Drip Dual-STA 5167 Limiter

[morls]

-All voltages within 5% (Increased R23 from 150-220 ohm to get -12V @ cathodes 6v6)

Sounds interesting. I'm still trying to work out how to balance these 6V6s. I've seen posts detailing a method of inserting a 300Hz signal (with no input to compressor) to the grids of both 6V6s, which is pin 5 I think, and then adjusting the trimmer following R23 for lowest noise. I haven't found a way to do this yet, maybe at the front of R21 and R22?

I've also changed R24 to a 2W. I don't know if I missed something in the Drip BOM or documentation, but it was 0.5W while the original schematic has 2W There was some heat damage on the 0.5W I replaced.

-Now running matched 6BA6 on a t-bar mod. (works very fine, even more compression then some of the JJ 6386)

I changed R8 and R9 to 56R here, to adjust for the T-Bar/6BA6.

I also checked all voltages at 15dB compression (pink noise), and they're really close to the schematic. I went through and reflowed all the solder joints. I don't know if it was this, the change to R24, or both, but both channels now sound fantastic, I can push the compression at time setting 1 to 25-30dB without any thumping. Levels are much better matched between channels as well.

 

[schrobbelbop]

ve also changed R24 to a 2W. I don't know if I missed something in the Drip BOM or documentation, but it was 0.5W while the original schematic has 2W There was some heat damage on the 0.5W I replaced.

Just before i sent this message i've noticed R24 needs to bee 2W indeed. I'm currently having the 0.5W which is overheated so maybe that will help replacing. might be the problem right there... wrong on the bom/pcb

I changed R8 and R9 to 56R here, to adjust for the T-Bar/6BA6.

Why do the need to be adjusted?

For balance 6v6 i adjusted the trimmer so voltages are equal on both kathodes.
Same for the 6ba6 balance.
You can also crack the output to max and listen for any hum, the 6v6 balance will (almost) cancel the hum
when correctly balanced.

 

[FarisElek]

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

This happened to me when I had wires carrying voltage touching wires that carry audio touching eachother near near control panel. I zip tied wires together to keep them away from others.

 

[morls]

i've noticed R24 needs to bee 2W indeed. I'm currently having the 0.5W which is overheated so maybe that will help replacing. might be the problem right there... wrong on the bom/pcb

Let me know if this makes a difference, I think it did for mine, especially in headroom, but I did reflow the joints as well…

 

[schrobbelbop]

I'm reflowing everything too now, why did you bring R8 R9 to 56R?
thanks

 

[schrobbelbop]

changing R24 to 2 Watt and reflowing didnt solve the thumping.
it only happens when going from 0 compression to a little bit.
Deep compression sounds fine.

When I pull out 1 6v6, the thumping dissapears so i guess
it must be an imbalance somewhere...

Changed all resistors to 1% metal films.

Currently running JJ 6V6 / EH 12AT7 / JJ 6368 or ALGRA EF93 / Telefunken 6AL5 / Philips OB2

Ordered Diffrent brands for 6V6 (Genalex/Mullard) and Philips NOS 12AT7 balanced. let's try that...

 

[JMan]

Hey everyone, sorry for the little aside here. Though it pains me to do, I just put my unused boards for the Dual-STA project up for sale in the black market, as I don’t know if/when I’ll ever have the chance to build it due to that old friend Changing Life Circumstances. If you’re a lurker on this thread and want to get the boards at a significant markdown from retail, I hope you’ll consider my listing. I also have the Ultra British project for sale.

BM Thread

 

[schrobbelbop]

SOLVED.

Had a wrong cap value at C3 (0,22 instead of 0,022).

on the pcb there's marked 2 caps *(.1-400v) or interstage? should i leave them out
since i have an interstage transformer?

 

[juneaudio]

Wow, totally didn't catch that i didn't need to use 5v for the diodes. Thank you for saying that . I bought Simpson 27 model 200ma meters for $20 a pop. I photoshopped the sta level meter onto a scan of the 200ma meter and made sure that the farthest left and right of the scale matched. Happy to send you the pdf. It should print out exactly the right size. Then you can print it out onto a sticker, exacto knife it out, and stick it on. Unless you're okay with spending $400 on meters. If you can afford it will definitely look nicer but oy vey they're more than the transformers!

I would love a copy of the pdf for the meters if possible

 

[juneaudio]

Hi all, Im down the road a long way on building my dual sta but stuck on a few things. Hoping Greg might get back to me on some of these questions Ive sent him but if any of you are willing to answer I sure would appreciate it.

1) What is the correct size for the led drop resistor? Also info (part number?) for the led itself?

2) the main boards show 2 27k resistors together where power enters, but the BOM shows 28k resistors, which is correct?

