Use one big amp, or bridge two smaller ones?

[Dave D]

I am curious of what the advantages or disadvantages would be by each of theses scenarios:

1) a single MC 602 driving current hungry 4 ohm 95dB Legacy Focus 20/20
2) or bridging two MC 352s the drive these same speakers (or MC 402s)

Is there anything sonically given up by bridging? Is it better to run two separate amps, each having their own dedicated 20amp service over one big amp? Would the bridged 352s deliver equal or more current than a single 602?

BTW, are there any advantages the 402 has over the 352 other than the 50 extra watts of output and display lighting (and age)?

Amps in general, and in particular McIntosh amps, seem to make my head spin. It is tough to audition combinations, so I thought I would post here to see what people have found for themselves.

Thanks,

Dave

 

[ron-c]

When you get into the MC602, a pair of 501s, the MC1201 (and very much the MC207) we are talking about the supply of AC to the amp as far as power goes. More is beter. Dedicated lines are good. The MC352 and 402 will use up a 15 amp line and be happy. Two amps will need two lines.
How many watts are your speakers rated? Don't over power them.

Ron-C

 

[Dave D]

When you get into the MC602, a pair of 501s, the MC1201 (and very much the MC207) we are talking about the supply of AC to the amp as far as power goes. More is better. Dedicated lines are good. The MC352 and 402 will use up a 15 amp line and be happy. Two amps will need two lines.
How many watts are your speakers rated? Don't over power them.

Ron-C

Ron,

In your first sentence, do you mean that the wall outlet is essentially the limiting factor with the 602, 501, 2101, and 207?

Is it preferred to have a pair of 501s or a single 602, or for that matter a pair of 352/401s? One thing I am after is the answer to - "is there anything given up when you bridge a McIntosh amp?"

My speakers (Legacy Focus 20/20) have a recommended amplification of up to 400 watts as stated in their manual. However, their amps that are designed for these speakers put out 600 w/c, or if you have their monoblocs as I did, 1200 w/c. One big factor in this is the ability for the amp to deliver current. The Focus rated at 4 ohms does dip below 2 ohms. When I switched from the Legacy Monoblocs (1200w/c and 90 amps) to the 352, I heard some nice improvements in sound (more natural and relaxed), as well as bottom end tightness and punch.

Now, I am not necessarily about to change my amp(s) right away, but I am wondering what the next step would be (I am always planning ahead). One easy solution is another 352, and bridge them as monoblocs. For packaging/real estate considerations, the 602 would be nice...then there is the 501s as well. Perhaps...just perhaps...I am fine with what I have and no significant improvement would be realized by additional amplification.

No matter what though, each amp will have its own 20 amp circuit. That part is easier in my installation than most, and already in the works.

An easier decision is the processor (since you rep McIntosh, I am throwing this in), I plan on demoing the MX119 as soon as I am home for more than just a couple of days.

Thanks,

Dave

 

[ron-c]

Dave,

In the case of the MC352 and MC402, these amp have two identical amps per channel where each handles one half the waveform and they are combined in the output autoformer. The MC352 uses two 225 watt amps and the 402 two 250 watt amps per channel. In mono these amps parallel the outputs of both the left and right channels. They do not bridge.
Speaker manufacturers usually put a power rating on their speakers which reflect long term use without failure. Crossover components as well as the individual speaker drivers have power and thermal limits. As we increase the power these components heat up, their resistance rises and the increased power is burned off as heat. Since the power is turned to heat, not sound, this is called thermal compression.
For any speaker you need to supply enough watts where the speaker is normal on loud passages but does not enter the thermal compression stage which will cause a collapse of dynamic range.
The amps ability to 'control' the speaker or make the drivers start and stop as rapidly as the music waveform is related to amp power, the speed and size of the power supply section, the use of capacitors with rapid charge and discharge characteristics (ESR), etc. Watts are important but not the only factor.
20 amp lines will allow these amps to deliver all they can. On peaks the MC352 and 402 will deliver power far in excess of their rating.
The MX119 will allow great two channel or multi-channel performance. I like mine a lot.
Ron-C

 

[Cleve]

A question remains - assuming that sufficient electrical power is a given, I've always heard that an amp bridged to mono doesn't sound as good as if left in stereo mode.

In other words, if you took two MC2225s and bridged them to mono (500 watts x 2), they wouldn't sound as "good" as a Mc2500 (500 watts per channel)?

Is that true? At one point, a gentleman on Ebay had several Mc7100's available for sale. I had considered buying two and bridging them to mono for a rated 300 watts per channel into 8 ohms. But the seller told me I'd be better off looking at a 2205 or 2255 since they'd sound and perform 'better' than the two smaller amps bridged to mono.

 

[ron-c]

Cleve,

Bridging an amp usually results in an increase in noise and distortion. Many 'balanced' amps are bridged if you look at their schematic. The new 'Quad Balanced" design of the big Mc amps, MC1201, 352, 602, 501, MC1000, and MC402 only will work with the output autoformer. With the autoformer the noise (-124 Db) goes down not up.
On the older McIntosh amps bridging will have all the normal drawbacks. Many McIntosh amps can have the outputs run parallel mono which will not cause an increase in noise and distortion but will drop the impedance taps to half their normal value. The MC252 can be run both ways bridged or parallel and is unique so it will deliver 500 watts into 1,2,4,8,or 16 ohms.
If you bridge a direct coupled amp like the MC7100 it will see a eight ohm speaker as a four ohm load so low impedance speakers are out. Depends on your speaks I guess.
The MC2255 and MC500 should sound very similar as they are of the same design vintage.

