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Old 22nd November 2006, 06:24 AM   #1
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Smile Adcom GFA-565

General question. Did Nelson Pass design the Adcom GFA-565 power amp? Or is that power amp design prior to him getting on board with Adcom?
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Old 22nd November 2006, 08:02 AM   #2
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I believe the design was from Walt Jung (Linear Technology), but I'm not 100% sure.
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Old 22nd November 2006, 10:57 AM   #3
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Nelson designed the 555, not even the 555ii or later models.

the 565/585's were as djk says, a Jung and Victor Kampos collaboration.
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Old 22nd November 2006, 03:14 PM   #4
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Default Adcom GFA-565

Thank you for the info?

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Old 22nd November 2006, 04:40 PM   #5
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Default Adcom, GFA-5800 & GFA-5802

I have read in many different articles that he did design the both of these power amps, GFA-5800 & GFA-5802. Is this not correct? When people are selling these power amps they advertise this fact. Also I have an article from December 2001 audio/video revolution, comparing the 5802 to Krell and Mac stating it is a Nelson Pass Design. So his influance went further than the 555 & 585.

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Old 22nd November 2006, 05:53 PM   #6
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Default mosfets...

Much like his 555 design provided a starting point for the 5x5 amps. I think Nelson made an initial design for Adcom that seeded the mosfet generation of amps. Perhaps he'll comment on which, if any, of the current models are his work.

IIRC Based on marketing material I read from their introduction, the first mosfet amps Adcom made were for use in cars, though the car line didn't make a reappearance after the initial lineup.

Though Adcom are happy to publicise NPs initial involvement, they are much quieter about the point of divergence, when they've modified his designs to be unrecognisable. I wouldn't assume any of the current models are in any way representative of an NP design, unless you hear it from the man himself.


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Old 22nd November 2006, 09:20 PM   #7
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The 5800 was an NP design, not sure about the 5802. As Stuart says, NP gave them their starting points...
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Old 22nd November 2006, 10:03 PM   #8
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Question Adcom GFA-565

Back to the GFA-565. Is the output stage of this amp Mosfet?

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Old 22nd November 2006, 10:16 PM   #9
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Default nope

the 565 has a vast collection, well 10 pairs anyway, of toshiba bipolar output transistors. 2sb424/2sd554. I think these are discontinued now, but the spiritual successor is probably something like the mj15003/4 pairs from on-semi.

I had 2 pairs of these in the distant past, liked them a lot after they had been playing for half an hour or so, seemed like something in the mix had to be hot before everything was really jamming.

Through a couple of accidents with electrostats that have lousy transformers, a buddy cooked a couple of these, so if you fry your outputs (not sure how you'd do this), as opposed to the driver PCB, I'll be able to sell you a complete set for one or two amps, if you decide to rebuild...

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Old 23rd November 2006, 12:29 AM   #10
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Actually the successors to the 424/554 were the 1302/3281 both perforated emitter BJT's.

The 15003/4 and 15022/23/24/25 were powerbase MOT's, very tough cookies but not the same hfe as the Toshiba's.

Toshiba then sold the perforated emitter tech to ON who then made the 2119x's and all 1302 variants.
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