Drip Dual-STA 5167 Limiter

[FarisElek]

Also, are you sure you're not hearing audio from your output transformers? Not thay unusual. Happening to me on my channel 2.

Is your input transformer 1:8 or 1:4. The original 1:8 ratio is way too big of a step up for modern audio. I tried tried use it with my Lundahl but everything was distorting. 1:4 works great. Heard some people even like to use 1:1 when modding sta levels so they can cook the audio a little more.

 

[Martan]

Hey Morls, Can I ask where you got the boards for bootstrapping those tubes?

Thanks

 

[scott2000]

where you got the boards for bootstrapping those tubes?

Thanks

https://groupdiy.com/threads/sta-level-6386-to-6ba6-t-bar-wiring.78033/

 

[morls]

Thanks for all the replies, gives me a lot more to work through

Did you check the SMA connectors and cables (short/continuity)? The cheaper ones are crap sometimes

I've checked the SMA connectors and cables, all seem ok. I've found a connection to chassis in the "to atten" and "com" lines on the main board - both at the SMA connector and the header terminals on the board, so the short is somewhere on the main board. I'll take this out and check the lines.

Is your input transformer 1:8 or 1:4. The original 1:8 ratio is way too big of a step up for modern audio. I tried tried use it with my Lundahl but everything was distorting. 1:4 works great. Heard some people even like to use 1:1 when modding sta levels so they can cook the audio a little more.

I'm using the Sowter input transformers, so I'm not sure if there's an option to change the ration. The audio is coming in really hot though, I'm pulling down the DAW sends a lot to get the headroom.
There's a signal at the 1:8 teminal for Lundahl, the one closest to the transformer.

What kind of hookup wire are you using?

Using SMA connections all the way through

Hey Morls, Can I ask where you got the boards for bootstrapping those tubes?

The thread Scott quoted has more details. I got in touch with Manley and they were very helpful. I had to mod the boards, but it's working well, and the 6BA6 tubes are around $15 each which I like.

 

[FarisElek]

I've checked the SMA connectors and cables, all seem ok. I've found a connection to chassis in the "to atten" and "com" lines on the main board - both at the SMA connector and the header terminals on the board, so the short is somewhere on the main board. I'll take this out and check the lines.

---You're chasing a wild goose with this one. I was in this exact same hole. My problem ended up being that my input tranformer was faulty due to the Lundahls pins very easily coming lose if you overheat the pins. I think your input transformer is being driven too hard from your daw because i'm assuming the Sowter is a 1:8 and that the sound your hearing from your "ground" is coming from your output transformer because the lugs needs to be tightened on it and that's just how lots of output transformers are.

Like I said, if you've ever touched high voltage to your chassis on accident (yes I have...oops), you'd know that ground will draw massive amounts of current and you'll pop all your fuses. I originally had my lundahls set to 1:8 and it was distorted as hell.

Is there any other problem than output transformer acting like a speaker and distortion?


Here is a thread about sta level distortion that I think may be relevant:
https://groupdiy.com/threads/sta-level-distortion-grrrrr.66407/

 

[morls]

I tracked it down to the SMA socket from the main board, marked "to attenuator". The centre pin lug had a connection to one of the legs via a blob of solder, I must have gotten a bit excited when soldering this one in.

Both channels are now up and running, sounding great. Thanks for the heads up everyone!

The issue now is that the bypass switch doesn't change anything - with bypass in or out, there is always compression happening and the meters are always showing gain reduction. Everything else is working - time, pad are good. No bypass on both channels. Hmmm

 

[FarisElek]

I tracked it down to the SMA socket from the main board, marked "to attenuator". The centre pin lug had a connection to one of the legs via a blob of solder, I must have gotten a bit excited when soldering this one in.

Both channels are now up and running, sounding great. Thanks for the heads up everyone!

The issue now is that the bypass switch doesn't change anything - with bypass in or out, there is always compression happening and the meters are always showing gain reduction. Everything else is working - time, pad are good. No bypass on both channels. Hmmm

Very happy that you got that figured out. I recall the bypass being an obvious but not obvious thing. Basically the relays need power, and I think the power they need doesn't make it to the control board unless you have the lamp power going to the control board. I rigged it up so the lamp and vu go from the main board to the control board via sma and then I used wires from the unused ribbon traces to go to lamp and vu.

 

[morls]

Thank you Ryan! That is something I wouldn't have figured out easily, you've saved me a lot of trouble.

Everything is up and running now, and it sounds really good. I'm going to put some hours of running time into it, then get down and tweak the voltages around after things settle in.

Thanks again Ryan, and everyone who chimed in.

 

[morls]

It's been running a few hours now. A couple of issues so far:
- with matching input levels, channel 1 runs at a lower level - I have to push the input by about 10-20% to get the same amount of compression as channel 2, and the same level at the outputs (output attenuators at same setting). I've switched XLR connections, the issue remains so it's not the incoming signal that's causing this issue.
- the meter for channel 2 has stopped working. It's still compressing, but the meter doesn't move off zero.

