amplifier gain

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Charles Calkins

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amplifier gain
« on: 19 Jan 2019, 11:37 pm »

        Hi Guys:
               It's winter so I'm kind of stuck in the house until our weather gets better.
               I've been reading the advantages of bi amping. SS for the woofers and a tube amp for the tweeter.
                To do this the amplifiers should have the same gain. I have a Mcintosh MC352 amp and I can't find any
                information about gain. How do I find this information on any amp?

                                                       Cheers
                                                       Charlie

RDavidson

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Re: amplifier gain
« Reply #1 on: 20 Jan 2019, 01:41 am »
Look for a spec for input sensitivity.

The online manual says the MC352 needs 1.9V (to reach full output).

avahifi

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Re: amplifier gain
« Reply #2 on: 21 Jan 2019, 05:24 pm »
If you know the maximum output of your amplifier in watts, and know the input needed to drive it to max power, then you can calculate the voltage gain of the amplifier.

For example, assuming an amplifier of 125W into 8 ohms.  You would multiply the power rating, (125W) times the load impedance (8 ohms, assuming power is rated into 8 ohms) and take the square root of that result, in this case about 31.6.  Then take this result times the square root of 2 (1.414) and that will give you the peak voltage swing of this amp at clipping (about 45 volts).

Then divide this result by the input sensitivity, (in this case 1.9V) the result being about 24.  This means that 1 volt in will provide 24V out.  1.9V in provides about 45V out at clipping.

Of course you can convert voltage gain to dB using any one of the several voltage to dB sources you can find easily on the web.

Typical voltage gain of a normal power amplifier is about 25V, or 27.6dB.

Of course, two amplifier with the same input sensitivity can have wildly different power ratings depending upon the overall voltage gain of either.

Frank

RonN5

Re: amplifier gain
« Reply #3 on: 18 Feb 2019, 06:31 pm »
Question:  for amplifiers that have gain controls, does dialing the gain back to better balance with the preamp affect the sound...in other words, is the sound actually better with full amplifier gain?

avahifi

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Re: amplifier gain
« Reply #4 on: 18 Feb 2019, 08:09 pm »
If you have an amplifier with an input volume control you can probably improve the signal to noise ratio of your system by dialing back the gain on the power amplifier.

This will cause you to use more volume control level with the preamplifier.  Since the noise level of your preamplifier is mainly the residual noise of its line section, which is usually after its volume control, and this noise is a constant, then increasing the output of the preamp provides more signal (the variable) in relation to the fixed noise level.  Thus the signal to noise ratio is improved.

Of course this won't help if the basic signal to noise of the power amplifier is not acceptable in the first place.

The other limitation is if you have to drive the preamp line stage so hard in doing this that its distortion goes up.

No reason not to try this.

Frank


RonN5

Re: amplifier gain
« Reply #5 on: 18 Feb 2019, 09:14 pm »
Further Clarification if I may....since my previous amplifier and my current amplifier had L & R gain controls...at least the weren't called volume controls is it likely that they are controlling the gain with resistors that may affect the sound....or is there some other mechanism.

And second....why are gain controls on amplifiers $1000 and up the exception and not more common.

Thanks

mresseguie

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Re: amplifier gain
« Reply #6 on: 19 Feb 2019, 12:39 am »
If you have an amplifier with an input volume control you can probably improve the signal to noise ratio of your system by dialing back the gain on the power amplifier.

This will cause you to use more volume control level with the preamplifier.  Since the noise level of your preamplifier is mainly the residual noise of its line section, which is usually after its volume control, and this noise is a constant, then increasing the output of the preamp provides more signal (the variable) in relation to the fixed noise level.  Thus the signal to noise ratio is improved.

Of course this won't help if the basic signal to noise of the power amplifier is not acceptable in the first place.

The other limitation is if you have to drive the preamp line stage so hard in doing this that its distortion goes up.

No reason not to try this.

Frank

Frank,

Thank you for this explanation. I found it very helpful.  :thumb: