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Old 10th January 2011, 04:41 AM   #871
49 - for the 18th time
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ZM - U R up to early - or tooooo late!!! Either way - blurry eyed???

It is my bedtime - night night.
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Old 10th January 2011, 07:23 AM   #872
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Quote:
Originally Posted by Zen Mod View Post
more data , please

hope you didn't forgot to ground negative input , if you're using unbalanced
I am using unbalanced input. Grounded the -input. What data points should i measure and post? Please let me know. Earlier you posted someone else's document giving voltage points on aleph 30. I will measure similar points on aleph j and post.

Thanks.
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Old 10th January 2011, 07:39 AM   #873
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Rather check for a mistake. ( if all components are new)
Or you risk to enter into a long process and, at the end, find an error.
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Old 10th January 2011, 12:34 PM   #874
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measure voltages across R7 , R8 , R18,R19 and output offset
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Old 10th January 2011, 02:23 PM   #875
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Default Measurements

Left (Working) Right (Problem)

R8 .. 8.73 8.65
R7 .. 5.38 5.38
Z1 ... 9.4 9.5
R18 .. 0.518 0.521
R19 .. 0.514 0.526
R16 .. 0.525 0.525
R17 .. 0.489 0.500

DC Offset .. 22mv 18mv (Both channels reduce with increase in temperature).

Q4 (C-E).. 5.3 5.3
Q4 (B-E).. 0.32 0.32
Q4 (B-C).. 4.4 4.5

Q3 (C-E).. 5.25 5.23
Q3 (B-E).. 0.323 0.324
Q3 (B-C).. 4.9 4.9

I am completely lost. They seem to be performing identically in terms of electrical characteristics. Left channel sounds perfect, right channel has poor gain and distortion when input level is increased.

Thanks.
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Old 10th January 2011, 02:32 PM   #876
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basic DC conditions are there

double check all solder points , especially on neg input side ;

use magnifier

I hope you didn't burn jfets during soldering , but not likely - in this case DC conditions should suffer
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Old 10th January 2011, 04:14 PM   #877
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Quote:
Connected old speakers and checked
Isn't one speaker faulty?
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Old 10th January 2011, 04:42 PM   #878
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Default Problem persists, nothing identified

Removed the board from the heatsinks, checked each and every solder and polarity and values of passive components with a magnifying glass. Cannot find anything. Cleaned small solder blobs here and there and scrapped cleared with a knife the gaps between each terminal of jfet.

First connected the faulty amp to one channel of the preamp and one of my regular Fostex speaker. Played music. Low gain. Preamp volume control goes all the way upto 1/2 of the dial. Pronounced emphasis on treble and audible distortion, predominantly in the highs. DC offset around 22mv to begin with.

Disconnected the preamp and connected the good amp board. Same preamp feed and same speaker used, to eliminate variations. Played music. Full bodied superb and well balanced sound. Volume control around 1/4 of the dial.

Some component that alters the frequency response and gain of the amp seems to be the cause. To me JFETs are ruled out as bad, as I swapped between the good and bad amp. Can they be one of the caps - C1, C2, C3 or one of the Q2, Q3, Q4 ZTXs? No clue.

TIA.
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Old 10th January 2011, 04:51 PM   #879
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Check the Vbe of Q4 of both channels.
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Old 10th January 2011, 05:01 PM   #880
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voltage across R17 seems good ,same as offset, so Q4 probably isn't a problem

remove Q3 and try
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