• The move to the new server is done. There are some software and database maintenance updates in process. This has us passing the hat around to help out. We appreciate any donations. Seriously, even a dollar helps. The payment page may be found here - https://www.audiokarma.org/support.html

Mcintosh MC901

ABX tests are controversial. They are very difficult to perform properly as noted previously.

By the way they are by definition double-blind.

More people talk about them than actually perform them or participate in them. They are used mostly as a logical stalking horse in arguments with preconceived conclusions.

What would be more helpful is to say something like this. Especially if it were true:

“I used an Audio by Van Alstine (AVA) ABX test box and switched between (insert comparison equipment here) over a trial of 25 samples. I correctly identified sample A in 20 of the 25 tests, or 80% of the time, which is statistically significant.”

Or I correctly identified sample A in 13 of the 25 tests, or 52% of the time, which is statistically not significant.”

Extra points for conducting the test over a large number of listeners, over time.

So knowing the test conditions and the ABX test box, be it an AVA, or David Clark, or Crest, or DIY (suspect) is important. Complete documentation of the test setup with pictures is also a plus.
 
Last edited:
Moderation Note:

This thread has been cleaned up of the latest round of interpersonal back and forth, name calling, and thread derailment...AGAIN! This thread has already required far too much moderation to keep it on its rails. Dissuasive measures are available, and the thread can be closed.

Please, let's discuss, not fight, proselytize, or thread-crap.

Rich P
 
Last edited:
W9TR said:
ABX tests are controversial. They are very difficult to perform properly as noted previously.

By the way they are by definition double-blind.

More people talk about them than actually perform them or participate in them. They are used mostly as a logical stalking horse in arguments with preconceived conclusions.

What would be more helpful is to say something like this. Especially if it were true:

“I used an Audio by Van Alstine (AVA) ABX test box and switched between (insert comparison equipment here) over a trial of 25 samples. I correctly identified sample A in 20 of the 25 tests, or 80% of the time, which is statistically significant.”

Or I correctly identified sample A in 13 of the 25 tests, or 52% of the time, which is statistically not significant.”

Extra points for conducting the test over a large number of listeners, over time.

So knowing the test conditions and the ABX test box, be it an AVA, or David Clark, or Crest, or DIY (suspect) is important. Complete documentation of the test setup with pictures is also a plus.
Click to expand...
Very well stated indeed.
 
The 3500 is A nice vintage piece but in terms of looks and sound quality it's old technology.They have much better quality parts now.They have computer technology now that they never had back in the vintage days. Our newest Mc 275 is much better than the Dark sounding vintage tube models.I'm not saying measurements are everything . Also the Mc2301 is Far superior to Any Tube Amp on the Market. New technology, Superior quality parts. Far better than anything out there !!!
 
For those who were interested in the crossover and other pertinent information, you can now download the Owner's Manual from the McIntosh site.

Larry
 
Interesting reading. First the crossover slopes are 9 db per octave. Then if you set the controls for the same frequency you will end up with a 3 db rise at the crossover frequency. Ideally the response should be flat. Plus there is going to be another issue about how much phase shift there is going to be. 12 db per octave is 180 degrees at the - 3db point and 6 db is 90 degrees. So I guess the shift is going to be around 135 degrees. The Butterworth, Bessle and Linkwitz-Riley, etc crossovers issues such as proper matching and the crossover frequencies are corrected for . Digital crossovers can further correct for summing issues analog crossovers can't. So I would by pass the filters used in the amplifier and use a more sophisticated external crossover units depending on what your speakers require. Remember you have to bi pass the passive crossovers in the speakers. if you plan on using either external electronic crossovers or the crossovers in the amplifiers. Other wise I would set the low pass crossover of the SS amp an octave above the passive crossover for the woofer, and an octave below the crossover of the HF section as recommended with the MEN 220 to prevent audible coloration and extreme phase shifts in the crossover region most easily compromised. With Altec, EV , JBL, Bozaks and others where you can either by pass the passive crossovers or have to remove them deciding on whether to reverse the polarity of the HF section of the speajker due to the phase shift of the crossover filters is going to be up to you. Bozak and JBL owners should read posts on line about recommendations by. the designers. Older Mac speakers of the ML series and XR series that have critically damped woofers don't gain anything by bi-amping. Other speaker systems with critically damped woofers wouldn't either other than the sound of the tube section for the highs and midrange. Infinite baffle speakers like Bozak gain quite a bit from bi-amping after removing the woofer and low mid crossover passive sections. Altec and JBL gain with the horn loaded systems because of the vast efficiency differences between the horns and woofer sections. Some times close to 10 db. Unfortunately most horn systems can't handle the power of a 901. Maybe 150 watts on the bottom and 50 to 75 watts would be a better choice for the older efficient speaker systems. I still think the 901 would be a great choice for JBL's 4435 and DD 67000 that were purposely set up for the bi-amping option. Maybe some of the K series and other JBLs would be a good choice, too. I don't think personally that any of Roger Russell designed speakers for Mcintosh would gain any thing by Bi- amping. Maybe Tannoy and EV would but here again the passive crossover filters for the woofers and the low section of the mids would have to be removed. I wonder what Magneplanars 30.7 would sound like? That might be the perfect match. its a shame most of the top of the line speakers don't have provisions for bi-amping. Magico for instance, but here again they have almost critically damped woofers.
 
