[Bigload]

I have an AVAStar hybrid preamp.  I am wondering what the key differences are between that and the newer Fet Valve hybrid preamp.... other than silver faceplate.  Thanks.

[avahifi]

The Avastar and Fet Valve preamplifiers use different hybrid technology, based upon what was the best choice of active devices we could come up with at the time they were designed.

The AvaStar uses a dual triode voltage amplifier followed by a very fast and very low distortion solid state current amplifier (5 pin surface mount device) inside the overall feedback loop.  This provides a very low output impedance and the tube operates in a very linear mode, not even needing to drive its own feedback loop.  This works very very well.

The Fet Valve preamplifier uses a similar dual triode voltage amplifier, but followed by a high current, high voltage power mos-fet transistor inside the feedback loop with similar low output impedance and high drive current capability.

Although the solid state current amplifier used in the Avastar is a marvelous device, it internally contains many semiconductor junctions as compared to a single mos-fet device used in the new Fet Valve preamp.  Although we cannot measure it, we suspect that the improved musicality of the Fet Valve preamp may be due to the much less complex nature of the mos-fet it uses.

Note that the Fet Valve preamp has a bit of a back to the future design aspect.  We used a very similar topography with some earlier Ultra hybrid preamps, but before devices were available to make them perform as well as our current design does.  A drastically better mos-fet device, additional high voltage regulated power supplies (three per audio channel - - two for each tube, plus another for the mos-fet), a better layout and other useful circuit improvements make the Fet Valve preamp the best we have done.

Note that the a very similar circuit is used in the Fet Valve 400R and 600R power amps, these amps could be considered to be Fet Valve preamps on steroids.

Frank Van Alstine

[Bigload]

Thanks Frank.  I appreciate the explanation.

[modular747]

The Fet Valve preamplifier uses a similar dual triode voltage amplifier, but followed by a high current, high voltage power mos-fet transistor inside the feedback loop with similar low output impedance and high drive current capability.

Note that the Fet Valve preamp has a bit of a back to the future design aspect.  We used a very similar topography with some earlier Ultra hybrid preamps, but before devices were available to make them perform as well as our current design does.

Frank Van Alstine

Frank, when the "new" Fet Valve hybrid preamp was announced last year, it was said to use John Broskie's "Aikido" triode topology which featured zero global feedback.  What happened to that design?

[avahifi]

Actually we were working on two new high end preamp designs in parallel at that time.  We felt the no feedback Broskie based design was superior and started production with that circuit set  However we did not quit development on the alternate design and after a few months we realized that the overall performance of the somewhat more conventional but highly refined feedback based design had more potential.

Thus I put in the time and expense to design another all new mother board allowing even more design refinement and this design has proven to be superior, so it is in production now, replacing the no feedback board.

Not many of the original design units were shipped.  One way to tell is that the original used 6CG7 tubes, the new version of the Fet Valve preamp uses 12AT7 tubes.

If you own the original silver faced Fet Valve preamp and want to change to the new version circuit board, that is possible at a reasonable cost.  Please contact me about this if you wish.  Note that the sound quality is very close and some might even like the original better.  We would ask that you wait until we catch up with the sale backlog before considering this.

Best regards,

Frank Van Alstine

[Tom Alverson]

Actually we were working on two new high end preamp designs in parallel at that time.  We felt the no feedback Broskie based design was superior and started production with that circuit set  However we did not quit development on the alternate design and after a few months we realized that the overall performance of the somewhat more conventional but highly refined feedback based design had more potential.

Thus I put in the time and expense to design another all new mother board allowing even more design refinement and this design has proven to be superior, so it is in production now, replacing the no feedback board.

Not many of the original design units were shipped.  One way to tell is that the original used 6CG7 tubes, the new version of the Fet Valve preamp uses 12AT7 tubes.

If you own the original silver faced Fet Valve preamp and want to change to the new version circuit board, that is possible at a reasonable cost.  Please contact me about this if you wish.  Note that the sound quality is very close and some might even like the original better.  We would ask that you wait until we catch up with the sale backlog before considering this.

Best regards,

Frank Van Alstine

Which circuit is used in the Fet Valve DAC now?

Tom