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Old 8th December 2008, 03:23 PM   #1
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Default Aleph 5 problem 2

I am building the A5 monobloc. The sound from one channel is muffled and the other no sound at all. The muffled channel stats as follow :

R 11 = 5.32v
Z5 = 9.3v
Q5 between C and E = 4.67v
R 14 = 4.38v

R64 = 0.713v
R65 = 0.621v
R66 = 0.688v

Q18 between G and S =3.65v
Q19 between G and S =3.73v
Q20 between G and S =3.67v

R28 = 0.633v
R29 = 0.901v
R30 = 0.646v

Q6 between G and S =4.04v
Q7 between G and S =3.67v
Q8 between G and S =4.01v

R22 = 14.1mv
R23 = 13.8mv
R24 = 13.8mv
R25 = 14.3mv

Output = 2.4mv

Can anyone help? Thanks.
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Old 8th December 2008, 03:36 PM   #2
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Q6 between D and S =33.35v
Q7 between D and S =33.11v
Q8 between D and S =33.35v

Q18 between D and S =32.77v
Q19 between D and S =32.83v
Q20 between D and S =33.05v

What is causing the problem?
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Old 8th December 2008, 04:08 PM   #3
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Default The bad channel

Readings from the channel that produces no sound and the speaker cone moves in when the power is switch on :

Z5 = 9.03v
R11 = 5.09v
R14 = 4.65v
Q5 C to E = 4.61v

R22-25 = 0

R28 = 0.629v
R29 = 0.744v
R30 = 0.601v

R18 = 0.684v
R19 = 0.638
R20 = 0.655v

Q6 from D to S = 32.7v
Q7 from D to S = 32.62v
Q8 from D to S = 32.74v

Q18 from D to S = 33.3v
Q19 from D to S = 33.31v
Q20 from D to S = 33.27v

Output = -24.0mv

Why do I get a negative reading for the output?
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Old 8th December 2008, 08:35 PM   #4
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Can you post the schematic you are using so we dont have to guess what's what.

Bill
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Old 8th December 2008, 11:46 PM   #5
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It is the one that I download from Pass site
Attached Images
File Type: jpg a5-c.jpg (72.4 KB, 567 views)
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Old 8th December 2008, 11:55 PM   #6
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I can't post the whole service manual as it is too large. But you can download here http://vidar.hallais.no/media/downlo...05%20(60w).pdf

Thanks
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Old 9th December 2008, 12:16 AM   #7
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It looks close, everything is biasing up OK. The only thing I question is the voltage across R28-30 and 52-54.The cone movement is normal unless it's staying in. Check out your grounding to the power supply and your input wiring and connections. 24mv isn't terrible for output offset.

Bill
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Old 9th December 2008, 12:19 AM   #8
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The cone moves in when I switch it on and when I switch it off, it sorted of bounced back. I have not play any music on this speaker yet as I assume it will not sing.
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Old 9th December 2008, 12:23 AM   #9
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For the R28-30 and R18-20, is it ok to have more than 0.5v as recommended? I used a starground to connect all gnd wires, including the transformer.
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Old 9th December 2008, 01:36 AM   #10
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R28-30 on the schematic are grid stoppers, 221 ohm. The output fets are biased around 20W each, no problem unless the heatsinks cant handle it.
You have .9xx V for R29 on one channel, check which resistor you actually mean. If that's a source resistor that fet is way off spec.

Bill
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