High Current Version of B1 Buffer Preamp wanted

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tiefbassuebertr

tiefbassuebertr

Member
Joined 2005
tiefbassuebertragung.de
One-Stage Unity-Gain- resp. Buffer- (Follower-) Preamp e. g. for ML-1, JC-2 and JRDG C1

As replacement for preamp line modules (partly in versions in the potting compound) I am looking for an appropriate circuit topology.
The main reason therefore is the fact, that the sonic quality from line stages with voltage gain factor between 4 times (+6db) and 10 times (+10 db) or even more by far is not so good than without voltage gain (+/-0db).

I realized this clearly, when I compared a preamp version from a good friend - based on Andrea Ciuffoli's "Power Follower 99" - go to
http://www.audiodesignguide.com/my/Follower_99c.gif
with a wide range of diy op-amp based and discrete line stages so as commercial preamps from the top class like Krell KBL, Mark Levinson JC-2 and many more so as variuos preamps with tubes and integrated op-amps like OPA627, AD797 and National Semiconductor's LME range (until now I don't understand, why a line stage of a pre-amplifier needs voltage gain - unity-gain power amplifiers are not usual and line sources with low values of output voltage are also not usual)

A brief description of the mentioned preamp version you will find (post #45) under
http://www.diyaudio.com/forums/solid-state/82910-power-follower-99-a-5.html
and images of this preamp I have upload (post #1) under
http://www.diyaudio.com/forums/digi...e-connectors-special-outline.html#post3723081

What could be therefore the reason for this observations despite the present high parasitic capacitor values arround the used IRF710 in the mentioned preamp from the previous link ?

I strongly suspect that the chosen idle current of 1A (1000mA) from the mentioned preamp is the main reason. This means, no unwanted effects due to capacitive loads (e. g. provided by long signal cables) occurs.

But probably there are an additional important reason. The high complexity and the ever-present too high gain factors for line stages.
In my mind comes in this case some explanations of this paper :
https://www.passdiy.com/project/amplifiers/the-zen-amplifier

Here I read this - unfortunately back into oblivion on most of today's audio designer:

Einstein said, "Everything should be made as simple as possible, but no simpler." Simplicity is a common element of the best and most subtle designs. It is preferred for purely aesthetic reasons, but also because fewer elements color the sound less, and lose less information. ......

....... Many complex topologies have been justified by high quality of measured performance. By objective criteria, this is a perfectly valid approach. There are many applications where the need for measured precision is important and subjective performance is unimportant. Any application where the performance is crucial to obtaining accurate numbers, such as in an MRI field amplifier, should be judged by objective means.

...But this is not rocket science; our objective is to make listeners enjoy sound. If we justify this approach by calling it art instead of science, that is perfectly fine, even preferable.

These statements are, at least in my opinion, absolutely correct and have been confirmed in countless listening tests over and over again - both at power amps and pre-amps.

Therefore I have these concepts for the wanted line stage modul in the narrowest choice:

1) B1 Buffer Preamp
https://www.passdiy.com/project/preamplifiers/b1-buffer-preamp
2) SEWA-Seven-Watt-Amplifier (like power follower, but without CCS) go to post #27 under
http://www.diyaudio.com/forums/pass-labs/66822-sewa-seven-watt-amplifier-3.html
3) Andrea Ciuffoli's Power Follower 99 (for 50-60mA idle current)
http://www.audiodesignguide.com/my/Follower_99c.gif
http://www.diyaudio.com/forums/solid-state/3471-andrea-ciuffolis-power-follower.html
4) Linn LK-1 three transistor Buffer stage for the Tape out lead
http://diagramas.diagramasde.com/audio/Linn LK1.pdf (for schematic scroll down to the last page)
5) Andrea Ciuffoli's Hi-End super linear Headphone amplifier
the Headphone amplifier

The main disadvantage of the B1 Buffer amp is from my own view the too low idle current - so I think. I want to realize 50-55mA output (same value than the genuine resp. originale modules).

