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Old 17th September 2011, 10:47 AM   #101
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Quote:
Originally Posted by buzzforb View Post
Can this clever control mechanism (P3) be used on a differential pair with similar effectivieness on outcome?
Yes indeed.
-- you can do the same with a LTP such as in the BA-1/2 'consolidated' front end.

I used to have a preamp with tubes, and I biased the feedback triode just a bit off from ground and saw the second harmonic change (increase); very nice sounding effect; I used that because I could not use a trimpot in the common cathode because it was a seven-pin device.
A French audio designer called Héphaïstos wrote about this effect. It just changes the load-line a little bit if I understand it correctly.

As far as I see this is a little different from introducing a small resistance such as a 20 ohm trimpot in the common drains of that FET-LTP. Because then you are trimming the transconductance of the LTP input/feedback jfets, and changing their respective amplification factor in a hefty way that might even introduce higher order harmonics in a very low quantity too (that is just hearsay, I do not have a FFT).
albert
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Old 17th September 2011, 10:53 AM   #102
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yes , indeed - as I already wrote - you can do that , but under condition that you deliberately use "poor" LTP ;
with proper LTP you can even use dissimilar halves and still have proper balance
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Old 17th September 2011, 11:55 AM   #103
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Practical implementation question. If a person were to make a modular front end for the BA Amps, where the output stage is housed in a seperated chassis from the front end, with external lines connecting the two, like a preamp, would there be connection/noise problems? I can invision multiple small inclosures housing different front ends that can plug and play with volume pot in front and output behind.
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Old 17th September 2011, 12:33 PM   #104
Zen Mod is offline Zen Mod  Serbia
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just imagine it as preamp ;

every usual precaution/trick needed to implement - screening , grounding , safety gnd to audio gnd via NTC , etc.

usual things .....

just ask Generg ; he's Master of Papalego toys

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Old 17th September 2011, 01:26 PM   #105
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OK. That is what i thought. What is the advantage to the naked F4 BA-output) over the standard. I know Nelson talks using increased capacitance to clean up the square wave in BA-2. Is this main purpose. I assume the trade-off is the cap needed in signal path for coupling.
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Old 18th September 2011, 08:01 PM   #106
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Couldn't wait for the boards to arrive. Just had my first piano lesson. Cut out the middle men.
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Old 18th September 2011, 08:30 PM   #107
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Piano fine.....!

New situation with BA-3,

I took it out of the F4 case, put it in my preamplifier case ( Aleph P had to go), made of two aleph p PSU a symmetrical +-24V supply for BA-3, by changing the Zener diodes to 3x 9,1V. Works perfect!

In front of BA-3 I tried Warpspeed and a TKD 2P-2511 Stepped attenuator. Before I had the attenuators between cd-player and BA-3/F4. This worked not so good. The value of the pot, one time 10k and later 100k, interacted clearly with the cables.

When I put the pot before BA-3 as a pre, the output impedance of BA-3 could drive the 1m cable to the F4 much better.

I also tried the F4 with and without the F-fet input stage. Normally I preferred the F4 ( for instance with pumpkin) with the J-FETs, this time the sound was better coupling the BA-3 directly to the crippled output stage.

The sound is now combined with open baffles (Lowther/tone tubby) very unaggressive and very elegant and fluent like water.....

I know these words are not adequate to describe sound, but I do not find better...

It is (again) a different sound world and as Nelson likes to say you can hear your cd collection again all over....
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Old 18th September 2011, 09:22 PM   #108
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I am really trying to develop a setup where the output stage/F4 is in it's own enclosure. It will have either a dock station for a BA FE or inputs for using the standard F4. There would be a switch toggling between standard F4 FE vs BA setup. Multiple FE would be in small separate enclosures, which when plugged in, could run off F4 rails. If not using BA type FE, you have access to standalone F4 and all it's pleasantries or with out Jfet FE if you so choose. The brilliance of this setup is the fact that it is modular. If you like the output stage, you have a limitless amount of possibilities in front. The fact that you have had success with using the volume control before the BA FE, Generg, is encouraging. We audio addicts need as much versatility as possible.
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Old 18th September 2011, 11:00 PM   #109
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Quote:
Originally Posted by buzzforb View Post
OK. That is what i thought. What is the advantage to the naked F4 BA-output) over the standard. I know Nelson talks using increased capacitance to clean up the square wave in BA-2. Is this main purpose. I assume the trade-off is the cap needed in signal path for coupling.
The advantage is removal of the Jfet buffer and whatever contribution it
makes. Certainly the naked stage is simpler to build, and the BA-3 is
up to the job of driving it.

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Old 19th September 2011, 11:18 AM   #110
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Again, I guess that BA-3 must be a perfect match for a "very naked" simple follower known in these forums as SEWA amp. While it worked fine with BoZ, with BA-3 it must shine
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