Where to apply gain in the audio chain?

[thevinoman]

Question regarding where best to apply the most gain or percentages of gain in this scenario? (2 channel only)

Source: Oppo 105D (has output volume/level control)

feeding: Mcintosh MX110Z (has aux output gain for L and R, as well as volume control)

feeding: Mcintosh MC250 SS amps (monoblocked/bridged to 100w each) (each have gain control)

feeding: Klipsch Khorns/La Scala II/Heresy III

 

[MACKIE1975]

Fixed output on source, then preamp then power amp

 

[thevinoman]

Not sure I follow....are you saying highest gain from source, then scaling down?

 

[twiiii]

In complex sound systems all interstage pieces, such as limiter compressors, equalizers, crossovers are set to be equal in = equal out. The mixer is set so as to provide maximum level at +8db out. Then the Power amps are adjusted to give the final level necessary. So in home systems if your pre amp works optimally at 1.7 volts then you turn your the vol control so for the loudest recordings the pre-amp is putting out this level. The you set the gain on your amps to give you the level you prefer, if your speakers are that capable. So maybe you like to listen with 95 db peaks and your speakers need is 30 watts. So you set your amps so they put out 30 watts whether the amp is rated at 30 or 300 watts. You will still have extra gain for Cd's or LP's recorded below normal levels on the pre-amp Usually 12: 00 is the optimum setting for a pre-amp. They will still have 14 to 20 db gain left for those weak recordings and you should choose amps and speakers that have at least 10 db margin left in dynamic range to handle those rare instances where higher than normal peaks occur. You don't want your system to reach its full potential with the 12:00 setting by setting the amp levels to high. You want the level you are most comfortable with an extra margin for weaker signals or louder than average peak levels.

 

[MACKIE1975]

Set the Oppo output as Fixed since the volume on the Oppo is for analog and headphone only.
Set your gain on MC 250 to max. The preamp will control the level.
May need to adjust the MC gain to match the MX

 

[mnmmt]

From a practical standpoint, figure out where the MX110 volume knob tracks most equally, and set the MC250 gain so that you're using the most accurate part of the volume dial for most of your listening. I am about ready to have AC rebuild my volume pot, because mine shifts wildly all the way around the volume dial. It's horrible. (But it still sounds good). If it tracks equally, then do what they said.

 

[62caddy]

The lower the amplifier gain, the lower the noise floor.

Being the speakers are all high sensitivity, high SPL should be able to be obtained with relatively little amplifier gain.

I would set the preamp volume at ~ 2/3 up (2:00), begin playing music and starting with the gains at minimum, begin raising until the music is slightly louder than you could ever tolerate and you're done. The volume control will now be set for the greatest useful range as well as the optimal location for even L/R tracking.

 

[damacman]

Research the topics of gain structure and gain overlap. Well outside the scope of a thread such as this.

 

[kevzep]

The lower the amplifier gain, the lower the noise floor.

Yes but then you have to run the pre-amp higher, and so lifting the noise floor in the pre-amp....

 

[MACKIE1975]

So the egg come first or the chick?

 

[62caddy]

Yes but then you have having to run the pre-amp higher, and so lifting the noise floor in the pre-amp....

That's true but the noise is less likely to be noticed at those volume levels - at least in theory. When the amplifier gains are set relatively high, the higher noise floor is more or less permanent regardless of volume setting.

Using the least amount of gain possible while providing maximum useful range of the volume control seems to work best for me. YMMV.

Suffice to say it's a balancing act- depending on speaker sensitivity.

 

[damacman]

Actually, speaker sensitivity has nothing to do with it. Look at it like this - the amplifier(s) would reach clipping at the very same point that each other component in the chain arrives at its maximum unclipped output level.

Given that music is dynamic in nature, gain overlap is employed (at the amplifier(s) only) to offer the best compromise between system noise and maximum output capability of the system.

 

[twiiii]

You never set the early Mac power amps to full gain, thats .5 volt sensitivity, You are giving up 15 or 16 db of signal to noise and increasing distortions from your pre-amps by that amount. You set the controls like they tell you in the manual. With the volume control of the pre-amps set near the 12'clock position you advance the volume of the amps to a level just a little bit louder than you would normally listen. If you have very efficient speakers like Klipschorns or Corn walls you may find the amp controls at 10:00 o'clock, with something like LM-1's maybe 1 or 2:00 o'clock, but never wide open if you are using Mac pre-amps. Yes with later Mac pre-amps with very low output impedance having the control of the amp wide open gives you slightly lower distortion, but that will be covered up by the noise of the system, so which do you want to hear just a bit higher distortion or constant his and hum depriving you of a relaxing experience.. Wonder why the power amps of today don't have volume controls? Its to guarantee the proper relation ship between the HT processors, Stereo pre-amps, and external processors, from being compromised by well meaning but ill informed owners.

