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Old 9th March 2012, 07:57 PM   #1021
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Location: Athens Greece
[QUOTE=Backbones;2933245]
Quote:
Originally Posted by nikosgrgr View Post
One thing that i have notice also is that the transformer of the unregulated supply is bazing excessively and this mechanical noise is audible thru the speakers.
QUOTE]

What current and voltage is your transformer primary winding designed for? Buzzing can be caused by saturation i.e., transformer can't cope with the primary voltage.

Does it buzz when connected to the house power supply but with the secondaries unconnected?
Dear Backbones,

The transformer is rated at 1000VA / 220VAC primary and it bazing without a load on the secondary

I have 1,5-2VDC in the AC line this must be the route cause for this mechanical noise.
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Old 10th March 2012, 04:30 AM   #1022
JimM is offline JimM  United States
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Have you bypassed the soft start?
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Old 10th March 2012, 12:09 PM   #1023
Murdoc is offline Murdoc  Germany
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Hi!
Perhaps you have some DC on your line, and your transformer get's pre-magnetified and so humms. If you would like to investigate this, here is a goog starting point: DC Filter against humming Toroidals - Summary of the most interesting Comments
Kind regards,
Matthias
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Old 10th March 2012, 03:36 PM   #1024
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Quote:
Originally Posted by JimM View Post
Have you bypassed the soft start?
Dear JimM
I have bypass the soft start this is not the problem.
Today i have tried another approach

I have bypass all the front end regulated psu everything is dead silent no any noise what's so ever.
I thing that the problem lies with the regulated psu transformer secondary winding.
I will try to hookup separate transformers and report back.
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Old 10th March 2012, 03:42 PM   #1025
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Dear Backbones

If i do remember correctly you have used salas regulated psu for your BA-2 front end
can you please provide your wiring diagram in order to compare.
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Old 11th March 2012, 07:55 PM   #1026
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nikosgrdr,

I haven't got a wiring diagram. However, let's try and do it with words.

The 8 wires from the output of the Salas reg are joined to make two wires for the +ve, four for the ground and two for the -ve. I'm running it at -25-ground-+25.
The BA-2 board then receives these three connections.
I then also connect the ground of the BA-2 board to the star ground of the separate power supply which supplies the power boards (the design of this is identical to Nelson's circuit diagram in the BA-2 build including the CL60 thermistor connecting ground to the amplifier's chassis which is mains earthed).
If you don't connect the front end ground to the power board ground you will get a hum (from the loudspeakers not the transformers).

What is the voltage rating for your front end transformer? You may get saturation of your transformer due to poor manufacture or because it can't cope with the voltage input or both which can set up harmonic interference that can cause other transformers within the circuit to hum or buzz.
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Old 10th April 2012, 12:58 PM   #1027
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Default Humm Problem

Dear all,
The hum problem when both front end inputs where connected with the outputs of a pre amp has been resolved by using two separate transformers (one per front end regulator also the main psu transformer for the output stage has been changed having now (4) separate secondary windings).
The amp now is silent.
One additional question.
Can someone advise were we can find very closely matched IRFP240-9240 (i cannot find any in tech diy).

Thanks
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Old 10th April 2012, 01:08 PM   #1028
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Old 10th April 2012, 02:33 PM   #1029
GKU is offline GKU  Switzerland
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Default Close matched IRFP240/9240

Go to search:
look for h_a
F5 power transitors

He is a European diy Audio member and sell these well matched parts.
Have had good experience.

Rgds
gku
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Old 11th April 2012, 01:15 AM   #1030
JimM is offline JimM  United States
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Super job, looks good and should be a very good amp.
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