Potentially stupid question regarding pre-amp/power amp volume adjustment

Discussion in 'Audio Hardware' started by MrRom92, Nov 21, 2015.

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  1. MrRom92

    MrRom92 Forum Supermodel Thread Starter

    Location:
    Long Island, NY
    So, I am using a receiver for it's pre-amp outs to connect to a dedicated power amp. The receiver-cum-preamp of course has it's own volume knob. The volume knob does in fact affect the level output through the pre-outputs.

    The power amp also in fact has two (L + R) volume knobs, labeled "gain"

    So, dumb question maybe, but would it be better to leave the pre-amp all the way up and adjust the volume via the power amp? Or would it be better to leave the amp all the way up and control volume via the pre-amp?

    What would allow for the purest signal path and subject the signal to the least amount of processing? Figured I'd ask the electronic experts here :)
     
  2. Metralla

    Metralla Joined Jan 13, 2002

    Location:
    San Jose, CA
    I would have the gain on the power amp wide open.
     
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  3. MrRom92

    MrRom92 Forum Supermodel Thread Starter

    Location:
    Long Island, NY
    Super interesting, thanks for the response. I'm actually intrigued because I assumed it would be the other way around, so I'm definitely surprised and glad I asked. Is there a particular reason this method is better than the other? I'm assuming the knobs on each are attenuators but I have no clue.

    For what it's worth, the receiver is a Marantz 2240 and the power amp is a McIntosh MC2505
     
  4. The Pinhead

    The Pinhead SUDACA ROÑOSO

    Think it this way : inside your receiver the power amp is all cranked up and you control the volume with its preamp, which is integrated with the amp in the same box.

    If you're using just the pre with an external power amp, it's the same thing, with the added bonus that you can cut the volume say in half on the power amp to have a better control over hi-gain sources like cd players playing loud cds and still fine-tune the overall volume with the pre.

    But if you dont crank your power amp loud enough and send a high enough signal from the pre, distortion by overload is bound to rear its ugly head.
     
  5. DaleH

    DaleH Forum Resident

    Location:
    Southeast
    So this is not a dumb question at all too me.

    Gain structure theory would dictate maximum gain at each stage to avoid clipping, noise and distortion in the following stages.

    Volume controls are usually POTs and just attenuate the signal (increasing SNR). This dictates that the greatest clean signal in each component should be maximized.

    Turn the preamp to maximum and set the amp to the level that is the loudest you would ever listen at for lowest noise, unless the preamp distorts at this level

    Not as critical with modern solid state equipment but that old tube preamp may hiss more if you don't follow this rule. Of course that old tube preamp may sound terrible with a modern amp anyway but that is another thread,,,
     
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  6. RiCat

    RiCat Forum Resident

    Location:
    CT, USA
    Perhaps this will help you out. The controls on the power amp are not volume controls. They do adjust the "sensitivity" of the amp. At their lowest setting the amp requires the "most" input voltage to achieve a given power output. When at their max the amp requires the lowest output voltage from the pre-amp to to get that same given output. As an example let's say a pre-amp has a very "large" output as compared to another one. You might not be able to turn the pre volume much higher that say 9 O'clock position before the amp was at full power and everything was to loud or distorted. On the second one you might have had to turn it up to say 3 O'clock to get a usable level. So the amp gives you a control to set the sensitivity so that you have a usable range on the pre volume knob to get the softest and loudest level you want. Since the controls are rarely linear it is hard to say what position is what level of output. You may want to experiment a bit starting with the amp at max and see if you have a usable range on the pre-amp knob. As you back off the amp levels you will have to turn the pre-amp higher. You may not want to max out the pre as it gets close to it's max output the more likely it's specs worsen. So maybe try for a balance where the pre does not need to be higher than maybe 1-2 O'clock position to have things at the very loudest you want. Remember the amp controls do not change the watts per channel rating only the amount of input needed to drive the amp.
     
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  7. timztunz

    timztunz Audioista

    Location:
    Texas
    Totally interesting thread and not a dumb question at all.
     
