Amp output to 2 speakers

I would try using just one speaker first. It just might sound better...
Otherwise, do some homework on wiring in series or parallel.

DB, both amps provide three channels of amplification, and the dual sets of output terminals that are provided for each channel of the Amp 3 are undoubtedly just wired directly together inside the amp. So you have not been biamping the R107/2's (i.e., driving highs and lows from separate amplifiers or separate amplifier channels), you were just biwiring them, with the added convenience provided by the second set of terminals.

What you have been doing with the R102's is driving them in parallel, from a single amplifier channel. The amp was therefore seeing their individual 4 ohm impedances combined into an overall load of 2 ohms. Driving 2 ohms is asking a lot from an amp, especially one that, like the AMP 3, does not have a 2 ohm rating, and is not rated to deliver twice as much power into 4 ohms as into 8 ohms (the ratings being 250W and 150W respectively). I would think that the reason the amp stayed out of trouble was probably that the volume levels you were using on the R102's were modest.

I suspect that the HPA 3, being more powerful than the AMP 3 and being rated to double power into 4 ohms (500W) relative to 8 ohms (250W), will do at least as well and probably better than the AMP 3 into the two parallel-connected R102's. If you do encounter any problems, though, try connecting them in series, which would result in the amp seeing an 8 ohm load. Connecting speakers in series is probably a reasonable thing to do in situations where the two speakers are identical, although I would expect the existing parallel connection to be preferable provided that the amp can handle it.

Regards,
-- Al

Almarg,

I bought my original PAV and Amp 2 about 20 years ago, and hadn't looked at a manual for the amps since. I now have three Amp 2s and an Amp 3, a PAV, and a PAV/PDSD. Rereading an amp manual informs me that you are correct. The two pair of binding posts for each channel are to facilitate biwiring.

You wrote: "Connecting speakers in series is probably a reasonable thing to do in situations where the two speakers are identical, although I would expect the existing parallel connection to be preferable provided that the amp can handle it." Why is a parallel connection preferable? I ask because I can change the connection to serial. The Amp 3 is only mildly warm to the touch even after hours of use -- you can leave your hand flat on the top of the unit comfortably.

I appreciate your advice, and especially want to know if it's OK to continue using a parallel connection or if I am unduly stressing the amp.

db

Why is a parallel connection preferable?

1)Overall sensitivity and maximum overall volume will be approximately 6 db less for a series configuration than for a parallel configuration. 6 db corresponds to a factor of 4 difference in power delivery.

2)No two speakers will have electrical characteristics that are perfectly identical. To the extent that those characteristics differ, sonics will be adversely affected in a series configuration. For example, if the variation of impedance as a function of frequency is slightly different for the two speakers, the frequency response flatness of both speakers will be affected. Obtaining good results from a series configuration is premised on an equal division between the speakers of the voltage being put out by the amplifier, at all frequencies. An equal division will not occur to the extent that there are differences between the two speakers in how their impedance varies as a function of frequency.

3)In a series configuration, each speaker might reasonably be considered to be part of the cabling connecting the other speaker to the amplifier. From a philosophical standpoint, it would seem expectable that a speaker would not be an ideal choice for use as a speaker cable, although the reasons may not be fully explainable from a technical standpoint.

I appreciate your advice, and especially want to know if it's OK to continue using a parallel connection or if I am unduly stressing the amp.

As I indicated, the HPA 3 would seem likely to be able to handle the parallel-connected speakers better than the AMP 3. And that in turn has done well with them, without ever getting more than mildly warm as you've now indicated. So everything seems to point to there not being a problem.

Regards,
-- Al

Thanks, Al. I think I'll stick with the parallel connection. I've been using that now for at least a couple of years without getting the amp very warm. The sound of the center channel is excellent for voices (DirecTV and movies) and 5.1 music SACDs and operas on Blu-ray. The little KEF 102s are excellent speakers and their tweeters match well those of the 107/2s.

That raises the question of how to connect the 2 channel unbalanced 102 KUBE (active equalizer) -- the 107/2s areusing a 107/2 KUBE. I could split the long balanced cable from the Cary Cinema 11a to two Jensen ISO MAX transformers, go through both channels of the KUBE, then convert to a single input to the amp. Or I could take the balanced cable to a single ISO MAX, split its output to go through the 2 channel KUBE, then recombine for the single input to the amp. Any suggestions?

db

I don't understand the references to splitting and combining. If I interpret correctly that you are addressing insertion of a KUBE into the signal path to the single amp channel that is driving the paralleled R102's, just use one channel of the KUBE and leave the other unconnected. Convert balanced to unbalanced at its input with one single-channel Jensen transformer, in the same manner you successfully used for each of the main channels as discussed in this thread.

Regards,
-- Al

Thanks, Al. I'll buy another ISO MAX PI XR to convert XLR to RCA, take the RCA through the 102 KUBE followed by a short RCA-XLR cable to the amp. I'll also change out the RCA cables between the 107/2 KUBE and the amps for RCA-XLR cables, according to your post at the earlier thread.

PS: I emailed my audiophile friends about the problem, and included your suggestions. The most knowledgable of them wrote back that your advice has always been good.

db

Sounds good! And thanks for the feedback.

Regarding the RCA-to-XLR cables, be sure to note that per Figure 2.1 of the Jensen paper I referenced in the earlier thread the cable should be two-conductor shielded (which is what is generally used in XLR-to-XLR cables), not coaxial (which is used in many RCA-to-RCA cables), with the connections at each end as shown in the figure.

Best regards,
-- Al

The system can generate such a strong centered image in stereo I've found myself putting ear to center channel to confirm I'm listening to stereo. So I decided to try 4.1 rather than 5.1 by setting the menus of the Oppo 95 and Cary Cinema 11a to turn off the center channel. (The Oppo output is analog but the DirecTV HD-DVR is HDMI.) 4.1 seems entirely satisfactory, so I suppose the issue of two speakers with one amp could go away. For the time being, I'll leave the dormant center channel in place. I assume without a signal, the 2 ohm load is moot. Is that true?

db

I assume without a signal, the 2 ohm load is moot. Is that true?

Yes, that is true.

Best regards,
-- Al