Panasonic XR with 4ohm speakers

[ultrachrome]

I thought I read somewhere (can't find the post now) that the amps in the Panasonic and maybe other digital amps may have problems with 4ohm speaker loads. Could someone elaborate on this?

I just picked up an XR45 while my other amp is on the bench and I am really pleased with how it sounds. Running my ten year old Rotel changer through the optical input sounds great. Only problem is those speaker connectors.

I'm almost scared to get my AKSA/Foreplay running again for a comparison.

thanks.

[fcserei]

I'm running electrostats with them ( <2ohm above 10k ) without any problem, but it's also true int the main band where most of the music happens the impedance is above 10 ohm.

[Brian Brown]

Originally posted by ultrachrome
I thought I read somewhere (can't find the post now) that the amps in the Panasonic and maybe other digital amps may have problems with 4ohm speaker loads. Could someone elaborate on this?

All of TI's Equibit driver chips with integrated MOSFETs are rated to drive four ohm loads. Your SA-XR45 is based on the TAS5182 which uses external MOSFETs. There isn't a published recomendation for a minimum load, but it should be similar.

As with most other amplifier designs, the output power increases as the load impedance decreases. The main limitation with the Equibit design is that at lower load impedances, the voltage drop of the output MOSFETs and the output filter consume a subtantial percentage of the total power. Efficiency drops way down and it's more likely to run into the thermal limitations of the output MOSFETs.

The SA-XR45 has two protection mechanisms: a heat sink temperature monitor, and output overcurrent protection. Both of these cause the output to shut down. Before these happen, there shouldn't be any loss of sound quality.

So in other words, as long as you're not causing the amp to shut down, everything should be fine.

Brian.

[ultrachrome]

Thanks. Your posts are extremely informative.

[Tube_Dude]

Here is a very interesting paper about measuring digital amplifiers...a new callenge!

http://www.audioprecision.com/ftp/pu...ifiers_web.pdf

Regards