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  8. mds

    mds Forum Resident

    Location:
    PA
    Yup, I just learned a lot about gain settings on an amplifier, and how to balance the pre with a power amp, thanks.
     
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  9. Ellsworth

    Ellsworth Forum Resident

    This is a very timely subject for me. I just hooked up my new 2 watt Decware SuperZen amp this week and ran into the same question. I have a passive preamp in front of it and was trying to calibrate the settings between the re and power amp. The preamp is a Tortuga LDR DIY version. Raising the volume with the remote just produces a signal with a beeping light but gives no indication what the level is set at.

    I ended up with the power amp set at 90% of full volume. With only 2 watts to work with I ran out of power when the volume at the power amp was set at 65%. So far so good with these settings.
     
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  10. MrRom92

    MrRom92 Forum Supermodel Thread Starter

    Location:
    Long Island, NY
    Great explanations everyone, really appreciate it! I'm going to try turning the amp's pots all the way to the right, should be wide open and at max sensitivity. This has the added benefit and convenience of not having to control the output separately for L/R which would probably induce OCD in the most level-headed among us. :p
     
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  11. Robin L

    Robin L Musical Omnivore

    Location:
    Fresno, California
    As far as I can tell, potentiometers increasingly mangle sound the closer they get to muting the signal. I have been told that the best gain structure is akin to the best adjustment for stylus overhang, one has to compromise to get the closest to an ideal result. I'd set the power amp about 3/4 of maximum output so that the pot on the preamp throttles the signal a little less.
     
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  12. The Pinhead

    The Pinhead SUDACA ROÑOSO

    And you can always lower the gain on the louder channel as well instead of fiddling with those obnoxious balance controls. Cool !:cool:

    Sounds like an oxymoron to me if you're talking about the preamp volume, no disrespect intended.
     
  13. Agitater

    Agitater Forum Resident

    Location:
    Toronto
    Yikes, no. Full gain=full noise. Too much gain also induces all sorts of filtering in the amp. Too little gain induces clipping and other problems.

    Amp gain setting is always one single point that makes best use of the variable volume range (as you vary it with your preamp) you normally make use of when listening to music, movies, etc. So you have to take a look at the amp specs for its gain control and then initially choose a setting that matches your preamp output spec. That's your starting point.

    The other use for amp gain controls is to help match their output in systems with two or more amps.
     
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  14. jupiterboy

    jupiterboy Forum Residue

    Location:
    Buffalo, NY
    I'm pretty sure a big part of synergy is gain matching in the signal chain, and it's where I concentrate most of my energy. I suspect the reason many dislike a piece of gear is because it is a bad gain match.
     
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  15. MrRom92

    MrRom92 Forum Supermodel Thread Starter

    Location:
    Long Island, NY

    I see, I guess it's a bit more complicated than I imagined, as mentioned- much like aligning a cartridge, and it would be a delicate balance between the two to minimize distortions. I will have a look at it today and see what I can do. I can use tones at any level to calibrate anything if I may need to, if that may help.
    At first I thought it would be a matter of "disabling" the potentiometers on one piece of gear by leaving it wide open to minimize the affect that two in conjunction may have with eachother, but this has definitely been an educational experience and I appreciate all of your responses. I'm definitely glad I brought this up instead of just setting something up based on my misconception of how the process worked.

    When you say full noise, what kind of noise do you mean? And also what kind of filtering would be happening?


    When I turn the gain on both channels up and set the meters to the highest sensitivity/lowest range setting, I see only the absolute slightest deflection in the meters, barely visible. I'm guessing this would be the noise referred to?
     
  16. Robin L

    Robin L Musical Omnivore

    Location:
    Fresno, California
    I've done that to a headphone amp. I have Stax Signature Earspeakers and an energizer/amp that drives it. I measured the resistance of the potentiometer adjusted to a level where, if I hooked up the headphone amp to the preamp driving it, the range of levels was such that a normal listening level was when the volume control on the preamp was set around 2/3 open. I made a resistor network to set the headphone amp to that level. I was using the headphones for recordings, often had the headphone amp connected to the variable outputs of my recorders or mixing boards. When adjusted this way the self-noise of the pre-amp was less of an issue. This also slightly improved the sound quality.
     
