Valves in the pre or power amp?
- Thread starter richardg
- Start date
Steven Toy
Accuphase newbie
You can't really generalise. Output valves in the power amp probably count more than anywhere else though.
Coda II
getting there slowly
from a purely practical point of view, and generalising to a greater or lesser extent:
pre amp valves don't get nearly so hot*, last much longer and are cheaper to replace
whereas
power amp valves get very hot, have a shorter life span and are more expensive to replace
and then - depending how much power your speakers require, a valve power amp may or may not be a viable proposition in the first place
* eg. a Croft valve pre runs cooler to the touch than a class A SS Sugden
pre amp valves don't get nearly so hot*, last much longer and are cheaper to replace
whereas
power amp valves get very hot, have a shorter life span and are more expensive to replace
and then - depending how much power your speakers require, a valve power amp may or may not be a viable proposition in the first place
* eg. a Croft valve pre runs cooler to the touch than a class A SS Sugden
Chops54
pfm Member
IMO a valve pre/SS amp is a nicer sounding combination to my ears than a SS pre/valve amp. I use a Grounded Grid valve preamp to drive my NCC200 monos and it sounds far nicer than when driven with my 42. A good friend of mine also uses this particular valve preamp with his NCCs too 
sergeauckland
pfm Member
If a valve amplifier has any character it will be because of the output transformer and the results of limited open-loop bandwidth and the resultant distortions at the frequency extremes. This affects power amplifiers only.
On the other hand, pre-amps don't have output transformers, and their performance as line-level input selectors and volume controllers can easily be transparent and sonically identical to a SS pre-amp. That leaves valve phono stages, which generally, but not always will have more noise than a SS phono stage, but much better headroom.
Overall, my view is that valve amplifiers don't necessarily have a "valve sound", but if they do, then it's due to the power amp.
S.
On the other hand, pre-amps don't have output transformers, and their performance as line-level input selectors and volume controllers can easily be transparent and sonically identical to a SS pre-amp. That leaves valve phono stages, which generally, but not always will have more noise than a SS phono stage, but much better headroom.
Overall, my view is that valve amplifiers don't necessarily have a "valve sound", but if they do, then it's due to the power amp.
S.
Steven Toy
Accuphase newbie
My valve power amp measures flat from 5 to 100,000 Hz.
Serge, that's exactly what I was going to say. There is no point to having valves in a pre-amp.
Louballoo
Mine would be pretty quiet without them.
I guess it depends if you can get away with a passive preamplifier or not. If not, a tube active linestage is better and generally less expensive than a transistor preamp. I recently heard a Conrad Johnson Classic ($2000) and a Croft Micro 25 ($1400) and both are much better than a Nac202!
Tony L
Administrator
I know people who run tube preamps with either high-power solid state power amps or active speakers, both with great success. The tube pre brings much of the attributes of a full tube system, plus allows considerable scope for tuning to taste (e.g. a Mullard ECC83 sounds very different to say a Telefunken or RCA) - it gives the tube sound without losing the ability to drive awkward or demanding speakers. I've never seen the appeal of doing it the other way round, e.g. solid state pre & tube power.
I think someone has been reading Stereophile again...................
Tony L
Administrator
No, just relating direct personal experience of some systems I know very well. Nothing wrong with Stereophile either, as you know full well given you run a fully Stereophile-compliant system yourself - Linn, CJ, LS3/5As etc, all highly recommended there.
RustyB
Registered Ginga
In my rounder days I ran tube pre/SS power for many years, it works well for exactly the reasons Tony describes.
The only proviso is to make sure that the output impedance of the pre is not too high wrt the input impedance of the power amp, which can easily occur.
Some tube preamps eschew a cathode follower, and these can have an output impedance of around 1K or more.
Match such a preamp with a solid state power amp with a 10K input, and the result will not be happy.
The only proviso is to make sure that the output impedance of the pre is not too high wrt the input impedance of the power amp, which can easily occur.
Some tube preamps eschew a cathode follower, and these can have an output impedance of around 1K or more.
Match such a preamp with a solid state power amp with a 10K input, and the result will not be happy.
sergeauckland
pfm Member
sergeauckland
pfm Member
Yes, valve amps can have decently wide closed loop response. However, the open loop response will be rather more limited, which affects distortion at the frequency extremes. Have you measured the distortion at even 50% of full power at 50Hz, 1kHz and 10kHz? Unless you amplifier is most unusual (and I can't think how that would work), then the 50Hz and 10k distortions will be many times greater than the mid frequency distortion due to limitations in the output transformer and phase shift in the preceding stages affecting the open-loop response.
S.
There's always one........
S.
More than one, actually....
EAR, Audionote, Shindo etc.
Just goes to show, generalisations "pre-amps don't have output transformers" are fine until they aren't=)
sergeauckland
pfm Member
You're right there! I was unaware that any designer would be so daft as to use an output transformer when a cathode follower would do, probably rather better. But then, when I look at the circuits of some of these products, I really do wonder at the engineering credentials of the designers.
S.