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Old 12th December 2012, 01:53 AM   #101
stk435 is offline stk435  Australia
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Default Negative rail in output

folks, Can you please help me out here. This is my second diy project and struggling to get this to work. I am using the silicon ray 2005 jlh board with their PSU, i am measuring negative 26 volts on my output.
I am using MJ15003 for output, BD139/140 and BC560
replaced all the transistors one full round with no results. Any help will be much appreciated.
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Old 13th December 2012, 06:18 AM   #102
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so you got full negative supply rail on the output? start with confirming thet the PSU is working. du you got +/-26V or there about?
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Old 5th January 2013, 01:14 AM   #103
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he asks for help. but do not visit the tread for over 20 days after asking for help. that tells me he realy don't want help. so i'm out of it.
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Old 11th January 2013, 04:34 PM   #104
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Hi,
so finally I've assembled my very first amplifier, and my very first JLH amplifier. After putting it all together in a chassis I've figured that the left channel is louder than the other. I assumed it could be corrected with VR2, but nothing changed.
As a background, I might have used some transistors from a different batch on the second board.
Is it possible to adjust the board from the VRs, or should I resolder all transistors to be from the same batch?

thanks
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Old 11th January 2013, 05:40 PM   #105
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Hi
I f you can measure HFE, match the transistors between left and right especially for the input transistor..
You can't adjust the unbalance with vr2.
Can you post the shema ?

Last edited by killmister; 11th January 2013 at 05:42 PM.
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Old 12th January 2013, 11:01 PM   #106
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The gain is determined by the feedback network so I think the HFE of transistors won't affect it very much. I think haiduc32 should check the soldering first. For example, the fault soldering parts at the input stage will affect the loudness.

VR2 is used to adjust the 0 point, don't adjust it when it's balanced!
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Old 12th January 2013, 11:33 PM   #107
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how many watts does this amp have ?
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Old 12th January 2013, 11:59 PM   #108
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10W
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Old 13th January 2013, 06:41 AM   #109
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Mine is 16 watts . Psu is 32v and bias current 1.5A.
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Old 13th January 2013, 06:33 PM   #110
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hi,
thanks for the replies, I don't have a DMM with HFE so no way to pair the transistors. I think I'll try to resolder the second board with transistors from same batch and see if that works out, but that'll be possible only in 2 weeks, I'll post back when I try.
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