MC225 hookup to Russound AB2.2 help

[Alfmonster]

Has anyone hooked up a MC225 or similar with the 4/8/16ohm taps to a Russound AB2.2?

I’m needing to power a 15ohm speaker and am not sure which tap to use when hooking up the MC225 to the Russound —
Any help would be greatly appreciated!

 

[whoaru99]

The Russound thing appears to be just a switch. Use whatever tap is right for the connected speaker(s). If you have a 15 ohm speaker the 16 ohm tap seems the logical choice.

What's the point of the switch though? Using two different amps with one pair of speakers or using two different speakers with one amp?

 

[Alfmonster]

The Russound thing appears to be just a switch. Use whatever tap is right for the connected speaker(s). If you have a 15 ohm speaker the 16 ohm tap seems the logical choice.

What's the point of the switch though? Using two different amps with one pair of speakers or using two different speakers with one amp?

Thank you so much! I’m looking to safely and transparently split the one speaker with a MAC4100.

 

[whoaru99]

Some tube amplifiers do not at all appreciate being operated without a load which could happen accidentally with a speaker/amplifier switch.

I would like to think McIntosh is robust in that regard, but I'm not familiar enough with McIntosh circuits to know for sure if it can be a problem or not. Hopefully a McIntosh expert can advise further.

 

[Alfmonster]

Some tube amplifiers do not at all appreciate being operated without a load which could happen accidentally with a speaker/amplifier switch.

I would like to think McIntosh is robust in that regard, but I'm not familiar enough with McIntosh circuits to know for sure if it can be a problem or not. Hopefully a McIntosh expert can advise further.

Ah yes, the 225 will be on its own power switch and off when I’m running the 4100 and vice versa unless I’m doing an AB test of something.

This should be okay?

 

[62caddy]

Ron-C just addressed this very question.

If a Mc Tube amp is on without a load no problem. If you are driving it with a full range signal as in bi-amping into a speaker's passive crossover the amp will survive BUT it will not be happy and the tubes will have a shortened life. Tube amps do not see passive speaker crossovers like a transistor [amp] so the best solution is to have an electronic crossover in front of the tube amp to limit the frequency response closer to that of the speaker's passive crossover.
Thanks,
Ron-C

 

[Alfmonster]

Ron-C just addressed this very question.

Ah yes, that’s what I figured. I got a little confused regarding the Bi-Amping part - is this referring to using the 225 as a mono block?

If a Mc Tube amp is on without a load no problem. If you are driving it with a full range signal as in bi-amping into a speaker's passive crossover the amp will survive BUT it will not be happy and the tubes will have a shortened life. Tube amps do not see passive speaker crossovers like a transistor map so the best solution is to have an electronic crossover in front of the tube amp to limit the frequency response closer to that of the speaker's passive crossover.
Thanks,
Ron-C

 

[62caddy]

Ah yes, that’s what I figured. I got a little confused regarding the Bi-Amping part - is this referring to using the 225 as a mono block?

The bi-amping part is irrelevant to the question of no-load condition which was the matter of concern. Should not make any difference whether operated in stereo or mono mode when the amplifier is operated without a load, ie speaker(s) connected. I would nevertheless shut down the tube amplifier that is not being used to save energy & tube life if nothing else.

The caution regarding bi amplification whereby the amplifier is used to drive one portion of the audio specturm doesn't come into play here unless that's what you're doing. This is a separate issue from the no load condition which according to Ron will not pose a problem.

 

[whoaru99]

He does say the amp will survive but will not be happy with no load. For me, that would be enough to dissuade me from live A/B switching, but it's your gear.

 

[SaturationPt]

In the case of most solid-state gear (without autoformers) you're somewhat protected against accidentally paralleling the amplifiers when powered down as they have a relay that disconnects the output terminals from the amplifier (when off). In the case of the McIntosh autoformer amplifiers OTOH, the output transformer is always connected to the speaker output terminals and forgetting or failing to disconnect properly from the McIntosh amp and driving it from the other amplifier will excite the output windings, what damage and even if it could cause damage to the Mc amplifier I do not know, but am not willing to find out.

I have played with the idea of putting a switch on my amplifiers as you're considering, but have decided that transferring the speaker cables leaves less opportunity for error. Your choice of course (the curse of being raised by a commercial Pilot).

 

[62caddy]

What I found particularly noteworthy is the warning not to use one of these tube amplifiers in passive bi-amp arrangement whereby the full audio spectrum is fed to only one section of the speaker's crossover.

This should be of particular concern since there are many who have (and who have suggested) using a tube amplifier power the Mid/High frequencies while using another amplifier (usually SS) to feed the LF section of the speaker.

