Jung/Gallo "LT" preamp and op-amps... - diyAudio
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Old 25th September 2008, 04:21 PM   #1
FidPup is offline FidPup  United States
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Default Jung/Gallo "LT" preamp and op-amps...

Hi, All,

I am wondering if any forum members have had experience
building any version of the "Linear Technology" preamp that was
described in The Audio Amateur issue 2/1990. The preamp is based
on an op-amp driving a Linear Technology LT1010CT Buffer IC.

The basic circuit was designed by Walt Jung as a "no-compromise" unit,
that would showcase Linear Technology products. The final preamp
circuit was tweaked and described by Gary Galo in Audio Amateur.
( I believe Walt's version of the circuit was used in the Adcom
GFP-565 preamp.)

Anyway, back in 1991 I built a rediculously overbuilt version of the
Jung/Galo LT preamp. I built the unit completely
dual-mono, with seperate external raw DC supplies driving onboard
Sultzer ultra-low-impedance power supplies. I used all high-grade
parts, connectors and switches, even a teflon circuit board!

The preamp sounds really good, and at the time I built it
it actually came out on top in some preamp "shootouts",
when compared to some friends' commercial preamps in
the $1500-$2500 range.

The original Jung circuit used the LT1056CN8 op-amp as a driver,
but I built my preamp using LT1122 op-amps on the recommendation of
Gary Galo in A.A. 4/1990 (smoother high end, more inner detail with
the LT1122).

I am generally happy with the preamp, but when I use it with
my high-gain McCormack DNA-1 deluxe amp and Vandersteen 3A speakers
I hear a constant low-level hiss from the preamp. The noise is very
unobtrusive, but is sometimes noticeable on low-level material.

The original LT1056 op-amp specified in Walt's design
(and used in the Adcom preamp, I believe)
was designed as an ultra-low-noise audio op-amp. The LT1122 used in
Gary's final design was not specifically designed for audio use.

I am SURE there are newer op-amps that are better than either the LT1056
or the LT1122.

What I would like to know is, has anyone else built a similar
preamp? Any suggestions as to what op-amps would sound as good and be
a bit quieter? Uncharacteristically for an Audio Amateur project,
there were never any further suggestions or tweaks in later issues.

Also, I cancelled my AA subscription about two years after it was
reorganized into Audio Express, and I've definitely lost touch with
diy audio over the past 10 years(it's not as much fun since the advent
of digital and increasing use of surface-mount parts)!

Anyway, I am intertested to know about good possible replacements for
the LT1056 in the Jung/Gallo preamp.

Thanks !

Ken
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Old 25th September 2008, 04:41 PM   #2
mlloyd1 is offline mlloyd1  United States
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Location: illinois
i have experimented with these a bit in the past and found i was happier with walt's ad744 + ad811 combo or an opa627 + lm6321 combo. the lm6321 buffer is no longer available, but national has release another buffer in their high performance audio devices series. i have some but haven't listened to it yet.
the lt1010 has never been an exciting part to me.
i would be interesting to hear the lt1210 in the buffer position of a composite circuit but i never got around to trying it out.
btw, walt also had a composite design that used the ad823 + ad815. i still like the earlier ones better.
your mileage may vary ...

mlloyd1
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