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Current Mirror Discussion
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Old 16th November 2008, 12:07 AM   #141
lineup is offline lineup  Sweden
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sandyK
can you attach a simpl drawing of your found mechanism
Remember: one image tells a 1000 words
... when, like me, many people not even have english as mothertongue,
using images and graphical explanations is a good universal tool of communication
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Old 16th November 2008, 12:28 AM   #142
sandyK is offline sandyK  Australia
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Default CM Discussion

Lineup
The 15W/Ch Amplifier and Preamp use basically similar circuitry except for the output stage, and a few other minor changes. The 15W /Ch has a 4.7uF polyprop input capacitor, and doesn't currently use an Offset Corrector.
The version used by vhfman has a CFP VAS, and uses the diode in the CM method, and the value of the VAS emitter resistor is slightly adjusted to achieve a similar balance, and a fairly similar performance.
SandyK

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Old 16th November 2008, 12:36 AM   #143
jam is offline jam  United States
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homemodder,

Thanks for the feedback. Any chance of sharing the results of the sim?

Regards,

Jam
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Old 16th November 2008, 12:43 AM   #144
ostripper is offline ostripper  United States
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Click the image to open in full size.

Speaking of "blameless"heres the guinea pig. These are the 3rd
& 4th amps, and for these I added the buffered widlar
and schottky diode w/ trimpot. As I didnt want to make new boards all mods are smd underneath.

As far as self amp being "bland" , I listened to this one's
driver stage with headphones (like in pix) ..standard CM
..buffered mirror, and with all mods.

Standard sounds noticebly better than my HT receiver,
with either or both of the 2 mods "eerie" is the only
word for it.

How good "eerie" sounds is dependant on the VAS current,
I've found 14ma for the VAS is the ideal.(adjustable current
source).

Strange about the 3 tranny mirror , the offset trim has
a much wider "zero range" almost like auto offset comp.
measuring the LTP only microamps of difference.

OS
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Old 16th November 2008, 12:50 AM   #145
jam is offline jam  United States
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Well,

....................eerie could be good or bad.

Jam
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Old 16th November 2008, 12:55 AM   #146
cbdb is offline cbdb  Canada
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for those new to I sources/mirrors heres a web page that explains the basic types of current mirrors and LTPs with current mirrors.

http://www.zen118213.zen.co.uk/RFIC_...cuits_Page.htm
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Old 16th November 2008, 01:26 AM   #147
ostripper is offline ostripper  United States
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Quote:
eerie could be good or bad
Eerie is the amp that haunts your dreams because you can't wait
to get up in the morning to listen to it.

Quote:
The version used by vhfman has a CFP VAS
Is not that VAS cascoded?? (as would say yoda)

Os
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Old 16th November 2008, 01:46 AM   #148
homemodder is offline homemodder  Portugal
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Hi Sandyk, I have no problem with blameless type amps, I have a 15 year old clone although I wouldnt call it a clone as its more based on JLH s design ideas that sounds comparable to 12 000 pound electrocompaniet monoblocks I have. The biggest changes Ive made with the blameless is compensation and fine detail into component selection and small tweaks into current sources and mirrors. Balancing ltps which is beneficial has always been a small headache which is why my interest in this thread. Its beneficial with other topologies too. I wasnt thinking of the CM diode trick, I dont think Id use that although sims tells me it could be of some value. The idea of all the current mirrors is to balance the 2 halves of the ltp while getting the added advantages that CM bring. By better balancing the CM youll get the better balance in the LTP. Try simming the combination I proposed and youll find that you get much closer ltp balance.

Lineup dont worry this is not a groupthink, its actually quite the opposite, read carefully what groupthink entails and how its characterised. True there are some threads where this can be seen but here people are giving their own innovative ideas and experiences which is the quite the opposite. Nobody here has so far put a stance and the others followed it without challange or investigation.
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Old 16th November 2008, 02:02 AM   #149
sandyK is offline sandyK  Australia
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Default CM Discussion

homemodder
There are many ways to get a much closer balance. What I am saying is that since 1987 I have found with many different amplifiers, using different topologies,i.e. with or without Current Mirrors, that if the LTP transistors are selected for a close balance in HFE, and a very close balance in VBE, that the sound quality markedly improves when the voltage difference between these well matched transistor's collectors is within +-5mV. I agree that this doesn't sound plausible, but it has been verified by several DIYAudio members in both U.K. and Australia, as well as one from India who was open minded enough to try the suggestion. The member from India also commented that he was then able to hear the noise floor of some CDs.

SandyK

Many thanks also, to AKSA for having such an open mind, and daring to post the original diode suggestion.
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Old 16th November 2008, 02:18 AM   #150
ostripper is offline ostripper  United States
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Quote:
Many thanks also, to AKSA for having such an open mind, and daring to post the original diode suggestion
Yeah , without aksa I would have to settle for plain.
(not that it is bad)

Quote:
that if the LTP transistors are selected for a close balance in HFE, and a very close balance in VBE, that the sound quality markedly improves when the voltage difference between these well matched transistor's collectors is within +-5mV.
Now I have a hard time unbalancing the diff. <1mv

Quote:
Lineup dont worry this is not a groupthink, its actually quite the opposite, read carefully what groupthink entails and how its characterised. True there are some threads where this can be seen but here people are giving their own innovative ideas and experiences which is the quite the opposite. Nobody here has so far put a stance and the others followed it without challange or investigation.
Maybe because it really does work.
OS
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