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Old 20th January 2012, 08:58 PM   #11711
sippy is offline sippy  United Kingdom
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thats the one, i prolly saw that car competing in the 85/6 RAC rally.........mind-warpingly rapid, as was the Pug T16, Audi s2s, metro 6r4, manta 400, fords rs200 and rs1700t, a rather surprising Skoda and a few others that escape my older mind.
On topic.........yes, the F5 Turbo will be elegant, cos Mr. Pass has that kind of mind set.
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Old 21st January 2012, 07:09 PM   #11712
Dzius is offline Dzius  Poland
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I put P3 across R1 and R2 resistors like on attached picture to bring some 2nd harmonic to music.
P3.jpg
Unfortunately I've got not distortion analyser on hand. Does any body have any suggestions how much of imbalance in ohm is needed to make F5 play more a bit warmer?
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Old 21st January 2012, 07:51 PM   #11713
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Quote:
Originally Posted by Dzius View Post
I put P3 across R1 and R2 resistors like on attached picture to bring some 2nd harmonic to music.
Attachment 261676
Unfortunately I've got not distortion analyser on hand. Does any body have any suggestions how much of imbalance in ohm is needed to make F5 play more a bit warmer?
You don't really need a distortion analyzer -- you can use a sound card FFT program and observe the 2nd and 3rd harmonics as you adjust the potentiometer.

The amplifier sound can be tweaked a bit by changing the output devices from IRFP240/9240 to Fairchild equivalents -- unfortunately these are only available as TO-220 so they might perspire quite a bit under the heavy bias used for Class-A.

I'm going to guess that changing the output stage source resistors changes the net transconductance of the output stage, so going from 0.47R to 0.68R may change the sound as well. I haven't done this, and don't know if there is a hearable difference.
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Old 21st January 2012, 07:55 PM   #11714
tpark is offline tpark  Canada
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This is probably off-topic and discussed earlier in this thread. I have used this circuit previously with a regulated supply at much lower currents ( 100ma and higher source resisters of 4.7 )on the output devices as a headphone amp with no issues. My current toroidals at 24 volts put out around 35 volts and I need to drop around 10 volts. I thought Nelson's power supply for the Zen amp using a zener reference would work and does if circuit is not connected. I use a 15 and 13 volt zener which gives the 24 volts. unfortunately the circuit pins the supply to around 4 volts on the positive side and does not work. Hooked directly to the supply at 35 volts there is no problem. I have old SK147 and SJ72 FETS and have them cascoded to keep within tolerance. I am using a LM329DZ at 6.9 volts for the cascode reference with no filtering but can't see that being the problem. I don't have fancy test equipment except for a oscilliscope and don't see any high frequency stuff but this scope is limited in its range. Any suggestions.
Tom
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Old 22nd January 2012, 12:58 PM   #11715
Dzius is offline Dzius  Poland
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Thank you jackinnj for advice and encouragement. I was not an easy stuff but I have done it. At first while turning P3 clockwise my distortion spectrum looked like this:
F5_distortion_spectrum_initial.jpg
And long minutes I couldn't produce anythnig else. But I change P3 turnnig counterclockwise and finally have got something like this in both chanels:
F5_distortion_spectrum_tuning.jpg
So now F5 distortion spectrum is similar to the that of F3:
F3_distortion_spectrum.jpg

Great.
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Old 22nd January 2012, 05:04 PM   #11716
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THANKS Guys for all the help! The 6L6 thread is just gorgeous.
Cheers
Chris
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Old 22nd January 2012, 05:19 PM   #11717
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Quote:
Originally Posted by Dzius View Post
Unfortunately I've got not distortion analyser on hand. Does any body have any suggestions how much of imbalance in ohm is needed to make F5 play more a bit warmer?
Presumably you can hear the differences between middle and the two
extremes. If you can't then perhaps it's not of great consequence.

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Old 22nd January 2012, 05:36 PM   #11718
Dzius is offline Dzius  Poland
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Dear Nelson there is difference in sound comparing to previous version and setup. No doubt about it. Additionaly looks like 3rd harmonics has gone from my F5 ? I wonder how it's possible. I was obsesed in carefull choosing all the resistors and transistors (2SK170, 2SJ74 and IRFs) but nonetheless it should be there. Don't miss it though second is enough. Still I can find it in my F3. Right now both amps are closer in sound characteristic than before.
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Old 22nd January 2012, 07:50 PM   #11719
6L6 is offline 6L6  United States
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Originally Posted by Reibradi View Post
The 6L6 thread is just gorgeous.
Thank you very much!
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Old 22nd January 2012, 08:18 PM   #11720
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Originally Posted by Dzius View Post
...my distortion spectrum looked like this:
May I know what you used as a Spectrum Analyzer?
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