[BUILD] STA LEVEL PCB OFFICIAL BUILD & HELP THREAD

Help Support GroupDIY:

fallout

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Jun 3, 2004
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Caldwell, NJ
HerbertR said:
All diodes and Capacitors are correctly placed with their poles. What could.be the problem....🤔?

Sounds like you have a short or a bad tube/part somewhere. Did you try powering up the circuit without the tubes installed? I would first replace R3 and power up the PSU without the main PCB connected, check voltages and make sure the PSU is ok. Keep in mind, your voltage readings might be a little higher than expected without a load connected to the PSU. If all is well, I would connect the main PCB without the tubes installed and check voltages again (without tubes installed, the voltage readings might be high). I would then install 1 tube at a time (obviously install tubes when power is off) and see if you could locate the problem. Or, you mentioned the EL90 is getting hot, perhaps start there and try removing the EL90 and see if the problem persists. Could be a faulty tube? This is assuming you scrutinized your soldering for shorts/bridges, etc.

In short, I would fix the PSU and then  systematically work your way through the circuit to narrow down where the problem is.
 

hazer-drum

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Feb 22, 2019
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London, UK
My 3W-rated R3 at 1k keeps frying. I know some people recommend using a 25W chassis-mounted resistor but I see build pictures with PCB-mounted resistors. Would a 5W resistor do the trick?

EDIT: I think I found the answer myself actually. If my calculations are correct, the current after rectification and smoothing cap C9 is max 0.2A * 0.62 = 0.124A which equates to a power dissipation of 7.23W at 470Ω and 15.38W at 1kΩ. Therefore, I definitely need that 25W resistor, correct?
 

Dr_J

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Jul 5, 2011
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270
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Germany
Hey Hazer-Drum,

i didn't check your calculation, but what i can say from my side my build is running fine with [email protected] called by the BOM.
It's not getting very hot...

ROCK-ON
 

hazer-drum

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I ended up installing the 1K 25W resistor and got my B+ down from 360V to 319V (which seems a bit more reasonable now). Also swapped the meter resistor R7S to 100Ω since I couldn't zero-adjust my 1mA meter within the original trimmer range. Works flawlessly now!
 

Sorr

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Sep 16, 2005
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250
Location
Australia
schrobbelbop said:
My Dual sta from drip is still thumping in the low end when compression kicks in
especially with fast release times.

I've tried the 6ba6 t-bar's with no luck, other pairs of 6v6, other brands... no diffrence.

myguess is the psu, it measures rock steady on all voltages points, the only
thing i've chosen for is not to use a choke but an extra resistor in that b+ path.
i've ordered the 5mh choke and see if it will help.

could it be something with the power feed? how to meaure that? there is an diode rectifier
into seperate voltage regulators for both channels.

i've read something about old 6AL5 tubes that could be causing this too?

I must admit it's one of the best sounding compressors on guitars, vocals and bass lines.
super rich harmonics, adds nice detail of highend character and rock steady bottomend.
try it in parallel :)

Do you have a pot between the 6V6 cathodes?  If so how are you attempting to balance them?  It must be adjusted for AC balance not DC balance.                                                      I would also remove the two feedback resistors from the 6V6's and measure them to see if they are the correct value.
 

schrobbelbop

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Mar 7, 2010
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141
Location
Eindhoven, Netherlands
Do you have a pot between the 6V6 cathodes? If so how are you attempting to balance them? It must be adjusted for AC balance not DC balance. I would also remove the two feedback resistors from the 6V6's and measure them to see if they are the correct value.
There is a pot to balance the 6V6's. i try to trim it so that i have the least amount of humm. i'll check the resistors.
 

Sorr

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Sep 16, 2005
Messages
250
Location
Australia
What I do is turn input off, release and attack slowest. Output full. I feed a 100Hz sine wave signal into where the bottom of the input pt connect together. Signal typically 1.2V RMS. But you may change that.
So you are feeding a signal that is in phase to the grids of both control valves (tubes)
Listen to the output. You should hear a buzz type sound.
You can also measure the AC voltage across the two capacitors that come of the 6V6 anodes (plates)
I like to do both.
As you adjust the 6V6 balance pot. You should get a spot where the noise drops off. And as you keep turning, it goes up again. So you adjust it for the null.
This will work only for reasonably matched valves. All of them.
If say your 12AT7 had one side that was low and one side high, you might run out of adjustment, ie you cannot get a null. If you buy your 6V6's as a platinum matched pair. Then there is a good chance you can expect them to be reasonably matched.
Using a new expensive JJ 6386. You should expect that to have matched sides.
Which leaves the 12AT7.
 

ampman1961

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Joined
Mar 18, 2009
Messages
22
Hello to the group, again. It’s been a long time.
I would like to find out if a kit has been compiled for an entire build and if so, where can it be purchased?
Thanks in advance.
Billy
 

morro2k

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Joined
Oct 17, 2020
Messages
1
Hi Bernd
In the pcb there are only two relays, and 3 different ones in the BOM, which one should I use?
thanks
 

dmp

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Oct 28, 2009
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3,092
Location
Madison, WI
meter scale if anyone is still looking for it
 

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grapyofire

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Jun 16, 2021
Messages
30
Location
Brooklyn, NY
My apologies for dummy question, but I would like to confirm. Do I need voltage selector if I'm in US? I plan to use it in US only, so I don't need 220V switch, but BOM says optional for EU, so I assume that psu board was originally design to power from 220V and guys from US need voltage selector with CX2 to turn voltage on way in 2 times down. Or no... Anyway I confused. After 9v guitar pedal world I feel lost with those voltage selector options.
 

zayance

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Feb 25, 2009
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France/Swiss
My apologies for dummy question, but I would like to confirm. Do I need voltage selector if I'm in US? I plan to use it in US only, so I don't need 220V switch, but BOM says optional for EU, so I assume that psu board was originally design to power from 220V and guys from US need voltage selector with CX2 to turn voltage on way in 2 times down. Or no... Anyway I confused. After 9v guitar pedal world I feel lost with those voltage selector options.
Switch is there for people who would like to build a more international gear, for who knows if one day the equipment is sold in a 220V country.
So up to you really.

Best,


T.
 

wrentema

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Dec 16, 2020
Messages
20
Location
Berlin
Hi!
I’m slowly starting to organize my parts. And was wondering if it’s also doable to build this into a 2U 19” enclosure.. Has anybody tried? Does the Edcor Output transformer fit?
I don’t care that much about the original look and trying to save some space.. (might build two..)
 

NannerPuddin

Member
Joined
Feb 12, 2011
Messages
12
Have any of you guys used the a case from Dan at Collective Cases? I am curious which power lamp you used. I can't seem to find one that I won't have to drill out the hole and I was hoping not to have to do that.

Thanks,

Doug
 

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