Drip Opto6 LA2A voltage issue

[mmattanthony]

Hey folks,

I'm having one or 2 issues with my Drip Opto 6 LA2A build and thought I might run them by this forum to see if anyone had some insight...

Some info:
I'm getting 552V AC of the transformer. Using a 6X4 tube I'm getting 295V off of the filter caps. Heaters are 6.56V AC. All the other voltages seem OK when referenced to the PCB labels except around the 6AQ5 tube...

I've measured with and without the 6AQ5 tube installed and it has the same issue:

292V at R35/220K resistor (should be around 136V)
292V at C11 (.01uF cap) (Should be around 90V)

I've tried taking out the T4s and the voltages are basically the same…


I tried the unit out and sonically the result was that it sounded OK until it was compressing/limiting at which point it got very distorted.

I was trying to calibrate the unit but the meter will not display any gain reduction, the meter only functions in "Output" mode for some reason. I suspect it is possibly the trimmer pot for the stereo adjust as even though I turned it clockwise I never heard or felt a "click" as I did on the limiting trimmer next to it. Not sure…

I have ordered a new trimmer pot and a new 6AQ5 tube just in case although I suspect something else is going on as the voltages around R35, R34, R38 and C11 seem way too high (they are basically full B+ voltage). I will check on those resistors after I remove the PCB.

Wondering if anyone can shed any light on what could possibly be the problem or how to narrow down the trouble. Again, the voltages around the 12BH7 and AX7s seem fine.

Thanks in advance!

-
Matt

 

[Deepdark]

Check aroudn R34/R35 to be sure they are the right values. Is C11 (0.01uf) blocking dc? Check also for a bad stereo trimmer / limiter trimmer, a short at the 6aq5 (any solder bridge)

 

[mmattanthony]

Thanks for the response. Checking into it now. Just removed the PCB.
I just noticed that C11 on the Drip board specifies .01uF but the original LA2A C11 is  .1uF. Anyone know what the proper value of this cap should be for the Drip?

 

[mmattanthony]

I just noticed on another schematic it is .01uF...
I removed c11 and R34,35 and 38 and they all look OK on my meter. I didn't notice any solder bridges.
I replaced the Stereo Adjust trimmer although that seemed OK as well. We'll see what happens...

 

[Deepdark]

C11 = 0.01uf

 

[Rob Flinn]

It sounds like the 6AQ5 isn't drawing current.  Check the connections both ends of any component that connects to it,  Check you have the right value resistors.

 

[mmattanthony]

Could be a bad tube as well. I'll try another this weekend and see...

 

[Deepdark]

check if your R34 is at least 2W

 

[mmattanthony]

Hey guys. The good news is I got it all into spec and it sounds fantastic! It turns out it was a bad tube
Should've tried that first but I didn't have a spare...
Thanks for the replies and help!

Best,
Matt

 

[Winetree]

I'm going to start the build for the Drip Opto 6 LA2A. I've got the P.S.B, the 2 optos, and a mundorf 10uf supreme output cap.
What transformers, caps, tubes, case did you use? I found a mod where you can use the 2 optos together.
Any inside pictures? How does it sound?

 

[mmattanthony]

I used the Sowter transformers and the mundorf cap as well. I got the case from DIY racked. The rest was stock from the BOM. I'll get to use it over the next few weeks in the studio and really get to hear it and evaluate it then. I haven't done and mods/changes from the spec. Keep me posted on your build! I'll post some pics in the coming days.