Axiom Home Page Forums General Discussion Technical Questions Reciever Specs Question

Mike's question in the HT forum regarding whether or not his HK 7200 will drive a couple of VP150s got me to thinking about something....

I've read everywhere that this receiver will drive 4 ohms speakers, I have searched through my owners manual and online for H/K's answer to this question and I cannot find it. Keep in mind that I am in no way by any means competent whenever it comes to electronics, so with that in mind and given the specs for my AVR 635 below...what tells me that this receiver is capable of delivering the power for 4 ohm speakers *and* what is the minimum ohms this receiver can drive?

In reply to:

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Stereo Mode
Continuous Average Power (FTC) per Channel : 90 Watts per channel, 20Hz – 20kHz, @ <0.07% THD, both channels driven into 8 ohms
Seven-Channel Surround Modes, Power per Individual Channel :
Front L & R Channels : 75 Watts per channel @ <0.07% THD, 20Hz – 20kHz into 8 ohms
Center Channel : 75 Watts @ <0.07% THD, 20Hz – 20kHz into 8 ohms
Surround Channels (L & R Side, L & R Back) : 75 Watts per channel @ <0.07% THD, 20Hz – 20kHz into 8 ohms
*****Input Sensitivity/Impedance Linear (High-Level) : 200mV/47k Ohms***** Is this the answer?
Signal-to-Noise Ratio (IHF-A) : 100dB
Surround System Adjacent Channel Separation :
Dolby® Pro Logic® I and II : 40dB
Dolby® Digital : 55dB
DTS® : 55dB
Frequency Response at 1W (+0dB, –3dB) : 10Hz – 130kHz
High Instantaneous Current Capability (HCC) : ±50 Amps
Transient Inter modulation Distortion (TIM) : Unmeasurable

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Thanks!

Nope. That's not the spec you're looking for. What you highlighted just tells you the impedance of your high-level inputs (the RCA jacks). There isn't really a spec you can turn to about the capability of driving 4 Ohm speakers unless they tell you outright, with a spec like:

Continuous Average Power (FTC) per Channel : 180 Watts per channel, 20Hz – 20kHz, @ <0.07% THD, both channels driven into 4 ohms

Since the specs for 4 Ohm speakers aren't listed, it seems as though H/K doens't officially rate this amp to drive a 4 Ohm load. This doesn't mean it cannot do it, though.

See there, I told you I was incompetent with this stuff.

Thanks Peter, but to be quite honest I'm still a bit confused. I guess about the only real answer can come from the Harmon Kardon folks by asking them via email or some other appropriate means. I appreciate the time Peter, thanks again.

It's my experiance that you could expect around a 50% increase in power @ 4 ohm for most amps and receivers ( the ones that can handle it ).I had an old Kenwood amp that was 205 @ 8 ohm and 315 @4.My Rotel is 200 @ 8 ohm and 300 @4.

Bob: the problem with those specifications is that you just can not infer what it will do at 4 ohms, or for 2 ohms for that matter. It all depends on the circuit design and the component specifications.

I thought most amps can drive a 4 ohm load really but the problem is to deliver 90W to a 4 ohm load requires basically twice as much current as to 8 ohms and the wires and power supplies can be skimpy and not meant for that kind of current. So a 4 ohm load would de-rate the power rating of the amp and the potential exists for too much current to be drawn and some poping and fizzing results.

In retrospect I'm not really answering your question at all am I. Well it was more enjoyable to type then the 'real' work I'm about to have to do.

A 4 ohm load would take double the current as an 8 ohm load if the same voltage was applied at the input terminals. But, with current limiting and over voltage protection, etc., it is not obvious that all amplifiers that can drive an 8 ohm load will also equally drive a 4 ohm load. The truth is that they just can't.