Re: OT: previous post about true inexpensive tube preamps

[andy butler <akbutler@tiscali.co.uk>]

> always was  abit on the noisy side for me.  From what I read the 
> presonus has a circuit which feeds the tube (12ax7) a full voltage 
> current and not the "starved plate" variety found in many budget range 
> tube gear.

afaik the difference between a budget tube pre, and a "genuine" tube pre 
is this.

The budget model uses a regular pre-amp circuit , then passes the signal 
through a tube stage,
usually a 12ax7 ( in UK speak thats an ECC 83 ).
The "genuine article" uses a valve (perhaps a specially designed pentode) 
to do
the pre-amplification.  

I don't know how much running at low voltage (starved plate?) affects the 
sound of 
a valve stage, it probably reduces the signal to noise value, but that 
wouldn't
be significant if the valve isn't used to do a lot of amplification. (which
in the cheap units, it isn't, it's just there to color the sound).
( and the valve will last for ever at low voltage )

Genuine valve pres are tend to be a bit on the noisy side compared to an 
equivalent transistor unit.

Conclusion
A "real valve pre-amp" isn't likely to be cheap, and any sonic advantage 
sends to come a the expense of a bit of extra noise.
In a budget design it's the quality of the transistor parts which is 
likely to be significant.



andy butler