Upgrade Mosfets

[S Clark]

I finally got an old Moscode 300 amp back to George Kaye for repair.  He's come up with a way to double the number of mosfets for supposedly a magical and mystical improvement- at a price that isn't crazy.  Anyone here know what doubling the number of mosfets would effectively do?

[HAL]

Scott,
I believe that a company called Magnetec in the UK at one point was able to put two of the Hitachi style power MOSFET die in one case to effectively make two in one.  That would drop the device output impedance in half and allow greater output drive current capability. 

It would also double the input capacitance of the MOSFET device, so mods to the driver stage might be needed.

A friend uses them in his power amp design and he started with the Hitachi devices years ago like Hafler used in the DH200 amps.

[S Clark]

... That would drop the device output impedance in half and allow greater output drive current capability. 

It would also double the input capacitance of the MOSFET device, so mods to the driver stage might be needed...

... so, more headroom, more open and spacious???

[HAL]

Probably more bass control or lower extension with more current drive.  With no driver stage change, might roll off the top end.

[tmazz]

Does the double Mosfet mod change the output power?

[rollo]

... That would drop the device output impedance in half and allow greater output drive current capability. 

It would also double the input capacitance of the MOSFET device, so mods to the driver stage might be needed...

... so, more headroom, more open and spacious???

   Maybe. Are you able to hear one before mod ? Hard to say the outcome.

charles

[HAL]

Does the double Mosfet mod change the output power?

The double MOSFETs should give more output power to low impedance loads if the power supply can handle the extra current required.

[S Clark]

Well, when George gets back to me, hopefully before I leave this planet, I'll pass along what he says about it.  This old amp has been sitting too long, and needed to be junked or repaired, so inquiring about an upgrade was also a motivation to get him to respond to my repair request.  I also sent him a pair of 17 000 uF caps that can be strapped to the original power caps.  It will be interesting to see how he responds. 

[S Clark]

   Maybe. Are you able to hear one before mod ? Hard to say the outcome.

charles

Well honestly, I haven't heard it in 7-8 years as I replaced it with a Moscode 401HR that had some upgrades.  It's been driving my GR  LS9's ever since.

[tmazz]

I have to say, over the years my Moscode 600 made 3 trips to George for upgrades and I was always very happy with the results.

[S Clark]

George Kaye responded to questions about the double mosfet upgrade:   "Deeper soundstage, better bass control, increased damping factor, more power into low impedance (4 ohms or less) speakers." Seems like Rich pretty well nailed it in his response.  My LS9's are moderately efficient, but have high back EMF that requires some power to keep under control. It will be interesting to see if the old Moscode 300 can work as well or better than it's younger, more powerful cousin, the HR401.