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Old 29th May 2008, 10:02 PM   #11
st2_998 is offline st2_998  Italy
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Well, I don't really think of something possibily blowing up.
I don't have a variac but I can disconnect the channel fuses isolating the PS and checking voltages before reconnecting the audio circuitry.
Thanks.
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Old 28th January 2009, 08:12 PM   #12
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Default 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
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Old 29th January 2009, 02:59 AM   #13
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IIRC, you can tap the transformer at 240V and just crank up the bias.

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Old 29th January 2009, 03:08 AM   #14
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Here's a schematic.
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File Type: jpg forte1.jpg (89.9 KB, 1188 views)
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Old 29th January 2009, 02:24 PM   #15
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Default 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
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Old 30th January 2009, 08:36 PM   #16
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Quote:
Originally posted by Nelson Pass
schematic
Cool location of the thermal breaker.
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Old 30th January 2009, 09:34 PM   #17
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Default Re: Forte Model 3 cap upgrade/conversion

Quote:
Originally posted by ForteMan
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.

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Old 31st January 2009, 10:18 AM   #18
st2_998 is offline st2_998  Italy
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No advice for recapping then? (see also old posts at top of thread)
Thanks for sharing your knowledge, Mr. Pass.
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Old 1st February 2009, 12:34 AM   #19
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I advise you to re-cap at your convenience.

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Old 2nd June 2011, 09:11 PM   #20
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Default 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

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