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Old 25th July 2002, 05:31 PM   #1
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Default Question about Preamps

Hi All,

I'm reading Morgan Jones' "Valve Amplifers" book 2nd Ed.
On page 384, he talkes about the perfect preamp. fyi, no preamp.
He makes the point that most formats, CD DVD, DACs, etc. already output 2 VMS, so that a preamp is a unnecessary component in the way that will add cost and possibly sound degragation to you system.

I was wondering what people's opinions on this forum have to say about that?

Eternalightwithin
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Old 25th July 2002, 05:43 PM   #2
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Currently I have the same opinion. If you don't need the gain why use preamp. I integrated volume at the output of my DAC and it's the only source I'm using at the moment because I believe that source switching degrade sound too.
Probably the better place for volume control would be at the input of the amp but I didn't get to it yet.
Some people claim that by using preamp they achieve better dynamics but if your stages are properly matched I don't think it should be an issue. Although there were times I didn't believe AC cords make difference either.
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Old 25th July 2002, 05:45 PM   #3
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Eternallight,

If the output and inputs are all direct coupled and will not be affected by any external variation in load, then yes, a potentiometer or a switched attenuator might be the perfect preamp.

However, The devices involved will be affected to a degree by the variation in load of a potentiometer/attenuator. So sound will change some throughout the range.

Also, that 2 volts is at maximum output. If the amplifier's inut sensitivity is 2 volts for full output, fine. But there are many amps that need more input. And most music is not recorded with that full a range.

As for preamps degenerating the sound... some preamps may actually enhance the sound. Some preamps are so good they do nothing for the sound but amplify it (inaudible distortion and coloration).

A preamp gives you more flexibility. For example, unless all you are going to do is listen to CDs on a CD player, the audio sources will vary. For instance, I have satellite, a VCR, and a DVD. The DVD of all devices is low volume output. I guess so as to give the biggest dynamic range impact. Without a preamp I would hardly be able to hear it. The Satellite OTOH sounds ten times louder.

It is up to you. If the input sensitivity of your amp is low, then do not use a preamp. Of course, you will need some sort of attenuation, otherwise your neighbors and ears will not like you for long.


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Old 25th July 2002, 05:52 PM   #4
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Quote:
Originally posted by Gabevee
Some preamps are so good they do nothing for the sound but amplify it (inaudible distortion and coloration).


Gabe
If a foot of wire has its own sound signature, input jacks have different sound, PCBs material influence the sound, volume controls sound different, different power supplies sound different, a perfect preamp will never exist. It will always change the original sound; in case of an inferior source or an amp it may be sometimes for better.
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Old 25th July 2002, 06:19 PM   #5
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HPotter,


Of course. I didn't say nor mean to imply that there are perfect preamps, etc. I mean that the changes are so inconsequential so as not to be heard. As for wire, etc., there is a point of diminishing returns where even the most scrutinous of listeners can't hear a difference. Not that it doesn't exist, but why bother if one can't hear it?

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Old 25th July 2002, 07:02 PM   #6
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I agree with you, if one can't hear the difference why bother. But what about those who can?
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Old 25th July 2002, 08:07 PM   #7
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Harry Haller started a huge thread on a shunt passive attenuator -- or passive-pre if you prefer. For pocket change you can slap together a prototype and give it a try.

Everyone's system is different, and everyone has different needs, expectations, and ability to hear so the final arbiter is you listening to your system.

It is all about enjoying the music...

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Old 25th July 2002, 08:14 PM   #8
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Hpotter

"I agree with you, if one can't hear the difference why bother. But what about those who can?"


I guess they are SOL.

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Old 25th July 2002, 08:32 PM   #9
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I think preamps are necessary for technical and practical reasons. Practically, it is a pain in the *** if you have to switch cables to listen to your SACD instead of your FM radio. The preamp is a natural place for source switching. The preamp is also a handy place to convert single-ended signals to balanced for transmission to the amplifier.

On the technical side, I think it is handy for an amp to take a 20Vrms balanced input. Less gain in the amp means less transmission noise gets amplified.
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Old 25th July 2002, 08:53 PM   #10
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I'm using five different systems. The reference doesn't have source switching because I use only one source. If I listen to radio or tape or DAT or turntable I'm using other systems. If I decide to use balance connection to an amp the main sources would be balanced too.
Don't get me wrong, I too used to be once under the impression that preamp was necessary. Even my first DIY project was a preamp . But it was long time ago.
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