I think, this is possible basically in the same kind than BUNTA's variation of Andrea Ciuffoli's Power Follower - go to
http://www.diyaudio.com/forums/soli...uras-mosfet-power-follower-3.html#post3804254 (post #27, first image),
i. e. to create a Sziklai darlington consisting of a 2SJ170/BF245 and a FZT753 (DIODES, same as ZTX753, but for solder heatsink mounting)

Additional I want to replace the CCS by a normal high wattage TO220 resistor like Caddock MP820 for heatsink mounting (more simply), because I don't expect any disadvantages while listening comparsions (please note: it isn't a power amplifier for driving loudspeaker-loads).
But here I am not really sure whether on such preamp application audible disadvantages can be perceived.

The main disadvantage of the concept from No 5) is the too high complexity - I don't like this for a unity-gain line-stage.

What about Linn's tape-buffer used in the LK-1 (go to No 4 - corresponds to the concept from the B1 Buffer preamp - I don't discover any differences except the fact, that here are BjT's in use) ?

In the moment friends of me want to have one-stage unity gain stages (50-55mA idle current) as replacement for the line-stages of follow models:

1) Mark Levinson ML-1 and JC-2 (Class-A LINE DRIVER)
http://www.hifido.co.jp/photo/11/230/23062/l.jpg
http://2.bp.blogspot.com/-dkKKu4T-wvU/U3BK37LH68I/AAAAAAAB8RU/62llPiGaNus/s1600/ML1+inside.JPG
Schematic is here:
http://2.bp.blogspot.com/-mlcZvhfjp...g/0P-iBO5nAgw/s1600/JC-2+schematics+blocs.jpg

2) JRDG Coherence ONE - opened line stage modules from second generation with an OP-AMP - same versions like here:
http://img.canuckaudiomart.com/uplo...rence-one-series-ii-preamp-w-lomc-modules.jpg

Probably more important details for creating than mentioned above are to be considered - thank you very much for your additional hints in advance.
 
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tiefbassuebertr

tiefbassuebertr

Member
Joined 2005
tiefbassuebertragung.de
Thank you very much, Mr. Pass.
from the P1086 there is this datasheet:
http://www.onsemi.com/pub/Collateral/P1086.pdf.pdf

But from the 2SJ112 there is to find only a TO-3 outline - go to the pdf under
(PDF) 2SJ112 Datasheet PDF Download - MOS FET
Maybe you mean the J174 - J177 (also sourced from process 88) - go to
http://bns.com.pl/data/files/MMBFJ177/MMBFJ177.PDF
or maybe the J112 instead 2SJ112
http://www.onsemi.com/pub/Collateral/J111-D.PDF
If yes, all outlines are TO92 without heatsink mounting with low thermal resistance.
Are there jFET's with same parameter also available in an outline similar to SOT223 for heatsink mounting ? - go to
http://s12.postimg.org/wmyno1hd9/IMG_6371.jpg
https://www.infineon.com/export/sites/default/media/press/Image/press_photo/SOT-223.png
https://www.infineon.com/export/sites/default/media/products/MOSFET/dpak.JPG
for examples

A plug-on heatsink like that one under
575200B00000G | Heatsink, TO-92, 60°C/W, Plug-On Collar Mount | AAVID THERMALLOY
don't provide enough reliability because its too high thermal resistance (there is only a plastic outline).
 
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tiefbassuebertr

tiefbassuebertr

Member
Joined 2005
tiefbassuebertragung.de
2 picoDumbs said:
I was going to try these http://www.digikey.com.au/scripts/DkSearch/dksus.dll?Detail&itemSeq=232227656&uq=636346634221416200
Not specifically designed for to92, but the spring should hold them firmly against the heatsink.
If not just add shims to increase spring tension.
Click to expand...
URL shows only digikey's table of contents (overview).
Maybe you mean a heatsink like this from page 68:
https://www.aavid.com/sites/default/files/products/boardlevel/aavid-standard-heatsinks.pdf
refer also page 11 for explanations concerning thermal resistance
 
tiefbassuebertr

tiefbassuebertr

Member
Joined 2005
tiefbassuebertragung.de
R

res07njc

Member
Joined 2005
tiefbassuebertr said:
another approach is the use of the BF862 (SOT23 package, SMD marking code "2Ap") and large copper plain for the "D" (drain) PIN. I think, the thermal resistance is lower as from a TO-92 outline (200K/W) due a shorter lead - go to
https://www.modelithics.com/models/Vendor/NXP/BF862.pdf
http://www.mouser.com/ds/2/408/6909-57550.pdf
Here the appropriate threads:
BF862 Preamp
MOSFET Source Follower Headamp
http://www.diyaudio.com/forums/head...llower-headphone-amplifier-3.html#post1130743
Click to expand...

