Forte Mod 1 / 1A

[WolfgangL]

Hello
is there a big difference between Forte Modell1 and Model1A ?
Or they are similar ? A schematic would be very helpful.
On web I couldn´t any detailed informations
thx
Wolfgang

[Nelson Pass]

The primary difference was a JFET input stage on the 1A,
replacing bipolar devices.

I don't seem to have a schematic, but the circuit was ordinary
enough - N channel JFET diff pair followed by a PNP common
emitter voltage gain stage, both of these constant current
sourced. Vbe multiplier for the bias, and complementary
emitter followers for output stage biased into Class A. Very
simple.

[WolfgangL]

Hello Mr. Pass
thanks for your fast answer. I will get a Modell1 next week, my first NP amp. Perhabs do you remeber which tranis used in output-stage and how much is voltage usually for rails, so i can look for electrolytic caps
thx

[jacco vermeulen]

My first NP amplifer too.

Recently i read your question from a couple of months ago.
The Forte Model1A combined very well with Quad ESL's.
I have not heard it on Audiostatics, the 200's are a lot easier to drive than 63's though.
The Model1A i compared to the Audio Analyse A9, a 50 watt class A amp, and the JH50, an EL34 tube amplifier from Jean Hiraga.
All three i heard on the ESL's and the 1A sounded way better.
Mr Pass prooves he can toss out half of the components, if i had the brains to think of the circuit i could have built it myself.

The 1A was rated at 50 watts i think, Audio or Stereo measured it at over 60 continuous output.
The 1A was even the cheapest of the 3, call me Dutch

(3000 DM for the 1A, 3800 DM for the A9, the JH50 was 5000 DM in Holland )

[WolfgangL]

hello
my Forte1 come in an it runs nice. On headsinks I read low temperature about 40 degrees Celcius. Across the emitter resistors ( 3,6 Ohm ??) my meter shows 460mV. Works this amp in right condition? What is right value for bias ?
thanks
Wolfgang

[Nelson Pass]

Originally posted by WolfgangL
hello
my Forte1 come in an it runs nice. On headsinks I read low temperature about 40 degrees Celcius. Across the emitter resistors ( 3,6 Ohm ??) my meter shows 460mV. Works this amp in right condition? What is right value for bias ?
thanks
Wolfgang

I think you can safely crank it up to about 45 deg C. Do it
carefully, and monitor the current for an hour or so.

[Daveis]

Has anyone turned up a schematic for the Model 1 or 1A?

Used Model 1's are coming onto the market and I want to be prepared.

It seems there's an upgrade article for the 1A in

audioXpress May 2003
* "A MOSFET Update of the Forte 1A Amplifier, Pt 1"

which I probably have somewhere. But I'm thinking of purchasing a Model One since the price is right.

[WALTER BURKHARD]

WolfgangL if you need you can contact me

walter

[WALTER BURKHARD]

i can made a copy for you from audioXpress May 2003

"A MOSFET Update of the Forte 1A Amplifier, Pt 1"

[Daveis]

If you were the new father of a Model 1, what would you do to it?

The Audio Amateur article (thanks Walter) is almost a complete replacement reusing the power supply and chassis. It's basically a new amp when you're done. (I do have some unpopulated A75 PCB's laying around, perhaps an A75-lite?)

Is there something less drastic you could do, other than replacing the now old electrolytics caps?

(Have soldering skills, not design skills, yet)

Still haven't found a service manual for this yet. The guy I may get getting this from doesn't have the manual or know where to get one.

Probably not interested in turning it into an Aleph. At 30-watts or so its too little power to be a main amp and too much to be a bi-amp tweeter amp.... although... could be an excuse to make the next speakers hi efficiency horns.