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Old 9th December 2006, 02:04 PM   #1
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Default Preamp hiss and my fancy new GC :)

I think I mentioned it before somewhere, and I would like to learn a bit more about it basically. I can't realistically afford an oscilliscope to "see" it though. I have read hiss is quite an ordinary thing - electrical noise.

With no input or shorted on the GC, no noise at all. Dead silent. This is quite possibly to be expected...

With the GC plugged in to the pre-out on a Cambridge Audio A5, the tweeter has a white noise sort of hiss. I can't really hear it unless I have my ear right up to the tweeter, until the volume is at absolute maximum... then it's audible from listening position (which is about 1m away, if that!)

Today I have plugged the GC straight in to my computer soundcard (Audiotrak Prodigy 7.1LT). The hiss is quite a lot quieter at full volume (which is actually much louder than my normal listening levels with the pre-amp, if you get what I mean). The hiss has a very slight clicking noise to it though, which I don't hear with the preamp.

Just wondering, is there any significance to this clicking? Oscillation? :-O Might this just be because of the low output impedance of the sound card (I don't think you generally want to stick a power amp straight on a sound card output..)? Specs say the output impedance of my card is 100ohms on the analog outputs. Input impedance of the GC is, I assume, 15.33k (15k to ground at input, and 330R between input and opamp non-inverting).

Given that there's no noise at all from the GC with no input, would this mean that the source (the sound card) is the generator of the hissing? Or is a shorted / no input not really an indicator of how much hiss it generates?

For the record, I have only connected it straight to my sound card because I wanted to see what kind of effect the preamp was having on sound quality I seem to be hearing a much nicer sound straight to the sound card, but then this might just be brain tricks. It's not exactly a blind test or anything
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Old 10th December 2006, 06:42 AM   #2
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The clicking noise you hear might be the HDD's or other hardware in the PC...PC's are terribly noisy creatures.
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Old 10th December 2006, 07:30 AM   #3
zBuff is offline zBuff  New Zealand
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I've encoutered clicking many times on computers before, like DigitalJunkie said, it's normally the Harddrives, but I've had the CDrom do the same thing and even a mouse everytime you moved it or used the scroll wheel. What harder is how to fix it, the simple might be just making sure IDE and SATA cables don't go near soundcards(so tying them back to the case), as hard to pin down as drivers or IRQ conflict and interference. sheilding your soundcard(with the dangers of shorting something) or what alot of guys on this forum seem to do is use external DACs and soundcards.

About the hiss in general, you could try using different interconnects, making sure they don't run parallel to things like powercables or anything with a decent magnetic field. It doesn't seem like an awful lot of hiss you have though, got another amp to crosscheck it with?
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Old 10th December 2006, 09:05 AM   #4
AndrewT is offline AndrewT  Scotland
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Hi,
if the power amp is silent with a shorting plug in it then it is silent.

If adding the pre-amp and shorting it's input and you now hear a little noise then the pre-amp is producing the new noise.

If adding your source is noisier than the pre+power then the source is noisy.

Decide if you can tolerate it.
If not, then junk the idea of computer generated quality music.
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Old 10th December 2006, 09:53 AM   #5
Nuuk is offline Nuuk  United Kingdom
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Quote:
If not, then junk the idea of computer generated quality music.
At this point it may be a good idea to differentiate between computer generated music using an internal sound card (playing back through kmixer), and something like an external USB audio convertor or a Squeezebox, the latter two producing no unwanted sound at all!
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Old 10th December 2006, 01:33 PM   #6
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Quote:
Originally posted by DigitalJunkie
The clicking noise you hear might be the HDD's or other hardware in the PC...PC's are terribly noisy creatures.
Noisy they are indeed!

Quote:
Originally posted by zBuff
I've encoutered clicking many times on computers before, like DigitalJunkie said, it's normally the Harddrives, but I've had the CDrom do the same thing and even a mouse everytime you moved it or used the scroll wheel. What harder is how to fix it, the simple might be just making sure IDE and SATA cables don't go near soundcards(so tying them back to the case), as hard to pin down as drivers or IRQ conflict and interference. sheilding your soundcard(with the dangers of shorting something) or what alot of guys on this forum seem to do is use external DACs and soundcards.

About the hiss in general, you could try using different interconnects, making sure they don't run parallel to things like powercables or anything with a decent magnetic field. It doesn't seem like an awful lot of hiss you have though, got another amp to crosscheck it with?
I don't get any noise from moving the mouse or CD drive. I used to get that with one of my first PC's though. I'll try tidying up some cables and things, though I am fairly sure none run close to the card at present.

It's not a terrible amount of hiss at all really, no. (See below regarding other amp)


Quote:
Originally posted by AndrewT
Hi,
if the power amp is silent with a shorting plug in it then it is silent.

If adding the pre-amp and shorting it's input and you now hear a little noise then the pre-amp is producing the new noise.

If adding your source is noisier than the pre+power then the source is noisy.

Decide if you can tolerate it.
If not, then junk the idea of computer generated quality music.
Ok. Well, I have tried shorting the preamp inputs and disconnecting that from the source, and there is still hiss. The hiss on the pre doesn't seem to get any louder when plugging it in to the sound card. Straight to the sound card is so much quieter though. Maybe it's adding it on but I can't really tell the difference or something.

I'll get a proper external hifi CD player one of these days no doubt

Quote:
Originally posted by Nuuk


At this point it may be a good idea to differentiate between computer generated music using an internal sound card (playing back through kmixer), and something like an external USB audio convertor or a Squeezebox, the latter two producing no unwanted sound at all!
Tried and tested no noise sort of thing? I'll have to look in to those too then

Thanks!
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Old 10th December 2006, 02:05 PM   #7
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Good news for me, my uncle has a spare scope that he's donating to me!

I am not sure what it's like, model etc... but I am not gonna complain for free!

Don't suppose anyone has a 'tutorial' how to use the beasts? I found a thread on here which had some stuff about how to use one safely... but it seemed a bit complicated!
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Old 10th December 2006, 03:07 PM   #8
AndrewT is offline AndrewT  Scotland
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Hi,
plugging in the pre amd becoming noisier points the finger to the pre.

It may simply be noisy or it could have gone faulty.
Maybe it just has too much gain, you did say it got worse as the volume went to max.
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Old 10th December 2006, 03:10 PM   #9
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Quote:
Originally posted by AndrewT
Hi,
plugging in the pre amd becoming noisier points the finger to the pre.

It may simply be noisy or it could have gone faulty.
Maybe it just has too much gain, you did say it got worse as the volume went to max.
Yeah, with the volume right up (as in.. absolute max) it becomes audible from 1-2m away.

I have a friend with the same amp and speakers. I asked him to listen for hiss, and he says his also hisses too.
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Old 10th December 2006, 05:44 PM   #10
owen is offline owen  United Kingdom
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Your Pre is noisy.

I found exactly the same with my Meridian 501.2 ... Hisssssssssss.

My home built pre using an antique LF353 was SILENT, and sounded pretty damned good. So good infact that a new GC is in the works, with a new pre... The current rig will be sold when they're built.

Owen
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