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Old 31st July 2012, 08:55 PM   #11
PKI is offline PKI  United States
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Is it ok that on the boards there are only 4 1ohm 3w resistors and 6 of them on the schematic? And why there are two resistors in parallel on output boards(source)?
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Old 31st July 2012, 09:45 PM   #12
generg is offline generg  Germany
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Quote:
Originally Posted by PKI View Post
I was looking through the schematics from post #4
Another: DC adjustment, is it R106 or R8
I used a 5k multiturn pot parallel to R14 (392R) to adjust the offset.

As for the number of 1R resistors I would go for the original number and take 6. Of cause doing this you must also use all the other original values.
You can solder the two more resistors a bit higher simply over the four, they are all parallel......
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Old 1st August 2012, 12:34 AM   #13
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Quote:
Originally Posted by generg View Post
I used a 5k multiturn pot parallel to R14 (392R) to adjust the offset
and why not R8 and R1 (original notation)?
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Old 1st August 2012, 04:44 AM   #14
generg is offline generg  Germany
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Quote:
Originally Posted by PKI View Post
and why not R8 and R1 (original notation)?
R8 and R14+pot do the same .....changes of the resistor value give more or less voltage at the gate uF the Output IRFs. Adjusting them bring the value of the offset to Zero.
But warming up may change the value again.....or when your input Mosfets are not perfectly matched...
And R1 does the trick to keep these changes nevertheless very small!
So R1 is one of the perfect ideas of Nelson to minimize the offset changes!

R8 or R14 only bring the offset in the beginning or after an hour near zero but do not avoid the small changes over the time that can go up to 100mV.

R1 makes a kind of automatic minimizing the offset changes all over the time......

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Old 1st August 2012, 04:54 AM   #15
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Thanks, got it (sort of :-). So, R1 should be variable, yes?
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Old 1st August 2012, 07:58 AM   #16
generg is offline generg  Germany
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R1 is experimental, you start with the recommended value of some megohm and you observe the offset.....for instance when it is beginning with around 10-20mA and stays in this ballpark after some time you have won...
if the value is still too great you start to change....... make it bigger and smaller and see the effects direction coming to the goal of 10-20mV at the output. You stay with this value.

Works really fine and if the input Mosfets are closely matched you even do not need the pot I mentioned or any change of the other mentioned resistors.....

good luck....

I do the same at the moment, I use this Mosfet input stage to drive two Semisouth and I prefer the sound at the moment over the 2SJ109 input stage.....

not so detailled, but simply more sound.......! I like this kind of mosfet bloom!
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Last edited by generg; 1st August 2012 at 08:00 AM.
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Old 13th August 2012, 04:34 PM   #17
PKI is offline PKI  United States
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I am about to order at mouser; thermal paste:
I have some from CPU/cooler combo, is it good, or it is better to order this:120-2 Wakefield | Mouser (or some other from mouser)?
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Old 13th August 2012, 05:37 PM   #18
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that one from Mouser is good enough



I'm not using those for CPU - some are/were electrically conductive

better safe than sorry
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Old 22nd August 2012, 06:30 AM   #19
PKI is offline PKI  United States
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I just realized that I bought wire-wound vishay dale 1ohm 3w resistors, not metal film... How bad is it ?
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Old 22nd August 2012, 07:25 AM   #20
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that works fine.
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