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Old 16th February 2018, 01:43 PM   #751
marconi118 is offline marconi118  Germany
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question about the output cap:

in signe rail PP amp the output idle voltage is at 1/2 Vrail so the output cap is always porlarizedi in the same way, an electrolitic can be used

in the MoFo the output voltage is around 1V (very low resistance of the choke)
when it swings with the audio signal, will the polarisation if the output cap be reversed? do we need non polarized electrolitic?

Is-it better to reference the output (and maybe the input too) to the +V as done here
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Old 16th February 2018, 02:28 PM   #752
Zen Mod is offline Zen Mod  Serbia
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input reference - pretty much always ref. to side where source of mosfet is ;

in fact , disregard that sentence ..... it really depends of particular case

and , it's wise to arrange that GND is on same side , just because gnd is usually cleanest rail in system

though .... where to reference load is another issue

looking at left side of pic you posted - "normal design" - input is flawless , speaker return can be moved from gnd to drain of mosfet for some benefits

looking at right side of your pic -"exclusive design" - only speaker is connected in best way ....... input side is very troubled ...... move generator marked as 1/2Vb to gnd side , and everything is suddenly OK

I'm surprised that we can't see anti-parallel resistors there .......
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Old 16th February 2018, 03:33 PM   #753
marconi118 is offline marconi118  Germany
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ok
I will use the original MoFo schema but connect speaker on the +V side...

input will stay referenced to -V

No ground connection for me, I trust isolation of my toroidal transformer
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Old 16th February 2018, 04:12 PM   #754
Michael Rothacher is offline Michael Rothacher  United States
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Quote:
Originally Posted by marconi118 View Post
...do we need non polarized...
I haven't had problems in practice with inductor-loaded L'amp, etc. with music as the source, but it's the builder's choice.
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Old 16th February 2018, 06:29 PM   #755
Michael Rothacher is offline Michael Rothacher  United States
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Quote:
Originally Posted by marconi118 View Post
I will use the original MoFo schema but connect speaker on the +V side..
Fine, but PSRR will go down, not up in the case of MoFo. The drain of the MOSFET offers much higher resistance than the inductor. The inductor is not a constant current source.
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Old 16th February 2018, 08:29 PM   #756
316a is offline 316a  England
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Quote:
Originally Posted by Michael Rothacher View Post
Fine, but PSRR will go down, not up in the case of MoFo. The drain of the MOSFET offers much higher resistance than the inductor. The inductor is not a constant current source.
I have run various choke loaded output stages with BUZ900P , RD16HHFN1 and Semisouth 085 . Subjectively I found the sound a lot brighter with the output connected across the MOSFET each time I tried . I preferred taking the output across the choke . Chokes used were the Thomas Mayer specified LL2733 700mH/175mH

You are right about PSRR . LCLC supplies are the way to go

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Old Yesterday, 01:18 PM   #757
marconi118 is offline marconi118  Germany
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you are right about pssr
connecting the tweeter across the mosfet i could ear the noise from the laptop 19v smps

back across the choke and dead silent
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Old Yesterday, 05:02 PM   #758
marconi118 is offline marconi118  Germany
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For tweeter Amp (compression driver) is it better with inductor or lamp?
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Old Yesterday, 05:41 PM   #759
xrk971 is offline xrk971  United States
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What does output across the choke mean?
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Old Yesterday, 05:48 PM   #760
marconi118 is offline marconi118  Germany
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Taking output referenced to - v is indeed quieter
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