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β22 Build Help

beta22

β22 Build Help

Postby darkstargtk » November 24th, 2018, 7:57 pm

Hey All!

I’m just wrapping up the build of (4) B22 Boards that will be powered by (2) Sigma 22 boards in a separate chassis.

The Sigmas seem to be working A-OK. I’m having some trouble with the B22 boards - maybe someone out there can help me out!

I initially mounted Q1-4 to the boards according to the silkscreen and applied power. After realizing my mistake I went back and corrected their mounting positions (V1.02 boards). I started through the setup steps but haven’t made it past the first one - I’m only getting about ~500mA across R9. VR1 has no effect on the voltage either.

Is it possible I cooked part of the board with Q1-4 mounted incorrectly? I’m testing two of the boards for +/- one of the channels and both boards are behaving the same way - whatever I’ve done aparently I did it the same on both boards. At least I’m consistent.

I will try to include some detailed pictures of the boards incase anyone is able to spot my error!

Edit:
After checking back in the forums I’ve found a few instances of builders with a similar issue to mine. All of my D11s on all four boards are reading way high. It seems that I’ve blown all of my Q25s.

I’m wondering if the incorrect mounting of Q1-Q4 blew the Q25 out?

Either way - I’ve ordered a bunch more and will keep trying later this week.

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Re: β22 Build Help

Postby amb » November 25th, 2018, 5:41 pm

It’s possible that the incorrectly-mounted JFETs led to Q25 blowing out, but it’s not certain that is the cause. Whether the JFETs survived is something you’ll need to determine when you do the initial setup again. The only other way to test the JFETs is to remove them from the PCB and check them in a special test circuit. I don’t advocate that at this point, because you risk damaging the PCB.
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Re: β22 Build Help

Postby darkstargtk » November 25th, 2018, 6:28 pm

I ended up pulling 3 550s from one of the boards and replaced the failed Q25s on three of the boards. The setup procedure went flawlessly on the three live boards. I’m going to let them warm up for an hour or two and recheck.

So long as I’m able to get the required measurements in the setup procedure is it safe to assume the incorrectly (now corrected) JFETs are ok?
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Re: β22 Build Help

Postby amb » November 26th, 2018, 12:35 pm

Yes, you can assume they are ok. Nevertheless, the real proof is when you get to listen to the amp.
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Re: β22 Build Help

Postby darkstargtk » November 29th, 2018, 5:59 pm

Well - the Q25 replacement across all 4 boards was indeed the issue. They're all working perfectly now. Coming from a BH Crack and a Nelson Pass W.H.A.M.M.Y the B22 is absolutely amazing so far - Low end is the most noticeable change for me so far. I cooked one of my E12 boards messing about, but that's another story... :(

Ordered some MuMetal foil to shield the transformers below, my only current option is to stack right now. The mains hum is only audible with low impedance cans - my 300 or 600ohm cans are dead quiet.

One other thing - I had a high pitched ground loop problem somewhere, the only way I could get rid of it was to tie the LCDuino into chassis ground. Not great, I know, but I couldn't find another way?

Anyway, here she is - the plexiglass front is temporary until I have the real front machined, a little wire management, a rebuilt e12 and I'll be set!

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β22 Build Help

Postby amb » November 29th, 2018, 6:16 pm

Yes, the LCDuino-1 digital ground should be connected to the chassis. This is typically accomplished with the δ1/δ2 board stack mounting hole next to L1. It will connect the digital ground to the chassis when you use a metal standoff and metal machine screw. It appears that you used a different mounting scheme, thus that ground connection isn’t established and needed to be connected manually.
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