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Old 12th August 2005, 09:12 AM   #1
aht is offline aht  Thailand
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Lightbulb Some topology of current feedback amplifier

I modified this schematic from original voltage feedback topology which I had designed 75WRMS/CH.

I use some of idea from input stage of Accuphase E407 and use driver/power from my original schematic.

In the future I'll control it into class-a such as Krell KSA50 (hope).

Please suggest me if I had wrong design

Regard
AHT
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Old 12th August 2005, 09:47 AM   #2
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Hi,
You use some simulation program to do that sch and simulate probably - which one if this is not a secret - and .... where to find simulation models for other types of devices?
I this sim good (if You use it offcourse)?
I am not an expert on solid state (more in tubes acctually - so I wouldn't like to expertise arround Your circuit - but it looks nice and interesting from what I could see) but would like to try few things - first sim than build so a good sim would be nice.... maybe You could help...
bes regards
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Old 12th August 2005, 10:07 AM   #3
aht is offline aht  Thailand
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Smile Ok...following picture

I use 2.305mA for first stage Q3,Q5,Q1,Q4 and 2.404mA for current feedback stage Q2,Q6 and use 95mA for idle current on output Q16,Q17.

My schematic can be operate in bandwidth around 1-1MHz from CFA theory and it use over current protection ,too

For DIYER PCB coming soon :-)

ECG188/189 = MJE15030/31
ECG87/88 = MJ15024/25
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Old 12th August 2005, 12:06 PM   #4
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Meanwhile you can check mine and Sonny's CFB amps which works pretty good.

http://mirand.dk

QRV-06
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Old 13th August 2005, 04:44 AM   #5
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Lightbulb Cool !!!....simulation nearly succeed

From my experience about a voltage feedback amplifier I think a current feedback amplifier quite good flat sound (from simulating) anf more stability than VFA but I don't know why there're some (a few) brand name use CFA ? such as Accuphase, Arcam, Denon, Marantz, Jeff Rowland, as well as it's a good designing and a new topology.

Or I don't know about schematic of hi-end brand as use CFA
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Old 13th August 2005, 04:59 AM   #6
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Lightbulb picture of truely current at each stage

Following point :

A=Q3,B=Q5,C=Q1,D=Q4,E=Q2,F=Q6,G=Q7,H=Q8,I=Q12,J=Q1 3,K=Q14/15,L=Q16,M=Q17

After I simulated I just understand a theory of CFA it's as same as typical VFA but there's a few concept that adventage more than VFA such as

1.Slew rate
2.THD
3.Stability
4.Frq response
5.Sound (I think so)

Now I'm completely start to work with CFA 100% if anybody have other idea please suggest me, too

Regard
AHT
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Old 13th August 2005, 02:26 PM   #7
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Default Re: Cool !!!....simulation nearly succeed

Quote:
Originally posted by aht
From my experience about a voltage feedback amplifier I think a current feedback amplifier quite good flat sound (from simulating) anf more stability than VFA but I don't know why there're some (a few) brand name use CFA ? such as Accuphase, Arcam, Denon, Marantz, Jeff Rowland, as well as it's a good designing and a new topology.

Add a few brand:BB,AD.....

AD844,OPA660....etc is the same topology as the sch you post.

X.G.
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Old 13th August 2005, 02:49 PM   #8
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One quick comment; the 660 Ohm working against a Vbe and 82.5 Ohms in the first stage is a little dicey with respect to temperature stability. You might not need the little gain boost you get, and might just go with a current mirror arangement instead.
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