I say go for the win borrowing the theoretical usage similar to opc's NTD1.

to wit - Using high(er) voltage and current. In this case, good THD figures were found using the Fairchild part with 45V rail supply at 160mA. Assuming the use of a higher wattage 2-300 ohm Caddock as current source. Heatsinks required, but that's what we like anyway. :D

Output parts obviously worked for Mike R's Luminaria too. :)

While both of those designs were seeking voltage.. seems like something worth experimenting with.
 
Nelson Pass

Nelson Pass

The one and only
Joined 2001
Paid Member
If a B1 with high current is what you want, you are probably best off with
paralleling the same Jfets in that circuit. The 2SK170/2SJ74 and the LS
versions are still the best for performance IMHO.

Biased at 10 mA, they will deliver more than that with a 20 ohm or so
output impedance at lower distortion than anything else I have played with.

Paralleling them will give you the increase in current and the output impedance
reduction that you would expect - The Beast with a Thousand Jfets is an
excellent example.

Other parts, such as Fairchild's work, but only to approach that performance.
 
M

marconi118

Member
Joined 2008
Nelson Pass said:
If a B1 with high current is what you want, you are probably best off with
paralleling the same Jfets in that circuit. The 2SK170/2SJ74 and the LS
versions are still the best for performance IMHO.

Biased at 10 mA, they will deliver more than that with a 20 ohm or so
output impedance at lower distortion than anything else I have played with.

Paralleling them will give you the increase in current and the output impedance
reduction that you would expect - The Beast with a Thousand Jfets is an
excellent example.

Other parts, such as Fairchild's work, but only to approach that performance.
Click to expand...

what Fairchild part numbers?
P and N channel?
 
tiefbassuebertr

tiefbassuebertr

Member
Joined 2005
tiefbassuebertragung.de
Low Impedance Unity Gain/Buffered Line Preamplifier as commercial available Device ?

Currently I am looking for an overview of such preamps both in solid state and in tube version.
Such preamps seems to be very rare despite the fact, that voltage gain in a line stage is nonsense in cases, when the associated power amplifier works with usual voltage gain between 30 and 60.

The most significant disadvantage of signal stages with voltage gain is the fact, that the sound is colored more and less - independent, whether transistors, operational amplifiers or transistors are in use. Also a disadvantage is the fact that the volume attenuator knob provide the maximum undistorted sound pressure level sometimes already in the 9.00 a'clock position.

Therefore naturally unity gain stages in pre-amplifiers provide in all cases the better sound quality and the less hassle of finding the correct position for the volume control knob.

Check out in this case also post #18 and #19 under
Buffered Preamp or Passive Volume Control?
and pot #26 under
What is wrong with op-amps?
and post #85 under
Dan d'Agostino MOMENTUM: Sonic Character like pure ClassA/SE despite low Idle Power ?
Thank you for an advice

Concerning tubes I start this thread in the same topic:
https://www.diyaudio.com/forums/tub...r-otl-headphone-amp-overview.html#post6576107
 
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J

joensd

Member
Joined 2002
Once you start searching for headphone amps and buffers you´ll find enough literature (here) to read for months on end.
Though I don´t know why you would want that much output current.

If looking at BJTs I´d suggest diamond buffers.
Just fired up a Sapphire from RJM that is really nice as headphone amp and preamp (min. 6dB gain I believe but you just use the current output).
RJM Audio - The Sapphire Headphone Amplifier
Preamp-Buffers - simple idea
https://www.diyaudio.com/forums/analog-line-level/350773-discrete-buffers-3.html[/URL
 
M

marconi118

Member
Joined 2008
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