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Old 20th June 2011, 08:17 PM   #10701
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Nelson,

I have just had an inquiry about resistor selection for an F5. Looking at the THD plot (Figure 9 http://www.firstwatt.com/pdf/prod_f5_man.pdf) I was wondering if you also ran these curves at a lower frequency to see if the third harmonic distortion was a thermal artifact indicating a resistor type source?

ES

(Yes I am too lazy too look at all of your .25 zillion posts to see if this has been addressed. )
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Old 20th June 2011, 10:08 PM   #10702
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I did not, but the answer is that the 3rd harmonic is primarily a function
of the transistor characteristic.

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Old 20th June 2011, 10:12 PM   #10703
udailey is offline udailey  United States
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Nelson, Which schematic editor do you use? I like the looks of your schematics. Sorry for OT but I bet other guys are a bit interested to.
Uriah
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Old 20th June 2011, 10:36 PM   #10704
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Quote:
Originally Posted by Nelson Pass View Post
I did not, but the answer is that the 3rd harmonic is primarily a function
of the transistor characteristic.

Thanks for the prompt reply.

Based on my resistor measurements I would suspect that at around 10 volts the distortion from the Panasonic resistors of the types I measured would begin to be dominant as shown used in this applications feedback loop. Not sure of your exact choice other than you mention Panasonic.

Just curious, as I suspect modern designs are getting good enough that such issues are emerging.

Last edited by simon7000; 20th June 2011 at 10:41 PM.
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Old 24th June 2011, 10:48 PM   #10705
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Default F5 hum, only one channel.

My F5 is now at service for 2 months. At the beginning I noticed a hum, only at the left channel and only audible when I put my ear close to the speaker. So no problem I thought. Sound is fantastic.

Now I planned a bias Vdc check last week and after this the hum changed . Adjustment were small, Vdc around +/- 10 mV and measured V sourceresistor is 0.6V, but the character change of the hum was big. After switching on the "cold" amp there is silence at first from the left channel, that's new. Seems good but after a few minutes suddenly it starts humming, first like a engine sputtering but then constantly and only the left channel. Not loud but audible. Tried to measure it: left 9 mV AC, right 0.5 mV AC. Sometimes after a while when the amp is more hotter it stops. This is suddenly worse than before. Guess it's not a grounding issue, right? Anyone an idea where to start? TIA

Regards,
Joffrey
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Old 24th June 2011, 10:56 PM   #10706
juma is offline juma  Germany
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Quote:
Originally Posted by TheAnaesthetist View Post
... Anyone an idea where to start?...
google for "cold solder joint"
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Old 25th June 2011, 08:40 AM   #10707
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Quote:
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google for "cold solder joint"
Thanks Juma, for your quick respons. After a short phase of denial (me, make a cold solder point ) it makes sense. So ... I have to resolder all connections left channel, I guess. Nice weekend job.
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Old 26th June 2011, 10:32 AM   #10708
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Hi,

is F5 good in reproduction for rock music mainly? If so, what preamp would you recommend? SS or tubes?

Thanks.
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Old 26th June 2011, 10:39 AM   #10709
AndrewT is offline AndrewT  Scotland
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CD and similar high output sources can drive an F5 to almost maximum power.
You don't need a pre-amp.

Lower level sources will need more gain than can be provided with a buffer for incapable sources.
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Old 26th June 2011, 10:46 AM   #10710
_henry_ is offline _henry_  Australia
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i second that.

i used beyma12cx and alpha15, with f5 for beyma and symasym for the alpha.

they are great.

cheers
henry
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