OMG!!! New MC1.25KW !!!

[kevzep]

Thanks.

While the intent is to be not audible...
http://sound.whsites.net/articles/soft-clip.htm
"Unfortunately, at lower levels there will still be some distortion. For any circuit to clip 'softly', it must start to introduce distortion well below the clipping voltage (set by the power amp's supply rail voltage). As discussed in greater detail below, you will end up with 1-2% distortion at around half power (sometimes even less), with the distortion climbing rapidly as the amp delivers more power. This is not hi-fi!"

This here has nothing to do with Powerguard or McIntosh. PG as previously stated is not a soft clip circuit.

When under the threshold of PG, it is not detectable, that would have been a design consideration by the engineers who developed it.

 

[E-Stat]

Of course, which is why having an amplifier which is powerful enough to provide the necessary headroom is the way to go.

Agreed! Clipping is easy to hear.

Apparently though, John Atkinson found that the 501 doesn't like continuous power testing at the one-third power level and the PG LED illuminated.

 

[kevzep]

Agreed! Clipping is easy to hear.

Apparently though, John Atkinson found that the 501 doesn't like continuous power testing at the one-third power level and the PG LED illuminated.

There has been some discussion about the heatsink/thermal management of the 501 being a little "light".
Also depends what waveform they are using to do the continuous power testing.

Is it a 1khz tone? Pink noise? Maybe a low frequency?
I can send a Crown Macrotech into thermal current limiting using a particular arbitrary wave file at 50% power.
So we need more information to make an accurate assessment. I find these guys never divulge such information, I wonder why!!

 

[62caddy]

Agreed! Clipping is easy to hear.

Apparently though, John Atkinson found that the 501 doesn't like continuous power testing at the one-third power level and the PG LED illuminated.

"The heatsinks are relatively small for an amplifier with a continuous rating of 500W. I must assume that McIntosh decided that continuous running with sinewaves would be sufficiently rare that they could economize in this area. When this circumstance did arise, their Sentry Monitor circuit, which monitors heatsink temperature, would protect the amplifier against thermal runaway."

- Sounds to me like the PG lamps indicated the Sentry Monitor was active, not as a result of overdrive prevention.

- 1/3rd rated power is the most stressful on an amplifier. A steady 1/3rd power of sinewave material for a duration of minutes not a situation ever likely to be encountered in music.

"I thought the McIntosh amplifiers sounded simply superb when I auditioned them in Paul Bolin's system in the spring. Nothing in the MC501's measured performance causes me to doubt what I heard.—John Atkinson"

 

[E-Stat]

There has been some discussion about the heatsink/thermal management of the 501 being a little "light".

Apparently.

Is it a 1khz tone?

Since the power tests found below use a 1 khz sine wave, that would be my guess.

 

[kevzep]

Apparently.


Since the power tests found below use a 1 khz sine wave, that would be my guess.

It wouldn't have a hope in hell with the arbitrary wave file I have then!!

 

[E-Stat]

- Sounds to me like the PG lamps indicated the Sentry Monitor was active, not as a result of overdrive prevention.

I thought that feature was always *active*. Is the one on your 452 always illuminated?

 

[62caddy]

I thought that feature was always *active*. Is the one on your 452 always illuminated?

Monitoring is what is continuous; the system is only "active" when a thermal condition is detected (and action taken). Green PG lamps indicating normal function are otherwise always illuminated.

Bear in mind, Sentry Monitor is a separate protection system than PG however it seems the same red panel lamps are used to indicate when either is active.

 

[kevzep]

Wait wait wait!!! STOP!!

The sentry does not have anything to do with the PG circuit. The sentry circuit is a current limiter, so if the current exceeds the pre determined value, then the sentry transistors steer current to ground before the output transistors. They are always in circuit but have absolutely no effect on anything until a particular threshold is reached.
PG operates on its own.

 

[E-Stat]

The sentry does not have anything to do with the PG circuit. The sentry circuit is a current limiter, so if the current exceeds the pre determined value, then the sentry transistors steer current to ground before the output transistors. They are always in circuit but have absolutely no effect on anything until a particular threshold is reached.
PG operates on its own.

That's what I thought. Which returns me to Atkinson's observation.

 

[kevzep]

That's what I thought. Which returns me to Atkinson's observation.

I think his assumption on what the sentry circuit was doing is actually incorrect.

Sorry guys I have a mountain of work to do so have to go sadly.

