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Kilowatt 9th December 2001 03:28 AM

What if a tube driver stage was used to drive a solid state output stage? Would it have the nice sound of a tube amp with the other benefits of solid state amps?

rfbrw 9th December 2001 04:14 AM

Its been done with varying degrees of success. You could start with a web search on the Conrad Johnson Evolution 2000 and the Counterpoint Natural Progression Series.

timc 9th December 2001 12:10 PM

There are a couple of articles on Hybrid Amps at TubeCad,

Also some other projects on the web,

It is something that I would like to try. I am working on a
Hybrid design of my own.


avxt 9th January 2002 06:27 AM


I'm a newbie and interested on building the hybrid 5687 with magnatec amp but can't find the magnatec.

Any replacement for magnatec BUZ900P and BUZ905P?
If there is replacement need any changes on the circuit?


timc 9th January 2002 09:22 AM

The Magnatec web site is
and they seem to sell online.

As far as replacements, the BUZ900P/BUZ905P sould be prity mutch straight interchangable with most of the power mosfets commonly used in audio, you shouldn't need to change the circuit at all.

Some devices you could use are,
Hitachi 2SK1058/2SJ162
Exicon EC10N16/20
International Rectifier I am not very familiar with, but something like IRFP240/IRFP9240 looks about right.


avxt 9th January 2002 09:54 AM


Just curious, which mosfet sound better if there is a different ?

timc 9th January 2002 10:03 AM

It is a question that gets asked quite offten, maybe try searching this forum, particularly the Pass Labs section.

I have only ever used the Hitachi devices.

I think that the Hitachi, Exicon and Magnatec are all very similar devices though.


filippo22 10th January 2002 06:23 PM

get a look at my Hybrid One


PS the problem on my schematics download area is now fixed

avxt 15th January 2002 10:23 AM

May I know how to adjust the bias for the hybrid amp 5687 and magnatec mosfet at

website ? ( the first project )

timc 15th January 2002 11:15 AM

The BIAS for the output section is set by trimpot P1. The DC offset is set by P2 and P3.

I would read the schematic as showing a 100mA BIAS current, so you sould adjust P1 to get a 0.022V (22mV) drop across R5 or R6.


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