Ohms, my - help me understand


Apologies if following questions are dumb but some of this stuff is befuddling to me:

Just bought a pair of used Thiel CS2s, after auditioning with my Arcam Alpha 8 integrated. At home I had paired it with an Arcam Alpha 8 power amp to bi-amp B&W DM601 S2s.

Both amps are 50 watt amps at 8 ohms for two channels, 100 watts at 4 ohms single channel.

The Thiels, according to online reviews, are 6 ohm speakers that can handle 40 to 250 watts.

I had read Thiels were hard to drive so I was worred. But Larry at Hollywood Sounds said my amp would work fine and it did. They sounded terrific in his shop with just the integrated and even better at home, much richer and more detailed than the little B&Ws. It is true that expose bad recordings, particularly on CD, but the upside is spectacular). The Thiels have single binding posts so at home, I am now using the intergrated as a pre-amp, with the power amp running the speakers.

So here are the questions:

* How many watts are my amps producing with these Thiels. Is is as simple as splitting the difference between 8 and 4 ohm output, meaning 75 watts?
* The power amp can be turned into a monobloc, but the integrated can't so am I correct in presuming with single speaker posts that running one amp to each speaker is out?
* If I picked up a matching power amp, could I use the integrated as a pre-amp for both or would I need to buy a whole new preamp? The integrated has only on set of pre-amp input jacks.
* If I had matching Alpha 8 power amps to run each speaker, how many watts would be going to Thiels? 125?


As you can see, this is all about increasing power. I am thrilled with results in new set-up but from all I have read about Thiels, it makes me wonder what they would sound like with more juice. I don't have the budget to simply swap out whole system but wondering if a second power amp would be worth the bang for the buck.
maverick18
* How many watts are my amps producing with these Thiels. Is is as simple as splitting the difference between 8 and 4 ohm output, meaning 75 watts?

Yes, the rating would be 75 W/ch into 6 ohm based on the specs.

* The power amp can be turned into a monobloc, but the integrated can't so am I correct in presuming with single speaker posts that running one amp to each speaker is out?

You can run two separate monoblocs, one to each speaker rather than a single stereo amp if you want, but you should use two matching monoblocs for good results. Only stereo amps designed to be used alternately as a monobloc amp should be used.

* If I picked up a matching power amp, could I use the
integrated as a pre-amp for both or would I need to buy a whole new preamp? The integrated has only on set of pre-amp input jacks.

In general, you should be able to use any two matching mono power amps with any stereo pre-amp having pre-amp OUT jacks, not input jacks, as long as you have the proper interconnects (RCA connectors or balanced connectors are the most common). Of course the resulting sound will vary depending on exactly what components are used together.

* If I had matching Alpha 8 power amps to run each speaker, how many watts would be going to Thiels? 125?

You should only use one amp per speaker unless the speaker supports bi-amping in which case it would have more than two terminals. Bi-amping generally means that one amp is used to drive the woofer and a separate amp is used to drive the tweeter.
The speakers actually use only what the music demands.
Thus playing a solo acoustic guitar at low levels the actual power being used may be under 1 watt.
If you are playing a rock concert at 110DB your amp is not enough.
The 'recommended' power given to speaker specs is for average use.
It would be 67W. not 75W into 6 ohms but the impedance varies with frequency so that is just an average.

If you are sticking with what you have why not run them from the integrated and sell the power amp and the interconnects.
An amplifier like this would be very nice to replace your Arcam amp, and it's not that expensive: http://www.audiogon.com/cgi-bin/cls.pl?ampstran&1256985387&/Musical-Fidelity-A308CR-dual-m
You could actually use more power than this if you have the money. This works very well with the Thiel's: http://www.audiogon.com/cgi-bin/cls.pl?intatran&1257285399&/Musical-Fidelity---KW500---tra

This way you could sell your integrated and amplifier, the connecting interconnects and one power cord to help pay for it.
You have to remember the 6 ohm rating is an AVERAGE. at some lower frequencies, it may drop to 4 or 3 ohms... and may be 8 ohms at some higher frequencies.. (I don't know exactly what the Thiel's impendance curve is but many speakers exhibit a curve of sorts that varies with frequency and then some speakers are designed with a fairly flat impendance curve).
The Thiel CS 2's were rated as being 6 Ohms nominal, 5 Ohms minimum. Steady impedance characteristics are one of the Thiel hallmarks. The CS 2's might be the easiest of all Thiels to drive. I used them for 18 years. On the other hand the, the ported low end can be a be a bit soft and the upper end can be unforgiving. These speakers beneift from the proverbial "iron fist in a velvet glove" amplifier. Thiel recommended 50-250 Watts per channel into an 8 Ohm load that could double down into 4 Ohms. I'd suggest a minimum of 200 Watts into 4 Ohms and double that to get the most out of them.Just make sure they're high quality Watts. In as much I usually subscribe to the idea that ones speakers should usually cost more than ones amp, the Thiels (especially used) offer such value that coupled with their transparency the argument to spend more on the amp can be easily justified. I'd suggest amps such as the; Krell KSA 250, Threshold S 500 II and the conrad-johnson MF 2500A. A tube pre, isn't a bad idea either.
Thanks for responses! The message seems to be I need more power.

Herman: Good idea. I'm probably not gaining much of anything with the power amp since I don't have biamping options with the Thiels.

I'll think about an amp upgrade down the road a bit because for the moment, I've worn out the wife's goodwill. The Musical Fidelty option sounds like a good one but rich for my current budget.

Unsound, thanks for advice. I've auditioned a lot of speakers, new and used from $400 to $2500, over the last couple of years and I agree these Thiels seemed like a terrific value for the money ($450 in 8/10 shape). Maybe it's just because they're new (to me at least) but they've been a tremendous upgrade from the small B&Ws. At the volume levels I use, which are modest, the Arcam seems to handle whatever they're demanding.

The bass is tight but evident enough, maybe because they're close to wall. I did find that a few old and cheap CDs sounded thin but so far only discovered a handful of those and records sing. I will definitely be keeping them for quite awhile.
When the time comes, let us know what your budget is. Please understand that Thiels require quality first and extra power second. While Thiels will work with modest amps, they really benefit from a quality amplifier and a quality high powered amp even more so.
Unsound: you are probably right about Theil's impedance.. I could not remember theirs in particular but it sounds like they are one of the companies that try to provide fairly flat impendance curves.. yes from what I remember they require high quality amps with good current dumping and dampning factor... I remember hearing the bigger ones years ago and enjoyed them.
I just looked up the 'road test' of the CS2 and indeed, the impedance is a fairly mellow line.
NO phase data provided, but the test remarks opin'd that they are indeed a fairly easy load.
Again, however, when dealing with speakers at this level, better amps produce better results power / listening levels considered.