McIntosh amp taps vs current
 

Hey gang. Help me understand this relationship.

In the context of a speaker with a nominal impedance of 8 ohm and a minimal impedance of 3.1 ohm in bass region (Focal Scala EVO).

From what I’ve gathered, speakers that have low impedance in the bass compared with the nominal impedance work best with high current amps that always seem to be capable of doubling watts as the impedance is halved (eg 200w @ 8 ohm, 400w @ 4 ohm, 800w @ 2 ohm).

I understand that the McIntosh autoformer results in ability to supply the amplifier’s rated output whether using 2, 4, or 8 ohm tap which is great when the speaker nominal impedance is fairly flat across freq spectrum.

But what happens when we use 8 ohm tap on the MC601 for example and the bass impedance dips down to 3 ohm? Is this a problem?

If one picks the 4 ohm tap, that helps the bass current needs but what about the higher impedance for the remaining freq?

I know we can try whichever tap we want and pick whichever sounds best, won’t hurt amp or speaker but before purchasing said speaker, is a McIntosh amp able to properly drive a speaker like this compared with a different amp that is capable of doubling watts with decreasing impedance.

Are McIntosh amps considered “high current” amps or is that term only reserved for amps capable of doubling output?

If the manufacturer has correctly stated the nominal impedance in this instance 8 ohm, the 8 ohm tap should be used. For Wilson speakers all of which have a nominal impedance of 4 ohm the 4 ohm tap should be used. I own an XVX with a minimal impedance of 1.6. I use the 4 ohm tap with my 1.25 KW's. The amps never get more than warm and never require more than 120 watts.

Solid state amps should never be stressed. Folks that run their speaker with a 4 ohm nominal impedance off the 8 ohm tap will certainly get a "larger" amp that produces more current at the expense of over stressing the amp and shortening its life.

A typical example was the review of the Sasha DAW in Stereophile where the 8 ohm tap was used with the Mac 611 because it sounded better. I don't doubt this. However, the proper Mac amp for the DAW is the 1.25 KW which if used off the 4 ohm tap would sound better and significantly outperform the 611 used off the 8 ohm tap.

Here is the rule and I know this will result in a million comments: With Mac amps always choose the tap that best matches the nominal impedance. Disregard the minimal impedance. If the speaker is 6 ohm nominal impedance use the 8 ohm tap. If the speaker is 3 ohm nominal impedance use the 4 ohm tap.

If the speaker is less than 3 ohm nominal impedance and you really want it, use an amp other than McIntosh.

Best

Charles

McIntosh amp taps vs current
 

Great question!

The math says that on a McIntosh transformer coupled amp the lower impedance taps will produce the most current for a given output power.

There is another consideration, and that’s the output impedance of the various taps. With a varying impedance load like pretty much every speaker ever made, the output impedance of the amp ends up in series with the speaker, slightly impacting the frequency response of the system. The resulting response deviation is small.

You would expect the lower impedance taps would have the lowest output impedance, but that’s not always true as evidenced in the review link below, where’re the 8 ohm tap of an MC 462 has a lower output impedance than the 4 ohm tap.

https://www.stereophile.com/content/...r-measurements


Some SS amps without output transformers can ‘double down’ when the speaker impedance halves. This speaks to these amps having really hefty power supplies that can supply the current needed to ‘double down’. Do these amps sound better than ones that can’t ‘double down’? Not necessarily. Are the parts required to do this more expensive? Absolutely.

Are these amps better at driving speakers whose impedance drops in the bass region?

Not necessarily.

There are just so many things that go into a power amp design that this one factor does not determine their suitability.

Are McIntosh amps high current? My MC 602 puts out 150 Amps per channel. I’d say that’s high current. :)


Anyway, sure, a McIntosh amp can drive properly drive a speaker with highly variable impedance.

Compared to an amp that can ‘double down’?

I don’t think it matters.

This is when everyone having an amp that doubles down will say the transformer coupled amp they had before sounded flabby in the bass. :)

I believe the Amp used for the DAW review was the 462. A 611 is plenty for a Wilson Sasha DAW. If you follow my rule you can never be wrong. Best Charles

Charles
connect your XVX to the 8 ohm taps and you will get a much better sound, don't be afraid, you won't spoil anything. 1.25 will be slightly warmer, it will work for the next 50 years

Greg, This topic comes up about once a year. Do you own Mac amps? Could you state your signature? I'm bad about not doing so but will state mine below. I appreciate your comment but it is incorrect.

