Review: Audio Research SP-6b Tube preamp

Category: Preamps

I purchased an ARC SP-6B 3 months ago to
replace my Quad 33 preamp. I'd always wanted
to try a tube preamp and this one is a great
start. It is similar in age to the solid-state Quad,
but the sound is much nicer. The sound is warmer
and the phono sound is better. The phono gain
is also quite large, allowing me to use my MC
cartridge directly. I still prefer to use my
separate Sota head amp to improve impedance matching
both to the MC and the SP6 phono input.

One problem with the SP6 (and amps of that vintage)
is their large gain - way too much for current CD
devices. One can hardly adjust the gain past 9 o'clock
and the volume is too high. With the stepped
incremental gain control on the SP6, 2 clicks can
be too little and 3 clicks too much volume.
There ain't no 2 and a half on the SP6!
And signal/noise is better at a 12 o'clock
setting, or so. To solve this problem.....

I also use a Creek OBH-12 passive preamp and
it gives a super clean sound. But the warmth
of the SP-6B beats the OBH-12. I use them together
now, to get the convenience of the remote volume
of the Creek. It also allows me to adjust the
gain of the SP6 midway (12 o'clock) improving it's
signal/noise ratio compared to a 9 o'clock setting.
I can then use the Creek to adjust the volume.
I put the Creek in the tape loop of the SP6
which sounds much better that with the Creek
between the SP6 and the power amp.

The unit I purchased
needed to have some of the nuts holding down the
RCA input plugs tightened (due to age and use
I'm sure). The previous owner said it had
been re-tubed, but two of the tubes looked shot.
It uses 6 12AX7's and I replaced the lot.
This removed some annoying sound dropouts and
reduced the tube rush somewhat. If you get one of
these, expect to have to do a bit of work on it.

I listen mostly to classical and jazz. I typically
use Chanticleer, Count Basie, Diane Krall,
and Stravinksy's Firebird for test setup.
For finer tuning, I'll try some piano
(I like Krystian Zimmerman playing Chopin,
Paul Jacobs playing Debussy on those GREAT
old Nonesuch LPs). I listen for clarity
and good separation of instruments in large
ensembles. For vocals, if I can feel the
emotion (conveyed in suble breathings, subtle
dynamic changes) I know the setup is a winner.
I love the drum solo on Diane Krall's Stepping Out
CD, "Devil and the Deep Blue Sea."

Strengths of the SP6: nice tube sound, lots of gain,
good phono section, solid build.

Weaknesses: too much gain for CDs and other modern
input devices, may need retubing and/or cap
replacement due to age. It takes 2-5 minutes
of warmup before the SP6B is useable, due to the
auto-muting circuits.

I enjoy the SP6 and it's a great deal (mine was $500).
I think all the older ARC tube preamps are worth
trying. I'm still going to try newer tube preamps,
looking for less tube rush and queiter background.
Yes, money is an object and for the price the
SP6 can't be beat.

Associated gear
ARC Classic 30
Creek OBH-12
The SP-6B in its day was an excellent preamp, however
it has been eclipsed by more recent designs. The noise
floor is excessive, and frequency extremes are attenuated.
The midrange is smooth, airy and typical of the better
tube units. More recent ARC preamps (i.e. SP-14) are
notably superior, for a modest increase in expense.
I beleive you can lower the gain with an internal switch or jumper change. Check with ARC, I'm sure you'll get the needed help.
I also own an ARC SP-6B. You can adjust the gain via a switch on the rear panel (make sure you are powered OFF before changing the setting). I think the SP-6B is one of the best bargains in the used market for anyone looking to get into the hi-end world. I prefer the higher gain setting to complement my medium powered tube ARC. It makes it sound a bit more dynamic, especially with the likes of Maggies. And it sounds just fine and detailed through my current Sonus faber Concertos. Tube rolling makes quite a bit of difference and can affect the overall presentation, including the softening, and the opposite of that, in the frequency extremes. Enjoy!