Hiss from my Adcom GFP-565

Can someone help me out by explaining why my Adcom GFP-565 preamp makes a continuous hissing sound play through speakers? It does not appear to be affected by turning the volume up or down. I had a GFP-555 that did the same thing. My Marantz 2325 receiver from the mid 1970's is actually considerably quieter in this respect than the highly-regarded (I think) GFP-565. What's the source of this noise? I know zilch about electronics on the inside...just know how to use them. The hiss never varies and it's the same on each side.

All powered equipment has some inherent hiss.

Can you hear it from across the room, or do you have to put your ear really close to the speakers to hear it? If it's the latter, that's normal.

If the hiss, as Markw has suggested, is audible from across the room, then there's something wrong with your Adcom preamp, though it could also be coming from your power amplifier too. I have a GFP-565 and it has no audible hiss that I've been able to detect. And you're right - it was "highly touted." Stereophile reviewed it against a $7,000 Audio Research preamp, and stated that while the AR unit was better in most regards, the difference wasn't particularly extreme, and that the phono stage of the Adcom was actually much better. As the 565 initially sold for $700, it was considered far and away the better value.

I hooked up my Adcom GCD-575 CD player directly from the variable outputs to my GFA-535 amp and there was no noise.

Testing the hiss right now, I think I can hear the noise up to about 4 feet away, maybe a bit less. At that point, my computer across the room comes to within 10 feet of me and is louder than the audio equipment.

Back to the comparison against the Marantz...maybe it's not quite fair. The Adcom probably has more-revealing speakers (Focal Cobalt 806S) than the Marantz has (JBL S38) and I have not tried switching them for a fair comparison.

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Originally Posted by 02audionoob

I hooked up my Adcom GCD-575 CD player directly from the variable outputs to my GFA-535 amp and there was no noise.

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It would seem that what you're hearng is residual noise from the preamp.

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Originally Posted by 02audionoob

Back to the comparison against the Marantz...maybe it's not quite fair. The Adcom probably has more-revealing speakers (Focal Cobalt 806S) than the Marantz has (JBL S38) and I have not tried switching them for a fair comparison.

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Good thinking. Speakers with a more pronounced high end tend to accentuate hiss more than neutral or more subdued speakers. Switching them would be a good test.

An update on this question...I was wrong about one thing. The hiss is actually affected by turning up the volume. It just has to be turned up farther than I had tried. I have also now found that turning up the treble all the way causes a slight increase in the sound level of the noise.

On the topic of the comparison with the old Marantz...I tried the Focal speakers on it. The hiss the Marantz makes through the Focal speakers seems like what I'd call less than half as loud as the Adcom makes.

Anyway...If anyone has any further thoughts on the situation, I'm always interested in learning from experts and/or others' experiences...especially if there's the possibility that the situation can be improved.

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Originally Posted by 02audionoob

Can someone help me out by explaining why my Adcom GFP-565 preamp makes a continuous hissing sound play through speakers? It does not appear to be affected by turning the volume up or down. I had a GFP-555 that did the same thing

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Do you have very sensitive speakers ? I once owned Adcom GFP-555 and GTP-555II preamps that both had audible hiss at the listening position with my fairly high sensitivity speakers. The advice I got from the Adcom factory regarding the GFP-555 was to "just use it in bypass mode," which I found unacceptable. With the GTP-555II, there would be an audible hiss from the center channel when in surround mode.

I do have fairly sensitive speakers, but not extremely so. But I'm puzzled as to why the GFP-565 would be so much noisier than my Marantz 2325 receiver. If I had to guess without ever having heard the two systems, I would've guessed a GFP-565 was quieter than a Marantz receiver. This noise does occur in bypass mode (and in main normal and main lab) and especially when set to Phono, even when the turntable is not powered up. It can be reduced just slightly by turning the treble all the way down, but of course that can't be done in bypass mode.

This thing is so noisy in Phono mode, I'm tempted to replace it...I just don't know what I'd replace it with. I had a GFP-555 and I replaced it with a GFP-565 with the expectation of a superb phone stage. I guess it sounds good...maybe musically as good as its reputation...but with Beethoven cranked up to halfway on the volume knob, I hear noise in the quiet parts.

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Originally Posted by 02audionoob

This thing is so noisy in Phono mode, I'm tempted to replace it...I just don't know what I'd replace it with.

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Used Parasound Halo P3 or Classé.

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Originally Posted by Glen B

Used Parasound Halo P3 or Classé.

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I'll look into those. And what about thoughts on a phono amp? I see a PS Audio phono amp on eBay. Maybe this is a good avenue?

What's you budget for a phono preamp ? There's lots of choices from a couple of bills upward. There's Bellari, Creek, Monolithic Sound, Pro-Ject, etc. I owned a Monolithic Sound PS-2 with the optional HC-1B power supply that I sold last year because I was lucky to find an optional (discontinued) internal phono stage board for my preamp. The Monolithic was a pretty good phono preamp and extremely quiet, paired with my (low-output) Audio-Technica AT-OC9 MC cartridge. You may or may not find it a bit pricey at $879 brand new for the two pieces.

I guess I don't know what my budget is, but I would like to see what's out there for maybe $300...with the assumption I'm shopping the used market.

A used B&K Sonata PRO-10MC or MC-101 preamp will run you around $300.00-$350.00. Both come with a very good MM/MC phono stage. I owned an MC-101 during the 1990s. The MC-101 and PRO-10MC are the same internally, except that the former has tone controls and the latter does not. There are a number of decent options in a new phono preamp for around $300.00.

http://www.needledoctor.com/Online-S...ERPRICE&range=

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Originally Posted by 02audionoob

Can someone help me out by explaining why my Adcom GFP-565 preamp makes a continuous hissing sound play through speakers? It does not appear to be affected by turning the volume up or down. I had a GFP-555 that did the same thing. My Marantz 2325 receiver from the mid 1970's is actually considerably quieter in this respect than the highly-regarded (I think) GFP-565. What's the source of this noise? I know zilch about electronics on the inside...just know how to use them. The hiss never varies and it's the same on each side.

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I've owned the 565 for a number of years and I've noticed the same thing since I got the unit. Prior to this I had a Proton preamp which did not have any audible noise at all. I'm looking at a Cambridge Audio 840E preamp and the new Insight EC preamp by Van Alstine as possible replacements with an outboard phono preamp.