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Distortion sound at all volumes
Distortion sound at all volumes
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Old 7th January 2018, 05:54 AM   #1
sulan is offline sulan
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Default Distortion sound at all volumes

Hi everyone, my first post on this forum so hopefully this is in the right department.

I got a PROEL SMART12MA powered speaker that gives some kind of distortion sound at all volumes.
I opened the speaker and connected the amp to another speaker and same distortion sound appears so I have ruled out that the woofer or tweeter driver is damaged. I also noticed that the original transformer may have been replaced. Looking at the fitting bracket (photo attached) I suspect a toroidal transformer was fitted at factory but somebody have installed 2 smaller linear transformers with the following specs, the first one: 110V-220V 60/50Hz 17-0-17V 2A and the other one 110V-220V 60/50Hz 18-0-18V 2A.
Now I am not sure if this is what causing the distortion sound but if I where to replace it, would a transformer like this one be suitable ? DAC - 24-0-24V X 1, 18-0-18V X 1 - Toroidal Transformer - 434VA
The thing is that there are 2 secondary wiring needed, the circuit board have 2 sides of it where it needs to be connected, one says HI AC IN and the other one LOW AC IN, How much hi and low is supposed to be I am not sure but I have written to manufacturer and hope they will reply.
Any guidance would be appreciated.
Thanks

Rick
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Old 7th January 2018, 07:29 AM   #2
Keruskerfuerst is offline Keruskerfuerst  Germany
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You donīt know the power handling of the original transformer.
And the secondary voltages of the original transformer might also be different.
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Old 9th January 2018, 06:53 AM   #3
sulan is offline sulan
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Thanks for your reply, after a lot of search on the net I may found the wiring diagram for the MA160 amp with the original power handling of the transformer and it looks quite different. (attached)
Its seems I need to find a 20-0-20 VAC, 33-0-33 VAC output transformer.
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Old 9th January 2018, 05:31 PM   #4
Keruskerfuerst is offline Keruskerfuerst  Germany
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Now I guess the power handling:
300W/400W.
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Old 10th January 2018, 11:37 PM   #5
MAAC0 is offline MAAC0  Portugal
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According to this it's a 160W amplifier


PROEL - SMART SMTV12MA - MONITOR AMPLIFICATO - Zecchini - Strumenti Musicali


The high AC could be main power and the low AC could be pre-amp power. Follow the traces and the capacitors after should tell You what voltage the board is expecting.
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Old 10th January 2018, 11:45 PM   #6
MAAC0 is offline MAAC0  Portugal
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Schematic and parts download here. Just wait that processing stuff..
PROEL SMART 12A AM160 AM161 AM321 AM320 AM320S SM Service Manual download, schematics, eeprom, repair info for electronics experts
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Old 10th January 2018, 11:46 PM   #7
scottjoplin is offline scottjoplin  Wales
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It could be crossover distortion because of inadequate bias current due to the low voltage supply
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