High Current/Low Budget - Big Speakers/Little Understanding

[Guest159]

A commonly used indicator of a high current amplifier is one that has 50% or more power at 1/2 load ie:

200wpc@ 8 ohms/300wpc@ 4 ohms

Not high current:
200wpc @ 8 ohms /220wpc@ 4 ohms

I think this is a simplistic and wrong explanation. Those figures really only tell you what the limits of the power supply are and don't reflect the amps current delivery at 28 watts into 8 ohm. Perhaps that 15 volts into 4 ohm will deliver 45 or 50 watts because it's not challenging the limits if the power supply.

 

[Tedrick]

OP, you have an incredible pair of speakers that are deserving of the best upstream equipment you can afford. Please spend some time in the Infinity subforum. There is a huge collective of knowledge there that will help you immensely. In particular, check out the thread that lists and discusses what amps members are using with their vintage Infinity speakers.

For the record, a good indicator of a high-current amp is one that "doubles down" e.g. an amp that outputs 200 wpc @ 8 ohms will output 400 wpc @ 4 ohms and 800 wpc @ 2 ohms. These types of amps typically have large power supplies and are heavy and expensive. Affordable brands include Adcom, Acurus, Forte, Aragon, Carver. Pro amps from Crown and others are also an affordable option.

 

[Northwinds]

I am running a Cerwin Vega A-2200 amp (200wpc 8ohms.400wpc 4ohms) with Infinity Quantum 5s in the garage with no problems. The amp was used for the Earthquake movie back in the 70s in theaters to be used with the BGW amps. Your Yamaha units should be just fine though. As someone else mentioned, use sense with the volume knob. I don't know if your speakers (not familiar with them) have Watkins dual voice coil woofers but they will kill a lesser amp quickly

 

[tubed]

^^^^^^^
If the the LCR circuit in the crossover is working properly, the Watkins woofer should operate at around a steady 5 ohms of impedance, as stated in the QLS-1 white paper.

 

[Tedrick]

The RS 4.5's are rated as a nominal 4 ohm load, but the woofers are known to drop down to less than 3 ohms at certain frequencies. I would want an amp that is stable into a 2 ohm load to drive these speakers.

 

[MAVRICK]

Voltage is cheap. Amperage is expensive.

"High Current" in common usage (advertising copy and other propaganda sheets) means the amplifier is suitable for use with 4-ohm nominal speakers.

"High Current" in real life means the amplifier is suitable for use with 1-ohm nominal speakers, maybe sub-one-ohm.

Then some manufacturer starts throwing around silly "amperage" specifications that have zero relevance to a real-world speaker load or music signal. If you're seeing some goofy amperage spec like "40 amperes" or "80 amperes" you'd better be questioning their methodology.

Of course, there's more to speaker load than just the impedance. Capacitance and inductance matter, too. The best amps can throw power into reactive loads, not just resistive.

You seem to have your mind around this stuff very well. I wish I did. Is there a simple shortcut answer as to what specs to look for when shopping for an amplifier. All I know for sure is that I have speakers rated at 4 ohms and that they are advertised to need at least 100 watts. I'm also told, they need lots of current. Each of my 12" woofers (2 per speaker) have dual voice coils (1 ohm and 2 ohm). I f I understand anything I'm learning, I'm pretty sure that will suck the guts out of a cheap amp?

 

[TomBig58]

Some very good explanations here as well as rule of thumb knowledge. It's nice to have information provided that just doesn't suggest amp make/models to try. E-stat's pics are very telling.

 

[musichal]

If looking for high power and high current, then include the weight of the amp among the power specs with a rule of thumb that the heavier, the better. Like any ROT, it's an approximation that won't hold up with every comparison, but too light a weight is suspect.

 

[Tedrick]

Have you perused the Infinity subforum yet? Tons of good info there from guys with years/decades of specific first-hand experience with vintage Infinity speakers.