#163282  by wayfaerer
 Fri Nov 09, 2018 11:57 am
Hi, first post here. I'm learning a little bit about power amps and was wondering what it is about McIntosh power amps that makes them important to Jerry's tone? Are they brighter than other power amps? Do they compress or distort more or less? Or are they just the best at recreating the desired tone at any volume without any coloration?

Another way to phrase it is if I was going to get a different (less expensive) power amp, what features/qualities would I be looking for to get in the ballpark?
 #163285  by wayfaerer
 Fri Nov 09, 2018 1:05 pm
Thanks! The thread title is similar, but I had a look at the thread and didn't find an answer to the question. There are a few comments about how great the McIntoshes sound, and some mentions of note clarity and dynamics, but the rest of the thread is about installing a preamp output in a combo.

I was hoping for a less subjective understanding... I'd guess from the comments about clarity and dynamics that maybe there's some compression happening, for example?
 #163449  by SarnoMusicSolutions
 Tue Nov 20, 2018 11:32 pm
They were engineered brilliantly, simply, ruggedly, robustly, militarily, fundamentally, reliably. McIntosh was an absolute champion of magnetics; the art of transformer winding, from the space age, a time where America's best and brightest engineers, extreme scholars of the academic arts of electrical engineering put theory to task and built things as good as they could. It's economically unfeasble to do that today, but back then it was the way of the high end of things. The result was a line of products that satisfied audiophiles and aircraft carriers and the Grateful Dead.

In practice, for players like us that seek tone and sound, the McIntosh transistor series of amps delivers a clean, neutral tone - faithful to the signal that feeds it, but as guitarists that naturally push our electronics to the brink, and beyond, into the realm of clipping and distortion, testing the limits - the McIntosh handles that quite differently than most solid state amplifiers. It handles it without failing, without harshness, but with a toughness and a warmth that somewhat resembles tube amp clipping but stiffer, more solid, and without ugliness. Since the output of these McIntosh amps uses autoformers, technically one half of a transformer yet similar in that it is built on the winding of coils, this seems to be a piece of their formula that contributes to the warmth of the clipping and distortion characterics when we slam them with guitar signal. But much of the tone is in the overall design of the amp circuit and the power supply that powers it.

It's amazing to me that one can buy a Mc2100 or Mc250 or Mc50 for under $3000 today. Actually for under $1000 which is ridiculous. The Mc50 is a miniature gem that weighs under 20 lbs and delivers about 70 watts of power. The combination of a clean, Fender-ish tube preamp signal into a McIntosh into some JBL 12's is just a special thing and something that Jerry learned to wrangle, learned to master actually. It's not a forgiving rig - it demands mastery of guitar picking dynamic control.

There are other ways to emulate and get close to the Tube pre into McIntosh sound, but a real Mac is the sound we know and love, the way the gently distorted Mac is so sweet and squirty and musically fun to hear when pushing a JBL to its limits... it's hard to replicate that guitar sound with anything else. We can get close, but that is a special combo.

B
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 #163450  by Jon S.
 Wed Nov 21, 2018 7:09 am
Great post. I'm confused about this, though. I recall reading here that some advise disconnecting the sentries from the power amps for better tone. Is the sentry related in any way to the autoformers?

My own MC50 tested as putting out a solid 75W before clipping. That's damn loud and more than enough power, in practice, for the applications many have for them!
 #163451  by waldo041
 Wed Nov 21, 2018 10:42 am
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For anyone interested in the questions pertaining to the Sentry Monitor and how it relates to the McIntosh AutoFormer can use this to read the answer.

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~waldo
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 #163454  by Jon S.
 Wed Nov 21, 2018 3:04 pm
And/or this (thank you, DuckDuckGo; thank you also, Mr. Wald, for the schematic):
The McIntosh Sentry Monitor

Although the autoformer provided an efficient match between the power transistor output and a variety of load impedances, a short circuit at the amplifier output or a load that was much lower than the selected autoformer tap could cause excessive current to flow in the output transistors. To complement the new transistor amplifiers, the McIntosh Sentry Monitor circuit was developed which prevented destructive current levels from occurring under any conditions. This circuit sensed the dynamic operating time, voltage and current of each amplifier output stage and controlled the current flow, confining it to non-destructive limits. The arrangement assured complete circuit reliability for all load conditions. The Sentry Monitor did not limit the rated power output available from the amplifier in any way. McIntosh power amplifiers continue to use the Sentry Monitor circuitry.
http://roger-russell.com/mcintosh1.htm#sentrymonitor
 #163456  by waldo041
 Wed Nov 21, 2018 4:08 pm
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It should be stated that if you do not mismatch your McIntosh higher output tap to a lower speaker load and create the environment inside the amp which would cause that Sentry to be not only active but sucking signal to ground off the input of the drivers when ever you hit that note. There would be no need to remove the Sentry because it would not being doing any of that of which it is designed to do.

