted signal with a reduced low end on both units so the relays are not very important for the moment.
I'll post back once I've sorted this mess

 

[dogvoid]

Hello everyone

I'm with the first tests and it sounds fantastic (I think it's my favorite compressor) Mode and recovery work perfectly and give it a lot of versatility.
The only problem is the output level, it is very high, the transformers are the pair of sowter 9062 and 9185, and everything checked and it is ok.
I need another h-pad between the pcb and the xlr? (That seemed to me understand reading other post)
The R40 does not appear in the original scheme, what function does it have?
R32 could be considered a kind of "treshold"? It would be fair to adjust an earlier compression.

Thank you all!
I hope to share some photos and demos when he is ready.