Aleph 5 problem 2

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pmchoong

pmchoong

Member
Joined 2008
techgrafic.com
Hi

Thanks William, now I am happy that at least 1 channel is working. I have changed the layout of the gnd connection for the other channel (the one which sounds bad) but the problem is still there. The sound is just not clear, like static. I measured the output, 2.4mv. I have even changed the bad fet (0.901v) with one that matched to 0.01 but when I made the measurement, it reads 0.881v. The rest are as follow :

Z5 = 9.30v
Q5 from c to e = 4.68v
R14 = 4.65v
R11=5.32v

R40 = 0.636v
R41=0.881v
R42=0.661v

R64=0.722v
R65=0.635v
R66=0.716v

I am very happy about the output though, the speaker cone doesn't move at all when i switch on or off the amp. i can only hear a 'tick' sound. But when I play music, there's lot of static noise.

I am going to changed the other channel's gnd layout to see if I am able to achieve the same result.

Thanks.
 
pmchoong

pmchoong

Member
Joined 2008
techgrafic.com
Which way is correct in connecting the Gnd wire? Diagram 1 or 2?
 

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B

Bill Fuss

RIP
Joined 2005
Can you clarify that one channel is now working correctly, your post was a little confusing to me.

Your bias voltage of .88V is still way off of target, did you happen to check that source resistor while you were replacing the fet, seems like the R value must be higher than 1 ohm.

Bill
 
pmchoong

pmchoong

Member
Joined 2008
techgrafic.com
Yes, Bll, 1 channel is working, just that that speaker cone move when I turn the amp on.

I did not check the resistor (stupid me). I measured the fet though. It reads 3.69v while the other reads 3.66v. I measured one fet from my lots that reads 3.67v and replaced it.

I have took measurement before I soldered in the resistors onto the pcb, they ranged from 0.95 to 1.10 ohm.
 
B

Bill Fuss

RIP
Joined 2005
That's very good, your bias is probably fine, 1.1 ohms will read a higher V than .95.

Now that you have a good channel to refer to you can start trouble shooting by comparing voltage readings on the two channels. Do it without speakers for safety. When you find a reading that doesn't match you can start looking for the reason. Start at the output and work back towards the input.

Bill
 
pmchoong

pmchoong

Member
Joined 2008
techgrafic.com
I took measurement while the amp is switched on and damaged the bad channel. XLR wired by using:

pin 1 = ground
pin 2 = hot
pin 3 = cold

There is another small metal piece mark 'G' on top XLR but I did not make any connection to it.

Do i take measurement with the amp switched off? I measure the output between the 'output' on the board and the star ground on the PSU while the amp is switch on?

Thanks
 
B

Bill Fuss

RIP
Joined 2005
With no connection on input and output turn the amp on and take all your voltage measurements over. The DC offset is the voltage present at the binding posts. Use a copy of the schematic and write down all of the voltage readings next to the component that was measured. Then do it on the good channel and compare them.
If we're lucky that should be enough to figure things out.

Bill
 
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