Matching impedances...


New member
Username: Mrlee123

New york, Cdcdcdc

Post Number: 1
Registered: Jan-19
I have a Denon PMA-900V that I bought in 1987 along with Polk Audio SDA-2As. At the time, I thought I was making a good decision. However, the Denon is rated to be used for speakers that are rated between 6 and 10 Ohms (I believe) and the Polks are at 4 ohms. I cannot run the Denon at an elevated volume for a time without it REALLY heating up. Is there a way to raise the impedance between the Amp and the Speakers? Would this improve the sound also?

Platinum Member
Username: Jan_b_vigne

Dallas, TX

Post Number: 18638
Registered: May-04

There's no simple or easy or inexpensive way to increase the load of the Polks. You could place a transformer or an autoformer in front of the speakers but that's going to cost some cash for a decent component.

Speakers are not one single impedance load and their problems become compounded by what is termed "electrical phase angle". Here's a bit more about phase and impedance;

The problem you're experiencing with the Denon is common with mass market receivers. To save money in manufacturing, mass market receivers often cut back on the power supply quality which will minimize current delivery. Low impedance loads require current from the amplifier.

The solution to your problem is to buy a system that is better matched in simple electrical values.

In the meantime, make sure your receiver has adequate ventilation. It should have at least 1" of air space around every dimension. 2" inches is better.

If it's in a cabinet, take it out of the cabinet.

You can place a small whisper fan beneath the receiver to push air through the chassis. Do not place the fan on the top of the receiver as this is the far less efficient manner for air to flow through the receiver. Prop the fan up sufficiently to allow air to flow from beneath the fan up through the receiver.

This is is a stop gap solution and not intended to be a permanent fix. You need to replace one of the components, either the receiver or the speakers or settle for the point where the receiver begins to have distress. Constantly stressing the amplifier will result in a shortened life span.

If you decide on replacing the speakers, it would be a good idea to look for a system with higher "electrical sensitivity". 70103475/?mkwid=sVGBOhs1j&pcrid=30980760979&pkw=&pmt=&gclid=EAIaIQobChMI0smt7oOH 4AIVzrbACh1Z3wtiEAQYBCABEgIuCvD_BwE

This fan is sold without a 120 Volt plug. Make sure you can adequately install a plug on the end of its leads.


Gold Member
Username: Magfan


Post Number: 3527
Registered: Oct-07
One MINOR help for Jan's answer.

It IS ok to place a fan on top. Just NOT blowing down. You generally want to take advantage of the fact that hot air rises.

If you place a fan on top, have it blowing UP.

And by any and all means, get that poor receiver out into the clear so you don't cook it.

A company named 'AC Infinity' makes cooling solutions for HT receivers. Reasonably priced, they also get reasonable reviews. A shock.

Other solutions exist. I think Emotiva made one...or was a 'rebranded' something else.

And depending on how 'handy' you are? A DIY is not out of the question. The KEY is to use the quietest fan you can find.....Like NOCTUA, which are leaders in this field.
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