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Old 24th April 2012, 08:49 PM   #12301
Itsmee is offline Itsmee  England
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To prevent smoking the outputs, lift up one leg of R13 & R14, power up and feed a signal in, scope up the drains of the JFETS, do they work ok?
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Old 24th April 2012, 09:23 PM   #12302
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I have disconnected one leg of R13 and R14, and power up with a signal (1KHz sine). The signal comes from the soundcard (no preamp).

I see:

- Voltage across R12 = 1.3VDC
- Voltage at output = 4.5VDC and rising
- I have measured the signal at R13 and R14 with scope (connected to drain of the JFETS). The signal at R14 has lower amplitude than at R13 (about 1/3 in amplitude). The shape of the signals is a bit of a skewed sine.

Interestingly, when I switch off the power supply to the amp, the signal at the drains of the two JFETS become both a very nice and smooth sine (equal on both JFETS) for some time, until voltage drops below about +/-5V.
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Old 24th April 2012, 10:07 PM   #12303
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I guess the difference in amplitude is due to different settings for p1 and p2...
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Old 25th April 2012, 09:55 AM   #12304
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I found an incorrectly supplied resistor: R6 was 3K9 and should be 100R

Can somebody please give me the correct values for measuring across R8/R5/R7/R6 in circuit? I get on one channel 40R (bad) and on the other 12R (the good channel!)

Thanks
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Old 25th April 2012, 12:36 PM   #12305
Zen Mod is offline Zen Mod  Serbia
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you're chasing your own tail

do what I already told you
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Old 25th April 2012, 05:42 PM   #12306
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Quote:
Originally Posted by studiostevus View Post
I found an incorrectly supplied resistor: R6 was 3K9 and should be 100R

Can somebody please give me the correct values for measuring across R8/R5/R7/R6 in circuit? I get on one channel 40R (bad) and on the other 12R (the good channel!)

Thanks
GND of output move to GND of board.
check all part if ok-->reduce value of R feedback down to lower 600ohm (50ohm may be more..and increase when it ok).original circuit is simple theory (read again working Jfet,mosfet..)
Q3 open feedback control by Q1 ( Q4,Q2 is the same ).
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Old 28th April 2012, 07:18 AM   #12307
Charly1 is offline Charly1  Australia
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Default Red board for stereo

Hi Gents any body used this board for two transformer 2 bridge configuration? I think we need to cut the center to seperet them>
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Old 28th April 2012, 09:08 AM   #12308
AndrewT is offline AndrewT  Scotland
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You need a dual secondary to build a dual rectifier dual polarity PSU.
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Old 28th April 2012, 09:17 AM   #12309
Charly1 is offline Charly1  Australia
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Quote:
Originally Posted by AndrewT View Post
You need a dual secondary to build a dual rectifier dual polarity PSU.
Thanks Yes thats why I have two transformer with each center tap winding. My problem is how can I use this Jims board with two seperate bridges.
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Old 28th April 2012, 10:08 AM   #12310
AndrewT is offline AndrewT  Scotland
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Ask Jims
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