Crack 5998 low volume

[adamct]

AAAAAAAAHHHHHHHHHHHH!!!!!!!!!!

My cup of frustration runneth over. I took today off. My wife is out with the kids. My GEC 6AS7Gs finally arrived. I wanted to sit in my chair, put on my headphones, and relax in bliss while doing some reading. Instead I'm sitting here cursing the world. I love the Crack, but frankly this has been a frustrating process (none of which was due to the Crack per se). The stock 6080 was bad and i had to wait for a replacement. I later ordered a 5998 that turned out to be bad. I bought and struggled to install film caps, then spent many long nights trying to figure out what the problem with the film caps was before I found out one of the leads was bad. I had to wait for, and install the replacement. I wanted to upgrade the volume pot and because the wiring instructions on the sellers website were wrong, I miswired it, then stayed up all night rewiring it. Every time I need to do ANYTHING to the amp, I need to desolder and resolder my film caps. Now this. I know it is my fault because I keep trying to upgrade stuff, but it is getting to be a severe PITA. 

[Doc B.]

The first suggestion is, as usual:

-redo all voltage measurements and please post any variations from the manual that are more than 15%.

[adamct]

I figured you were going to say that. Ugh. That mean desoldering my film caps yet again. And with the speedball installed, accessing the terminals to test voltage and resistance is no minor task. Frankly, it makes me uncomfortable, since it is tough to see and I always fear I will short something...

[adamct]

Quick question: should the octal socket connections be my primary focus, since the only thing that changed between when the amp worked, and when it didn't, was installing the new 6AS7G?

[Doc B.]

Are all of the LEDs lighting up?

[Grainger49]

Adam,

Get some jumpers, alligator clips on each end.  Clip them to the test points then turn the amp on.  You can safely get the voltage readings.

[adamct]

Just realized....I can't check voltages, at least not tonight. I have to desolder my film caps to open the case, and I can't attach them when the case is open without a pair of leads with clips. Grrrrrrrr......

[Jim R.]

Adam,

This sounds to me a lot like your new tubes may have had some crap (wax?) on the pins and when you first inserted the one and then the other, you gunked up your socket pins.  Get some pipe cleaners, some round wood toothpicks and some kind of solvent like mineral spirits or 409 or something and try a good, deep cleaning on the sockets and then on the pins themselves.  If this is what happened the trick of pulling and inserting the tubes will do nothing.

Also, when using pipecleaners, have the unit off and unplugged and all charge drained off -- they are metal spines and you don't want to be zapped when doing this.

This is assuming that the LEDs are all glowing and that there is no obvious damage to rectifieers, etc.

HTH,

Jim

[adamct]

First,

Apologies to everyone for my rant yesterday. I was frustrated, and although I'm still frustrated for reasons explained below, I've calmed down a bit.

So....the issue wasn't the Crack at all. I went out, bought some pipe cleaners, cleaned the socket, and then tested the Crack with a portable source. It worked fine. So I put it back into my rack and hooked it up to my system via a line router. Only low sound again. I'll spare you the 20 intermediate steps used to diagnose the problem, but the bottom line is that the balanced outputs on my DAC work just fine, but the unbalanced RCA outs are only putting out a very, very, very low signal. I'll open it up to see what the problem might be, but if anyone has any ideas, I'm all ears. Could using signal attenuators have caused a problem?

Best regards,
Adam

[adamct]

OK, now I'm totally stumped. I opened e DAC. The unbalanced RCA outputs are just connected to the balanced XLR outputs and the wiring is all perfectly fine and intact. The balanced outputs work without any problem. The unbalanced don't. How is that possible? I even checked the unbalanced interconnects in a different setup. How is it possible for both channels to suddenly not work (or rather only work at very low volume), when the balanced outputs are fine? They are connected. If one works, the other should, too. I'm totally flabbergasted and have no idea what to do next.

[Jim R.]

That's an AudioGD dac, correct?  Do you have the ACSS engaged by any chance?

-- Jim

[adamct]

Yes, it is. Good thinking...unfortunately, this model doesn't have a button to select between ACSS and other outputs -- all outputs are active all the time. You can only select gain and input. Besides, since the unbalanced outputs are wired to the balanced outputs, if one works, the other should, too.

[Grainger49]

If the unbalanced is wired to one balanced hot and ground you get 1/2 of the voltage out there.

[Jim R.]

Try turning the ACSS off -- it may have an effect as ACSS is a current loop interface.

-- Jim

[adamct]

The unbalanced outs are indeed wired to one balanced hot and ground. But the DAC puts out 5V balanced and 2.5V unbalanced. I've never had a problem using it this way before. The signal was plenty strong. If anything, it was too strong.

As for ACSS, I can't turn it off. I have other Audio-Gd DACs where you push a button for ACSS vs. RCA, but the Ref. 5.32 doesn't work that way. ACSS is always on, as are the balanced and unbalanced outputs. And again, I don't really see how it is possible that the unbalanced outs wouldn't work if the balanced outs do.

I thought maybe there was a cold solder joint or something, but everything looked fine and it isn't that the unbalanced outs don't work at all - if I turn the Crack or one of my other amps up all the way, I can hear a signal, but it is very, very faint. It's not 1/2 as strong as the balanced output - it is more like 1/50th or 1/100th. And I have this faint sound in both channels, not just one. None of this makes sense to me.

Please understand that I appreciate your help and brainstorming here. I just don't think we have hit upon the answer yet.

Signed,
Confused in Connecticut