We have steered this well off topic too, oops.

 

[E-Stat]

I think his assumption on what the sentry circuit was doing is actually incorrect.

What assumption? He simply observed that the amp shut down and the PG LED illuminated:

"To my surprise, the McIntosh shut itself off after just five minutes—the orange Power Guard LED on the front panel illuminated..."

 

[kevzep]

What assumption? He simply observed that the amp shut down and the PG LED illuminated:

"To my surprise, the McIntosh shut itself off after just five minutes—the orange Power Guard LED on the front panel illuminated..."

When this circumstance did arise, their Sentry Monitor circuit, which monitors heatsink temperature, would protect the amplifier against thermal runaway.
Sentry is a current limiter, has nothing to do with monitoring heat sink temperature.

 

[E-Stat]

Sentry is a current limiter, has nothing to do with monitoring heat sink temperature.

I remain with you!

What assumption did JA make? And why did Powerguard trip during the FTC one-third power test?

 

[62caddy]

Judging from the description of the events, it sounds like the red PG lamps serve to alert of a thermal condition as well as of PG activity.

PG should never become active at 1/3rd output power under ordinary use.

 

[E-Stat]

Judging from the description of the events, it sounds like the red PG lamps serve to alert of a thermal condition as well as of PG activity.

Now, that's an assumption!

 

[62caddy]

Now, that's an assumption!

I don't know what you're saying but it's a perfectly logical one to make. The statement was that the PG lamps came on while the amplifier was shut down in thermal protection mode.

In other words, when no signals are passing through the amplifier, there is nothing for Power Guard to act upon.

 

[4-2-7]

So if anyone reads your post on the open forum they would know your disdain for McIntosh.

So it begs the question..... Why would you go into the McIntosh specific forum?

I know I have never made any comments in sub forums I have no interest or like the equipment, why would I?

While the intent is to be not audible...

We have steered this well off topic too, oops.

Well that's E-Stats intent,

he does this stuff in every thread, he's got magic golden ears, noting is good but what he owns. His main argument if someone doesn't believe they can benefit form cables and other high dollar gear is you need to have hands on expedience with the equipment. But then he goes on to argue when he's never owned any mac gear, siting one time he listen to a mac system.

This is why I asked the question above, the only reason to be in this thread is to argue with mac owners and run the thread off the rails. And he'll be infatic siting internet gossip as fact and the basis of his argument.

 

[4-2-7]

Protection Circuits
The MC501 incorporates a version of the McIntosh Sentry Monitor Output Transistor Protection Circuit. Refer to Figure 17. There is absolutely no compromise in sonic performance with this circuit, and it ensures safe operation of the amplifier under even the most extreme operating conditions. The different types of protection circuits incorporated in the MC501 insure a long and safe operating life. This is just one of the many characteristics of McIntosh Power Amplifiers that make them world famous.

The MC501 also includes the unique patented McIntosh Power Guard circuit. Power Guard eliminates the possibility of ever overdriving the amplifier into clipping. Refer to figures 18, 19 and 20. An overdriven amplifier can produce both audible and inaudible distortion levels exceeding 40%. The audible distortion is unpleasant to hear, but the inaudible ultrasonic distortion is also undesirable, since it can damage valuable loudspeaker system tweeters. You will never experience the harsh and damaging distortion due to clipping

The Power Guard circuit is a waveform comparator, monitoring both the input and output waveforms. Under normal operating conditions, there are no differences between the shape of these waveforms. If an amplifier channel is overdriven, there will be a difference between the two signal waveforms. When the difference exceeds 0.3% (equivalent to 0.3% harmonic distortion), the Power Guard activates the PG light and a dynamic electronic attenuator at the amplifier input reduces the input volume just enough to prevent any further increase in distortion. The Power Guard circuit acts so fast that there are absolutely no audible side effects and the sonic purity of the music reproduction is perfectly preserved. The MC501 Power Amplifier with Power Guard is not limited to just the rated power output, but will actually produce distortion free output well above its rated power due to the McIntosh philosophy of conservative design.

 

[4-2-7]

Apparently though, John Atkinson found that the 501 doesn't like continuous power testing at the one-third power level and the PG LED illuminated.

There has been some discussion about the heatsink/thermal management of the 501 being a little "light".

The high efficiency circuit design of the MC501 contributes to low operating temperatures. More than 1,045 square inches of heat sink area keep the MC501 operating safely with convection cooling. No fans are needed.