F5 power amplifier - Page 1071

simon7000 · 20th June 2011, 08:17 PM

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. )

Nelson Pass · 20th June 2011, 10:08 PM

I did not, but the answer is that the 3rd harmonic is primarily a function
of the transistor characteristic.

udailey · 20th June 2011, 10:12 PM

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

simon7000 · 10:41 PM

Quote:

Originally Posted by Nelson Pass

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.

TheAnaesthetist · 24th June 2011, 10:48 PM

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

juma · 24th June 2011, 10:56 PM

Quote:

Originally Posted by TheAnaesthetist

... Anyone an idea where to start?...

google for "cold solder joint"

TheAnaesthetist · 25th June 2011, 08:40 AM

Quote:

Originally Posted by juma

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.

kacernator · 26th June 2011, 10:32 AM

Hi,

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

Thanks.

AndrewT · 26th June 2011, 10:39 AM

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.

_henry_ · 26th June 2011, 10:46 AM

i second that.

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

they are great.

cheers
henry

20th June 2011, 10:12 PM	#10703
udailey Passive Aggressive diyAudio Member Join Date: Mar 2008	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 __________________ You can purchase LDRs anytime to build a standard LDR attenuator or to build my new LDR Attenuator "A Lighter Note". Email me. diyldr@gmail.com

24th June 2011, 10:48 PM	#10705
TheAnaesthetist diyAudio Member Join Date: Oct 2009 Location: Maastricht	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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20th June 2011, 08:17 PM	#10701
simon7000 diyAudio Member Join Date: Nov 2008 Location: Oakmont PA	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. )

20th June 2011, 10:08 PM	#10702
Nelson Pass The one and only Join Date: Mar 2001	I did not, but the answer is that the 3rd harmonic is primarily a function of the transistor characteristic.

26th June 2011, 10:32 AM	#10708
kacernator diyAudio Member Join Date: Jan 2008	Hi, is F5 good in reproduction for rock music mainly? If so, what preamp would you recommend? SS or tubes? Thanks.

26th June 2011, 10:39 AM	#10709
AndrewT diyAudio Member Join Date: Jul 2004 Location: Scottish Borders	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.

26th June 2011, 10:46 AM	#10710
_henry_ diyAudio Member Join Date: Jun 2002 Location: Australia	i second that. i used beyma12cx and alpha15, with f5 for beyma and symasym for the alpha. they are great. cheers henry