Bad thermal switch on my SDA-1C's??

[icravcarver]

Got a problem when I push the Polks a little hard.  The left tweeter cuts out, then comes back on after a few seconds after lowering the volume.  I believe it is a bad thermal protection switch (at least from what I've read on various forums), but is there other possibilities?  How do I check it out?  Just want to make sure I just don't go blindly replacing things that don't need to be replaced.  (Plus the fact it returns to normal after lowering the volume)!

[F1nut]

You've got a hyper-sensitive polyswitch. They become hyper-sensitive from being tripped too often or sometimes just from old age. If you have tripped them in the past, you either need to keep the volume levels down or get a better amp. If you have not tripped them in the past and this just started, it's probably just an old age issue.

The poly is located on the crossover board in the position marked S1. Yours should be marked RXE135 on the case, which is 1.35 amps. Places like Mouser should carry them. Parts Express also has a few selections.

Tweakers tip: You can replace them with a .5 ohm, 12 watt Mills resistor, but only if you have never tripped the polys under normal use. I repeat, only do this if you have never tripped them under normal use.


BTW, if you still use the SL2000 tweeters, you would do well to replace them with the vastly superior RD0194-1 tweeters available from Polk.

[icravcarver]

Thanks Jessie.  I was reading about exactly what you are discussing on the Polk forum last night  (not a member, just a lurker - hell, I haven't had a chance to post on the Carver forum in ages - I know, I'm going to hell in a hand basket.)

It hasn't cut out at all at normal to somewhat louder levels, plus, my TFM-55 was rebuilt this past January/February @ Rita's, so I am confident the amp isn't the problem.  Also, I am at least the third go around for these bad boys, so I was assuming it was the thermal switch, which I had read before.  Just wanted to make sure there was nothing else to check out before I went in hacking away and later finding out it wasn't the problem. 

Should I do the same to the right speaker even though it is not presenting any problems, i.e. keep everthing consistent for the pair?!?  I am tempted to try the 0.5R in lieu of the thermal switch.  My power source shouldn't pose any problems, at least it better not, it ended up being the most expensive piece in my setup, after repairs that is!

I'm not too concerned with the protection as much either.  If I end up blowing one, then,  hey, great reason to upgrade to the RDO194's.   

[F1nut]

I'm not saying that there might be something wrong with your amp. What I am saying is that it might not have the balls to drive the SDA's at the volume levels you want. I know it's rated at high wpc, but wpc isn't what is needed. High current (peak to peak amps) are.

Anyway, back to the polys. Yes, whatever you do to the one speaker, do it to the other.

Do yourself a huge favor, don't wait for a SL2000 to blow or whatever, get the RD0194-1's now. You will thank me.

[icravcarver]

I know that you meant current, not power, but I thought the 55 would/should be capable of driving them to a decent level (it cuts out below 11 o'clock on the knob). 

As a side on that topic, I was reading somewhere, maybe even in my C-16 manual, that if I couldn't turn my volume knob on the pre to above 12 o'clock, that I should lower the input level of the amp so I can use the full range of the volume knob.  (Doesn't make sense to me, but I know I read it somewhere).  Not sure why it would matter if you are able to "crank" up the volume on the pre?

Is thereany advantage to the .5 ohm resistor vs. jumpering the connections?  (Besides keeping the crossover at its original design parameters?)

Lastly, I've read about the upgraded tweets, but not sure what gain people experience.  Smoother highs??  No one ever really talks about the improvement over the stock SL-2000's - they just say they noticed and improvement.

[F1nut]

  I was reading somewhere, maybe even in my C-16 manual, that if I couldn't turn my volume knob on the pre to above 12 o'clock, that I should lower the input level of the amp so I can use the full range of the volume knob.  (Doesn't make sense to me, but I know I read it somewhere).  Not sure why it would matter if you are able to "crank" up the volume on the pre?
 

That sounds to me like they are talking about impedance matching. See if you can't find that info again.

Is thereany advantage to the .5 ohm resistor vs. jumpering the connections?  (Besides keeping the crossover at its original design parameters?)
 

That's exactly why you should use the .5 ohm resistor.

  Lastly, I've read about the upgraded tweets, but not sure what gain people experience.  Smoother highs??  No one ever really talks about the improvement over the stock SL-2000's - they just say they noticed and improvement.

For one thing, the SL2000 has a nasty 5dB spike at 12-13kHz, the RD0 gets rid of that.

[icravcarver]

In the C-16 manual it states the following:

"The gain of the Carver C-16 is set to provide normal loudness levels with the Volume control set at midrotation.  In some installations with a high output source, a highly sensitive power amplifier, and very efficient loudspeakers, a Volume settion of 10 o'clock might produce the highest Volume level you ever use. This condition has several disadvantages:

 - The signal-to-noise ratio of the system as a whole is not optimum, since the full headroom capability of the preamplifier is not being exploited, while it is operated close to its "noise floor."

- The Volume control taper rate results in a greater level-change per degreee of rotation than at higher settings.

- The residual mistracking of channel levels in the Volume control will more closely approach its 1 dB maximum specification at settings below 8 o'clock.

The output level of either Main Output is programmable in gain capability. A simple modification can be performed to reduce output level in 3, 6, and 8 dB steps, as required, to extend the range of the Volume control and correct for the problems described above.  Contact Carver Corporatoin Technical Services for further information."

That is what I was referring to.  I have heard about the impedence matching before.  Not sure how critical this may be.  I was going to experiment with the input level of the TFM later to check it out.   At least while the kids are awake so I can crank it up without having to get a divorce!!!

[F1nut]

Ah ok, definitely play around with the settings.

[icravcarver]

Well, I played with the settings on my TFM-55 (lowered input knob - ended up at 10:30 or 11:00 on the knob) and all I can say is, WOW!  I can't believe it, but it seems to make a difference in the quality of the sound coming from my setup!

I definitely don't hear as much background noise, obviously since it is reduced and not being amplified, but there is just enough difference in the overall output of my system that I have to say it made an improvement.  Now, maybe if I was running Amazings or something of the sort that needed more power than the SDA-1C's, maybe it wouldn't make that much of a difference.

Now I just have to find the time (and money) to work on the Polks!!

[OldiesButGoodies]

I followed F1nut's advice on the poly switches - it works great.

Pepe