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Old 24th September 2012, 02:24 AM   #91
Salas is offline Salas  Greece
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Quote:
Originally Posted by haiduc32 View Post
I'm running fast out of components..

I've resoldered the board. removed C3 and shorted it as in some previous post. without connecting it to the speakers the output voltage is 25V. tried to play with VR1, VR2, VR3, the output voltage did not change.
any ideas?
Smaller pictures please. No more than 1200X900.
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Old 25th September 2012, 12:00 AM   #92
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Quote:
Originally Posted by haiduc32 View Post
I'm running fast out of components..

I've resoldered the board. removed C3 and shorted it as in some previous post. without connecting it to the speakers the output voltage is 25V. tried to play with VR1, VR2, VR3, the output voltage did not change.
any ideas?
on the first pic, you sure have a blown transistor. and the cables to the output transistor have been very hot.
do you massure 25V on speaker output?
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Old 25th September 2012, 02:51 AM   #93
clm811 is offline clm811  United States
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Oh...look at the time, it had been sold before our galaxy formed.
So that was the big bang I heard...

Hard to design a stable amp in an oscillating Universe...

-Chas
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Old 25th September 2012, 06:49 AM   #94
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Salas, sorry, thought they would be scaled correctly.

AudioSan, yes, the output is 25V. the wires were not hot, it's the smoke from the blown transistor, too bad I didn't record it, it was pretty awesome..

while testing, the input should or should not be connected?

it's my first audio DIY project and I am still struggling to understand how things work.. I'm waiting to get some free time to start debugging it, checking voltages along the way, may be verify the transistor states...
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Old 25th September 2012, 11:28 PM   #95
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then its no wonder you are massuring 25V at the output
first you need to figgure out why the transistor went to transistor heaven
did it blow rigth away? or did it take some time?
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Old 26th September 2012, 05:52 AM   #96
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AudioSan, it blew up after I messed arround with VR1. Unfortunately yesterday i shorted the Q3 again (always use goggles) with the test probe, while measuring the voltages , so now I'm out of components for further testing.. but the preliminary tests showed that the voltages for tr1 - tr4 do not have the values (I mean translated to 25V rail) they should be according to the JLH test table. it's on hold till I get the spare components to blow up.. er.. fix it.
but thnx for trying to help, may be I get it right in a year or so..
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Old 27th September 2012, 12:35 AM   #97
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If I were you, I won't connect the power to the board directly right after soldering. I always put 2 10W 20 Ohm resistor in serial with V+ and V-. At least that will avoid the transistors from taking a cigarette.
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Old 2nd October 2012, 11:24 AM   #98
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Hello ! I am very interested in this amp.
Is it always possible to order two printed circuit boards?
Thank you.
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Old 9th November 2012, 09:02 PM   #99
clm811 is offline clm811  United States
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Question VR1,VR2, Vr3?

Hi.

I cannot find a good link for the referenced website for the original JLH info .

Can(will) anyone here tell me what pots VR1, VR2 & VR3 are for (i.e. offset, bias, etc.)?

Thanks in advance for the info.

-Chas
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Old 12th November 2012, 12:47 PM   #100
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I don't know what are vr1, vr2 and vr3 but.
one pot is for input volume
the second is for bias current setup
the third is for voltage balance between the two output transistor (u/2)
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