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Old 29th February 2012, 06:34 AM   #1
wijgers is offline wijgers  Netherlands
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Unhappy F5 and Rails Difference

Finally I could try to start the F5, waiting almost 2 years now.

When trying to stabilize one channel I had a very hard time to get similar values over R11 and R12 0.47 3W there was .1 volt difference between the two resistors.

I did check the power supply and gave an neat 26 V when nothing was attached.

How ever when I checked the rails again while setting up the F5 I discovered a difference in RAILS. There was over 1 V difference between + and - (24.3 and 25.6)

What could be the cause of this difference in RAILS? (bad rectifier?)

Seeing this difference I did not setup the other channel. First I want to have a good supply!

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Old 29th February 2012, 06:31 PM   #2
eyoung is offline eyoung  United States
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did you use the F5 p/s board or did you use something else???

Regards, Elwood
"Lead me not into temptation...I can find it myself."
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Old 29th February 2012, 10:51 PM   #3
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Wijgers.....no need to post your same item to more than one thread (i.e., here, and on the "F5 Power Amplifier" thread). It's confusing (multiple threads/responses), and only takes up time and space.

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Old 1st March 2012, 01:02 AM   #4
6L6 is offline 6L6  United States
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wijgers -

Can you bias both channels of the amplifier to .5v across R11 and R12 with zero offset?

If you can, then measure your rail voltages.
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Old 1st March 2012, 07:03 AM   #5
h_a is offline h_a  Europe
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What could be the cause of this difference in RAILS?
Might happen due to slightly different transformer windings, no big deal at all.

High Octane phono preamp Wiki
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Old 1st March 2012, 07:55 AM   #6
wijgers is offline wijgers  Netherlands
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@ eyoung: PCB is from CVILLER and also followed his values. and also use the Cvillen F5 PCB v2 using Tech DIY F5 kit for components C's are rated 40V 15000F each

@ CanAm man: Youre right! made a mistake in that respect.

@ 6L6: Will try after measuring unloaded rails, but now the + and - both and not just 1. Hopefully tonight. As far as I could see nothing bad happened to the board

@ h_a: I didn't expect this from a AMPLIMO trafo.

@ triode_al: I cannot measure the precise values of R11 and R12 My meter doesn't go that low. it shows for both the same value.

Thanks all for responding

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Old 1st March 2012, 07:57 AM   #7
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Originally Posted by h_a View Post
Might happen due to slightly different transformer windings, no big deal at all.

I got for that especialy no big deal at all part
Or different values on the R part of CRC again no big deal

The P and N chanels are different and require big different VGS
5and a bit V and 3and a bit volt you sorth this out with pots vhen you set bias

1 Volts difference in rails not big deal deal

set it up at half bias null the offset and let it warm up
increase bias and let warm up keep the ofset as low as you can get
repeat till You got right bias
Take your time with this (I let the thing run for 12 hours) then reset Ofset

As long as bias is near about what you need and ofset stay low you be fine.

Ofset main thing to worry about IMO

Once it is stable play same tunes and kepp eye on suply voltagge
If it stay the same no big deal

LOW value resistor mesurament

If you have LM317 see data sheets for constant current
set it up say for 100 mA and mesure V drop across Resistor you need to mesure
Quite precise and cheap

Last edited by Bksabath; 1st March 2012 at 08:01 AM.
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Old 2nd March 2012, 05:50 AM   #8
wijgers is offline wijgers  Netherlands
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Default :D

Don't ask why and how, but yesterday evening everything was OK...

I think the figures are good as they are to burn in the components.

0.515 V over R11 and R12, and 4.1 mV DC offset! I probably can tweak it to zero DC.

Both channels at the same BIAS but a slightly different offset.

This weekend will be a good one for further setting up the amp!

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Old 2nd March 2012, 06:53 AM   #9
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my 0.02EUR
Different ESR in caps, swinging values of resistors (resulting in different cumulative resistance of cRc) could affect PSU to supply different volts under idetincal load. I seriously doubt bi-wound torroids or bad graetz-bridge would fault like this but it is not excluded.

get 2 pairs of 12V/50W downlight reflector globes in series and connect each pair to your PSU. If any difference in + or - volts, swap pairs accross (just to cancel error in globe wattage) and if volt difference exists at same half, it narrows down fault to previously mentioned.

2 identical Amp meter in series with + and - rails on amp will confirm balance in current draw.
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