signal bottleneck

sriegel

Member
2001-11-24 1:24 am
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
 

sriegel

Member
2001-11-24 1:24 am
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
 
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

Member
2001-11-24 1:24 am
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

Member
2000-11-24 12:02 am
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

Member
2001-11-24 1:24 am
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,
 
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

Member
2001-11-24 1:24 am
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,
 
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
 

sriegel

Member
2001-11-24 1:24 am
macka,
i pulled one channel completely out of the case and am starting to go over it even more finely. question, i have a 13.8 dcv power supply. can i hook that up to the negative and pos rail and see if power goes through the system? or, more to the point, is it okay, cuz i did and the power supply sounded like it was straining quite a bit so i turned it off. what do you think?

thanks,
scott
 

rtirion

Member
2000-11-24 12:02 am
OK, Z5 was bad. So the current source will never work.
You will have to replace that, before going further.
If you do not have any zener's left, use one from the other channel, preferably one of Z1..Z4.
Please do hook up only the single "repaired" channel to the PS and start testing things around Q5.
You can soft test your channel using a 15w/220V light bulb in each rail from your power supply. (one bulb for +ve and one for -ve).
If you see some voltage drop between Q5 collector and Q5 emitter (Vce), and no DC (very little) on the output, and no smoke of course, you can take out the bulbs.
Hook up your channel normally to your PS, (don't forget connecting -IN to ground if your going to use an unbalanced i.e. RCA input) and do the measurement around Q5 again.
Vce should be between 3.5 to 5 volts. Check the voltage drop accross drain resistors (R40-R42 and R64-R66) to be 0.5 volts or so.

If this is the case, your channel should be working.

Hope this helps a little more

regards
 

sriegel

Member
2001-11-24 1:24 am
when you say 'don't forget to connect -in to ground for unbalanced' do you mean;

a) to the ground connection on the board

or

b) directly from the -in to chassis ground.

and how will this effect operation of the channel in regards to any voltage readings? won't i still be able to get the correct readings without inputs connected to anything?
thanks,
scott
 

rtirion

Member
2000-11-24 12:02 am
Do not make a permanent connection for -IN to ground during testing. A temporary one will do.

Connecting -IN to a ground in the final setup (i.e. working channel in your chassis) is necessary when you want to drive the ALEPH unbalanced.

Connecting -IN to ground on the board or chassis depends on the grounding scheme you use.
Most of the time you will need to exepriment a bit to find the best result.

Normally connecting -IN to ground will not affect the DC measurements.

Regards
 

sriegel

Member
2001-11-24 1:24 am
well,
i got one channel up and running, but the other can only muster 3.26 vdc across r114???

i get 5 across r11 but q3 doesnt get above 4 vdc, it sits at about 3.8. don't i need at least 4 volts to turn everythin else on? i replaced that mosfet with another but it didn't effect the measured voltage.

and i get only .16 volts across q5??

any thoughts out there?
scott
 
aleph 5 project fault

Scott,

I am interested to know what board you are using, as this may be adding to the confusion.

If you continue to have difficulties can I respectfully suggest you check out the boards Mark Finnis used for his Aleph 4.

The reason I say this is that without a board over lay for the location and orientation of all the parts and wiring it is easy to slip up.

Marks site has excellent construction notes also (NB see the diy Gallery @passdiy.com).

The amp is quite simple and should go first pop, provided there are no wiring errors or damaged or wrong part values.


regards

macka
 

sriegel

Member
2001-11-24 1:24 am
macka,
these are mark's boards. i replaced q5, but it may be that something's wrong with Q1 or2? because i get really close to 4 volts from q3, so the input mosfets should turn on and give more than 3.26 volts, right? i measured vgs of q1 and q2 and get equally around 3.8 volts.

any thoughts?
thanks,
scott
 
I may have mis interpret your response,

I have just check my reading (aleph 5) with 35 volt rails ,

across r14 should be between 4-5 volts
across r11 " '" " '
across Q5 emittor - collector 4-5 volts

If you get this plug in the speaker and music should happen.
make certain the signal board ground is connected to 0 volt ground for the power supply.

regards

Ian