RF-7 and Amplification Exposed

[PrestonTom]

" ..............

but what specific quality makes one amp able to handle the impedance dip on an RF-7 better than another amp. ......."

One spec that is being left out of this discussion is the amplifier's ability to deliver sufficient amounts of current (amperage) for peak levels (short durations). There is not a standard measure to describe this, although many manufacturers call their amps "high current" and may even indicate how many amps can be delivered for a short period of time. However, the "duration" will typically not be defined and it will also differ across manufacturers. I don't believe this problem (lack of a standard spec) has yet been been resolved.

Two things you can look for are 1) do they list any measure of how maximum amperage can be delivered, and 2) does the spec for wattage approximately double when it is listed for "4 ohms" compared to "8 ohms". This second criteria; however, is not a foolproof way of determining whether an amp can deliever "lots of current". Home amps that typically can provide lots of current (for transient periods) include Adcom, Harman Kardon, the old Luxman, Crown, Parasound, Bryston, etc.

Good Luck,

-Tom

[Deang]

Isn't their a strong relationship between slew rate and transients?

It's a hard to imagine any solid state amp not being able to handle a 3.8 ohm dip in impedance. In fact, all the tube amps I've ever run, including zero feedback types -- didn't seem to have a problem with the RF-7 either. I'd tend to worry more about peaks and wild swings, and from that perspective the RF-7 isn't that bad.

[Deang]

"I bet in the end the higher powered amp is just simply a better amp and your not really using more the the 50 watter could provide if all other things in the both amps were equal."

This is what I think too. Most companies just build their bigger stuff better. You won't see a 50 wpc integrated as their flagship product, but their 300 wpc arc welder is packed with the best parts and the price tag typically reflects that. You have to move away from big name mass market stuff to get the highest quality in low to moderate power solid state: Blue Circle, YBA, Music Fidelity, Unison Research, Creek, etc. Maybe an exception would be the Crown D45 and D75A, Leo likes his D45 quite a bit.

[Duke Spinner]

Isn't their a strong relationship between slew rate and transients?

yes... there is ....

but any decent SS amp can deliver more than 30 microvolts/ per second ...

and ... that is the ..Delineator.., for Audio, anyway's

[stormin]

Home amps that typically can provide lots of current (for transient periods) include Adcom, Harman Kardon, the old Luxman, Crown, Parasound, Bryston, etc.

?[*-)]

[picky]

For the last 3 years I have powered my RF-7's with my Pioneer Elite VSX49TXi receiver, which Pioneer rates as 130 wpc into 8 ohms. This receiver, which weighs in at nearly 70 pounds, was Pioneer's top flagship offering when I purchased it. I consider it to be quality amplification. I can tell you that, despite being told by numerous people that I should have at least 200 wpc for RF-7's, at no time during the past three years has the sound from these RF-7's ever noticably suffered while powered by this receiver. We often play our music and DVDs at concert level. Using -10db as a volume control reference while playing the 'Master and Commander' DVD "Under Attack" chapter, our system consistanly achieves 123 db (C-weighted) measured at 12 feet from the front array with no noticable distortion. The 123 db is most-likely a sub bass transient because the overall sound does not seem that loud. If it did, I'd be turning it down!

Our room's response curve from the right channel RF-7 at one meter (measurement courtesy of Dr.Who):