2. amps-preamps
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Choosing proper gain for preamp. Am I screwed?

I am in the process of selecting a new preamp. Some candidates offer customized gain (output), all offer only three inputs (good forme: CD, DVD, cassette deck). I find it amazing how diverse my CDs are in their playback levels. For example, for normal listening levels some require my preamp volume be 15, and some 38!? I can understand some discrepency, but not that much. If I could turn my pramp up to 250 this would not be bothersome. But much past 42 seems to kind of approach maximum voltage territory to my power amp. My CDP puts out 2.3v RMS. My DVD player puts out 2.0v, yet I always have to crank the volume way up on my preamp to hear dialogue adequately (again, upwards of 38). (And my tape deck 490mv.)

What I do not want to do is have a preamp built for me which limits the gain so that I'll not be able to reach adequate levels for DVDs and my wimpy CDs. But I think I'd rather not have the standard 20dB of gain either. My power amp's sensitivity is just over 2v. Way more (10 times?) than my power amp can ever use.

I guess my first question is, what is likely the major cause of the playback level discrepencies?

And,not knowing what the gain is on my preamp (because it is an integrated and they don't specify), am I destined to specify 20dB gain on my new preamp outputs just to be safe? (Seems to me, 10 times the amount of gain necessary to drive my amp to full power would make for crummy low-level listening and also add a bunch of unecessary noise.)

Any ideas would be appreciated. Thanks.
rockadanny
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rockadanny OP
1,226 posts
 
I may not have been clear in my above post. I guess what I'm asking is: has anyone else experienced such diverse output levels on the basis of different CDs or DVDs? Perhaps this is just a common occurrence people just live with? Perhaps there is something inherently askew with my integrated being used as just a preamp? I didn't pay much attention when I used just the integrated to what volume I was remote dialing from my couch, since I cannot see the numbers anyway.
unsound
7,329 posts
 
You may be able to get a pre that has different gain settings for different source inputs.
plato
1,543 posts
 
Well, preamps can be built with widely varying amounts of gain, generally from unity gain to over 20dB of gain. And volume controls can have different tapers. Some give you most of their volume in the first half of their rotation and others are more uniform in their volume increments.

For example, when I have my preamp in its high-gain mode if I turn the volume knob a quarter of an inch I'll get a large increase in volume. If I switch it to its unity-gain mode, I have to turn the knob more like an inch or so to get the same apparent volume increase. And yes, different CDs are recorded at different levels, but how far you actually need to increase the volume will vary from preamp to preamp.

Maybe a good solution to your problem would be to get a preamp that offers both and active gain stage and a unity-gain stage. That would allow you to adjust for a very wide range of recording levels as well as the differing output levels of your components.

The Adcom GFP-750 has that feature and I believe one of the Rogue Audio tube preamps (the 99, I think) has adjustable front-panel gain settings. Also, I believe the PS Audio Gain Cell preamp has independently adjustable gain settings for each input.
audphile1's avatar
audphile1
5,131 posts
 
what is the input impedance on your amp? IMO that should be a factor in selecting a new preamp. 20db gain is high. I think on many tube preamps the gain is normally 6-12db single-ended and 12-18db balanced. Also you have to look at output impedance of the preamp. I think some BAT preamps have adjustable gain. You may want to contact your amp manufacturer for a recommendation on what gain should be optimal for a preamp to drive and not over or under drive the amp. And it's probabl a good idea to look for a preamp with fine stepped volume control. This way you can dial in what you like.

I also found that some CDs are recorded lower than others. For example, when I am listening to Patricia Barber Cafe Blue, track 9 Too Rich For My Blood, recording level is pretty low, especailly at the beginning of the track. I have to turn it up to about 1 o'clock on my preamp. But take PB's Modern Cool and the optimum volume is at about 11 o'clock. This is just one example. I beleive this is OK.
rockadanny OP
1,226 posts
 
Hmm ... an active gain stage and unity as well. Good thought. Thanks.
hdm
1,062 posts
 
Frankly, I wouldn't worry about it. I've experienced exactly the same thing with my setup and would bet that many others have as well. The digital volume readout on my integrated is typically anywhere from 12-20 on most of my CD's, with DVD's I more often than not end up in the 30's while watching movies (and this is playing both CD's and DVD's on the same player). With vinyl (and 62 db of gain in my phono preamp with a Denon 103R), I run anywhere from 18 to the mid 30's depending on the record and how loud I want to listen). If it sounds ok, relax and forget about it.
swampwalker's avatar
swampwalker
5,138 posts
 
Just one quick thought- too much gain with a pre, unless it has VERY fine steps/taper, will be a real problem. Most attenuators/volume pots are very non-linear at the beginning of their travel. The l & r channels will tend not to track well. Plus, if you have a stepped attenuator, you may not be able to find the "right" volume.
eldartford
4,262 posts
 
When they "cut" a CD (just like an LP or a mag tape) someone needs to decide on gain, so that the loudest moments do not saturate the recording medium. In the case of a CD this maximum recordable level is exact...all 16 bits used. (For an LP this maximum level is not exact because it all depends on how well the playbact cartridge can track the groove. For mag tape it depends on how much increased distortion is considered acceptable). When a recording has a wide dynamic range most of the time it will be recorded at a low level so that when that loud moment comes along saturation does not happen. A recording with little dynamic range will be louder most of the time. "Compression" is a process that automatically varies the recording gain so that there is less dynamic range. Your CDs that sound loud have been more severely compressed than the others.
rockadanny OP
1,226 posts
 
All good thoughts. Thank you all. I appreciate your input.
rockadanny OP
1,226 posts
 
I ended up specifying gains for my soon to be built preamp as: 10dB, 10dB, 18dB. Thanks for your input.
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