Power Guard

VintageMac

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I know that McIntosh Power Guard was first introduced after the demise of the original McIntosh tube equipment. Power Guard has been used in all the solid state amplifiers since introduction. It is a wonderful innovation and has saved many speaker drivers from destruction!

However, I notice that the “newer” tube amplifiers (MC 2000, MC 2102, MA 2275) do not have Power Guard, even though they sport more recent refinements such as wireless remote control, power control, data ports, external sensor inputs, etc.

Is this because of the inherently higher distortion levels of the tube amps? Or is it because the tube amps utilize transformers vs. autoformers. Is there another reason? Maybe Ron-C or someone else knowledgeable about the Power Guard circuitry could shed some light on this for me.

Thanks!

VintageMac
 
Power guard has never been used in tube amplifiers, no real need to due to the type of distortion introduced and the inability of a tube amplifier to introduce DC to the speaker terminals. A SS amplifier can be driven to the point that a square wave at B+ rail voltage is presented to a speaker; hence most all SS amplifiers use some type of protection circuit. McIntosh has recognized that when an amplifier is pushed hard into clipping and before clipping the distortion levels increase rapidly, with power guard the input and output signals are compared to each other, if the difference is over about 1% the input level is decreased automatically to keep the distortion level at or below this distortion level. This type of over load or should I say overpower protection is unique in that it protects using a distortion level that is independent of speaker impedance and output current or voltage.
 
Power Guard was introduced on the MC2205 in the mid 70s. Ron Evans invented it and the MC2205 was his first amp design. Another engineer started the MC2205 but the design was a failer as it made less power than the MC2105 so the engineer quit. Ron Evans took over the design and reworked it, added / invented Power Guard plus ended up with over 200 watts per channel. The MC2205 was a very reliable and popular amp.
Ron Evans is the current head of engineering at McIntosh as VP, Engineering.
Tube amps do not hard clip so power guard was not applied.
Ron-C
 
So, just to see if i have this right...

The transistor amps are have a faster rise-time (slew rate) than the tube amps, so are more likely to produce square waves when overdriven?

Is the slew rate the factor that makes the difference between "tube sound" and "SS sound"?

VintageMac
 
Who said transistors are faster than tubes? Tubes are much faster especially at high frequencies. Faster equals bandwidth. Tube amps more or less collapse when overdriven where solid state amps start to pass the power supply rail voltages with high distortion. This can and will damage speakers. Big tube amps can also damage speakers with determined abuse but not as fast as solid state.

Ron-C
 
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Power Guard was the hook that drew me into learning about Macs in the first place. I noticed just after I got my Klipsch CF-4's last February that deep bass notes, played with 'gusto' on either on DVD or CD through my 50 w/ch integrated A/V amp would cause my CF-4's to make a "clik" or 'pop' sound. I thought at first I had a bad driver(s), then I realized it was clipping. Horrified, I wanted to find a solution to protect my 'new' speakers and quickly. After a great deal of reading and study on the internet, I realized that Power Guard and McIntosh was the way to go in amplification. It's also nice to know that Sentry Monitor protects against DC damage.

Therefore, less than a month after I got my Klipsch speakers, the Mac4100 arrived at the house, joined a few months later by the Mc2205. All spurious sounds disappeared like magic. The Power Guard works so wonderfully that I wouldn't know it was functioning if not for the red warning lamps. Did I mention that, at the time I firmly believed that ALL amps sounded alike, provided that frequency response curves were similar? I was absolutely shocked and DELIGHTED to be proven wrong. The Macs have a warm rich sound that is far superior to my A/V amp. I also had some issues with listening fatique with the 'bright' CF-4's that went away with McIntosh amplification.

So now I'll always be a Mac believer.
 
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