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-   -   signal bottleneck (http://www.diyaudio.com/forums/pass-labs/1983-signal-bottleneck.html)

sriegel 19th January 2002 04:01 AM

signal bottleneck
 
here i am again, at my wits end.
i am troubleshooting a stubborn aleph5 and somehow, voltage is not reaching my circuit. :confused:
i have ~33 volts at the rails, fine

but i'm reading on the order of millivolts across everything from zeners to input mosfets to resistors.

what gives????

cheers,
scott

Geoff 19th January 2002 10:20 AM

Scott

This is the third thread you have started on exactly the same subject. It would be much easier for everyone to follow (or avoid) the topic if you had restricted yourself to one.

Geoff

sriegel 19th January 2002 05:09 PM

geoff,
sorry about the redundant threads. i'm trying to troubleshoot this amp and thought that if i could think of another route, i.e. something different that may be causing problems that it would be easier for people to see what direction and/or progress i've made by starting a new thread on that. sorry again for the confusion.

cheers,
scott

PassFan 19th January 2002 06:15 PM

Golden opportunity
 
Scott:
Reading your posts about your problems reminds me of a few months ago when I was having trouble getting my driver circuit working on my A75. It was frustrating looking for this or that and taking readings that meant nothing to me as I didn't quite grasp the math behind the magic. I dug out an old scam of the aleph 2.0 and I can't but help envy you. There is not much here to look for compared to the driver circuit for the A75. My last post from Nelson ended with "this is your Golden Opportunity to learn something" as it is almost impossible to fix something from across the country. Well, my final solution was to reload the card one set of components at a time. First I tried all my zeners, then all my caps, then I took out all my transistors and checked my resistors and then reloaded with all brand new transistors. One of my transistors was bad, I couldn't tell you which one but one was bad. I found it through stubborn persistence, and I learned something. You don't have to understand the math behind the magic to fix anything. It might take a little longer but don't give up. I guess this is more of an encouragement than an answering post, but I hope you find it. And, believe me it will be much more satisfying in the end. Good luck.

sriegel 19th January 2002 06:27 PM

skippy, and anyone else out there,

first and foremost, i want to make my position clear:
- i'm a newbie at this, with a very basic understanding of electronics

-i LOVE good music

- i love the fact that it may be possible to fabricate a great piece of gear myself (with lots of help )

that said, i really appreciate this forum, and remain undaunted, albeit continually scratching my head. i realize my questions and/or problems are very basic but i really need to put them out there in the hopes that someone will say 'hey, dumby, you did this wrong'.

i will keep trudging on, because i am learning quite a bit and like this tinkering.

anyway,
here's an update;
i still have voltage at the rails, but somehow, there is no voltage making it to the driver transistor Q3. i checked it out last night and it IS working. i don't know why the voltage just stops there. i feel that this is probably a main problem as it can't turn on Q3, which feeds Q1&2, which feeds the outputs. so nothing is being turned on! especially me!

thanks again,
cheers,
scott

rtirion 19th January 2002 06:41 PM

Did you use IRF9610 or other P-channel dev. for Q3?

Try taking Q3 out and implement the simple matching circuit to see Vgs 3.8-5V. If it is this FET is OK.

Make sure the orientation of the 9.1 V zener is correct. Check ground on R13 (10k). Measure voltage drop over R11 should be between 3,8 and 5V. Be sure to have used the correct resistors. Do not just read the color band's but try measuring the actual resistance. Preferable resistor out of circuit. This is done easy when you desolder one of the pins and do a quick measurement. If OK solder back in.

I hope your CS will start working, better would be sound from your ALEPH

Regards

sriegel 19th January 2002 07:00 PM

i tested all input mosfets like you mentioned last night and all are fine. resistors measure fine. zeners are oriented correctly ( i even went to an online tutorial about zeners and how they work). so i don't get it, how can the voltage just stop once it gets to the first component? is there a grounding issue maybe that's causing this? i've brought up grounding several times and noone's addressed that, maybe cuz it's not the cause of my woes.

thanks,

PassFan 19th January 2002 07:28 PM

Scott:
You did mention that you had 30vdc at the output. Perhaps it is effecting the front end through the feedback of r7 and r10. Perhaps one of your other transistors is not working. After fixing my A75 I came to realize that one end of the circuit has an effect on the other. Perhaps something in another stage is effecting the input. It would only take one short device to through the whole balance into confusion.

sriegel 19th January 2002 07:42 PM

i'm not getting dc at the outputs anymore. i had mis-wired a connection between the board and the output mosfets. i fixed that and the dc ended, i'll try measuring the vdc at Q4 and Q5 to see what i get. i don't think that my output mosfets are damaged, as hardly any voltage is running through them, i think that something's wrong with the main amplifier stage somehow.

we'll see,

macka 19th January 2002 09:31 PM

aleph 5 project fault
 
Scott,

Have you sorted the fault yet?

It sound like a stpid fault I had with my Aleph 5 when I converted the Aleph 3 to a 5 and damaged the pcs tracks that supply the positiive rail to Q3 and surrounding components.

Suggest you careful test for faults o fine cracks in the pcb tracks or a dyy joint as what you describe suggests this is the case.

ie the voltage just stops

regards

macka


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