This is a copy of my post on the SMART Bulletin Board to Greg regarding the hiss noise:
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Hi Greg,
We have sold many of the CS-3X, Jr. units, and have only had one report of noise besides yours. In his case it turned out to be a hum casued by a ground loop problem caused by his DVD player. I have asked several people if the unit was quiet, and everyone has said yes, no noise problems at all.
So with that said, lets look at what could be causing your noise problem.
All electronic equipment produces some noise. the trick is to minimize it as much as possible. This is done through careful circuit design, choosing high quality components, proper shielding and grounding, and paying attention to the gain structure in a system.
I believe that you may have a gain structure problem. My guess is that you do not have a strong enough signal going into the CS-3X, Jr. Therefore, you are having to turn the CS-3X, Jr. output gains up too much and are increasing the amount of noise going to the amplifiers. This is a common problem in professional applications where the gains must be properly set at all points in the system to achieve the optimum signal to noise ratio.
The solution, if it is possible on your processor, is to increase the volume of your processor surround channels and decrease the output levels of the CS-3X, Jr. You may have to turn the processor surround channels up several dB or more to achieve this.
One other thing you did not mention is where you are in relation to the speakers when you hear the noise. Are you at your normal listening position or are you up very close to the speakers? What really counts is what the system sounds like at the normal listening position.
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Here is Greg's reply to me in an e-mail:
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Oscar,
I believe you are correct that this is likely a gain problem. The unit
hisses even without the inputs connected from the main processor. That is,
with just the 3X jr. and the output amplifiers in the circuit. The output
amps are dead quiet with the 3X jr. in the "off " position.
I cannot increase the surround output from the main processor without
causing many other problems in the system. Is there a preamp available to
increase the output from the main processor before connection to the 3X
jr.or would that just cause more noise in the system?
With regard to my proximity to the speakers when the hiss is audible, a
person seated six or seven feet away can hear it without strain. That is
unacceptable. I'm sure you would agree.
Please make whatever suggestions you can to assist in this problem.
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In general, I believe the CS-3X, Jr. is a quiet product. Not perfectly quiet, as no electronics product has zero noise, but in most cases acceptably quiet. This has been borne out by comments from a number of users who tell me that they have no significant noise problems and find the noise level to be NO problem.
The CS-3X, Jr. signal to noise ratio is typically better than -70 dB referenced to a -10 dBV input level, a level which is fairly typical in HT and home hi fi equipment. It has a 85dB dynamic range which is the range from the noise floor up to the point of 0.1% distortion at 1kHz.
I am at a loss to know what to do for Greg, but it does appear that in 99% of the cases, noise has not been a problem.
I can only think of one additional thing that could impact the problem, and that is the amplifier gain. Greg, is it possible for you to turn the amplifier gains down a bit? The CS-3X, Jr. has one output stage whose noise level is not affected by the level adjustment trimpots. The noise from this stage could be overly amplified if your power amps have too much gain. By turning the amp gain down some and re-adjusting the CS-3X, Jr. level trimpots, you may reduce the noise.
I will be glad to look at Greg's unit if he likes to see if perhaps there is a problem that needs repairing. Greg, just e-mail me if you would like to do that and we will arrange things.
Best regards to all,
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Oscar Neundorfer
Chief Engineer
SMART Devices, Inc.
[email protected]
