Hey All,
I have a customer with an old McIntosh tube integrated amplifier, wanting to power several pairs of speakers (some in-wall, some bookshelf). He also wants volume controls in each area. I've used autoformers with impedance matching on the solid state gear in the past, but this will be my first "tube job".
I've seen some "audiophile" grade controls from Phoenix Gold, loaded with resistors, instead of autoformers, and was wondering if these would be a better choice.

What do you think?
Thanks for the help.
Scott

Personally I wouldn't use a tube amp for that application. Just too much potential unreliability. As for the PG resistor VCs I tried them several years back. They definately sounded better but they get hot in the wall and the volume switch itself was cheap and noisy. I never used them again.

The Niles MSA10 will give you the best sound.

Marc

[Link: nilesaudio.com]

uh yeah I would like to pull my 50ft Bertram with my Porsche 911, can you hook that up for me?

"uh yeah..."
That's real helpful mr2channel.

Marc, thanks, I was thinking about the same device. I used one once about 10 years ago, and I remember that thing maintained an 8 ohm load to the amp even when one speaker out of about 8 pairs was dead shorted.

well I appologize for the sarcasm, but the question I would be asking myself is , is this really the right product for the application at hand? well I would have to say not really. if he has enough $$ for MCIntosh tube gear (regardless of how old, or when he got it) then he at least knows the difference between crap and nice gear and if you explained to him that he would be much better off with a solid state amp then he will most likely listen to you.

I understand.
I've been thinking about suggesting using the McIntosh with a nice pair of bookshelf speakers in one area, and simultaneously feeding a solid state amp to power the speakers in the rest of the house.

I guess I could have figured this out myself, but tube amps, even as old as this one is, are a new subject for me. I was thinking that there might be some other considerations, besides the age of the amp. I vaguely remember reading a speaker selector manual once :) and mention of floating grounds or some such relating to tube amps. Didn't apply then, or since, so I figured I'd ask the "knowledge bank" here.
Thanks.

First off, you'd grab at least a 100 watt/ch amp for running several zones. His Mac is likely 30 or 40 watts per ch and isn't adequate. And if by rare chance he has a Mac 275 (4 output tubes per chan) then it's nutso to use a smooth $7000 amp to run in-walls. Tell him to save it for a dedicated 2 channel room (perhaps the room where his nicest speakers are, or where he seriously listens) and add a bigger amp for the rest.

Amen, Tom. His Mac is built for high end, and probably high efficiency speakers. Totally wasted on D.A. 2 channel is GREAT and gives you the opportunity to install a "listening" room with proper acoustic treatment, additional speakers, etc. There is so much available for both analog and digital sources that you owe it to yourself to give him a demo of great music. I wish you the best!

Make the point to this guy that any sonic value he has in his tube integrated will be lost running it through volume controls. Better that he use the pre out on this unit to drive a separate amp to run the DA, and have a pair of dedicated speakers in the room with the amp for fine listening. This comes from someone who owns a couple of C-20's, a couple of MC-240's, an MC-30, MR-71, Marantz tube, etc, etc.

Isn't the MR-71 the FM tuner? Who needs one of those anymore? just kidding.

but you make a good point. If he really wants to use this for multiroom then use a NuVo or Russound basic keypad system and send the pre out lines to this amp in one room with a nice set of bookshelfs. He gets multi-room with basic keypad control, which sounds a hell of a lot better than any VC system, and still gets to use his amp.

It warms the corner of the room left after the preamp and two amps warm the other three.

yes, never have the t-stat in the same room as the hi-fi or the rest of your house will be rather chilly.

I went through hell and back to get an MR71 rebuilt for a client. Parts were no longer available so it had to be modicated by one of the original engineers.

It was worth every penny. I wish modern FM tuners had a 1/10 of the ability to pull in stations the way the old ones could.

I used to be part owner of a retail stereo store in the northwest suburbs of Chicago, and would display my old tube stuff for yucks. One day a guy dropped by, killing a few minutes before he picked up his kid at the day care next door. He eyed my MR-71 at length, and then opined "Thats a nice tuner." I thanked him, and we started chatting about FM tuning in general. He let slip that he built FM tuners, so I asked which one? "The Day-Sequerra; you probably haven't heard of it." I about fell over, not knowing that the Sequerra tuner was built in my little 'ol town.

The basic idea of a bulletproof transistor amp is that it puts out a clean signal up to a particular voltage, and the amount of current that comes out of it depends on the impedance of the load. An ideal (i.e. bulletproof) transistor amp will have the same sonic characteristics with a 4 ohm load as with an 8 ohm load. In the real world, hardly anyone spends the money any more to build a transistor (IC, actually, usually) amp where the voltage doesn't drop when you go from 8 ohms to 4 ohms, but the sound is still the same if not driven to the point of distortion. You won't be able to tell that because the speakers won't sound the same, but the response of the amp won't change, or will change infinitesimally.

With a tube amp, there are different taps for different speaker impedances because the output transformer and the speaker have to be of particular impedances for the tubes to perform properly. There is also a connection between the proper impedance being chosen and the proper amount of distortion-lessening negative feedback being sent back to the input stages.

The extreme proof of all this is that you can run a transistor amp with no speaker connected and it will be just fine, but if you try that with a tube amp you just might literally see sparks inside of the output tubes.

The amp might actually sound different when changing from 8 ohm to 4 ohm speakers; it's hard to tell because the speakers will sound different. But this necessity for matching so the tubes will operate properly means a tube amp is actually in danger if used in a multiroom scenario, unless used at very low volume. That CAN'T be what anyone has in mind!