3) above those 2 27k resistors the board says 57, 360=300V use 3 watt. Wondering what this applies to or what this means for me with components

4) it seems you would recommend using SS power rather than the Tube when doing the dual sta, but there is talk online about the pros and cons of the sound. Im having a very hard time knowing what to populate on the board and which way to go. Ive read all of the errata but it still eludes me. Any clarification would be very helpful

5) on the control boards there is something labeled “fixed resistor” wondering what that is / what value I need, maybe its not needed if a trimmer is used?

6) there are 4 diodes listed on the control boards, D9 and D10, are these needed if the relays are installed? If so what are the values?

7) The large cap on the power supply board says 10uf and 22uf, wondering which I should be using.

 

[Sc]

Hi

I think the main bug with some of your questions is, that you will have to decide first whether to use the GZ34 or diodes, with or without (which) choke - it will change the value of the B+ resistors. GZ34 has a larger voltage drop than diodes. As to my experience with a double mono STA-Level and other projects you will need to find the correct B+ voltages by pots in the range of about 5W (or a set of resistors in the range) for your build - once it works fine, then you can install fixed resistors. Here the first two 5W will be safe (2 - 1W for the following B+ drop resistors also). But be very careful there - dangerous !
I prefer the GZ34 - with max. slightly higher original B+ cap values and choke. In this case 20uf as first cap before choke is original - the tube will not take more than 40. The STA has a tube stabilizing circuit - so no need to do the SS part of the HT anyway. While a GZ34 circuit in a guitar amp certainly changes the sound, it's maybe not that obvious in a compressor with a stabi-circuit (and far too much uF on the Drip boards).
Personally I just like sticking close to original first and maybe modify later if necessary. All the holy grail units of ProAudio were obviously thoroughly designed, and not easy to beat with mods. IMHO a stabilized and regulated 6.3V heater supply has it's advantages and was probably impossible to realize with tubes. Relay circuits instead of expensive, large, complicated rotary switches (e.g.) have their benefits too.
So I never used the Drip universal PSU - it's far away from original anyway. His main designs follow the original design rather close, or are easy to recreate by omitting or changing values, without need to modify the PCB. But you have to go deep into it.
The GZ34 original wiring could sure be realized on the board - think I could help you there, if you decide to go this way. But as said - just a personal point of view.
To 6: - it's standard to have a diode over the relay coil - maybe one in a parallel row of four would be enough, but I don't know.

Good luck
Walter

 

[juneaudio]

Hello all,
Ive managed to build everything, power things up and so far I haven't blown anything up! Im wondering if I might get some help from you regarding a low voltage problem. Im running the drip psu, and Im running it with 3 5watt 33ohm resistors before the output sma jack per the video that Greg put up on Vimeo. I am finding however that my voltages are low - Im seeing 256/257 instead of 315 and 5.3 instead of 6.3. If I measure voltage outputs without connecting to the main boards at all, Im seeing over 350volts and exactly 6.3volts. Can anyone help me begin to find where my problem might be?

Thanks in advance

Scott

 

[Sc]

Hi Scott

Super! You might play with resistor values to try to come closer. Do you have the link of this Video ? If you can't reach the voltages needed - since Greg had overheating problems (errata notes 2018) - I suppose the Hammond HX is not really strong enough for his design. JX would sure be better. It's a bit tricky - but in case you can (cautiously) measure AC current at the HT and heater windings, you could identify a possible overload on either side. But could be as well a faulty tube or component leading to overload - not easy to find sometimes.

Cheers & good luck
Walter

 

[juneaudio]

Ive managed to find problems and get the unit working and it seems to sound great. Could someone go over the procedure for calibrating / balancing the 6v6s and the 6386s?

 

[Riinehart]

Could anyone recommend chassis handles for a 3u case like this?

I've been a little confused by the measurements and data sheets. I've seen some data sheets (like the Hammond 1427u3) that show a 4.5" measurement from the center of one hole to the center of the other, but the actual measurement on the faceplate seems to be 4.5" from the bottom of one hole to the top of the other.

Maybe I'm overthinking it? Any recommendations for one that definitely fits?

 

[morls]

Not sure of the exact measurements, but I got my case from collectivecases. My STA is so heavy I’d never think of using the handles…

 

[JMan]

I think Greg often recommends Bud enclosures in his build docs. Those have optional handles you can order that will obviously fit so long as you get the corresponding size.

 

[Riinehart]

Thank you both, makes sense. I had already bought the DIY Racked case, and it didn't come with any.

And geez this thing sure is heavy. That's actually why I thought I should add the handles, not to put full weight on, but just to have some support options when maneuvering in or out of a rack.

As a side note, I don't think I'd recommend the DIY Racked case for this. It's got only two tiny (~1/4", if that) screws attaching the back panel to the rest of the case. With the giant power transformer and choke back there I don't trust it at all. Have to add some reinforcement. Also a lot of useless built-in standoffs that are a nuisance as they don't fit any of the current PCBs and have to be worked around. Nice looking face plate, though.

 

[morls]

Mine is so heavy, and the case so deep with all the weight at the back, that I have it sitting flat on my desk. I don’t think the faceplate/rack ears would last long if I put it in a rqck