Question regarding the Power Amplifier and SPL levels of RD-75

[Victor]

I have a question, - what is a reasonable power requirement for the power amplifier to drive an RD-75 driver operating from 500 Hz and up, in an dipole set-up? In other words how many Watts would be sufficient to achieve realistic SPL? Right now I am using about 150 Watt (6 Ohm) power amp and it is fine, but I am wondering if I can get away with much less.

Reason being is that I am in the process of assembling my ExtremA (http://www.hardwareanalysis.com/cont...diy-amplifier/ ) power amp. This is a Class A amplifier, and as such its heat-sinking requirement are considerable. To build a stereo 100 Watt Class A power amp is like building a monster that will end up weighing about 70 pounds it might be more.

So I am thinking about lowering the power to let’s say 50-60 Watts (6 Ohm). And here I am facing 2 choices that I need help deciding on.

Choice One: Build a Class A 60 Watt amp. But it may not be sufficient to drive my RD-75 section of my 3-way dipole speaker (http://home.comcast.net/~thomasw_2/VictorFront.jpg ) to realistic (read HIGH) SPL levels.

Choice Two: Build a 100 Watt amp that will operate in Class A only up to 30-35 Watts and if more power is needed the amp will depart Class A operation and will switch into Class B.

So what is the best course of action here?

Thanks in advance,
Victor

[ThomasW]

Good question. They have a 100 watt RMS Pmax rating, 88dB/1 watt/m. The thing we don't know is if that's for their 150Hz and up passband.

I power mine with a Ayre V5-xe (150/8 ohms, 300/4 ohms). The amp never seems to get much warmer than it's quiescent temp.

I guess I'd vote for choice 2...

BTW do you have the equipment to measure the amount of power your currently using?

[Victor]

Thomas,

Thank you for your opinion.

Well, I will need to think about what to do. The brute force approach is still on the table, - I may just simply get the monstrous heat sinks and make 100 watt Class A amp after all. We will see. I was hoping to hear votes for Choice One though.

I do not have a way to measure the power being used in my current set-up. I do notice, as you do, that my 150 Watt (8 Ohm) amp is barely working when SPL is about 90 dB which is loud already. That makes me think that even 60 watt amp should be fine.

Perhaps I can plug in the digital scope to the output of the power amp and see if I can record the signal level.

Regards,
Victor