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  17. RonW

    RonW Forum Resident

    Location:
    New York
    Set the power amp at full volume and use the receiver to control the overall gain of the system.
     
  18. RiCat

    RiCat Forum Resident

    Location:
    CT, USA
    Can you list the speaker, receiver and amp you are using pls? Maybe you ask yourself why so many power only amps have no level controls? They are a feature not a requirement. Props to the "Gain Balancing" reference. That is exactly what this is about. Since your pre-amp is not a standard stand alone design you are fortunate to have the control to balance the amp sensitivity to the pre-amp output control. You do not need any calibration tones or anything else. This is a convenience function. Do a bit of trial and error and find the settings that allow you to listen at levels you enjoy. From my point of view every device in the signal path is a potential source of error. I would start with the amp levels at max and see if there is sufficient range of adjustment at the pre to be usable. Adjust from there to get your desired gain balance. Also as you mentioned those amp controls are not perfectly balanced so that setting each to the same apparent position most likely will not yield identical results in each channel. You could run a test tone(s) and view the outputs on a scope to balance amplitude or measure output voltage to match channel balance...? My guess is when the amp controls are set max they are at the point of being "least in the signal path". As you adjust "down" they are increasing their influence on the signal path. Since the goal is to get the most enjoyable listening experience I say get on with it, start to listen to your music and tweak it up as you go. "How the magic's in the music and the music's in me" (Lovin Spoonful - Do You Believe In Magic).
     
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  19. MrRom92

    MrRom92 Forum Supermodel Thread Starter

    Location:
    Long Island, NY

    What you say makes sense, as do the differing opinions here, so I guess there is no right or wrong way and I'll have to take an afternoon to play around with different settings and hear what's best. You are right in that other power amps don't have any level control, at all so it may be best to just leave those wide open at the point where it has no effect on the signal chain, as if they were never on the amp at all. Some experimentation will be necessary.


    Here is the current setup

    Receiver (pre-amp outs) - Marantz 2240

    Power Amp - McIntosh MC2505

    Speakers - Wharfedale Mach 3
     
  20. Robin L

    Robin L Musical Omnivore

    Location:
    Fresno, California
    I'd hazard a guess that the preamp section of the Marantz 2240 is slightly higher than that of your McIntosh MC2505. I'd experiment so that you have the potentiometer running more 'open' than the power amp. But I'd listen for self noise from each first.
     
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  21. avanti1960

    avanti1960 Forum Resident

    Location:
    Chicago metro, USA
    Good advice.
    Too much gain can also induce clipping at lower volume levels as well.
    The best way to set the gain is to measure the amplifier output voltage.
    An amp should list a target output voltage (maximum power for a given speaker impedance, e.g. 24V @ 4 ohms).
    Disconnect speaker wires from speakers.
    Set the premp to 3/4 volume.
    Play a 1Khz test tone (available download) while measuring the output voltage across the end of a speaker wire.
    Set the gain for each channel until voltage reading equals target output voltage- e.g. 24Volts.
    You are now setup so your power amplifier delivers full output at 3/4 preamp volume level.
     
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  22. avanti1960

    avanti1960 Forum Resident

    Location:
    Chicago metro, USA
    Not optimal.
     
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  23. Robin L

    Robin L Musical Omnivore

    Location:
    Fresno, California
    Sorry, should have written: I'd hazard a guess that the preamp section of the Marantz 2240 is slightly higher in noise than that of your McIntosh MC2505.
     
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  24. avanti1960

    avanti1960 Forum Resident

    Location:
    Chicago metro, USA
    Your Mac puts out 50 watts / channel @ 8ohms. Power = Voltage squared/ resistance. 50watts= (20*20)/ 8 Ohms.

    You should set your gain so that you measure 20 Volts across the speaker leads of the 8ohm terminals at 3/4 preamp volume when playing a 1Khz test tone.
    At 3/4 volume your amp will produce rated power and leave you a little something in reserve.
     
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  25. RonW

    RonW Forum Resident

    Location:
    New York
    It's what is done. Optimize if you wish.
     
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