Author Topic: Upgrade Mosfets  (Read 955 times)

Offline S Clark

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Upgrade Mosfets
« on: October 23, 2020, 07:34:24 PM »
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?
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Offline HAL

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Re: Upgrade Mosfets
« Reply #1 on: October 23, 2020, 09:12:24 PM »
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.

Offline S Clark

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Re: Upgrade Mosfets
« Reply #2 on: October 24, 2020, 05:04:25 PM »
... 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???
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Offline HAL

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Re: Upgrade Mosfets
« Reply #3 on: October 24, 2020, 08:47:31 PM »
Probably more bass control or lower extension with more current drive.  With no driver stage change, might roll off the top end.

Offline tmazz

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Re: Upgrade Mosfets
« Reply #4 on: October 25, 2020, 10:23:17 AM »
Does the double Mosfet mod change the output power?
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Offline rollo

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Re: Upgrade Mosfets
« Reply #5 on: October 26, 2020, 08:42:48 AM »
... 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.

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Offline HAL

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Re: Upgrade Mosfets
« Reply #6 on: October 26, 2020, 10:28:52 AM »
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.

Offline S Clark

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Re: Upgrade Mosfets
« Reply #7 on: October 26, 2020, 06:18:40 PM »
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. 
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Offline S Clark

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Re: Upgrade Mosfets
« Reply #8 on: October 26, 2020, 06:29:50 PM »


   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.
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Offline tmazz

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Re: Upgrade Mosfets
« Reply #9 on: October 27, 2020, 06:58:48 PM »
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.
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Offline S Clark

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Re: Upgrade Mosfets
« Reply #10 on: October 31, 2020, 07:02:14 AM »
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.
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Offline S Clark

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Re: Upgrade Mosfets
« Reply #11 on: May 05, 2021, 05:22:29 PM »
I sent my old Moscode 300 to George Kaye last October... and just got it back today with a list of mods as long as your arm.  And I gotta say, as of the first hour or so, it sounds pretty darn good.  Which is a miracle.
UPS made it a personal challenge to try to break it into a thousand pieces.  The box was wet, one corner torn badly 5-6 inches, crushed in the center, another corner crushed 3-4" -- even the UPS driver was embarrasses and walked me though how to best word a claim. 
But I had expected it to be handled by lower primates, so it was double boxed with a 2" layer of styrofoam between boxes.  The inner box had a plywood bottom, and inch of styrofoam surrounding everything.  The inner amp was wrapped in 3" of bubble wrap.....

And so it's playing magnificently in my small system.  I'll let it go a bit, then move it into my big system. Honestly I haven't heard it in years, but it sure seems clearer and more detailed than I remember.  Bass control is also noticeably excellent.
Wasn't cheap, but so far so good.  :thumb:
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Offline P.I.

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Re: Upgrade Mosfets
« Reply #12 on: May 05, 2021, 06:57:52 PM »
I sent my old Moscode 300 to George Kaye last October... and just got it back today with a list of mods as long as your arm.  And I gotta say, as of the first hour or so, it sounds pretty darn good.  Which is a miracle.
UPS made it a personal challenge to try to break it into a thousand pieces.  The box was wet, one corner torn badly 5-6 inches, crushed in the center, another corner crushed 3-4" -- even the UPS driver was embarrasses and walked me though how to best word a claim. 
But I had expected it to be handled by lower primates, so it was double boxed with a 2" layer of styrofoam between boxes.  The inner box had a plywood bottom, and inch of styrofoam surrounding everything.  The inner amp was wrapped in 3" of bubble wrap.....

And so it's playing magnificently in my small system.  I'll let it go a bit, then move it into my big system. Honestly I haven't heard it in years, but it sure seems clearer and more detailed than I remember.  Bass control is also noticeably excellent.
Wasn't cheap, but so far so good.  :thumb:
:thumb:

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Offline Nick B

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Re: Upgrade Mosfets
« Reply #13 on: May 05, 2021, 07:30:10 PM »
I sent my old Moscode 300 to George Kaye last October... and just got it back today with a list of mods as long as your arm.  And I gotta say, as of the first hour or so, it sounds pretty darn good.  Which is a miracle.
UPS made it a personal challenge to try to break it into a thousand pieces.  The box was wet, one corner torn badly 5-6 inches, crushed in the center, another corner crushed 3-4" -- even the UPS driver was embarrasses and walked me though how to best word a claim. 
But I had expected it to be handled by lower primates, so it was double boxed with a 2" layer of styrofoam between boxes.  The inner box had a plywood bottom, and inch of styrofoam surrounding everything.  The inner amp was wrapped in 3" of bubble wrap.....

And so it's playing magnificently in my small system.  I'll let it go a bit, then move it into my big system. Honestly I haven't heard it in years, but it sure seems clearer and more detailed than I remember.  Bass control is also noticeably excellent.
Wasn't cheap, but so far so good.  :thumb:

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Offline S Clark

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Re: Upgrade Mosfets
« Reply #14 on: May 05, 2021, 08:00:15 PM »
:thumb:

I've always heard good things about GK!
I have to say that so far I'm impressed with the sound. Just don't expect George to get in any hurry to work on stuff.  I suspect that he works for a day, then takes off two.  I know he took 3 weeks on the amp before mine. 
But the time and money will be well worth it, I suspect. 
“In the end, we will remember not the words of our enemies but the silence of our friends.” Dr. Martin Luther King, Jr.