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Old 12th May 2012, 12:54 PM   #11
Zen Mod is offline Zen Mod  Serbia
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higher OLG , higher amount of feedback

most likely different THD spectra
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Old 12th May 2012, 01:10 PM   #12
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Thanks. ZM. I was being too narrow minded in my view of operating conditions. Although the ratio of feedback is the same, more devices provide more gain, thus more is thrown away through feedback. Got me a soundcard. Actually can see what is happening with distortion now. I will have to pull the fets and mesure single vs double. Thanks again.
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Old 12th May 2012, 01:30 PM   #13
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Originally Posted by buzzforb View Post
Rhetorical question, I presume. 400mV across bothe Rs. Roughly 3.2 A available bias with dual vs 1.6A with single pair. While i understand that more current is available, lets assume i never need more than 1A of current to drive my speakers to deafining levels. Why would two pairs ound better than one?
I am a firm believer we hear the power supply. Are you using the same volts and amp transformer for both? Same caps? If not, that could be the difference alone.
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Old 12th May 2012, 01:50 PM   #14
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Yes. I have dual trafo, with CRC 54KuF before R, 54KuF after. ZM's explanation is quite true now that look through those lenses. Maybe I can get the soundcard up and running and have some visual aids to add to what I am hearing.
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Old 12th May 2012, 02:13 PM   #15
Rush is offline Rush  United States
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Originally Posted by buzzforb View Post
Yes. I have dual trafo, with CRC 54KuF before R, 54KuF after. ZM's explanation is quite true now that look through those lenses. Maybe I can get the soundcard up and running and have some visual aids to add to what I am hearing.
That is great news, you are in a unique situation to have only the number of output devises as the lone variable.
I am excited to hear more from you on this.

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Old 12th May 2012, 04:21 PM   #16
AndrewT is offline AndrewT  Scotland
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Hu B,
are you able and willing to reduce the 2pr bias to less than 3.2A?
Maybe try 2A (1A/pr) or even 1.6A (800mA/pr).

This last bias would be capable of the same maximum ClassA output current as the 1pr version. This could sound the same, or it could sound different.

I am not sure if the 3.2A & 1.6A stated in post10 are bias currents or maximum ClassA output currents.
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Last edited by AndrewT; 12th May 2012 at 04:23 PM.
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Old 12th May 2012, 09:33 PM   #17
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They are maximum class A cuurents. Earlier in the thread I stated that I was dropping around 400mV across the source resistors. My build is 100% experimental. If you want to try it, let me know and we will give it a shot. I am hoping to produce measured results to correspond with each change.
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Old 13th May 2012, 01:47 AM   #18
a.wayne is offline a.wayne  United States
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4pr please ....
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Old 13th May 2012, 10:01 AM   #19
AndrewT is offline AndrewT  Scotland
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In which case state the Rs for 400mVrs and state 3.2Apk or 1.6Apk, rather than 1.6Adc or 800mAdc as quiescent bias current options.
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Old 13th May 2012, 07:22 PM   #20
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Thanks for the correction Andrew. Haven't got much done today. went camping with family for Mothers Day. Hope to use upcoming week to get measurements on individual fets used as well as on single pair output. Matching for the GB will begin as well. Beta builders should get their fets soon. I will probably place the large order this week for the diodes and fets. I am going to give the kits another couple of weeks before ordering. Sorry for no updates.


I would like to display my ignorance again and ask about how ripple current ratings relate to PSU capacitance levels. Does having a capacitor with much greater ripple capacity reduce the amount of capacitance needed. I have always viewed the problem in F and V, not considering the current rating of the caps, as this is usually in line when appopriately sized caps are used. For example, a PEH200 63V 10000uF has the ripple rating of 2 - 22,000 63V Panasonic
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