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Old 14th December 2005, 07:23 AM   #1
blink is offline blink  Germany
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Default Fairchild amp application

Hi, all

That circuit attached I found in a "old" Fairchild applications book.

(Application Note 336 - July 1977: 75 W Hi Hi Audio Amplifier with low transient intermodulation
distortion)

A PDF of the whole article ist available if you're interested (includes component and board layout - 392 KB).

As a bloody amateur I would be very interested in comments, and in your suggestions for replacments for the FT transistor types, as well.

Peter
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Old 14th December 2005, 09:11 AM   #2
djk is offline djk
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I've seen that Fairchild application note before, it's essentially a Leach, GAS Son-of-Ampzilla, etc. Accuphase and Luxman also made something similar.

They sound quite good. I would strongly consider the Leach as the parts are still available, a tried and tested design.
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Old 14th December 2005, 08:18 PM   #3
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Double differential input stage (pnp, npn), an ordinary AB power stage...
With all these components is possible to make almost (except output transistors) two channels and they are sounds better than this one :-)
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Old 14th December 2005, 08:40 PM   #4
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Quote:
Originally posted by widowmaker
Double differential input stage (pnp, npn), an ordinary AB power stage...
With all these components is possible to make almost (except output transistors) two channels and they are sounds better than this one :-)

Any schematic please? No FET inputs? What do I know?
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Old 14th December 2005, 10:22 PM   #5
Ejam is offline Ejam  Australia
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Default Fairchild Amplifier

For what its worth

The Fairchild application was the basis of several amplifiers mentioned above but probably the most interesting was the Audionics CC02 ampfilier. Robert Sickler, an Audionics technician modified the Fairchild resulting in a very good amplifier that played music. One of my favourites and still holding its own in today's Class AB company. A detailed story and circuit diagram of the CC02 can be found on Lynn Olsen's website: http://www.nutshellhifi.com/

If you can post the pdf of the Fairchild application note it would be much appreciated.

Regards Ejam
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Old 14th December 2005, 10:32 PM   #6
lineup is offline lineup  Sweden
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I found this article and schematics of the Audionics CC02 ampfilier
at the above website.
Wasnt so easy to find
so
A Tribute to Bob Sickler
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Old 14th December 2005, 11:24 PM   #7
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Default Re: Fairchild Amplifier

Quote:
Originally posted by Ejam
Audionics CC02 ampfilier. Robert Sickler, an Audionics technician modified the Fairchild resulting in a very good amplifier that played music. One of my favourites and still holding its own in today's Class AB company.
CC2 is a pretty good amp for the late '70s, though I prefer the GAS Grandson (I own both). Still has a following especially in bridged mono mode, they show up on eBay from time to time for about US$150. A real PITA to work on though due to the packaging, lack of PCB silkscreen, and the output stage bias thermal tracking is kinda loose. Try reconfiguring for inverting input, clarity is much improved but DC coupling for this one may not be your cuppa. There was more than one power transformer used, the one I has two isolated secondary windings so can be wired with two bridge rectifiers.
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Old 15th December 2005, 01:35 AM   #8
djk is offline djk
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The solder joints on the output transistors of the CC-2 fail frequently.

The mechanical design was poor. The leads are lap-soldered to the board edge, any mechanical stress on the chassis, or heat, and the connections fail.

The GAS Son and Grandson are made much better.
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Old 15th December 2005, 01:51 AM   #9
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Hi blink,

You're posted schema is a rather acadaemic design based on a non-event (TIM). It has poor PSRR due to the poor decoupling of tail currents and higher distortion than it could have ( the unnecessary 22K's as Vas collector load) and it is suseptable to hum pickup due to the high impedance of the input filter.

Rather than build something old, based on a false premise, why not build something new and fast using today's technology. Simple and efficient and patent pending.

http://members.dodo.com.au/~gregball/guru_004.htm

Cheers,
Greg
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Old 15th December 2005, 04:46 AM   #10
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Quote:
Originally posted by amplifierguru
Hi blink,
You're posted schema is a rather acadaemic design based on a non-event (TIM). It has poor PSRR due to the poor decoupling of tail currents and higher distortion than it could have ( the unnecessary 22K's as Vas collector load) and it is suseptable to hum pickup due to the high impedance of the input filter.
translated means....

A couple of minor mods and you'll have a half decent amp.

regards
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