uh oh AKSA 25n+ troubles

gonefishin · « **on:** 4 Feb 2005, 04:57 am »

Hi guys,

I hate to do this...but I'm finally to the testing stage of my low power AKSA55n+(25) and I'm having some troubles with the voltage drop across r21/22 in both channels. I have read and re-read the instructions and posts here in the circle, but I'm still missing something

My power supply is good with a +/- 25V

Voltage drop across r21/22 is 15V The trim pot is turned full CCW

The Output offset is bouncing from 1.1V to 1.3V

Output to earth is also 15V

Removing 12B makes it move up to 16.9V

Adding another resistor to 12b (to get 240R) got the 15V also

top fuse clip to output tag measured infinite power transistor

heatsink flange appears to be burr free

well, that's about all I got so far tonight...I'm tired

thanks guys (back at it tomorrow)

dan

AKSA · « **Reply #1 on:** 4 Feb 2005, 07:22 am »

Hmmm....... Offset is within reason, but output bias is not responding to increases in R12B.

I'd be looking at the drivers, making sure they are correctly installed; 4793 on left, 1837 on right, and checking the 5200 is on left, 1943 on right. Then check there is no short between center terminal of each of the four devices in the output stage and the heatsink, and finally checking the Vbe multiplier, T4, is correctly wired, with emitter crossing over to the right side. And check the trimpot; sometimes they stick in a low ohms position, so remove one end of R12B and place an ohmeter across it to check it can be adjusted from 0R to 100R.

Hope this helps!

Cheers,

Hugh

gonefishin · « **Reply #2 on:** 5 Feb 2005, 06:10 am »

I can't imagine how many times a customer must wire something wrong, only to catch it after your suggestions.

Thanks so much for the help...and I apologies for being a dang moron. I would have bet the barn that I crossed the emitter over the other two "flying leads" in the proper manner. Well, good thing I don't have a barn...or I would have lost it

So I fix the wiring on T4...power up and I get 1.22/1.22 on one channel and 1.39/1.39 on the other. It's late and my eyes were getting buggy so I left my project unfinished...but with a smile on my face

Thank you

dan

AKSA · « **Reply #3 on:** 5 Feb 2005, 08:21 am »

Oh how I love a happy ending.......

Cheers,

Hugh

gonefishin · « **Reply #4 on:** 7 Feb 2005, 04:51 am »

Hi all

ok...last night I did the rest of the testing on the AKSA amp....added a few more r3 resistors and all was good (although I do have to do some fine tuning here...but things are certainly good for now)

I had the amp on over 12 hours today and finally started to feel like I could tell what voice this thing had around the eight hour mark. Although it seems like it's continuing to improve even now. But still, I'm finally happy to go downstairs and listen and feel as though I'm getting an idea of what the amp sounds like. I'll have the thing playing all day at work with me (24 hours), so I'll have a few more hours on the amp tomorrow.

So far I've only listened to the amp on a spare set of 89db bookshelves that I have. They sound decent...but not near as revealing or dynamic as my main speakers. I just hope it's a good marriage

Either way...there will be more to come

I'd also like to say thank you to Hugh, AudioCircle and all the AKSA fans out there. Thanks!

dan

gonefishin · « **Reply #5 on:** 12 Feb 2005, 08:22 pm »

Hi Hugh,

Please check your e-mail...I sent another order in

gonefishin · « **Reply #6 on:** 25 Feb 2005, 02:22 am »

Hi Hugh,

I received both the aksa55n+ and AKSA100n+ today

The box looked like it just went half way around the world...it was a bit beat up, but it looks like everything inside was untouched.

just wanted to let you know they arrived ok

thanks,
dan

AKSA · « **Reply #7 on:** 25 Feb 2005, 03:01 am »

Thanks Dan,

Always nice to know it came through.

Any damage to the fins on the heatsinks? That's always the risk with package damage.......

Cheers,

Hugh