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Old 13th March 2004, 10:31 PM   #1
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Default tube preamps and gain

Hello,

I would like to drive my solid state Inter-m R500 (170W X 2) amplifier with a tube preamp. I recently heard a few tube preamps in a local stereo store with solid state amps, and this seems like the way to go. However, it seems like tube amps have an aweful lot of gain.. some even 30dB! How much gain should i get to run this amp? tia

Dave
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Old 13th March 2004, 11:15 PM   #2
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Hi,

Quote:
How much gain should i get to run this amp? tia
If your source is CD based you won't need any gain at all.

Considering that a CDP has an output of 2 VRMS, that's still 6V peak to peak, it should be obvious that gain is not the issue.

IMHO, what people look for in a tube preamp is some euphonic colouration to add some warmth and texture to most CDPs which tend to sound too clinical to most people.

With respect to the SS amps you'll probably like a tad gain, a few dB perhaps, but more importantly, you'll need a low enough Zout to drive the low Zin of the amp adequately.

If you search locally you should find at least one reference to a preamp using the excellent and cheap 12B4A.

Other candidates are the ECC99, 12BH7A etc.
If you feel you can do without the extra gain_ you'll do more attenuating than amplifying anyway_ then a good volumecontrol followed by a tubed buffer should prove to be a match made in heaven.

At the end of the day the results will always depend on the execution of the circuit and its power supply.

Cheers,
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Old 13th March 2004, 11:55 PM   #3
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There are 3 sources:
1. Rotel Cd Player
2. Toshiba Dvd Player
3. Realistic Tuner

Would it be a good idea to have some gain for these sources? At the moment i'm using a passive preamp based on an alps pot, and 2 so so quality resistors. The amp has signal lights on it, and they rarely light up at the volume i listen at.. However, if gain wasn't required for these devices, as long as i have a strong enough signal, then it's ok. Maybe this is what you were talking about with the input impedance of the amp and the output impedance of the preamp??

I agree with what you said about tubes- that "what people look for in a tube preamp is some euphonic colouration to ad some warmth and texture".. That pretty much hits the nail on the head


The input impedance of the amp is 10kohms (balanced).. Not sure what that means. There are two sets of inputs on the back of the amp- one of them is 1/4" jacks (the ones i use) and the other is xlr. So what would be a good output impedance to drive
this amp?

Thanks!

Dave
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Old 14th March 2004, 12:13 AM   #4
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Hi,

Quote:
However, if gain wasn't required for these devices, as long as i have a strong enough signal, then it's ok. Maybe this is what you were talking about with the input impedance of the amp and the output impedance of the preamp??
The only source I suspect could do with a little amplification is the tuner. OTOH, you don't seem to need it with your current (no gain) set up.

With in- and output impedance I mean to say that in order to drive the input impedance of the amp properly, the preamps' output impedance needs to be at least an order of magnitude lower.
I usually stick with at least a 1:10 relationship between the two just to be on the safe side.

Quote:
The input impedance of the amp is 10kohms (balanced).. Not sure what that means.
It's probably 10K unbalanced as well, balanced input requires a balanced output from the source as well. None of your sources are, as far as I can tell.

Quote:
So what would be a good output impedance to drive
An output impedance of 1K or lower should be able to drive the amps provided the interconnect is not too long and not too capacitive.

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