Why McIntosh Watts same @ 8 & 4 ohms?

[Smarshi]

What I understod from your posts (RonC and Know Talent) is that typically, high-end amps are designed for 4ohm loads and therefore will deliver less power into 8ohm speakers. Whereas McIntosh amps with the autoformer, enable you to utilizes fully the power of the amp if you match the impedence of the speaker to the relevant output on the amp.

However, in the case where you missmatch the impedence of speaker/amp, lets say you use the 4ohm output with 8ohm speakers, the amp will only provide half the power when the speaker operates in the 8ohm region. Am I getting this right?

 

[ron-c]

Basically yes. All transistors and amps obey Ohm's law including those with autoformers. The autoformer is like a three speed transmission that matches the engine speed to the road speed and the autoformer matches the amp to the load impedance.
If you run a 4 ohm load on the 8 ohm tap the McAmp will double power or on an 8 ohm load on the 4 ohm tap will halve power.
Many high end amps are designed to run low impedance loads. These amps will be weak on the very common 8 ohm speakers which many now make. These amps will tend to clip early on 8 ohm loads which usually damages tweeters.
Mass market amps are often designed for 8 ohm loads and have cautions on the back panels about running with speakers below 6 ohms. If you use a 4 ohm speaker with these the amps will run hot, shut down or blow fuses. Maybe other bad things can also happen.

A McIntosh amp allows you to run all speaker types and receive full performance.


thanks,
Ron-C

 

[Smarshi]

RonC,

Refering to the earlier post (see qoute below) discussing the measurement section of MC501 Stereophile Review, would you know why did they measure that 501 only provided 225W into 2ohms when using the 8ohm tap of the amp?

Thanks

Alberto, I have read this review before but I overlooked the measurement section, Thanx for bringing this to my attention.

I have just read it, and I am a little confused, the article said the following "The 8 ohm tap was limited to 225W into 2 ohms (17.5dBW), for example, while the 4 ohm tap delivered 1000W (24dBW), the 2 ohm tap 630W (22dBW)"

I am not sure why is the amp is limited to 225w into 2ohms using the 8ohm tap, I think I'm missunderstanding something. Also the article mentions that the amps shutdown while testing, is this unusual? Are you guys having similar experiences?

 

[Smarshi]

Basically yes. All transistors and amps obey Ohm's law including those with autoformers. The autoformer is like a three speed transmission that matches the engine speed to the road speed and the autoformer matches the amp to the load impedance.
If you run a 4 ohm load on the 8 ohm tap the McAmp will double power or on an 8 ohm load on the 4 ohm tap will halve power.
Many high end amps are designed to run low impedance loads. These amps will be weak on the very common 8 ohm speakers which many now make. These amps will tend to clip early on 8 ohm loads which usually damages tweeters.

Thanks for the explanation RonC, I now fully understand the benefits of the autoformer that Mcamps provide.

 

[ron-c]

At 2 ohms the amp should be on the 4 or 2 ohm taps. If you hit the amp with a standard 10 ms tone burst with a 2 ohm load on the 8 ohm tap it will produce well over 1000 watts but this can not be sustained with a sine wave. Music is a series of tone bursts though.

Thanks,
Ron-C

 

[Smarshi]

:thmbsp:

At 2 ohms the amp should be on the 4 or 2 ohm taps. If you hit the amp with a standard 10 ms tone burst with a 2 ohm load on the 8 ohm tap it will produce well over 1000 watts but this can not be sustained with a sine wave. Music is a series of tone bursts though.

Thanks,
Ron-C

Makes sense, the review tested the amp with a countinuos signal @ 2ohms and the big watts cannot be sustained except for short bursts. Thanks for the explanation

 

[clarbin]

OK - so if I have MC501's and B&W N802 speakers, which tap should I use since the speakers say 8 ohms?

Man - I'm gettin' confused.

 

[Know_Talent]

OK - so if I have MC501's and B&W N802 speakers, which tap should I use since the speakers say 8 ohms?

Man - I'm gettin' confused.

4 ohm posts :thmbsp:

8 ohm posts and you'll go eventually go into thermal shutdown as look at all the frequency ranges where the impedance is less than 8 ohms...

Talk about some wild impedance (and phase) swings!!! that is why the 802s are hard on amps

Now look at a Thiel CS7.2... much less impedance and phase variance thru the midrange :thmbsp:

I might try running them on the 8 ohm posts and mount some fans over the rear of the amps! j/k

 

[PHC1]

Now look at a Thiel CS6... much less impedance and phase variance thru the midrange :thmbsp:

Check out the Peak Consult Empress. Is this a well behaved speaker or what? :thmbsp:

 

[Know_Talent]

Check out the Peak Consult Empress. Is this a well behaved speaker or what? :thmbsp:

:thmbsp: It doesn't get much flatter than that!

Check out my previous post as I replaced the CS6 with the CS7.2...even flatter than CS6!!!

Since the measure response from JA's test in stereohile was 25-17khz...it's also very flat and alot easier on the amp vs. the likes of B&W offerings.
B&Ws can sound great but you need mondo amplification if you want them to breathe properly. That's why alot of people aren't impressed when listening to them...if they don't have thermonuclear powered amplification, they ain't gonna dance

 

[PHC1]

Since the measure response from JA's test in stereohile was 25-17khz...it's also very flat and alot easier on the amp vs. the likes of B&W offerings.
B&Ws can sound great but you need mondo amplification if you want them to breathe properly. That's why alot of people aren't impressed when listening to them...if they don't have thermonuclear powered amplification, they ain't gonna dance

I've said it many times as well. :yes: They don't call them "amplifier ball breakers for nothing".

 

[Know_Talent]

I've said it many times as well. :yes: They don't call them "amplifier ball breakers for nothing".

I once heard a salesperson recommending a 200W Rotel amp to drive 803s and I started laughing! I had the 1090 380wpc and that was adequate, the MA6900 would drive them ok unless I wanted to listen above ~ 85db and I found the MC501s to be the first amp that really made them come alive.

The 501s will drive the 802s ...but not as well as 1201/1.2KWs IMO

 

[ron-c]

The 802 can only handle so much power especially on the bass end. I would believe B&W when they say 500 watts. If you want to play them loud I would suggest 4 ohms. If you do not crank a lot 8 or 4 ohms will work fine.

Thanks,
Ron-C

 

[PHC1]

I once heard a salesperson recommending a 200W Rotel amp to drive 803s and I started laughing! I had the 1090 380wpc and that was adequate, the MA6900 would drive them ok unless I wanted to listen above ~ 85db and I found the MC501s to be the first amp that really made them come alive.

The 501s will drive the 802s ...but not as well as 1201/1.2KWs IMO

From my own experience of listening, the 402 did an ok job, the 501s were better and the 1201s were probably as good as it is going to get. The 802s still had a persistent mid/upper bass thickness and bloat that could not be completely resolved in a few rooms we tried them in.

 

[jdandy]

Serge.......+1 on the mid/upper bass thickness and bloat. A friend's 802s sound exactly as you described. He uses Reference 200.1 B&K amps, a class AB Mosfet output stage with 250 watts into 8 ohms. I have trying to convince him to go with MC501 amps, but he thinks he owns the best. I have given up trying to change his mind.