 

[62caddy]

Whenever I have the gains cranked to full, I always observed a higher noise floor than when set lower and the higher the speaker sensitivity, the noise floor is all the higher.

For example, with the 103 dB Heathkit/Altecs that I owned, I would never use the MC30/MC240 or MC2505 gains full on. Not only would it confine full volume to the first 25 - 30% rotation of the volume control where L/R tracking is not that well balanced, but the noise floor is considerably higher.

I know there are some who like having the gains set so high that just breathing on the volume control produces high loudness.

 

[Gearjunky]

I once read Steve Hoffman’s advice, to have the gain wide open for the mc30’s which is what I’ve been doing with mine. Seems ok to me. My speakers though are 92db efficiency and the mx110’s volume is at 1 o’clock or so. The CR7 then does all the volume adjusting.

My 2105 and 2100 are different in that they are set at the 12 o’clock position, pre at 1 o’clock. Also, a CR7 does the volume adjusting on this system too. This is how I’ve run mine but keeping an eye on this thread for other possibilities.

 

[kevzep]

Whenever I have the gains cranked to full, I always observed a higher noise floor than when set lower and the higher the speaker sensitivity, the noise floor is all the higher.

For example, with the 103 dB Heathkit/Altecs that I owned, I would never use the MC30/MC240 or MC2505 gains full on. Not only would it confine full volume to the first 25 - 30% rotation of the volume control where L/R tracking is not that well balanced, but the noise floor is considerably higher.

I know there are some who like having the gains set so high that just breathing on the volume control produces high loudness.

All the amps you are talking about are relatively high gain amps compared to something like a MC2205 and later.

All those amps you mentioned, in my book, would never run at full gain, and that goes for the MC2505.

However, a MC2205 for example, I set it to the 2.5V sensitivity, gains full, job done. Never had any issues, had plenty of fine control with the volume off the C33 I was running with it.

But if you are running a C33 with a MC240 for example, you would be running the gains at 12 O'Clock at the most....

Its about knowing you gear and knowing what you are trying to achieve.

 

[chef free]

However, a MC2205 for example, I set it to the 2.5V sensitivity, gains full, job done. Never had any issues, had plenty of fine control with the volume off the C33 I was running with it.

This is how I deal with my MC2200/C30 combo, Oppo 105 set to non-variable...

 

[c_dk]

Theory is just speculation in this case due to the mix of equipment and their actual noise spectra....

I would set the input level from the DVD and the amp to insure the volume control tracking between channels is in the sweet spot for channel balance and then lower the amp gain to minimize noise from there.

It will be a series of trials between lowering the input vs amp noise in the speaker.

Such is using 50 year old gear.

 

[kevzep]

Theory is just speculation in this case due to the mix of equipment and their actual noise spectra....

I would set the input level from the DVD and the amp to insure the volume control tracking between channels is in the sweet spot for channel balance and then lower the amp gain to minimize noise from there.

It will be a series of trials between lowering the input vs amp noise in the speaker.

Such is using 50 year old gear.

Theory is information to get yourself a good starting point....

 

[62caddy]

All the amps you are talking about are relatively high gain amps compared to something like a MC2205 and later.

All those amps you mentioned, in my book, would never run at full gain, and that goes for the MC2505.

However, a MC2205 for example, I set it to the 2.5V sensitivity, gains full, job done. Never had any issues, had plenty of fine control with the volume off the C33 I was running with it.

But if you are running a C33 with a MC240 for example, you would be running the gains at 12 O'Clock at the most....

Its about knowing you gear and knowing what you are trying to achieve.

I can't disagree with anything you've said regarding the comparative gain characteristics of the amplifiers you mentioned. My 2125s and MC2155 are similar to the 2205 and you're correct on how those behave compared to the earlier gen models. I still don't run mine at wide open however because of they way my speakers are set up - but that's for another discussion.

In any case the OP's amplifiers are a pair of MC250 which is also an earlier model with the older type gain circuit where full-on would not be advisable and certainly not with a pair of high sensitivity Klipsch speakers, IMHO.

Thanks.