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Old 29th April 2011, 10:45 PM   #1
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Default Help. A-30 Trouble

Hello,

I have build the A-30 mono blocks with brianGT PCB-s 2 years ago
You can see the pics here:
https://picasaweb.google.com/1078196...eat=directlink
They have worked flawlessly for last 2 years and brought many hours of great music enjoyment.
Unfortunately yesterday when I fired them up a huge buzz appeared on both channels. Since I was messing around my source and preamp last few days I thought that the problem is there. Investigating further showed that the hum and buzz is unfortunately from the amps...
So here is the problem: first with no load at all amps are silent but when I add any kind of balanced source there it is... I measure 147mV AC on speaker connectors. DC is less than 20mV after 2 min.
With RCA and jumper across minus and gnd on XLR all is fine...
No cap shows shortages no funny smells and
I have measured all currents fine

Since my knowledge in electronics are limited I just have no idea where to look further?

I have attached the schematic of the boards I have used.
Attached Files
File Type: pdf BrianGT board schematic.pdf (27.5 KB, 54 views)
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Old 30th April 2011, 05:03 PM   #2
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You're not being logical. There is no problem with the amps unless you have done something weird with the grounding in both your sources and the amps. Much more info needed, especially about your sources. How about schematics or drawings?
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Old 30th April 2011, 08:00 PM   #3
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Bill,

Thanks for the reply! I did not want to "overflow" first post with every info and measurement that come into my mind.
You say I'm not being logical... I seem unable to find - measure where is the problem but I can surely hear it. So there IS a problem with my amps.
And yes... the source... I admit I was playing around my source just few days before... I have a TP buffalo dac with legato1 boards...that I have modified into latest incarnation of legato3 (ref.Legato 3 - Look ma! No caps!).
Changes included taking out buffer, piggybacking Supertex TP0604 trios in place of BS250 and the thing I did on my own risk after measuring 0-6mV DC between - and+ I took out the coupling caps without trimming DC to 0 and with no gnd from the source!!! Yes I know should not have done that etc.
Such signal was passed threw my pre-amp which is an early incarnation of The Poor Serbian Man's Optical Attenuator
It sounded marvelous like never before for one and half day...

Gimme a hint where to look first
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Last edited by Bassivus; 30th April 2011 at 08:02 PM.
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Old 30th April 2011, 08:01 PM   #4
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Quote:
Originally Posted by Bill Fuss View Post
You're not being logical. There is no problem with the amps unless you have done something weird with the grounding in both your sources and the amps. Much more info needed, especially about your sources. How about schematics or drawings?
Does seem very odd that BOTH monoblocks would start to hum......I'd look at source or pre.

Russellc
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Old 30th April 2011, 08:04 PM   #5
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Quote:
Originally Posted by Bassivus View Post
Bill,

Thanks for the reply! I did not want to "overflow" first post with every info and measurement that come into my mind.
You say I'm not being logical... I seem unable to find - measure where is the problem but I can surely hear it. So there IS a problem with my amps.
And yes... the source... I admit I was playing around my source just few days before... I have a TP buffalo dac with legato1 boards...that I have modified into latest incarnation of legato3 (ref.Legato 3 - Look ma! No caps!).
Changes included taking out buffer, piggybacking Supertex TP0604 trios in place of BS250 and the thing I did on my own risk after measuring 0-6mV DC between - and+ I took out the coupling caps without trimming DC to 0 and with no gnd from the source!!! Yes I know should not have done that etc.
Such signal was passed threw my pre-amp which is an early incarnation of The Poor Serbian Man's Optical Attenuator
It sounded marvelous like never before for one and half day...

Gimme a hint where to look first
Well, it seems odd, but I suppose both amps could have been damaged Identically. Does a different source produce the hum? Usually you can short the input and fire up, if it is not the amps it should be normal? I havent built (not yet!) an Aleph, so listen to the experts before shorting the input, but I recall no warnings about doing that with an Aleph...but what the heck do I know?

Russellc
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Old 30th April 2011, 08:49 PM   #6
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Yes I did try it with other source. I have connected it and even without powering up the source the humm and buzz is present... That source on the balanced out has Jensen trafos also gnd lifted...
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Old 30th April 2011, 09:01 PM   #7
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few pics will help

I suspect that arrangement of gnd lead is culprit

especially if everything is fine with pins 1&3 tied
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Old 30th April 2011, 09:14 PM   #8
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I'm sorry, references to other projects is not very helpful. Your implementation is directly connected to your problem so make a detailed drawing of your arrangement so we can help you find your error. I realise that there is a slight language barrier, and it would help troubleshooting greatly.

You have given me the impression that without inputs connected the amps are silent. When you attempt to use the amps' balanced inputs it creates hum, so that would point to your preamp being the problem, not the amps. Is that not the problem?
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Old 2nd May 2011, 07:07 PM   #9
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Zen, a lot of pics on link in my first post...

Brian:
Lets forget my setup with preamp etc.

I have tried my amps with 3 different sources DIRECTLY to amp and there is a problem with balanced in...

Untitled-1.jpg

I measure HUGE DC over 16V peak on DMM at the fire up and it very slowly goes down...

BrianGT-aleph-schematic.jpg
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Old 2nd May 2011, 07:38 PM   #10
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sorry - I didn't saw a link

you know that I'm double blind


anyway - I recently made mistake , which took me 2 hours to solve - swapped gnd and hot neg. on XLR ;

be sure that :

pin 1 - gnd
pin 2 - hot pos.
pin 3 - hot neg.
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