According to Ron, this should only be done when the input to the amplifier is limited to the frequency portion it's expected to power - which would require the use of an (active) crossover.

As to no-load, I'm content to go with Ron's advice but I still would suggest shutting down the tube amplifier when not in use. In my own case when using a switcher, I realized I mistakenly thought I had the MC240 running the speakers during a listening session when in fact it was actually the MC2505 that was active and this was for over two hours. Needless to say I was terrified of the worst but was quickly relieved when the MC240 played perfectly once it was switched back to the speakers.

One may ask why did I leave the MC2505 powered up when I thought I was listening to the MC240? The answer is that I used the meters of the MC2505 to help monitor the output power being delivered by the MC240. This was possible by precisely matching the gains of the two amplifiers to produce the exact same loudness from each speaker when switching between the two amplifiers.

 

[62caddy]

He does say the amp will survive but will not be happy with no load. For me, that would be enough to dissuade me from live A/B switching, but it's your gear.

Not exactly. He says "If a Mc tube amp is on without a load no problem."

The time it's unhappy is when operated in the passive bi-amp situation described above.

 

[whoaru99]

Not exactly. He says "If a Mc tube amp is on without a load no problem."

The time it's unhappy is when operated in the passive bi-amp situation described above.

You're right, not exactly. But...

I read "On" with no load is one thing but playing a signal though the amp with no load is another and different.

The example using passive biamp means the amp effectively sees no load at certain frequencies. Ergo, it won't be happy with no load regardless of no load because of passive biamping or no load simply because there isn't one, when running a signal though it.

 

[62caddy]

You're right, not exactly. But...

I read "On" with no load is one thing but playing a signal though the amp with no load is another and different.

The example using passive biamp means the amp effectively sees no load at certain frequencies. Ergo, it won't be happy with no load regardless of no load because of passive biamping or no load simply because there isn't one, when running a signal though it.

Valid point. However I would think he would've made that distinction of on-no signal/on-with on + signal considering the length he went into about the passive crossover stuff. I'll have to look into this further to confirm but it doesn't seem that way from what he wrote...

In any case, my MC240 wasn't any the worse for wear when it was playing without a load for quite some time...

 

[whoaru99]

Valid point. However I would think he would've made that distinction of on-no signal/on-with on + signal considering the length he went into about the passive crossover stuff. I'll have to look into this further to confirm but it doesn't seem that way from what he wrote...

He did, IMO, in the context of the first sentence relative to the rest.

 

[dcgillespie]

If I can offer my 2 cents worth here, there are two conditions to consider:

1. Operation with no load under quiescent (no signal) conditions: In this scenario, the 225 is absolutely stable, with no tendency towards high or low frequency instability. In fact, the 225 is stable into any type of load (or no load) connected to it.

2. Operation with no load under dynamic (signal present) conditions: This is a very dangerous condition for amplifiers with high internal impedance and no or little NFB. Think guitar amplifier. With this type of amplifier, removing the load under dynamic conditions can allow the signal developed within the OPT to rise to very high (even clipping) levels, which can produce arcing within the output tubes and output transformer. The MC225 however has a very low internal impedance (for a tube amplifier), and employs global NFB along with the Unity Coupled Output Stage, so that there is very little change in output voltage whether the load is connected or not under dynamic conditions. What that means then is this:

If the Mac is playing along delivering a rather typical 5 watts of average power or so and the load is disconnected, no damage or harm will be done to the amplifier. In fact, as long as the power level is such that it is operating below maximum power output at all times, then removing the load won't do any damage. I'm hardly suggesting you do this, but saying that in those instances where it accidentally happens, then no worries. Now, if the amplifier is in a state of being over-driven and the load is removed, then all bets are off. Now the clipping events can cause huge back EMF levels to occur within the output transformer, with no load connected to absorb them. In this scenario then, the output tubes will likely arc, and likely even the best output transformer as well under this condition.

3. Operation partially loaded is the scenario presented when bi-amping with a full range signal presented to the amplifier, and the cross-over appearing at the speaker. If the amplifier is used (for example) to drive the mid and hi drivers, then because of the crossover, the amplifier will be unloaded at low frequencies since the impedance of the crossover will become very high at those frequencies. So, back to #2 again: If the amplifier is being driven within its normal power capability, then no damage will occur. But if the amplifier is driven such that LF signals would drive it into clipping, then potential damage can be done to the amplifier. This is why bi-amping should always be done with an active crossover before the amplifier. This will allow the mid and hi frequency drivers to be connected directly to the output of the amplifier so that it is always loaded, and no damage can occur from the possibility of being unloaded with large LF signals present.

Dave

 

[lordgarth]

As usual, excellent info from Dave.