5196106163

*

Just in case this was due to the con-tinuous test signals, wc tried doing tone-burst tcsts at 10kHz with the same 24:1 duty cycle as for the IHF dynamie head-room test. The results were virtually identical.

So it would appear that the Carvers don’t have a fiat power response — at least for continuous testing. This may not necessarily cause problems in prac-tice, as typical musical materiał doesn’t have much of its energy in the high fre-quencies. But when the Carvers are called upon to produce fuli rated output with musical signals, it’s possible that the materiał above 3kHz could amount to over 20W.

The normal frcquency response for both models was excellent, at 6Hz — 70kHz between -3dB points. Hum and noise were also quite Iow: the PM-175 gave approximately 98dB below 200W output into 8 ohms.

The channel crosstalk figures we ob-tained were all better than -60dB for both models, even at Iow and high fre-quencies. This shows how good the error correction circuitry must be in the two stereo channels.

An interesting result was produced when we did the standard IHF tests for dynamie headroom: the ability to produce higher instantaneous power for short peaks, than for continuous opera-tion. Here we discovcred that both models produced a figurę of virtually OdB — the output power available for peaks is the same as that for continuous operation!

Actually that’s hardly surprising, when you consider the way the Carvers operate. Essentially, they’re always capable of producing their peak output — on a continuous basis if required, not just in short bursts.

There were only a couple of other points we noted, both relativcly minor but interesting. One was that when tak-ing THD measurements below 800Hz, the distortion meter needle would “hunt" over a smali rangę, and the scope showed a slow beat component present in the residual signal. WeTe only talking about a Iow lcvel — vary-ing from typically .01% to .025% effec-tive THD — but it was noticeable on the instruments, for both models We suspect this is due again to some Iow level commutation effect.

The other point was that in the PM-350, the speed of the cooling fan varies according to the signal !evel. For smali signals it runs slowly, while for large signals it speeds up. This is quite appro-priate, of course, considering the way that the Carvers only draw and dissipatc power when they need it. Presumably it’s achieved automatically by running the fan motor from the commutated power raił.

In our listening tests, which were ad-mittedly a little limited due to lack of time and appropriate facilities, the Carvcrs sounded fairly clean. We couldn’t actually detect any adverse ef-fects attributable to the suspected commutation phenomena, suggesting that they may not to be a problem in real-world applications.

To summarise, then, the Carver PM-175 and PM-350 are very innovative am-plifiers. They certainly deliver a lot of power relative to their modest size, and seem very well suited for applications such as sound reinforcement, stage and PA work. But those residual commutation effects at higher frequencies seem likely to limit their appeal in the most demanding of hi-fi applications.

Recommended retail prices for the PM-175 and PM-350 are $2390 and $2850 respectively. Further details on these and the other Carver products are available from distributors the Odyl Group, 112 James Street, Templestowe 3106. (J.R./R.E.)    <D

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13

ELECTRONICS Australia, September 1987