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The AVA Hifi UltraValve

Industry Spotlight

In: June
2011

John Reekie
2

As one of the (many, I am sure) people who were introduced to tube
amplification through the Dynaco ST-70, I was intrigued by the Audio by Van
Alstine UltraValve amplifier. Well-received at shows like AKFest 2010 and
RMAF 2010, this amplifier could be viewed as the latest step in the evolution of
the line of upgrades to the original ST-70 sold as kits for many years by Audio
by Van Alstine. I asked Frank Van Alstine if he would be prepared to share some
of his insights with us.

JR – Hi Frank, thanks for speaking with us today. Let’s start with
the best part first – your Ultravalve amp has been very favorably received – you
must be very happy about that?

FVA – Yes, I am really happy about the very favorable recognition of the
musical quality and outstanding value of our Ultravalve amplifier.

JR – The UltraValve is the culmination of years of evolution based on
the original Dynaco ST-70, is it not? How much of the original ST-70
remains?

FVA – What remains is some of the circuit basics (although drastically
improved), the biasing scheme (also improved and regulated), and the basic 5AR4
vacuum tube R/C power supply (again hugely improved and supplemented). We also
have pretty much kept the overall physical layout simply because it worked well,
is very quiet, compact, and can be assembled at a rational cost. No point
re-inventing the wheel.

JR – Are there specific circuit refinements that you can share with
us?

FVA – The major refinement is actually making the tubes work the way they
were intended to. The original – as do all other vacuum tube amps I am aware of
– has hopelessly inadequate power supplies. A simple RC network, no matter how
big or how outrageously priced the parts are, no matter what the outlandish
claims for their wonderful sounding parts, simply fails in real world use
conditions. There is a huge undesirable interaction between the tube elements,
both channel to channel, and even between each separate tube section. This
occurs because the output impedance of the supply ends up being several hundred
ohms at some frequencies, no matter what musical qualities are claimed for the
parts. To eliminate this interaction, separate, isolated, high current, high
speed, analog, regulated power supplies with very low output
impedance are required for the plate of each tube. With the Ultravalve, we
have done this. The sonic results are the proof of the pudding.

We did make a bad original design assumption in the first iteration of the
design, in the early production Ultimate 70 version. We tapped the raw supply
for the regulators ahead of the choke as we could measure no ripple at all after
the regulated supplies. Later, thanks to some very useful advice on our forum
on AudioCircle, we changed this to after the choke and that made a huge sonic
improvement, although there were no measurable differences in the performance,
either of the regulated supplies’ purity or at the output. The listening
comparisons were instant no-brainer improvements.

JR – What about output transformers? Tube lore has it that the
original Dynaco A470 output transformers are among the best ever made. How do
modern transformers stack up (pardon the pun)?

FVA – We really do not hear any differences between the various versions of
the output transformers that have been used over the years. Ours are made by
Dynakitparts to our own specifications and we are very happy with the
results.

JR – Could you outline for us your evaluation methodology? How do you
decide which of numerous circuit alternatives is the one to go with for
production?

FVA – Normally we evaluate by building one new channel in a production unit,
keeping the other channel as it was. We then have someone scramble the
interconnect and speaker wire connections and then leave giving us a random
setup. We then listen in mono and use the balance control to swap from channel
to channel. We make notes answering two questions: First, can you hear any
differences at all? Second, are they better or worse differences? Sometimes
the results are instantly very obvious, sometimes there is nothing at all,
sometimes what is obvious is that the changes made things worse. We also test
in general on two very different kinds of speakers, the Salk HT3s with ribbon
tweeters and a metal cone mid-range, and on a set of highly upgraded B&W 801
speakers. Both are difficult loads, both are highly regarded, and both easily
show up design flaws in electronics, but differently.

JR – Were there moments of frustration during the design process of
the UltraValve, or was it all smooth sailing?

FVA – The only real frustration is the amount of time it takes to put
everything together for production and get it right the first time. We are too
small and don’t have the financial resources to make significant mistakes.
Fortunately I have a great mechanical design engineer who is turning out perfect
chassis designs for us time after time and I am pretty good with circuit board
layout and between us and all the other internal advice and design help, we are
pretty good at getting it right the first time.

JR – If you had a time machine, which decade would be the one in
which you would most want to be designing amplifiers (and why)?

FVA – Actually it would be really fun to jump back in time to when David
Hafler was designing the original Dyna ST-70 along with a supply of the
necessary regulated power supply parts (not available back then), and make the
amp work then the way we can do it now. It was a killer in the marketplace
then, I wonder how the Ultravalve would have done.

JR – What about music? What are some of your personal
favorites?

FVA – I like many kinds of music from bluegrass to steel drum bands to opera.
Just as long as it is a good performance well recorded.  For live music, I
only have one rule: no electricity allowed! I want to listen to the music, not
some terrible PA system thrashing around.

Thanks much for this opportunity.

Frank Van Alstine

Readers' comments

nunhgrader

June 25, 2011

Reply

Great interview – I like his work and he’s a living legend – will be buying
one of his preamps one day in the near future!

Don Nicol

August 12, 2011

Reply

I agree with Frank. It would have been great to have had the Ultravalve
available in the mid-60′s. I became so frustrated with my ST70 due to
floppy bass and a noisy transformer, and lack of useful feedback from
Dynaco, that I threw in the towel and sold it and the PAS-3 to a college
prof. Sure wish I had it back but, I’m happy with a pair of Eico HF-12′s
driving open baffle Stephens 80fr/s complemented by an open baffle
sub.

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June 2011

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