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

This is from a Parasound's amp owners manual regarding:

Level Controls
Each channel has its own rear mounted "set and forget" input level control. Your amplifier will
sound best with these level controls set to maximum, where they are effectively out of the audio
signal path. However, if your preamplifier has very high gain, and its volume control cannot track
properly for left-right channel balance near its minimum position, it may be necessary to reduce the
input level control settings on the amplifier. When using the HCA-2205A in a THX installation, each level control must be set at maximum to correspond to 0 dB THX reference level

 

I've decided to set it and forget it with the pots wide open. Sounds great to my ears. Too great. Now to upgrade every other component in the chain!

 

The most simple rule of thumb is that your max unclipped volume setting at the pre-amp should be at about the 2 o'clock position. If the pre-amp volume clips at below the 12 o 'clock position, or if the power amp gain must be set below 12 o'clock (to not play too loud), then there is a mismatch.

If the power amp gain settings are wide open, and the pre-amp volume control is pretty much at the 2 o'clock position (thereabout) to obtain full volume, this is ideal.

To set the power amp gain, start with them at near minimum setting, set the preamp at 2 O'clock (your target max volume with normal program) Then raise the power amp gain controls until you reach the loudest you care to listen, or when the amp just starts to clip .. be careful .. then back off a few degrees on the amp gain controls. They should be at about the same 2 o'clock position as the pre-amp volume controls, or higher.

As many members have commented, lower sensitivity settings (gain settings) tend to veil the signal, although it may take good ears to tell the difference. The best signal quality and openness is realized at higher potentiometer settings... all potentiometers in the signal path. There is very little difference between 2 o'clock and wide open, quality-wise.

It is good to be aware that almost all preamps have an extra gain stage as a reserve to compensate low level sources, such as a 2.5 mv cartridge, or a 1st pressing 80's CD mastered at -10 dB.

 

I want to make absolutely sure I understand this . I use a Parasound pre amp with a Parasound amp. I know that the manufacture recommends leaving the amp's gain controls on full. Is this really producing the optimum sound, or might I be better off reducing the amp gain and increasing the pre amp volume when I listen? Right now 9 to10
o'clock is loud when I listen.

 

You may be thinking that gain and volume are the same things. They're not. Setting the amp's gain to full increases the sensitivity of the amp's inputs. Using the volume control on the preamp then makes use of the quietest part of the preamp's circuitry while at the same time getting full advantage of everthing (headroom, current, dynamic range, damping factor, etc., etc.) that the amp has to offer. Just as the manufacturer recommends: amp on full, preamp controls the volume. The amp will be more responsive, your preamp will be running in its ideal range, and I think you'll be happier with the sound.

 

I've been running the past few months with the gain pots open and I don't know why I ever overthought it so much. It sounds beautiful. Guess I just never had an amp with adjustable input senitivity before. Everything sounds great.

 

Assuming this is true, why do companies like Parasound even bother putting gain controls on amplifiers instead of a pre-setting that automatically keeps the gain on full? As you can tell, I know very little about this.

 

From a post above:

In almost all pre-amplifiers, this is never an issue.

 

Like Chili re-posted, some preamps don't fully track left/right channel balance properly. I also agree with Chili about most preamps not having the issue. But there are a lot of different preamps out there too, and because Parasound sells its amps separately it can't guarantee the best possible match with whatever non-Parasound brand a customer might have.

 

Just for the heck of it, I reduced the gain on the amp from 12 o'clock (fully open position) to about 10 o'clock. I definitely had to turn the up the volume on the pre-amp significantly higher. The overall sound seemed different to me also (a little less brighter, more bass). Does this sound normal, or do I have a problem?

 

No problem. There is tons of research that confirms even slightly louder music is always judged better. There is even some recent stuff show brain area stimulation by louder sounds that translates to excitement and preference for the louder volume. Even very small level differences produce a preference for the higher one. So without very precise level matching in your comparisons, your comparisons may not be objective. In the end go with what you like the best. I would set the amp to full gain and use the pre section as needed for room volume.

 

. . . which is why the amp makers advise running their amps at full gain when using a separate preamp. Controls are usually present to change things, and that's another reason that when you change control settings the system sounds different. Put the control settings back to where they were when the system produced the sound you prefer. Makes sense, no? There's nothing wrong with your system.

 

Thanks guys. I listened for a couple hours today and I actually like the sound better with the gain turned down from 12 o'clock (fully open position) to about 10 o'clock. The bass is definitely a bit deeper and the overall sound is smooth. I'll probably have to listen more to make a final determination.