SDA SRS Thermal Protection

[state228]

I have a pair of SDA SRS speakers that I bought new in the mid 80"s. They are powered by a Yamaha M-80 that I bought at the same time. For sometime now my speakers thermal protection has been cutting off the tweeters while listening at loud levels that used to be no problem. I contacted Polk about this before and they sent me some new thermal switches to install in my crossovers. That didn't fix anything. Could the problem be my Amp?

[DarqueKnight]

Have you changed the type of music you listen to recently?
What are you listening to when the thermal protection trips?

[state228]

Same music. Usually Heavy Metal. Does it with the same CD's I've been listening to for almost 20 years. Sounds good up until the point when the tweeters cut off.

[DarqueKnight]

Seems to me that your amp might be clipping. It is not unusual for the electrolytic capacitors in the amp's power supply to dry out over time. Call the the Yamaha Parts department at 714-522-9888. Ask to speak to technician Jim Bennett, he should be able to give you more insight into your problem.

I really like the older Yamaha audio gear from the mid 80's to mid 90's.

[state228]

I'll do that. Thanks for the help.

[Tour2ma]

Damn, was not even aware that my SRS's had thermal protection.

Have experienced the same thing in my left channel SRS and I know my M1.5t was not clipping. Just if driven hard the left channel would "go dull". Always assumed it was the amp, but...

state,
Ken Swauger of Polk CS will send you a trouble shooting guide for SDA's, including the SRS's. A series of VOM checks will let you know if your speakers have any issues.

[Tour2ma]

BTW raife, guy over here, http://clubpolk.polkaudio.com/forum/showthread.php?s=&threadid=9747 , has a unique SRS issue you might be able to shed some light on.

[DarqueKnight]

Originally posted by Tour2ma
Damn, was not even aware that my SRS's had thermal protection.

Have experienced the same thing in my left channel SRS and I know my M1.5t was not clipping. Just if driven hard the left channel would "go dull". Always assumed it was the amp, but...


Tour,

Amps can "soft clip" where you don't hear the audible distortion that is produced by "hard" clipping. Usually, the only way to tell if your amp is soft clipping is to attach an oscilloscope to the outputs and look at the output waveform.

The "dullness" of sound you experienced is what some audio reviewers refer to as a "hardening" of the sound. It is usually caused by an amp running out of power when trying to reproduce a demanding music segment.

All SDA's have a little semiconductor device to protect the tweeters. I always remove that device on the SDAs that I modify. The device does cause a subtle loss of high frequency detail.

If the thermal protection is tripped, you would not get diminished sound, you would get nothing at all. The device causes an open circuit when power levels are too high. Of course, you could have a defective device that does not break the connection completely.

I read the post of the fellow with the two left SRSs. I'll dig up my schematic and see if I can offer any insights.

[SDA SRS 1.2]

Originally posted by Tour2ma

Have experienced the same thing in my left channel SRS and I know my M1.5t was not clipping. Just if driven hard the left channel would "go dull". Always assumed it was the amp, but...

[/B]

I've had the same thing happen in either channel depending on the music. If I dial back on the volume momentarily, everything goes back to normal. Always thought it was the speaker's thermal protection - maybe it's the amp or my ears...:)

[bikezappa]

Whenever I listen to Janus Joplin loud, Ball and Chain or Summer Time for example I would lose the high end with my SDA SRS. I have experienced this problem for over ten years with various recievers. I always thought the amp was shutting down. Wrong, it was the thermal protection in the speakers kicking in. Basically I was driving a Porsche with low octane gas and worn tires. A 300 watt Adcom power amp allowed me to listen at that volume without the thermal proptection kicking in. However, I now listen to to Janus even louder and can still activate the thermal protection. It never ends, finding and fixing the weakest link can be expensive and fun.