Ron-C

 

[Dave D]

So Ron, Your initial response seems to indicate that the 352 that I have is enough and that using two might not yield much improvement, and may even stress the speaker's electronics over the long term. Is this an accurate summary?

It is interesting that your comment to Cleve mentions that noise goes down with your big amps.

Thank you for your detailed answers to all my inquiries. I very much appreciate it. I am quite convinced now that I need to be told what to try by someone (like you) who knows the details of how and why things work.

I am really impressed with the 352 and just want more. Hey, what can I say, I'm American, I always want more of a good thing...AND, bigger really is better! Ever seen the trees in Northern California? That shut my British friends up and solidified their "everything is bigger and better in America" philosophy. (BTW, they think the redwoods are fake - and we also faked the lunar landing...that's all Hollywood).


Dave

 

[Dave D]

In the various amp's specifications, there are different signal-to-noise ratios depending on using the balanced or the single-ended inputs. Does this mean that there is an advantage in the amplifier to using the balanced inputs?

Also, something I noticed over the weekend was that when playing at higher levels the backlighting to the meters seems to pulse when big demands are placed on the amp. Could this mean I am stressing the system in any way, or reaching the amps current delivery limit? It was faint pulsing, and it sounded great, with no protective circuit lights lighting.

I also noticed one channel seems to read a higher wattage number than the other (not a big deal to me). When I saw this, I shut everything down and switched the inputs. There was still a difference, but not as much. It sounded fine and the soundstage seemed correctly centered so I chalked it up to just two different meters or demands on the channels.

Dave

 

[ron-c]

Dave,

If the meters dim to the beat of the music your AC power is also dropping to the beat. The meter lamps are on a regulator but it can not make up for voltage dropping below 100 volts. Know any electricians?
The meters read everything connected to the amp which means the speakers and cables. On the big amps the meters look at current AND voltage. If you push on a woofer cone with the sound muted you will see the meeter move. Cool.

Ron-C

 

[Cleve]

Dave,

If the meters dim to the beat of the music your AC power is also dropping to the beat. The meter lamps are on a regulator but it can not make up for voltage dropping below 100 volts. Know any electricians?
The meters read everything connected to the amp which means the speakers and cables. On the big amps the meters look at current AND voltage. If you push on a woofer cone with the sound muted you will see the meeter move. Cool.

Ron-C

My 2205's meters dim also on drum and bass beats > 100 watts /channel. All of my gear is on the same breaker... does this actually mean I need MORE current?? It's only 200 watts per channel!

 

[Dave D]

Ron,

How would an electrician fix this?

The amp is already on a dedicated 20 amp circuit using 10 gauge wire.

 

[ron-c]

Put a voltmeter on the AC line and watch it. You may have a 20 amp line but the feed to your box has issues or the transformer on the pole, etc. Let us know what the voltage measures.

Ron

 

[Dave D]

I doubt I'll get to it today, and I am leaving for AL until Sat. I'd also like to hear Cleve's results.

How bittersweat is this?

Thanks yet again Ron!

 

[Dave D]

I measure 124Volts with no music playing. Do I need to crank it up and see what happens?

 

[ron-c]

Yep, play it so the meters are diming and see what the voltage is.

Ron-C

 

[Dave D]

When I first noticed this "dimming," I was playing the Burmester CD III, track 10, “Poem of Chinese Drums.” There is very big bass extension in this piece.

My outlet is in a location that is not in front of the amp, so I cannot look at the amp and the voltmeter at the same time. Furthermore, I measured from the unused outlet on the circuit that the amp is plugged into (right next to where the amp is physically plugged in). Also, I am currently using the stock power cord and a Shunyata Hydra 2.

So, while playing this track again, I watched my little voltmeter. Statically it reads 123.9-124, as I mentioned before. Dynamically (music playing) it would dip to maybe 121...I think. It definitely never got to 120 or below. It hovered more in the region of 123-122. The best I could do is watch for the last two whole number digits to change.

Now what?

Dave

 

[ron-c]

Dave,

With the 352 on the lights dim as the power supply is being pulled down faster than it can recover. I would not worry too much. Are you on the 4 ohm taps? Your speakers probably dip way down on bass transients which uses up the power supply amps.
Maintaining close to 120 volts is good enough.

Ron-C

 

[Dave D]

Yes, I am on the 4 ohm taps. I know the speakers do have a couple of below 2 ohm dips in the bass region. I have also heard of people using the 2 ohm taps for the bottom end of the Focus when bi-amping. I don't know enough to feel confident doing that sort of thing though.

BTW, the sound coming out of my speakers when all this is happening is EXTREMELY powerful. Feeling it in your chest does quite describe it. It is very impressive to me anyway. I have no complaints at all.

Yet one more thing, if I were to use a 252 for my center channel, would you recommend using both channels and bi-amping it, or "bridging" it and using it as a single monoblock?

Thanks again Ron for this Amplifier 101 course you are giving me.

Dave

 

[ron-c]

If you are going to use 500 watts on the center you may just want to buy the MC501 rather than the MC252. Which center channel speaker are you using and how many watts is it rated?

Thanks,
Ron

 

[arebalos]

Dave D
My five cents here. I have a 602 and 252 passive bi amping a pair of LS360. 602 for bass and the 252 for mid/highs.
It is the better sounding rig I had in my life. :yes:
best regards