F5 meets Buzquito

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gaborbela

Member
Joined 2005
Hello

Thank you Juma!
Also thank you Zen Mod, probably still better than simple voltage feedback.:)
One of my friend want to try these amp , I think these originally from you Zen Mod . To me it look like your design (I can be wrong).
Can you do some comment on these please.
Since He ask me to each the PC boars for these .
Thank you

Greetings Gabor
 

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juma

juma

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Joined 2005
Actually, every feedback is the voltage feedback (current flow is always a consequence of voltage). We just call some of them "current feedback" because they carry more current than usualy due to low Z of return point (and amp from post #1 qualifies too).

And about going berserk, you should see ZM's sister-in-law when... :rofl:
 
Zen Mod

Zen Mod

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gaborbela said:
Hello
........
One of my friend want to try these amp , I think these originally from you Zen Mod . To me it look like your design (I can be wrong).
.....
Click to expand...

that's Vangelis's construction - a guy enormously skilled in both schematic ( projects ) and pcb construction ;

Kudos where it belongs .

that amp was tried by me , and I couldn't decide which one was better - Babelfish J or this one .
 
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Zen Mod

Zen Mod

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gk7 said:
Well, to me it looks more like it´s a variant of a John Curl design.
Kudos where it belongs...
Click to expand...

question was - drawing - mine or someone else's ;

of course that origin is much older than that drawing .

nobody here wants to steal someone else's IP , so - just gimme a break with that , or we'll end up in tube era , searching for older and older origins
 
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fab

fab

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fabaudio.online
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THD vs VAS transistor type

I wonder if other members got the same results for THD as I have obtained in changing the VAS transistor types (keeping same VAS current of 50ma):
  1. Lateral Mosfet 2SK214/2SJ77 ----> worst THD
  2. Vertical Mosfet IRF610/IRF9610 ---> second lowest THD
  3. BJT medium power type --> lowest THD

For the BJT and Lateral mosfet types, they both require about same voltage across resistors of drain of input jfet thus the same input gain. For the vertical, b/c of higher VGS threshold, it produces higher input gain. I suppose that the Lateral provides less VAS gain than the BJT. Therefore, this test confirms that the THD is reduced as the amount of feedback increases and this effect is more important than the inherent linearity of the VAS transistor use. Is that a right conclusion?
Would the Lateral or Vertical sound better anyway and if so why? :scratch:

Thanks
 
juma

juma

Member
Joined 2005
Fab, it's to be expexted...
BJTs provide highest OLG so it logical that THD will be the lowest with them.
Laterals have the lowest transconductance and if you use them with small Id (i.e. in the non-linear part of the transfer characteristic) they will certainly exhibit high THD.
That's why I used pi-MOS k2013/j313 (they are very linear verticals and their Yfs is pretty high) with higher Id - it sounds best to my ears.
 
fab

fab

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Joined 2004
fabaudio.online
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juma said:
Fab, it's to be expexted...
BJTs provide highest OLG so it logical that THD will be the lowest with them.
Laterals have the lowest transconductance and if you use them with small Id (i.e. in the non-linear part of the transfer characteristic) they will certainly exhibit high THD.
That's why I used pi-MOS k2013/j313 (they are very linear verticals and their Yfs is pretty high) with higher Id - it sounds best to my ears.
Click to expand...

Thanks Juma for your comments an appreciation on the sound.
But I thought that 50ma was an appropriate current for the 2SK214 medium power Laterals...

If I can find the pi-MOS k2013/j313 I will give them a try.

Another question: How do you compare the sound of this amp of yours with your other F5 type including these pi-MOS k2013/j313 as output devices?

Fab
 
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juma

juma

Member
Joined 2005
fab said:
...How do you compare the sound of this amp of yours with your other F5 type including these pi-MOS k2013/j313 as output devices?

Fab
Click to expand...

The sonic difference is subtle but my preference goes to F5 with k2013/j313.

BTW, one batch of k2013/j313 that originates from Zhou Fang came to me tooo and I can confirm that those are the real stuff, no fakes.
 
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fab

fab

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Joined 2004
fabaudio.online
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juma said:
The sonic difference is subtle but my preference goes to F5 with k2013/j313.

BTW, one batch of k2013/j313 that originates from Zhou Fang came to me tooo and I can confirm that those are the real stuff, no fakes.
Click to expand...

Thanks again!

Other question: I had problem with thermal stability of the IRF610/9610 so I had to add thermistors in the drain load of the input jfet (like F5). Of course with laterals it was a non-issue and for the BJT the thermal stability is managable w/o thermistor (though I suppose it may help here too).
What is the behavior of the pi-mos type that you use in relation to thermal stability that may affect the VGS applied to the Lateral mosfets? Which heatsink arrangement (main, separate,...)?

Thanks
 
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