Oh those wonderful taps...

So I've spent a better part of the day once again playing with my system, specifically the subs and the active x/o.

In the midst of that I also started going back and forth between the 4 and 8 ohm taps on my 501s. With the changes of all the crossover points and various tap combo's, one thing stood clear the 8 ohm was clearly the better midrange or "musical" tap in the "presence region" while the 4 ohm tap gave me better mid to upper bass. :scratch2: Hmm.

When I first got the Guarneri Memento I knew it was a 4 ohm nominal type of a speaker and a bit more difficult to drive than the Cremona Auditor. So I fiddled with the 4 and 8 ohm taps and settled on 4 because I "thought" the bass sounded better that way. Keep in mind the woofers and low frequencies will usually require much more current when the impedance drops even with monitor speakers although not quite as much.

Then came the dual Fathom subs and an active crossover. The taps stayed the same at 4 ohms and off I went to tweaking the x/o and subs.

Playing around with the whole setup today, it all of a sudden hit me, "take a look at the impedance graph of the Guarneri".

Please take a look at the graph.



Notice those excursions into the 20 ohm+ between the 20 and 100 ohms? How about the peak in the "presence region" starting at 1Khz...

Well, that explained why the 8 ohm was by far the most musical and the clear winner of the "midrange" tap to use, much better match from 1Khz on up to 6Khz. :yes:

Let's remember that with direct coupled amps if 500w=2 ohm, 250w=4 ohm, 125w=8 ohm, 62.5w=16 ohms and so on... (if they can effectively "double down", not all can.) The taps offered on the autoformer amp gets you closer to an optimal load match.

So what if, I thought, "let the Fathoms deal with 100Hz on down, just as the impedance comes back down to reasonable levels with their 1500w amps, they can handle that load and I will use the 8 ohm tap on the 501s and concentrate on the midrange. Bingo!!! :thmbsp:

Switched to the 8 ohm tap, bumped up the crossover points to 100Hz, played around with slopes and WOW! Incredible!

Now the subs can do their dirty work and take care of all those impedance swings down low and the 501s can work their magic on the midrange. Worked like a charm.

Keep in mind, the Fathoms are simply incredible subs, no wonder they have completely swept all the reviewers off their feet and got so many awards. They are fast, articulate, effortless and can keep up with even the midbass drives of the monitors such as mine. Belive it! :thmbsp: I would not attempt this with just "any" sub, at 100Hz, most of them are anything but musical. The RELs are great subs but have you ever tried them at 100Hz... The Fathoms simply ROCK! :yes:

I have expiremented alot with bi-amping with my system, and found the added flexibility of the multiple taps to be very useful! I'm told by Chuck H at McIntosh, that there is a 3 db gain difference between taps. You just want to try to steer clear of the speakers' passive crossover points, to avoid any interaction with your active crossover. I used to set my active crossover, which I used for a high-pass, at least 50 HZ below my speakers crossover and it worked like a charm. Sounds like you have the makings of a really big sound. Ted.

Yardbird1 said:

I have expiremented alot with bi-amping with my system, and found the added flexibility of the multiple taps to be very useful! I'm told by Chuck H at McIntosh, that there is a 3 db gain difference between taps. You just want to try to steer clear of the speakers' passive crossover points, to avoid any interaction with your active crossover. I used to set my active crossover, which I used for a high-pass, at least 50 HZ below my speakers crossover and it worked like a charm. Sounds like you have the makings of a really big sound. Ted.

Click to expand...

Yes there is a 3dB or so difference, you can hear it right away so need to back off the volume 3 or 4 clicks (on the MDA1000) to compare. My speakers have 2 drivers so the internal speaker crossover point is way up higher. Loving the new setup! I found my cake and I am eating it too!

Bump for current discussions on taps and impedance.

Direct coupled amps halve down as impedance doubles unlike the Auto former amps. As long as a direct coupled amp matches the speaker load all is fine.

thanks,
Ron-C

ron-c said:

Direct coupled amps halve down as impedance doubles unlike the Auto former amps. As long as a direct coupled amp matches the speaker load all is fine.

thanks,
Ron-C

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Ron,

Your statement is confusing me so would you please clarify...

If I'm running off my 4 ohm posts and the speakers are working in a 8 ohm portion of the impedance curve...the MC501s are producing roughly half rated output...correct???

Ah, another design secret uncovered. Speaker designers assume the output of the amp will rise and fall with the impedance swings of the speaker. This will happen with brand-x or McIntosh Autoformer amps.
Tube amps do not respond the same way however which accounts for some of the change we hear when using tube amps on some speakers.

The taps discussion is about bi-wire and connecting the woofers on one value tap and the Mid/tweeters on another. This allows you to change the balance of the speaker to possible better match your room placement and acoustics.

When a speaker is described as a whatever ohm design this does not mean it will sound best on the same ohm tap of a McIntosh amp. We have a lot of speakers that are '8 ohm nominal', whatever that means but are actually 4 ohms or less in the power hungry bass area. This type of speaker will be best on the 4 ohm tap if you play loud.

