Power Amplifier - Pre Amplifier Unity gain - Voltage gain - where as royal way ? - diyAudio
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Old 2nd November 2009, 10:26 AM   #1
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Default Power Amplifier - Pre Amplifier Unity gain - Voltage gain - where as royal way ?

In amplifier systems I observe commonly in most cases voltage gain both by line pre amp (mostly between 5 and 10 times) and by the power amp (mostly between 20 and 50 times). At whole, one have a gain factor between 100 and 500 times, that must reduce about the volume control between this amp devices.

For me it is a bad solution. I would prefer one of both components with unity gain, because today's line level sources provides in most cases output voltages at least 1Vss.
Good experiences I have make with unity gain preamps (used with very high idle currents between 0,5 and 1A and therefore no sensitivity to all cable loads and well suited for multi-amp systems).

But what about at changed this rule? I. e., preamplifier with voltage gain factor arround 20 until 50 times and the power amplifier only with unity closed loop gain (regardless of the internal open loop gain)?
Thank you for your comments.

Last edited by tiefbassuebertr; 2nd November 2009 at 10:32 AM.
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Old 2nd November 2009, 10:40 AM   #2
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Check out Pass Labs. There's a unity gain power amp and at least two preamps specifically designed to drive it.
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Old 2nd November 2009, 11:10 AM   #3
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unfortunately I have found there only the unity gain preamp articles:
http://www.passdiy.com/pdf/B1%20Buffer%20Preamp.pdf and
http://www.firstwatt.com/downloads/B...r%20Preamp.pdf
but no article about unity gain power amps

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Old 2nd November 2009, 11:31 AM   #4
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F4. And both SS and tube preamps to drive it are discussed at length here on diyAudio.
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Old 2nd November 2009, 11:37 AM   #5
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Quote:
Originally Posted by tiefbassuebertr View Post

But what about at changed this rule? I. e., preamplifier with voltage gain factor arround 20 until 50 times and the power amplifier only with unity closed loop gain (regardless of the internal open loop gain)?
Thank you for your comments.
You have guessed my system exactly. I use a preamp with 20dB voltage gain + power amplifier with unity voltage gain, no global feedback push-pull wide open class AB (1A idle current).
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Old 3rd November 2009, 06:34 AM   #6
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Sounds like a good idea, one unit for voltage gain one for current gain, but not very practical. Isnt the problem compatibility. Those pres and amps can only be used with each other. You need both the pre and the amps to have the same rail voltages (or at least the pre to have higher rails than the amp), so pres have to be matched to amp power.
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Old 28th April 2011, 02:11 PM   #7
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Quote:
Originally Posted by cbdb View Post
Sounds like a good idea, one unit for voltage gain one for current gain, but not very practical. Isnt the problem compatibility. Those pres and amps can only be used with each other. You need both the pre and the amps to have the same rail voltages (or at least the pre to have higher rails than the amp), so pres have to be matched to amp power.
If I wanted to use all commonly audio devices with each other, you are right. For this reason there are no me known commercial audio amp devices available, where both preamp and power amp versions in "Unity Gain".
My question (this topic) was on the technical point of view, however, and not on the commercial point of view.
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Originally Posted by PMA View Post
You have guessed my system exactly. I use a preamp with 20dB voltage gain + power amplifier with unity voltage gain, no global feedback push-pull wide open class AB (1A idle current).
When there are signal leads between pre- and power amp between 10 meters and 30 meters, there are two opposite effects:
1) the signal to noise ratio would given better results causes higher signal levels than by using of preamps with unity gain and power amps with voltage gain (this means an advantage).
2) the parasitic dielectric absorptions of certainly isolating materials from certainly cables can provide unwanted audible effects than by using of preamps with unity gain and power amps with voltage gain (this means a disadvantage).
Outweighs the advantage or disadvantage ??

Last edited by tiefbassuebertr; 28th April 2011 at 02:22 PM.
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Old 28th April 2011, 02:37 PM   #8
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For preamp voltage amp I'd use a good opamp. Like the OPA2134.
I have tried using 6DJ8 triode tube in SPICE.
It is possible to get a fairly good voltage amp with 6DJ8 = no feedback

If one wants a perfect unity gain power buffer
I say we should use OPA541.
It is one power operational amplifier with very low distortion in unity gain.
A pefect follower we can say.
Unless we want power buffers with some distortion of signal.
OPA541 puts out 50W/8 Ohm and nearly 100W/4 Ohm

Click the image to open in full size.
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Old 8th June 2011, 09:17 PM   #9
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Quote:
Originally Posted by tiefbassuebertr View Post
When there are signal leads between pre- and power amp between 10 meters and 30 meters, there are two opposite effects:
1) the signal to noise ratio would given better results causes higher signal levels than by using of preamps with unity gain and power amps with voltage gain (this means an advantage).
2) the parasitic dielectric absorptions of certainly isolating materials from certainly cables can provide unwanted audible effects than by using of preamps with unity gain and power amps with voltage gain (this means a disadvantage).
Outweighs the advantage or disadvantage ??
No comments to this ??
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Old 9th June 2011, 06:49 AM   #10
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When there are signal leads between pre- and power amp between 10 meters and 30 meters
Who would do that ? would be better to have the dac or pre-amp as close as possible to the amp. I personally have 2-5X for my preamp (CD/TV/DAC) and all my amps are 32db gain. I would not bother with a preamp if my sources were all the same. On my soundcard /DAC , I run my source -3 - 6db , so as to have no chance of overload, and make up with +6 db on the preamp to feed any of my amps.

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