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avguytx

Bought an MC250. Almost done at Tech's

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5 hours ago, avguytx said:

 

Did you send them out to be done or did you do it yourself?

I sent them out.  A highly trusted tech north of me.

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5 hours ago, svberger said:

 

I'm currently using one, restored by Audio Classics, driven by a Mac MX110 pre, with my Cornwall II's. Would love to try a second one. What improvements, differences did you find when using them as mono blocks?

Well, obviously, having the headroom available to drive to higher levels is a definite advantage.  I  found that my Chorus II's responded with much greater "authority" when driven by an amp on each channel.

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18 hours ago, jimjimbo said:

Well, obviously, having the headroom available to drive to higher levels is a definite advantage.  I  found that my Chorus II's responded with much greater "authority" when driven by an amp on each channel.

You must be pulling those speakers out into the driveway to entertain the neighborhood, lol.;)

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On 9/28/2017 at 1:57 PM, jwc said:

I would contact and send here without hesitation....

 

http://www.northreadingeng.com/

They do nice work, but I have different ideals with regards to their upgrades. I can't help but wonder why, with so much gear out there to choose from, would one completely change an original Mc solid state Amp? These were built to sound a certain way. Changing that is risky in that you would like what you heard when you get it back IMO. I haven't heard of anybody not liking the sound of their vintage Mc Amp.

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13 minutes ago, paul79 said:

They do nice work, but I have different ideals with regards to their upgrades. I can't help but wonder why, with so much gear out there to choose from, would one completely change an original Mc solid state Amp? These were built to sound a certain way. Changing that is risky in that you would like what you heard when you get it back IMO. I haven't heard of anybody not liking the sound of their vintage Mc Amp.

Paul, as you know, changing the sound signature or simply restoring the unit to replace old caps/resistors/etc. are two entirely different things.  I would never want to, nor recommend a wholesale "change" of a Mc amp, solely on the basis of a change.

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Got a bunch of parts ordered from Mouser...resistors, caps, and transistors. Supposed to be in tomorrow. Sweet. 

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Well, I had hoped the parts would make it in Friday...but Fedex tried to deliver them on Saturday to my office address and, of course, no one was here.  I'd come by not 10 minutes before they stopped by on my way to get front end alignment on my truck and they came right after I left.  Would have thought they would be here today but says tomorrow.  Oh well.  I spent some time on the speaker project. 

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Parts arrived from Mouser today. Need to order the 2 multicaps from Hayseed and see what I can do on the 9300mfd cap replacement.  

20171010_104126-1024x832.jpg

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Two new replacement multi-caps ordered from one place and two new main filter caps ordered from Mouser today.  Looking forward to starting on this amp and may try to work on some things at night after homework, dinner, etc., are done.  Weekends are currently tied up getting Belle clones closer to being done.  ha

 

I think after I get this amp done, I am covered for about as much as I need to have around for awhile.  "IF" I do decided to get another amp later, be it building or buying, it will be a SE amplifier of some sort.  But that's later.

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New main filter caps and multi-caps are mounted and soldered in. Other caps on boards have been replaced along with all PNP and NON transistors replaced on input and output boards. 

20171103_221331_crop_709x1171.jpg

20171103_221345-1280x720.jpg

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8 hours ago, avguytx said:

And absolutely love my new Hakko soldering iron that came in yesterday. Highly recommended. 

I have one as well.  It's a great iron.  

 

 

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3 hours ago, John Warren said:

Would suggest bleeders on the 22000uF cans, 1kOhm, 2W.

 

 

Thanks John. 1kohm to each positive and other end to ground?

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On ‎10‎/‎3‎/‎2017 at 2:10 PM, paul79 said:

They do nice work

 

Thank you sir.

 

On ‎10‎/‎3‎/‎2017 at 2:10 PM, paul79 said:

but I have different ideals with regards to their upgrades. I can't help but wonder why, with so much gear out there to choose from, would one completely change an original Mc solid state Amp? These were built to sound a certain way. Changing that is risky in that you would like what you heard when you get it back IMO. I haven't heard of anybody not liking the sound of their vintage Mc Amp.

 

Couple of comments, not necessarily to refute what your saying but more to substantiate why revising the original is a worthwhile endeavor.  

 

The first gen amps are quasi-complimentary and, as such, have limitations regardless of how the front end or gain stages are modified.  That said, the input differential pair is a transconductance amplifier and the linearity of this stage (i.e. the transfer function that describes the relationship between small differential input voltage differences and the corresponding output current driving the base of the voltage amplifier stage) is absolutely critical for low distortion output.  If it's not linear here we're screwed.

 

The designs must be simulated before committing anything to hardware and with some experience simulations can predict with good accuracy.  The first graph is simulated transconductance of the McIntosh front end and the preamp I've designed to replace it.  The input is a 20kHz burst.  It's a huge difference and correlates directly with lower measured distortion at high frequencies, the key to reducing listener fatigue.   Common mode rejection is also much improved, the amps just quieter.

 

The measured results are with the board installed in an MC2100.

 

 

transconductance.jpg

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NRE_preamp_%THD.png

R2.1_3.jpg

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" Would suggest bleeders on the 22000uF cans, 1kOhm, 2W. "

 

Will run too hot.

 

Most resistor ratings are based on a 250°C rise above ambient.

 

With  ±35V rails a 1K resistor will be dissipating about 1.225W, a 2W part will thus be about 150°C above ambient (with a 25°C ambient the part will be running neat the melting point of 63/37).

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On 9/22/2017 at 8:12 AM, avguytx said:

It seems that most all of the iterations of the MC250 are similar in price and even around the range of the MC2100.  I still kick myself for not buying an MC2100 about 9 years back for $150 that was at a pawn shop in Denton, TX where I lived.  Oh well.  It's not that often that Mac gear comes up around here and it kind of scares me that the guy on CL has had these listed for months now and they're still there.    Makes me wonder if others have gone to look at it and then said....uh, pass.  

 

I do like those pretty blue meters, though.  ha

 

The local flippers have totally thrashed our local market for McIntosh and Klipsch. They keep all the prices high and scavenge everything in site. 

 

 

 

 

 

 

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2 hours ago, djk said:

With  ±35V rails a 1K resistor will be dissipating about 1.225W, a 2W part will thus be about 150°C above ambient (with a 25°C ambient the part will be running neat the melting point of 63/37).

 

I had MC2100 in mind here, 2W rating.  Going to higher power is fine.

 

image.png.a1c1845c09e83dfa7c9ecc556bcd44bf.png

 

 

 

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