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Old 24th January 2003, 05:55 PM   #21
jam is offline jam  United States
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Jonathan,

You are correct about cascodeing current sources I have found that this is one method to get the most of the current source.

With regard to the current source on the second differential would you not have to set it to twice the value compared to just using a current mirror only ?

Jam
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Old 25th January 2003, 10:40 AM   #22
jcarr is offline jcarr  United States
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Jam:

For the second stage in a dual-differential stage, the summing current-mirror is (almost always) operating at a 1:1 ratio (no gain), and can tolerate a wide range of currents without much difference in performance. I usually determine the currents that I will use on the basis of the differential devices' maximum ft (rather than noise), or whatever level of current is required to fully drive the succeeding stage (whichever is greater). If you calculate like this, I do not think that the amount of current desired will change, whether the loading (and/or summing) of the differential stage is accomplished by resistors, single active devices or a current mirror.

regards, jonathan carr
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Old 25th January 2003, 12:06 PM   #23
halojoy is offline halojoy  Sweden
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Default Theory is one thing - Circuits another

We have seen a practica example of a differential
in a schematic by Kaneda. See above!

Now there is a discussion about two different ways to design.
I want to see a good example
of this folded cascoded.
Elso and other posters have a liking of this type
of amplifiers.

Would be interesting to see a schematic.
Makes me and other fellows here
be more interested in your discussion.

We also want to know more!
And feel being a part of your theoretical discussion.

Regards to you all
halo
----------------------------
Schematic shows a differential input with bias set by resistors:
Kaneda preamp:
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Old 25th January 2003, 08:33 PM   #24
jam is offline jam  United States
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Jonathan,

Thanks for your reply, you certainly have helped improve my understanding of the dual differential topology. As Holojoy has put it, maybe you could give us a circuit (line amp) to analyze and build, maybe even start a new thread on. This seems to be one topology worth investigating further.

Thanks again.

Jam
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Old 25th January 2003, 10:41 PM   #25
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Hi,

The "Le Solstice" preamp surely was a standard setter back then.

I'm a tube fellow and I admit I had a lot of respect for this one although to my ears all Hiraga's tube designs beat it hands down on colours, dynamics and sheer musicality.

Not that those designs were perfect in any way...

The Kaneda,at least to the original specs is virtually impossible to build nowadays,not to mention the fact that almost all designs published in "L'Audiophile" contain deliberate mistakes.

Caveat emptor,
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Old 25th January 2003, 10:57 PM   #26
jam is offline jam  United States
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Frank,

You would not happen to have the schematic for "Le Solstice" would you? And if you do could you post it? ( for us hopeless solid state guys )

Jam
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Old 25th January 2003, 11:07 PM   #27
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Hi Jam,

I doubt it...

Jam,I'll look through my issues but I honestly doubt I have anything workable for you in my "L'Audiophile" issues.

This was a commercial design based on the Kaneda work with a lot of of attention to detail such as passive components.

You may be able to find a second hand unit though and if you need some English to French or vice versa translations I'll be happy to help.

Cheers,
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Old 27th January 2003, 10:27 AM   #28
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Default Kaneda ... folded cascodes ... 2SK30

If I recall correctly, the first commercial Kaneda, the DC1, had 2SK243 (a double 2SK43) in the first stage, and the later Solstice had 2SK240. These informations are in the numerous articles in the French L'Audiophile magazin. The 2SK30 is available without problems, at 50c each, but there are two versions, one in the normal TO92 case, and another, slightly different, in a more rounded case, with magnetic leads, which sounds less good. The Y selection has better Idss stability than GR, so I did choose Y for selection. Operating point is about 250uAmps anyway.

When I changed from the baisc DIY-Kaneda (2SK30 really sounds best there) to folded cascode, I needed a darlington output stage, because I lost some gain, and it wasn't enough for my active RIAA any more. I used 2SK97 (you can see it as a monolithic 2SK43) in the input. What I got was very good and detailed treble and midrange, but I lost in bass. This might be partly due to the active RIAA, but I also had the impression, that the thermal distortion of the second stage was mirrored by the input stage. I used resistors for biasing the emitter currents of the second stage,
thus a Vbe variation in the cascoding transistors translates in changing biasing currents - maybe with current sources this improves.

Anyway I got the impression that this kind of circuit needed more complexity to work satisfactorily and went back to double differentials.

Today I am using a simple double differential with current mirror and a complementary output, but I am using low impedances all through the circuit and a lot of local feedback resp. degeneration, too. I am working with bipolars only, no Jfets any more. There is no Jfet that I would like to listen music through longer than one or two hours. Most Jfets make the music sound like plastic, the best types sound a bit like tubes.

I intend to change my pre to passive RIAA and two gain stages. I found it extremely difficult to tune the stages of the RIAA circuit to have good treble as well as good bass performance.

I also tried a later Kaneda preamp, published 1995 in MJ, and found that it had way better resolution and soundstaging and all that, but lost some of the tube magic that the old circuit had.

regards,
Hartmut from Munich
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Old 27th January 2003, 01:36 PM   #29
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Default Leach preamp

Has anyone built the Wide Bandwith Preamp by Marshall Leach?
It looks similar to the Kaneda, but with a different output.

Sam
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Old 27th January 2003, 06:08 PM   #30
halojoy is offline halojoy  Sweden
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Default Leach preamp

Quote:
Originally posted by sdman
Has anyone built the Wide Bandwith Preamp by Marshall Leach?
It looks similar to the Kaneda, but with a different output.
Sam
Yes, sdman, it looks same.
Maybe because it is also old. 1977...
But then old designs can be VERY GOOD in some aspects.
###############

W.Marshall Leach - Links to his Ampdesigns/Papers

Leach - Wide Bandwith Preamplifier - Article PDF

###############

I did a CUT-OUT of the MAIN SCHEMATIC of this Preamp
It is also in my music & schematics website

/halo - web audio research
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