Dear Hugh
sorry if my silent was unpolite,
I thought my experience is obvious for all, and I would not like to start the discussion in this thread: for me thd up to a few % is acceptable if only the 2nd, 3rd, 4th harmonics are dominant.
if the harmonics 7th, 9th, 10th and higher are relatively high, the sound will be harsh, probably.
My favorite amp has dominant the 2nd and 3rd (~3%) and harmonic comb is quickly descending and the sound is extraordinary, but this is class A current amp without gnfb, please find attached asc file.
High amounts of nfb not mean the sound is harsh. For me better use very high gnfb or zero.
regards.
Pawel
Damir
Please accept light offtopic in your thread, thank you in advance.
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There's two amplifiers here. One for the voltage gain and one for the current gain. both has to be optimised to their specific purpose. And then there's the interface between the two. The error-correction buffer has heaps of feedback, and this for very good reasons, as it is the only way (Class A aside) to have reasonable performance. then there's the question on the Voltage stage.
Here the solution is ca non feed back current conveyor, with amazing specs and to my gut feel very good sound. This means I have a job to do with my OPS, and I must fit a jfet pair for the input... to make it interface better to the IPS.
That said, I believe the most important accomplishment here is the separation of the two blocks, not the absence of NFB in the Voltage stage.
Here the solution is ca non feed back current conveyor, with amazing specs and to my gut feel very good sound. This means I have a job to do with my OPS, and I must fit a jfet pair for the input... to make it interface better to the IPS.
That said, I believe the most important accomplishment here is the separation of the two blocks, not the absence of NFB in the Voltage stage.
here it goes:
.MODEL BF245C NJF(VTO=-5.0014 BETA=5.43157E-4 BETATCE=-0.5 LAMBDA=2.71505E-2
+ RD=1.20869E1 RS=1.20869E1 CGS=2.00000E-12 CGD=2.00000E-12 PB=1.24659 IS=3.64346E-16 XTI=3 AF=1
+ FC=0.5 N=1 NR=2 MFG=PHILIPS)
Here they are:
*2SJ74
*Toshiba Dep-Mode 20mA 400mW LowNoise pkg:TO-92B 2,1,3
.MODEL 2SJ74 PJF(Beta=92.12m Rs=7.748 Rd=7.748 Lambda=4.464m
+Vto=-.5428 Cgd=85.67p Pb=.3905 Fc=.5
+Cgs=78.27p Is=12.98p
+Kf=26.64E-18 Af=1)
*2SK170
* 20mA 400mW LowNoise Dep-Mode pkg:TO-92B 3,1,2
.MODEL 2SK170 NJF(Beta=59.86m Rs=4.151 Rd=4.151 Lambda=1.923m
+Vto=-.5024 Cgd=20p Pb=.4746 Fc=.5
+Cgs=25.48p Is=8.477p
+Kf=111.3E-18 Af=1)
Thanks Valery, it's set to 1.9 A, small Class A amp, I think that was visible from here http://www.diyaudio.com/forums/solid-state/255819-gainwire-class-poweramp-ngfb.html#post3918601
regards
Damir
Thanks gain Hugh,
here is the IPS output impedance, it's quite high(2Mohm) and that is why is not easy to find good power buffer with enough high input impedance.
Damir
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Hi Dadod,
yes, ngnfb,
maybe its voltage gain is ~1,
but please remember its current gain is h u d g e
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