It gets pretty warm, and I've taken to top off the case to get some cooling. I think it might need a fan, or to run with the top off. I've shut down for the night, will fire it up again tomorrow and see what's going on.

 

[scott2000]

It's been running a few hours now. A couple of issues so far:
- with matching input levels, channel 1 runs at a lower level - I have to push the input by about 10-20% to get the same amount of compression as channel 2, and the same level at the outputs (output attenuators at same setting).

Stereo levels can be frustrating depending on the topologies from my experience....
Have you tried swapping tubes?
.

 

[morls]

Stereo levels can be frustrating depending on the topologies from my experience....
Have you tried swapping tubes?
.

No, I haven't tried that yet. I was thinking that this would indicate a fault or something that I'd have to track down. If it's pretty common then maybe I don't need to worry too much?

I've got some voltages from the PSU - there is a test point on the board, in the top left corner "Test HV". I'm getting 339.3V
The high-voltage secondaries are reading 316V.

Into the choke is 386V, out of choke is 374V. Is this normal range?

 

[FarisElek]

It gets really hot. But all things considered, not too hot. Just don't let anything sit on top.

The 6V6 need to be very matched between channels to get same output volume.

VU's can be kind of sensitive. I had to be careful which sma my VU wiring was touching.

Those voltages look fine. You're basically seeing 340 before you bias the voltages on the main PCB's. The voltage of the choke is what you're seeing before it hits the 6V6 and those can handle way more than 374, but that's a good voltage as is.

 

[morls]

The 6V6 need to be very matched between channels to get same output volume.

I bought a closely matched quad of 6V6s, so I'll see how the levels sit once I get this stage balanced.

 

[scott2000]

Sometimes just moving tubes around can make things better. Are the 6ba6 not suspect?

 

[morls]

I've moved some tubes around, swapped the 6BA6s. There's still a big difference between channels 1 and 2, and the channel 2 meter isn't working. Something I notices is that when I touch the zero adjust pot for meter 2, meter 1 moves a bit.

I've measured some voltages, without compression and after 30min of idling. Most of them are pretty close, certainly nothing stands out. The voltages around the 6386 are up in both channels, but this is where I substituted the 6BA6s so this could explain the differences there.
Pin 3 of the 12AT7 is up in both channels, this is the cathode of the top half. The plate voltages of the 6V6s are also down.

One of the OB2s is glowing a lot brighter than the other as well.

Here are the measurements, I took the reference voltages from an original circuit diagram dated 5-26-58.

 

[FarisElek]

Have you while it's compressing taken the wire that goes to the non-working vu and move it to see if it starts working? My meter would not move when it was leaning against a certain other cable.

Also, have you already installed the new 6V6? When I was using close-ish matched NOS 6v6, one output would be at 9 o clock at the other at 2. It was pretty significant.

 

[morls]

Yeah, I've tried moving the wire, I've also re-stripped the insulation and double-checked the connection. It's a bit weird because it has been working, so I'm scratching my head a bit with this one.

The matched 6V6s are installed. I might try swapping one from each channel to see if that changes anything.

 

[morls]

I tracked down the issue with the meter to the control board of channel 2. After resoldering all joints it’s up and running, and the levels are more balqnced between channels.
I’m still going to swap some tubes around to try and match levels more closely, but it’s starting to come together now.

 

[morls]

I'm getting some voltage between chassis and ground, just wondering if this is an issue? Here's what I've measured, all with reference to chassis. All measurements done with unit powered, no signal:

PSU ground: -4.1mV
Chassis lug at Output Transformer terminal block: +1mV
Main board test points:
Ground: 2.2mV
6.3V Lo: 2.2mV

Is this something I need to sort out?

Also been checking the voltages in comparison to the list in post #3 of this awesome thread. There are a couple of points where voltage given is 0V - pins 2 and 7 (grids) of the 12AT7. I'm getting 4.1mV and 2.8mV respectively. Again, is this an issue?

Cheers
Stephen

 

[schrobbelbop]

I also have the drip Dual boards and they keep a little "thump" / motorboating when compression kicks in.
especially in the beginning of the range 0-10db's. When it's compressing deeper 10-30 db it all sounds very fine.
with a constant sine wave at a constant level of gain reduction (0-5ddb) it keeps thumping/motorboating so not only
on transients.

plate, voltages fluctuate when thumping
Control voltage fluctuates when thumping

What i did and check:
-All voltages within 5% (Increased R23 from 150-220 ohm to get -12V @ cathodes 6v6)
-Running the HV as stated in drips manual, Diode rectifier, Choke, Voltage regulators per main pcb.
-B+ is super steady at 300v
-Changed JJ 6386 ( i had 10 of them)
-Changed all tubes for different brands
-Now running matched 6BA6 on a t-bar mod. (works very fine, even more compression then some of the JJ 6386)
-All sowter transformers

both sides behave the same