Forté Audio Model 3: caps and schematics?

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I'm very satistfied of my new old :D amp!

Due to its age, I was considering a power supply recapping, I'm pretty sure someone worked on it and can give me some valuable advice :)

And... where can I find the schematics? I took a glance to Model 1's one but the PS appears to be wired in a different way.

Thanks everybody for dropping opinions and help.
 
I was thinking about swapping the two caps in series for each supply branch with one only (47.000 uF 100Vdc instead of 2x 24000 uF 65 Vdc, total Vdc present is 76 Vdc), leaving the secondaries' center taps unconnected (insulated). Possibily 10 uF poly bypass on each.
Is all that a bad idea?
Thanks.
 
I believe this is surely true for the 1A, as far as I can understand from the schematics. Unfortunately I don't have the schematics for the 3A power supply, but in the amp it seems that ground (a star center) is tied to one each of the secondaries' outputs (one +, one -), center taps end inbetween the two series supply caps and nothing is connected to them except power LED.
 
was thinking about swapping the two caps in series for each supply branch with one only (47.000 uF 100Vdc instead of 2x 24000 uF 65 Vdc, total Vdc present is 76 Vdc), leaving the secondaries' center taps unconnected (insulated). Possibily 10 uF poly bypass on each.

I recently opened up a Forte for a friend of mine. I believe it was a 3a. (did they make it up to 7a?)

If you can post a picture of the inside, I could provide some better comments (if its the same ps).


JJ
 
Here are the pics
An externally hosted image should be here but it was not working when we last tested it.

An externally hosted image should be here but it was not working when we last tested it.


Blue connected to ground (busbar)
Red connected to rectifier bridge and supply fuses to the channel boards
Orange should be center tap
It appears that using one cap instead of two could be possibile, center tap has to be disconnected but that shouldn't cause problems.
Is that right?
Thanks
 
Clearly that is different than the amp I worked on.

I wouldn't hazard to try to advise you on something I haven't done. If you don't mind the possibility of letting all the magic smoke out of your amp, then forge ahead with the PS re-do.

Otherwise, replacement in kind is always a safe way to go.

Good luck!

JJ
 
Forte Model 3 cap upgrade/conversion

Hi all. I am the proud owner of one of Mr. Pass' fantastic designs, (albeit one of his lesser works). The Model 3 is a (Threshold) 200 wpc (8 ohms) Class A/B design with a fairly high Class A bias, and the case and internals are virtually identical to the Model 1A, a 50 wpc Pure Class A amp. My amp is a low-hours unit, and sounds fantastic. Because it is an older model though, I am considering upgrading the caps. I am also considering converting the amp to the Pure Class A 50 wpc configuration. I understand this is a fairly easy process, as the internals are the same. Any suggestions on capacitor upgrades or the Class A conversion? Mr. Pass?? Thanks. -David
 
The one and only
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Here's a schematic.
 

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Forte Model 3 cap upgrade/conversion

Thank you Mr. Pass! One other question: The stock power cord is a smallish two-prong unit. This may seem like a "no-brainer", but do you recommend upgrading to an audiophile-grade cord with ground? If so, would you think it better to add an IEC male socket to the rear panel (to enable "cord experimentation", or pass a fixed cord through the rear panel & enlarge the port & grommet? Thanks again! -David
 
The one and only
Joined 2001
Paid Member
Re: Forte Model 3 cap upgrade/conversion

ForteMan said:
The stock power cord is a smallish two-prong unit. This may seem like a "no-brainer", but do you recommend upgrading to an audiophile-grade cord with ground? If so, would you think it better to add an IEC male socket to the rear panel (to enable "cord experimentation", or pass a fixed cord through the rear panel & enlarge the port & grommet? Thanks again! -David

The IEC socket would be preferred. You will have to deal with the
grounding if you use a cord with AC earth - the chassis must be
hard wired to the AC earth connection. A connection from the analog
ground to the chassis can then be made directly, or through a big
diode bridge and/or power thermistor which can provide some low
level isolation against ground loops but conduction against a primary
to secondary type fault.

:cool:
 
Capacitors in Model 3

Hi,

one question:

the two capacitors for each voltage in the Model 3 are wired in serial. As I learned some time ago ;) the total capacity then is half the capacity of one capacitor (24 mF turns into 12 mF).

Isn't that a drawback? Why are they not paralleled?

Cheers

:confused:
 
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