Creating an impedance mismatch in order to obtain better sound over stresses the amp. It can result in fat bass and this can "warm" up the sound. My sound doesn't need it.

I will give an example. Once I owned a Thiel CS5i. This speaker had an essentially resistive impedance of 2 ohm. I used a Mac 2600 stereo power amp. It was a monster amp designed by Sidney Corderman.

When running the CS5i off the 8 ohm tap the bass was fat. I eventually used the 2 ohm tap but later on went to a Krell FPB 700.

Anytime this topic come up folks chime in stating their belief in creating impedance mismatches for Mac amps. My suggestion is that if you desire the most balanced best overall sound, follow my rule.

Best

Charles

____________________
Charles Updated System: Wilson McIntosh Audioquest
Most recent updates: AQ Diamond USB replaces AQ Coffee; Wilson Audio Specialties Alexx replaced by Wilson Audio Specialties XVX Chronosonic; new subwoofer crossover; new Galaxy Grey Thors Hammer; Wilson Pedestals
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Preamp and DAC: McIntosh D1100
Sources: McIntosh MCD1100 SACD player, MVP881 BR player, MVP851 DVD player, MR87 tuner, Marantz 510LV Laser Disc player, ASUS laptop USB (JRiver Media Center 23)
Speakers: Wilson Audio Specialties XVX Chronosonic
Sub-woofer: Wilson Audio Specialties Thor’s Hammer (1) horizontal lie and Wilson Watch Controller (abbr: WC)
Cables main system: Audioquest Wel Signature speaker cables and balanced IC (preamp to amps); Wel Signature AES/EBU balanced digital IC for CD playback; Audioquest Diamond optical (1) for tuner, (1) for BR player, and (1) for LD player for total of (3); Diamond USB cable; McIntosh MCT cable for SACD playback; Dragon power cords (5 HC cords and 3 source cords for total of 8); Thunder HC power cord for tuner; cables for DVD player not listed
Cables subwoofer system: Audioquest Redwood speaker cable (1); Wolf balanced subwoofer IC from WC to amp; Wind balanced IC from preamp to WC; Hurricane HC (2) and Dragon HC (1) power cords
Power conditioners: Audioquest Niagara 7000 (1) and Niagara 5000 (3); (4) dedicated 20-amp lines with no. 10 wire straight out of fuse box
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Room (mancave): 40’L x 15.5’W A-frame; max ceiling height 8’ min 5’; wall within wall construction built of 2 x 6’s; built over garage with custom hardwood floor with gym seal with over 40 Lowes stiffened wooden I-beams supporting floor; complete isolation from rest of house.

My JBL L100 Classics are rated at 4 ohms. The sound is much, much better on the 8 ohm taps of my MA6600 integrated and that is where they stayed. In the 5 months since, the amp is not running any warmer, especially at the lower volume I listen to. When I spoke to McIntosh they told me not to overthink it and use whatever taps sounded better to my ears.

One consideration I thought I’d mention. When you are comparing taps, remember that the as you go from 8, to 4, to 2 ohms, the gain of the amp is dropping 3 dB each tap change. So you have to increase your preamp’s gain by an equal amount to create a fair comparison.

The easiest way to do this is with a test tone or pink noise and an spl meter placed close to one speaker.

If you don’t do this, the higher impedance taps will always sound better because they will be louder.

What Tom said.

In any equipment comparison, the easiest way to fool yourself is to not insure you are listening at equal sound pressure levels. Loudest (almost) always wins otherwise.

Charles

I have mc1.25kw, I play Kef Blade. Before that, I had the WA Alexia V2. Playing on 8 ohm taps has better drive, space, bass goes lower and is better controlled. give it a try, it's free. 3 minutes of work. You will be able to describe your experience, rather than sticking to the rules. You're probably missing out on better sound. You have it at your fingertips.