Last edited:
The meter movement wasn't quite what I was expecting, I'm not going to say its awful or whatever, I think its just an "out of the box sideways thinking" type thing, it could grow on me in time...
 
You could always turn off the lights on the meters. I guess it depends on the music you play how much those will be moving around.
 
Is there two sets of poweguard lights on the faceplate?

overall reliability always decreases as one increases quantity.

Are the individual amps quad balanced topology?
 
62caddy said:
RE: No PG on tube Mc amplifiers.

I found this - Power Guard Screen Grid Sensor™ (SGS). The 300 Watt vacuum tube amplifier section of the MC901 breaks new ground as it's our first amplifier to feature our new Power Guard SGS™ technology. Power Guard SGS helps prevent premature vacuum tube failure by monitoring the screen grid current in the KT88 output vacuum tubes. If the current becomes too high, a circuit in Power Guard SGS is activated which then dynamically attenuates the input signal in real time to keep the vacuum tubes operating at safe levels.
Click to expand...
 
twiiii said:
Interesting reading. First the crossover slopes are 9 db per octave. Then if you set the controls for the same frequency you will end up with a 3 db rise at the crossover frequency. Ideally the response should be flat. Plus there is going to be another issue about how much phase shift there is going to be. 12 db per octave is 180 degrees at the - 3db point and 6 db is 90 degrees. So I guess the shift is going to be around 135 degrees. The Butterworth, Bessle and Linkwitz-Riley, etc crossovers issues such as proper matching and the crossover frequencies are corrected for . Digital crossovers can further correct for summing issues analog crossovers can't. So I would by pass the filters used in the amplifier and use a more sophisticated external crossover units depending on what your speakers require. Remember you have to bi pass the passive crossovers in the speakers. if you plan on using either external electronic crossovers or the crossovers in the amplifiers. Other wise I would set the low pass crossover of the SS amp an octave above the passive crossover for the woofer, and an octave below the crossover of the HF section as recommended with the MEN 220 to prevent audible coloration and extreme phase shifts in the crossover region most easily compromised. With Altec, EV , JBL, Bozaks and others where you can either by pass the passive crossovers or have to remove them deciding on whether to reverse the polarity of the HF section of the speajker due to the phase shift of the crossover filters is going to be up to you. Bozak and JBL owners should read posts on line about recommendations by. the designers. Older Mac speakers of the ML series and XR series that have critically damped woofers don't gain anything by bi-amping. Other speaker systems with critically damped woofers wouldn't either other than the sound of the tube section for the highs and midrange. Infinite baffle speakers like Bozak gain quite a bit from bi-amping after removing the woofer and low mid crossover passive sections. Altec and JBL gain with the horn loaded systems because of the vast efficiency differences between the horns and woofer sections. Some times close to 10 db. Unfortunately most horn systems can't handle the power of a 901. Maybe 150 watts on the bottom and 50 to 75 watts would be a better choice for the older efficient speaker systems. I still think the 901 would be a great choice for JBL's 4435 and DD 67000 that were purposely set up for the bi-amping option. Maybe some of the K series and other JBLs would be a good choice, too. I don't think personally that any of Roger Russell designed speakers for Mcintosh would gain any thing by Bi- amping. Maybe Tannoy and EV would but here again the passive crossover filters for the woofers and the low section of the mids would have to be removed. I wonder what Magneplanars 30.7 would sound like? That might be the perfect match. its a shame most of the top of the line speakers don't have provisions for bi-amping. Magico for instance, but here again they have almost critically damped woofers.
Click to expand...


The built in adjustable crossovers are designed to cross the two amp sections over while the speaker's internal crossover is retained. The amp crossovers should be set to about 1/2 octave above or below the actual speaker's Low to Mid-High crossover frequency.
Example, if the speaker has a 350Hz crossover point the low pass should be 550 or 800 and the high pass should be 250 or 180.
This will make the two amp sections happy while maintaining the internal speaker's crossover design.

If you wanted to use an external crossover like MEN220 then you can bypass the MC901 internal crossover and send separate feeds from the external crossover.

Thanks,
Ron-C
 
You must log in or register to reply here.
Back
Top Bottom