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Old 26th February 2009, 10:50 PM   #1211
massimo is offline massimo  Italy
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Quote:
Originally posted by RCruz
You mean 6.8u is not suitable as an output cap ?
Generally speaking, the smaller (your system can support), the better. Salas is absolutely right. Check the input impedance of the following component and calculate the right value for 10 - 15 Hz.
As we are dealing with a less than perfect source, even if you cut a bit of low frequencies, is not that bad. Think about all the problem related to the warp of records and/or plinth resonance.
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Old 27th February 2009, 10:07 AM   #1212
RCruz is online now RCruz  Switzerland
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Thank you .

Now i understand the issues related with big caps.

I will stick to the 4.7u I am using now (quite good) and upgrade to a better quality cap.

Ricardo
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Old 28th February 2009, 05:08 PM   #1213
RCruz is online now RCruz  Switzerland
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Hi Salas

Just replaced all the resistors and placed everything in a new case.

It played for a while but only in one channel.. the right one only thundered and spet.

After cleaning the pcb, I have only rubble and no sound coming from the speakers.

What should be wrong ?

GND connections ?

Ricardo
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Old 28th February 2009, 05:50 PM   #1214
Salas is offline Salas  Greece
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Maybe too hot a desoldering & soldering cycle took out some semiconductor(s)? I would check the Zener voltage and the BC550 collector voltage. Also the drain voltages, and compare to the healthy channel. Also check for wrong new resistor values. If the channel that played initially, is silenced too now, then the problem may took the PSU too. Check for having correct B+.
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Old 28th February 2009, 07:57 PM   #1215
RCruz is online now RCruz  Switzerland
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Hi Salas

After a new clenup, the good sounding channel is grouling while the other is playing....

Zeners are good (both 8.4v)

Collector bC550 (Good channel 12.9 bad channel 12.33 ~ 12.29)

Between R6 C2 (Good 12.2 bad 9 ~ 12)

Output cap (Good 10.37 bad 9.86 ~11.1)

Where should be the problem ?

Ricardo
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Old 28th February 2009, 08:00 PM   #1216
Salas is offline Salas  Greece
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The way you describe it, the bad channel oscillates. I would see to change its BC550 first. Do you have a spare? B+ is stable?
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Old 28th February 2009, 08:06 PM   #1217
Salas is offline Salas  Greece
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Also measure ground points to chassis. Maybe some impurity sits in the small channels between ground planes and traces in your ground plane surrounded build. Lift the ground plane before you do more.
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Old 28th February 2009, 08:24 PM   #1218
RCruz is online now RCruz  Switzerland
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Just lifted ground plane... and replace BC550 on the bad channel.

Now I get 4.8 ~5.0 v on both output caps

BC550c collector good 12.8 bad 12.3 ~12.4
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Old 28th February 2009, 08:30 PM   #1219
Salas is offline Salas  Greece
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Continue with the JFETs one by one stage. Are you sure that the new resistors are all correct values in correct places and the ground scheme did not change?4.8-5V before caps?
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Old 28th February 2009, 10:33 PM   #1220
RCruz is online now RCruz  Switzerland
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I believe I found the issue... will report tomorrow.
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