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Amp hiss


jbsl
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I have KLF 20s and I just bought 2 Monarchy Audio SM 70 Pros with 80 watts as monoblocks. They sound great but the problem is that there is notible hiss. When the music is playing I don't hear the hiss unless I realy crank up the volume. The only time is when the volume is down all the way.

The real problem is I ordered new La Scalas which are 104 db while the KLF 20s are 99 db. So I'm worried with the LS the hiss will be unbearable. I added 2 prong adapters to the power cords but did not help.

Are their any other things I might try to get rid of or reduce the hiss? Any help would be appreciated!

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As I recall, this is called "thermonics". I believe it is the noise of the electrons boiling off the filiment. It can be a tough thing to tame. All amplifiers demonstrate this to some degree. I would suspect a slightly gassy tube. Many tube testers wont pick this up, so you may need to try tube swapping. If it isn't distracting when music is being played, you may have to learn to love it!

Is it in both L & R?

BILL

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I believe those SM-70s are solid state.

You need to find the source of the hiss. I'll bet it is your preamp. Run the amps with no input connected and see if the hiss is there.

La Scalas will make the hiss worse and perhaps unbearable. My old preamp was intolerable through my La Scalas because of hiss, even at 3 meters. I was able to control it by drastically turning down the input gains of my power amps.

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That is what I'm worried about with the LS John. I tried your suggestion and unplugging the preamp did not work. I'm going to contact Mr Poon about your idea of turning the input gains down and see if he can offer any other suggestions. Monarchy Audio has a DAC model 22c that has gotten good reviews if I cannot get rid of the hiss then I may see if I can send back the amps and do a trade for the 22c and a DIP Upsampler. The single SM 70 I have does not have extreme hiss like the pro does so I can run it with the LS until I can come up with an new amp. My preamp right now is a 1991 Luxman stereo reciever but I bought a 1983 Luxman C300 preamp that I'm waiting to be delivered. My friend has the same preamp hooked up to LS with a Hafler dh 200 that sounds great so maybe I will try a new Hafler or any ideas that you have. Thanks for the help.

James

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what "fix" could he possibly send you that would (externally) correctly get rid of the amps hiss? Some kind of choke or filter? I wouldn't buy that line for one second. Send em back now before it becomes too late.

An amp should not produce hiss at idle especially one so highly touted at the sm70pro.

My guess is that because you are running them in mono the hiss is even more pronounced. I have a pair of dynaco st400's that hiss noticably in 200wpc stereo but put them in 600w mono mode and it sounds like a frigging hurricane coming though the room on my Khorns!

I had a 255wpc hafler dh500 that was dead quiet at idle. Nice amps, those haflers.

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Hey Xman: Could very well be a ground loop problem. If you have any interface between tv/cable components, unplug them. If you have interface between components on different household circuits, unplug them. If problem is ground loop, solution is ground isolator; try jensen transformers on the web. Good luck.

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Hey Xman: Could very well be a ground loop problem. If you have any interface between tv/cable components, unplug them. If you have interface between components on different household circuits, unplug them. If problem is ground loop, solution is ground isolator; try jensen transformers on the web. Good luck.

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Jdyer may be on to something. I ran into a similar problem and found that I did not have a good ground. Some receivers will have a separate ground terminal that can be attached to a ground source. For a simple test, run a wire to a good known ground or to the chasis of another known grounded (uses a 3 prong plug) device to the ground terminal on the receiver or to a case screw thats bright metal.

In my case, the ground wire in the AC wall plug was never connected when they built the house. By powering off the circuit and fixing the plug (only try this if you know what your doing otherwise hire an electrican to check your ground circut.) the hiss totally disappeard.

Hope this helps.

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