Andy is building a DHT Pre for me (I don't need to add my own lack of
experience/expertise into the equation and risk crapping up a very
sensitive
bit of kit) and the only testing it will get here is a) I got to like
it
full stop and b) Swim's got to supply me with a string of 'better'
responses
when I get her to hear a various snatches of music over a period of
time
with it in/out, amp on its own, amp with Denon's pre section, amp with
Pre
vs. another amp on its own &c. &c....

I try to get as much feedback as I can for development purposes - you
have to beta test stuff to see where the drawbacks are on other
systems, because your own references can be misleading or atypical.
I've had all my colleagues laboriously listening for hours for
perceived differences, and I'm now putting these DHT preamps in
different systems to see how they sound in other rooms and setups, both
balanced and single ended. So far the DHTs have sounded better than the
preamps they replaced, both active and passive, which is encouraging.
But there are questions, of course. Frequency response is one,
microphonics another (some racks are very resonant, others excellent)
so it's a continued development process.
Last night I took a balanced DHT preamp over to my brothers. He has a
very classy setup - top Krell CD player, big Audio Research tube
preamp, Nagra VPA 845 amps and Apogee Caliper Sigs. Big room. His own
system has a sound which to me is a bit "thick" - lacking transparency
- and also a bit lacking in timbre on instruments, notably woodwind,
cymbals (especially with brushes) grand piano and voice. But it has
generally good "forward" tone and a lot of midrange presence, and the
amp and speakers are superb, better than the front end. The DHT preamp
showed more timbre and better treble and was a distinct overall
improvement, more than subtle but less than overwhelming. This was a
DHT preamp which had a previous version of the filament supply (now
superceded by a better one), so there's room for further improvement.
But better than a big ARC preamp is already a step in the right
direction.
The big change came when we put a Chris Found VDAC-4 digital board into
the system instead of the DAC in the Krell, fed by optical cable from
the Krell transport. Here the sound really opened out and started to
sound very transparent - really as if the hifi wasn't there. Very
natural, like listening to real musicians in the room. The DHT balanced
preamp was developed using this DAC in my system, and is biased to take
the output of the DAC straight into the grids of the DHT. Anyway, this
combination was quite special. My brother intended going to bed early
for an early morning start, but listened for a further 2 hours sitting
with his wife, pulling out CD after CD and listening to track after
track. A recording of a Rachmaninov symphony with Rozhdestvensky and
the LSO was quite gorgeous - rich lush strings, and woodwind plain as
daylight - you could follow the clarinet, cor, flute right through the
tutti parts as well as in solos. I asked my brother what he thought of
the sound - he said "very natural and detailed - better clarity and
instrumental timbre". This is a typical comment - clarity and timbre
are the two most obvious differences. His wife said the same and
clearly preferred it, and she's as (or more) discerning than he is. I
left the DAC and the preamp in his system so he could give me comments
after prolongued listening.
Discussion points: well, basically just frequency response. The bass
was a little lighter, though all there. The midrange was less forward
than before. We discussed whether this was enough to explain the
difference in sound, and we both felt that the difference in timbre of
intruments was too distinct to be explained by frequency response, and
that the clarity, again, didn't sound like a difference in frequency
response. This is a subjective judgement of course.
I don't believe all differences can be explained by differences in
frequency response, though clearly this plays a part. Having heard the
same DHTs in different systems with quite different frequency responses
(one was a big Tannoy system with really fine bass and rather rolled
off treble) I think I can recognise the common factors in the sound -
clarity and timbre. It's a sound that tends to delight classical and
jazz listeners (female vocals with jazz trio sounded spooky - right in
the room) - not sure what it would do for punk and headbangers. The
sound is quite delicate, though fast and foot-tapping.
My favourite rock'n'roll preamp tube is the 1626 ( a nice old ST shape
triode) , which is indirectly heated, but I prefer DHTs for everyday
listening, since my listening is almost all jazz and classical. When I
had my 1626 preamp in the system I used to turn the volume up and put
on Jimmy Smith - you literally felt like jumping up out of your seat
and dancing - it was like being hit by a treble vodka. Horses for
courses! Andy
PS reminds me of one of Ronnie Scott;s comments in his pre-set patter.
"And now I'd like to introduce you to our sound man......... John. John
is our sound man. John is the best sound man in the country. In the
city?............... Useless"