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Old 11th November 2006, 02:40 PM   #11
K-amps is offline K-amps  United States
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Yes they are to220 drivers... probably 25 watters at most, not even directly connected to the heatsink. The search will begin...
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Old 11th November 2006, 05:07 PM   #12
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Default need schema...

Hi,

The chances of everything working perfectly with half the supply voltage and no other adjustments is not nil, but unlikely...

Once you have the schematics you should be able to tell which parts if any will need adjustment to keep currents the same etc,

I have never seen or heard a Forte, so I have no clue as to the degree of voltage independence that will be part of it's design, but if it is an NP design he would be a good person to ask...he is very generous with his time and replies to emails if you don't manage to attract his attention with this thread...

If you go for the lowering of the voltage, halving it may be too far, going for 2/3 voltage will probably get you closer to what you need, but not quite as simple to arrange, since the primary and secondaries are unlikely to allow it trivially. I've only done thumbnail calcs, but as far as I can see to go from 4ohm to 2 ohm 'competence' you want to drive 40% more current with 40% less voltage...giving you the same peak power into half the load...

HTH

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Old 11th November 2006, 05:55 PM   #13
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Thanks!

Good info on the 40%, I was also going to go with 60% rails. I do not have the schema yet, but I'd guess it is similar to the Adcom 555ii. they were produced around the same time give or take and both were Nelson designs. Ofcourse this is aguess.

No DC servos and newer parts than the GFA-555ii, i.e. 1302/3281 instead of 2sd424/B554.
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Old 12th November 2006, 09:59 AM   #14
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K,

Just ran across this oldy on hFe, thought you might like to see just how good the hFe of the 1302/3281 is :

http://www.diyaudio.com/forums/showt...3938#post13938

The hFe comparison table is not out of the guy's imagination, but X'd from an oldy.

Asking the big guy himself by reposting in the Pass section is the best suggestion so far. He's given some assistance for questions on Forté amps before.
Having the output stage on half the rail voltage and rails for the front end with high enough voltage to get it going is another option, but a risky one.
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Old 12th November 2006, 10:14 AM   #15
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Sweet!

Almost like a horizon.


By the way (again I am guessing): but the Model 3 was designed to be interchangeable with Model 1? The 50 watt class-A version which was pretty much identical in every way (parts wise) to the 3.

Difference was, on the 3, Neslon had the trafo prims wired in paralell for higher rails and in the Model 1 had it wired in series for lower rails.

Also the main caps were 45v version not 90v wired in series for the model 3. Had he optimized the amp for 200w AB, He would not have used two 45v Caps in series but 90v versions.

That tells me the circuit had the same BOM, optimized for 38v rails (that could run on higher Vce's).

Additionally the buss bars that hold the caps have holes such that installed at a 90 degree, they can connect the caps in parallel vs. series for higher volts... too many clues
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Old 12th November 2006, 10:17 AM   #16
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Which brings me to trafos...

I have a 1kva Plitron 33-0-33vac and also have a couple of 1kVA (single tap) 43-0 's that together form a 2kVA 43-0-43.

I can use either one (leaning on the the dual 43-0's) but issue is, I have just one of each combo...


Anyone wanna trade???
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Old 12th November 2006, 11:35 AM   #17
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Quote:
Originally posted by K-amps
the Model 3 was designed to be interchangeable with Model 1?
The Model 1-A is my guess.

The M-1 i had did 40 in A, managed slightly over 45/8 in class AB.
It was succeeded by the 1-A, with 60/8.
Boils down to the same thing though.
Only seen pics of the insides of the model 3, looked identical to the class A numbers.
I've always been impressed by Nelson Pass's cost-cutting skills.
The Forté brand was a budget entry line, the way they were set-up for swift manufacturing makes the universal approach obvious imo.
That approach looks recognisable in the First Watt amps, especially with the FW revamped Aleph-J amplifier.
I'm never quite sure what to find the most interesting, P's designing skills or his lean and mean business talents.
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Old 12th November 2006, 11:49 AM   #18
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In those days his name sold easy. He figured it was time for non-Billionnaires to enjoy his work too :-)
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Old 12th November 2006, 12:53 PM   #19
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All things relative.
MSRP of the Model 1 was $950 in the US, here i had to pay $2K.
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Old 12th November 2006, 01:58 PM   #20
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You fed a lot of hungry mouths.... be happy with that thought.

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