Again, if you wire your speakers 4 ohm tap to 4 ohm load, or 8 to 8 or 16 to 16, you would not hear the involvement of the Sentry. And if you play it once a month, it may not matter at all.

~waldo
 #163459  by Jon S.
 Wed Nov 21, 2018 8:48 pm
>> Although the autoformer provided an efficient match between the power transistor output and a variety of load impedances, a ... load that was much lower than the selected autoformer tap could cause excessive current to flow in the output transistors.

>> It should be stated that if you do not mismatch your McIntosh higher output tap to a lower speaker load and create the environment inside the amp which would cause that Sentry to be not only active but sucking signal to ground off the input of the drivers when ever you hit that note. There would be no need to remove the Sentry because it would not being doing any of that of which it is designed to do.

To my best knowledge (based on experience but also often described expressly in the applicable owners manuals), most if not all of the guitar amps I've owned can successfully handle 2-1 amp output-to speaker-load mismatches (e.g., 8 ohms output into a 4 ohm load) with no need for sentry-like protection circuits. Thus it wouldn't occur to me to view a 2-1 mismatch as a load "much" lower than the amp's selected output tap. I don't know enough about solid state power amps, generally, or McI's specifically, to know whether McI's are similar. My guess would be yes but others may know for sure.
 #163460  by waldo041
 Thu Nov 22, 2018 7:03 am
Since Owners Manuals was interjected, Here is what has been available in various McIntosh Manuals for the amps used here.

Mc50
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Mc250/Mc2100
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Mc2120
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Mc2300
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I have worked on, tweaked and modified my personal Mcintosh mc2100 for over the past 10 years, and have had my sentry removed just about as long. Not missed it.

An amp may be able to handle the 2:1 mismatch and stay within operating range, but it will be running hotter and drawing more current and most likely changing the frequency response even if discernible or not.

Although one should never intentionally short out the output of their amplifier. If you trust the Sentry Monitor and the descriptions of it enough, short out the output of your Mac! First, you will see smoke blast out of the top as the emitter resistors fry and then, as Healy stated, the output transistors get "Frapayed". At that extreme you probably could weld with it!

Imagine using one for the PA system on a US Naval Vessel where 100's of berthing and storage areas have a speaker. I wonder what happens to the load if 20 of those speakers fell off? How would the system perform with no circuit like the Sentry Monitor in that environment?

~waldo
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 #163464  by Jimv
 Thu Nov 22, 2018 9:50 am
waldo041 wrote:Imagine using one for the PA system on a US Naval Vessel where 100's of berthing and storage areas have a speaker. I wonder what happens to the load if 20 of those speakers fell off? How would the system perform with no circuit like the Sentry Monitor in that environment?
navy ships are badass systems enginering accomplishments. ive not been in the navy, but i wired a tall ship w a retired navy systems enginer once. a navy ship is divided into a jillion watertight cubes or sections. blow a hole in any section and its sealed off from the rezt of the ship. all systems are run from a remotr location, or shut down from a remote location. (simplified answer). i wanna know how many friggin macs the us gov still owns, or how many on a ship... many im sure.
ok i cant take it anymore.... this thread, like many, is blowing my mind. i am learning to read these schematics slowly, they are somewhat self-explanitory and its easy to research what i dont understand. i just have no clue what all the individual components are or do, thus, the schematics are just meaningless circuts to me at this point. can anyone recomend a link or better, a book, that can help me start at the begining to learn audioelectonics? there is sooooo much out there, i dont know where to begin....
thanks everyone for contributing to this thread. awesome!
 #163465  by Jimv
 Thu Nov 22, 2018 10:19 am
waldo041 wrote:How would the system perform with no circuit like the Sentry Monitor in that environment?
right... like add salt water to the equation, chaos and more... incredible backup protetion on these amps! unreal! awesome point, waldo. and how many macs are underwater right now.
like a pallet of these mysterious caps is a drop in the bucket to the navy. imagine.....
 #163469  by waldo041
 Thu Nov 22, 2018 11:04 am
Jimv wrote:
Thu Nov 22, 2018 9:50 am

ok i cant take it anymore.... this thread, like many, is blowing my mind. i am learning to read these schematics slowly, they are somewhat self-explanitory and its easy to research what i dont understand. i just have no clue what all the individual components are or do, thus, the schematics are just meaningless circuts to me at this point. can anyone recomend a link or better, a book, that can help me start at the begining to learn audioelectonics? there is sooooo much out there, i dont know where to begin....
thanks everyone for contributing to this thread. awesome!

You can probably locate a pdf version, but i recommend this book. Basics covered.
https://www.radioshack.com/products/get ... onics-book

~waldo