Stereo, I am happy for you that you are achieving a better sound. Mac has increased the ability of its amps to deliver current so that with a modern Mac amp you can get away with an impedance mismatch. I think the key for you is that you amp is only warm. Rules are made to be broken. But if you used a larger Mac amp at the correct impedance you would achieve a similar or better result. The impedance mismatch mainly affects the bass and this affects the perception of the overall sound. I don't recommend it.

Best

Charles

p.s. When you ask Mac, that's their stock answer.

Greg, I am happy for you that the impedance mismatch is working for you. I assume you are using the 8 ohm tap. The Blade has a nominal impedance of 4 ohm and a minimal of 3.2 so there's not much stress on the 1.25, about the same amount as with my XVX running off the 4 ohm tap with minimum impedance of 1.6 ohm.

You went from an Alexia V2 to a Blade. That's a big step down in price but apparently to you not in sound quality. Did you run your Alexia off the 8 ohm tap?

Best

Charles

I run Blades on 2 MC611 using the 4 Ohm tap.

The manual is quite clear on that "If the Loudspeaker’s impedance is in-between the available connections, use the nearest lower impedance connection." and "For the best performance and safety it is important to always match the impedance of the Loudspeaker to the Power Amplifier connections.".

I agree. However, for a 6 ohm nominal impedance modern Mac amps have plenty of current to run off the 8 ohm tap. You can't go wrong following the OM. The multiple taps allow you to have a non stressed cool running amp. Match the nominal impedance to the nearest tap or follow my previously stated rule and you will never be incorrect.:yes:

Best

Charles

I was under the impression that the output transformer protected the output device (SS or tube) by providing a constant load regardless of the output tap used.

Mike S.

I think load is related to power or current. When the current becomes excessive for the transistors, Mac has a Sentry Monitor circuit. In a short circuit the impedance approaches zero requiring the amp to produce tremendous current. A speaker like a Thiel CS5i requires an amp like a Dag that is built off a 2 ohm tap so that it can efficiently (without stress) supply the current and watts. In my opinion, Mac amps should not be used with speakers with a nominal impedance below 3 ohms. Mac amps have tremendous advantages in that when the impedance drops below the nominal impedance they can sound very dynamic and have more bass. What creating a deliberate impedance mismatch does is carry a good thing to an extreme.:yes:

Best

Charles

As much as I respect Charles and his opinion, I still believe that McIntosh gave me the correct answer that to use whatever tap sounds best and to not overthink it. Shouldn’t the people that build the amps know best?

McIntosh amp taps vs current
 

It does. Every active amplifying device, tube or transistor, has a safe operating area, or SOA. The McIntosh autoformers allow the output transistors to always run inside their safe operating area by matching the speaker load to the amplifier.

Also, every amplifying device has an optimum linear operation point, allowing for the lowest distortion with the least amount of negative feedback and generating the least amount of heat.

Autoformers allow the output devices to run in their most linear range.

It's interesting to read some on the technical side of this issue, but I have had similar situations with Klipsch speakers (impedance varies with frequency, from just below 4 ohm on the lows to 12ish on the highs). I wondered and asked this question years ago, and got an answer one a Mac related forum that either 4 or 8 was OK, whatever sounded best, but it was the 8 ohm taps that sounded "proper". "Balanced". The 4 ohm was bloated in comparison - this on properly operating MC30 and MC250. It seemed pretty obvious that the 4 ohm was definitely "off". in terms of sonics.

Look at a MC 7300 owners manual. In the back they show how a 7300 can drive a 2 ohm load from the 8 ohm tap putting out more than 800 watts a channel. If you will look at a Stereo phile review of a MC 501 you will see how well a MC 501 drives a 4 ohm load from the 8 ohm tap putting out close to 800 watts still meeting specs. So I would not worry about you driving a low impedance from the 8 ohm tap of your 600 watt Mac amp. One of the British magazines tested a 611 and put out close to 960 watt peaks across 8 ohms. So there is plenty of current there so you don't have to worry. Now crossovers can compromise woofer capabilities and this may be why you are wanting more from your Mac amps. All I can say make the speaker lines large and short as possible and make sure you have 20 amp 120 volt AC circuit feeding each amp separately.

All speakers have dynamic limits and after reaching that level the speakers compress the sound not matter how much power you have available.