mcintosh mc275 heavy mods!! - diyAudio
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Old 26th December 2001, 05:58 PM   #1
richt is offline richt  Puerto Rico
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Join Date: Nov 2001
Location: puerto rico
Question mcintosh mc275 heavy mods!!

hi folks

i heavily modified my mc 275 with the time.
but the last week i had the bright idea to eliminate the neg feedbk.& eliminating a tube!

the inprovment was so huge & everything sounds so real,
instruments sound as the way should be.

if the neg. feedback honors his name (negative)why the companies usually designs with f*&^%$#@ circuit
destroying music & life.

thanks
richt
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Old 26th December 2001, 09:21 PM   #2
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Join Date: Sep 2001
Location: Fairbanks, Alaska
richt,

I was wondering how you accomplished this miracle of eliminating the feedback from a MC275. If my memory serves me correctly the MC275 has quite a number of negative feedback loops around the pre-drivers and especially the output stage though the cathode winding. In addition there are feedback loops to the screen grids of the output stage and front end.

Eliminating all these feedback loops would really be equal building a new amplifier in a MC275 chassis. Considering the value of a stock MC275 is this a wise thing to do?

I have been looking to buy a MC275 to restore to new condition using modern parts, but I don't believe that I would ever modify the actual circuit in any way. The MC275 is a fine sounding amplifier when all its parts are in good condition.

Negative of course simply refers to reducing gain though the application of a feedback signal that is at 180 degrees out of phase. The actual phase of the feedback signal can and most likely will vary somewhat with frequency due to time delays in the circuit the feedback is applied to.

John Fassotte
Alaskan Audio
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Old 26th December 2001, 09:53 PM   #3
richt is offline richt  Puerto Rico
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Join Date: Nov 2001
Location: puerto rico
hi alaska

everything in my amps are made with heavy duty toogle switches.
and you can setup as a factory any time.

i love eternally these amps but but!!!(i have 3 of them), 2 for b&w
nautilus 802 & 3rd one for subwoofer mono mode.

1 i notice, from stock, they sounds good (excellent) but i found
that the hi frequencies are not naturals as should be!!! &
the lows are not controlled in proportion with music.

switched to triode everything comes more opnness & the bass
is more natural & the transients are more controlled. his are lot more transparent & open.

2 i bypassed the 2 12az7 because it tends to distorts a lot faster
with these tubes. ok sounds crazy but these 2 tubes works
in series with the audio path & these 2 fu@#$% tubes works only when amp is used at 70 volts/600 ohms mode (you can see on schematics) easy to put back again but is worthless.
amp gain openness & hi transients responds solid without
decomposing like all tube amps does.

3 i have another switch that drives tubes class a/b or class a
(very usefull for low passages) you need good air conditioner for your room having 3 of them in class a mode!!!!!


4 the last thing that i never thought to do was eliminating the neg feedback tha honor his name!( a 3rd tube completly removed)

the amp got a super natural sounding that is so hard to belive
that i am listening every cd & lp over & over again.
i consider that mcintosh is the best amp of thr planet period.
instruments sounds real,airy,, you can drive the amp to maximum
drive!!! & have the same sound as on very low levels>
i never had that experience with other amps tha sound varies
depending on the volume level.

mcintosh is for ever!

thanks
merry critmas
richt
p.s. i am willing to buy a fouth one for surround>
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Old 26th December 2001, 11:08 PM   #4
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Join Date: Sep 2001
Location: Fairbanks, Alaska
Default McIntosh History - Interesting Reading

Here is a link to some very interesting McItosh History and information on the products they developed over the years. This is likely to be the best site to visit if you are interested in the McIntosh equipment.

A link to the history of the of equipment and people behind the company:

http://www.sundial.net/~rogerr/mcintosh1.htm

The main entry page for this site is listed below. Pictures of McIntosh equipment and specifications are available here:

http://www.sundial.net/~rogerr/aboutmc.htm


McIntosh equipment was "the" equipment to own back in the days when tubes were in their prime in the mid 1960's. McIntosh tube power amplifiers and the circuit designs they used are still highly valued all over the world.

John Fassotte
Alaskan Audio
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