As many have said you can try the different taps and use whichever you prefer. My statement is saying that if you pay for a 500 watt direct coupled amp that is 500 watts into 2 ohms and you have 8 ohm speakers, you will only get 125 watts which is not a value because the amp 'halved down'. With the MC501 you can have 500 watts with 2,4,or 8 ohm speakers. You will get all the power you pay for.

thanks,
Ron-C

ron-c said:

Ah, another design secret uncovered. Speaker designers assume the output of the amp will rise and fall with the impedance swings of the speaker. This will happen with brand-x or McIntosh Autoformer amps.
Tube amps do not respond the same way however which accounts for some of the change we hear when using tube amps on some speakers.

The taps discussion is about bi-wire and connecting the woofers on one value tap and the Mid/tweeters on another. This allows you to change the balance of the speaker to possible better match your room placement and acoustics.

When a speaker is described as a whatever ohm design this does not mean it will sound best on the same ohm tap of a McIntosh amp. We have a lot of speakers that are '8 ohm nominal', whatever that means but are actually 4 ohms or less in the power hungry bass area. This type of speaker will be best on the 4 ohm tap if you play loud.

As many have said you can try the different taps and use whichever you prefer. My statement is saying that if you pay for a 500 watt direct coupled amp that is 500 watts into 2 ohms and you have 8 ohm speakers, you will only get 125 watts which is not a value because the amp 'halved down'. With the MC501 you can have 500 watts with 2,4,or 8 ohm speakers. You will get all the power you pay for.

thanks,
Ron-C

Click to expand...

So I'm still getting 500W at 8 ohms even though I'm running off the 4 ohm posts?

Good thinking - and good experiment Serge!

Alberto

Know_Talent said:

So I'm still getting 500W at 8 ohms even though I'm running off the 4 ohm posts?

Click to expand...

No, that doesn't work for direct coupled amps or autoformer amps. With a direct coupled amp, if the 2 ohm =500w, then 4 ohms=250w and 8 ohms=125w. But, with the autoformer amp, you switch to the 8 ohm tap and you have your 500w. Capiche?

PHC1 said:

No, that doesn't work for direct coupled amps or autoformer amps. With a direct coupled amp, if the 2 ohm =500w, then 4 ohms=250w and 8 ohms=125w. But, with the autoformer amp, you switch to the 8 ohm tap and you have your 500w. Capiche?

Click to expand...

So on the 4ohm tap of say a MC501 you are getting how many watts for an 8ohm speaker?

On the bigger McAmps like the 501 the meters are reading both voltage AND amperage which means when they say 500 watts it is 500 watts. Its that Ohm's law thing again.

Thanks,
Ron-C

eljr said:

So on the 4ohm tap of say a MC501 you are getting how many watts for an 8ohm speaker?

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Can't say exactly because as you know the impedance of a speaker is all over the place. It may be 8 ohm at some frequency and something completely different some other place. All things considered, it is more important to match the bass impedance as it soaks up much more power (woofers) to allow maximum thermal power efficiency and achieve full power rating. So if the bass dips to 4 ohms and below, that will be the current hungry dip and that's where you want to maximize/optimize the impedance match.

The power split between bass up to 350Hz or so and the rest of the frequency spectrum is something like 80/20 with the 80% of available power being soaked up by the bass.

PHC1 said:

Can't say exactly because as you know the impedance of a speaker is all over the place. It may be 8 ohm at some frequency and something completely different some other place. All things considered, it is more important to match the bass impedance as it soaks up much more power (woofers) to allow maximum thermal power efficiency and achieve full power rating. So if the bass dips to 4 ohms and below, that will be the current hungry dip and that's where you want to maximize/optimize the impedance match.

The power split between bass up to 350Hz or so and the rest of the frequency spectrum is something like 80/20 with the 80% of available power being soaked up by the bass.

Click to expand...

Think I got it,
basically try both posts and see which sound I like better. :scratch2:

ron-c said:

On the bigger McAmps like the 501 the meters are reading both voltage AND amperage which means when they say 500 watts it is 500 watts. Its that Ohm's law thing again.

Thanks,
Ron-C

Click to expand...

So the MC501 can produce 500W into an 8 ohm load off the 4 ohm posts?

The transistors SOA graph dictating the Voltage & Amperage boundaries

Know_Talent said:

So the MC501 can produce 500W into an 8 ohm load off the 4 ohm posts?

The transistors SOA graph dictating the Voltage & Amperage boundaries

Click to expand...

Well we know that 501s can produce 500w of any of the taps. Actually they will put out 1000w into 2 ohms from the 4 ohm tap. The decreasing load allows them to develop more power than their rating. I doubt they can do that going the other way into an increasing load. Having said that,
since speakers are not a linear load, there is no reason why they can't develop full power into an 8 ohm nominal speaker load from 4 ohm taps. :scratch2: