[fishski13]

Adamus,
the B22 is a wonderful amp, but a double-edged sword. the Bijou is a perfect tonic for poorly engineered/compressed recordings. i switch between the two amps frequently depending on what i'm listening to.

 

[oneplustwo]

Hey folks... looking for some help with a sigma22. I've made enough mistakes with various B22 boards now that I'm pretty good at fixing those on my own, but I just finished my first sigma that didn't work on the first try. Not sure where to start. All I can tell you is that I get no output, no smoke, no LED at power up. But I did verify I am getting the AC from the trafo to the board ok.

Thanks is advance for the help!

 

[fishski13]

linuxworks,
i was about to rip you for the knob choice but then read your last paragraph. seriously, keep the wood. also, check out the Kilo knobs at Digikey. looks f'ing great too!!!

 

[Pars]

Read and follow the initial check steps on amb's website. Follow these sequentially; don't jump around.

The σ22 Regulated Power Supply

If you get through the initial check and get the LED working, continue on in the troubleshooting section of that page, there are voltage points for several different output configurations listed on that page. That should get you started.

 

[fishski13]

Quote:

Originally Posted by oneplustwo /img/forum/go_quote.gif Hey folks... looking for some help with a sigma22. I've made enough mistakes with various B22 boards now that I'm pretty good at fixing those on my own, but I just finished my first sigma that didn't work on the first try. Not sure where to start. All I can tell you is that I get no output, no smoke, no LED at power up. But I did verify I am getting the AC from the trafo to the board ok. Thanks is advance for the help!

do you have any measurements at operating points as outlined under "Initial Check"?

 

[fishski13]

Pars beat me to it.

 

[oneplustwo]

Yah, I don't get very far in the initial check section since my LED didn't light and I don't get any voltage at the output! So I was going to go through the voltage points but didn't know where to start. Is there a logic to start from the outside in, left to right, or other sequential order? I was scared to just start poking around since I didn't want it to just sit powered on for too long in case extended on time would lead to more bad stuff.

Quote:

Originally Posted by Pars /img/forum/go_quote.gif Read and follow the initial check steps on amb's website. Follow these sequentially; don't jump around. The σ22 Regulated Power Supply If you get through the initial check and get the LED working, continue on in the troubleshooting section of that page, there are voltage points for several different output configurations listed on that page. That should get you started.

 

[linuxworks]

Quote:

Originally Posted by fishski13 /img/forum/go_quote.gif linuxworks, i was about to rip you for the knob choice but then read your last paragraph. seriously, keep the wood. also, check out the Kilo knobs at Digikey. looks f'ing great too!!!

I may try a kilo at that size; there's only 1 that digikey carries that is at all large. may still not be big enough and it gets very pricey as you go up.

maybe time to try partspipe or something on ebay. I just hate having to go to HK to get parts; I really do.

 

[linuxworks]

one thing about power supplies, don't short anything while testing it..

should be obvious but sometimes its hard to test and look at the same time. what I will sometimes do is solder short wire-wrap wires to test points and use clip leads to grab onto those 'extension points'. you can work safer that way (as long as wire length doesn't affect things; and in this case it won't).

then again, dont' short THOSE test leads if you grow a lot of them on the board at once

I soldered some test cutoff leads to the .47ohm r's on the b22 for bias checking just to make THAT job easier, too.

 

[qusp]

I do that too with power supplies; especially for adjusting shunt regulators and their CCS

 

[dude_500]

I just started having a problem with my amp... I was listening to a vinyl recording and at first thought it was just a messed up LP, heard screeching. But then I paused it and the screeching continued for a little while. Then I'd hit play again and it would start up again.

I turned off my amp and the LED- instantly turned off and the LED+ turned off extremely slowly like there was no load on it at all. Q15 and Q16 on the sigma-22 were very hot after just a few minutes of use, much warmer than Q13 or 14.

I have not turned it back on since to avoid further damage. Any suggestions?

 

[Beefy]

Sounds like you have developed a short somewhere, and it is drawing a lot of current. Would be a good plan to go through the whole procedure of checking wiring, checking for shorts to gnd, etc.

 

[Pars]

Quote:

Originally Posted by oneplustwo /img/forum/go_quote.gif Yah, I don't get very far in the initial check section since my LED didn't light and I don't get any voltage at the output! So I was going to go through the voltage points but didn't know where to start. Is there a logic to start from the outside in, left to right, or other sequential order? I was scared to just start poking around since I didn't want it to just sit powered on for too long in case extended on time would lead to more bad stuff.

Since the LED is powered off the rails, and since you have no rail voltage, might not be anything wrong there.

The first thing I would do is go through every component, making sure it is the right part (particularly transistors) and that they are oriented properly. If that is fine, then with a schematic handy as well as the operating points, you probably want to start at the input and work towards the output until you find something that isn't right. Double check your transformer wiring as well.

 

[UKToecutter]

Hi all.
Just ordered my boards from AMB.

Can't wait !!!!!

 

[UKToecutter]

Oh, I forgot to ask.

Did anybody use the ε27 board to mount their pot?

Is it worth doing?