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Old 29th April 2009, 01:34 PM   #1
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Default Hissy Tripath amps?

Is it me or do all Tripath based amps give off a little hiss? Can this be reduced somehow?

I recently bought some active bi-amped studio monitors as spares and repairs, and one of the amps had blown in one of the monitors. The other one was working fine, and was a LM3886 based amp circuit.

Now, for the blown amp I decided to remove the amp and crossover, and see if I could use a Tripath amp instead. I'm using a DCX 2496 as source and crossover, and I've got the outputs from the DCX going thru a pot to reduce the gain.

I've tried a 41Hz.com Amp6basic and amp9basic, and a few of the pre-made amp-modules by sure electronics, and while the sound quality is good, there is definitely more hiss than the LM3886 based amp, mainly with the tweeter. My amp9b is running from and 24v SMPS, and my amp6b was running from Li-ion battery for testing...

As I'm using them as nearfield monitors I guess I'm in the worst case scenario for hearing the hiss, but is there a way if reducing this hiss? I was thinking I could put a high power resistor series with the tweeter, as I've already got the tweeter set to -6Db compared to the woofer on the DCX so I'm not worried about the reduced output.

Are there any other ways of reducing hiss? Shielding of the amp PCB maybe? If I could achieve a similar noise floor to the LM3886 circuit I'd be happy...

I've checked it not the source giving hiss as I'm still getting hiss with the amp inputs shorted...
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Old 29th April 2009, 05:55 PM   #2
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Well, after a little experimentation, I put a 10ohm 7W resistor inline with my tweeter, and the hiss has vanished.

Click the image to open in full size.

I figure many passive XO's do this anyway so why not give it a go.

Is 7W meaty enough? It doesn't get warm.... Anything else to worry about as this fix almost seems too easy!
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Old 30th April 2009, 02:56 AM   #3
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Mike are you sure the hiss is from the amps? I've Amp6 many, many times and a few Amp9s - never any hiss.

I have heard other Tripath amps with hiss, for sure, but not those two.
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Old 1st May 2009, 05:46 PM   #4
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Quote:
Originally posted by panomaniac
Mike are you sure the hiss is from the amps? I've Amp6 many, many times and a few Amp9s - never any hiss.

I have heard other Tripath amps with hiss, for sure, but not those two.
I thought so as well, but as I'm sat around 1ft from the tweeter and I'm guessing the tweeter is pretty sensitive, so I think almost any amp would make a little noise.

With the resistor in series, it is much less hissy so I'm now a happy man.
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