John,
I had similar questions and an audio guru explained this to me in an email (BTW, it is not 1mV, but 1V). Please see below for information you seek. It is a cut-paste from the email, and NOT my words. But it is an excellent explanation and I feel this community could gain some knowledge from it. So I wanted to share this. Hope it helps:
Thank you, that does help a lot. I thought the assumption of uniform attenuation might have been wrong, but without more information it seemed like a good guess
. Milpai, when you say 1v instead of 1 mv what exactly are you referring to? The tvc will work best with amps that have input sensitivities at or below 1v instead of 1mv? 1 mv seems very low for the standard promitheus tvc. And using the numbers/formula from your response, a pretty low voltage output from a dac/cdp would be needed to get 1mv or below out of a standard tvc. Using 1v out (stated in your reply as norm max for most cds), then even at full attenuation of 54db, the tvc outputs:
position 1, -54db, plug into the formula: 1/10^(27/10)=.001995 x 1v = 2mv, seems you would be over driving any amp with a 1mv or lower input sensitivity anywhere above the first click or two.
One of Nick's custom tvcs (60db or 72db of attenuation, see link in next paragraph), would have extra clicks before over driving a 1mv input sensitivity amp, maybe that is what Brown is referencing when he says below 1mv Input sensitive amps are the best match for the tvc. If less than 1mv is recommended, I would really like to understand why getting below that value gets the most performance from the tvc, don't see it in the numbers. I can see why it would not from the information and formula provided in your reply, and running some additional numbers in this post. Anybody have reasons why < 1mv is the best match ??
I have two tvc's (a standard, and a ref4) both purchased used in 2007. From Nick's reply here
http://www.audiocircle.com/index.php?topic=67939.msg629152#msg629152, the units I own are probably the earlier 48db as max attenuation, and such only 22 steps instead of 24 steps in newer versions. Not sure at what point, if at all -3b decrements begin on the older units, but until more information is learned, will use -2b steps for the first 18 clicks from minimum attenuation, and -3db for the final 4.....might not be correct, but it should be close, and gets me to the -48db value for full attenuation.
Revising calculations based on what you posted, here are some #'s for my equipment:
To reach the input sensitivity of the mono extremes (assuming 1.44V from the earlier quoted post is correct), the tvc would need to be near minimum attenuation (between 1 and two clicks from minimum):
1 click from minimum attenuation(position 21) : -2db, halving attenuation and plugging into the formula: 1/(10^(1db/10)=.794, multiply by the output of the paradisea dac, 1.58v.
2 clicks from minimum attenuation(position 20): -4db, halving attenuation, and plugging into the formula: 1/(10^(2db/10) =.631, multiply by the paradisea 2.0v output=1.26V
What usually works out to be my preferred setting when using this setup is at clicks 15, 16, or 17 gives the following:
click 15: -14db: 1/10^(7db/10)=.1995 2x20%=.4v, 400mv
click 16: -12db: 1/10^(6db/10)=.2512 2x25%=.5v, 500mv
click 17: -10db: 1/10^(4db/10)=.3981 2x 40%=.8v, 800mv
On the topic of cd recording levels,I do notice significant variations in the volume levels between flac files, taken from original cds. Some like "Heart shaped world" by Chris Isaak, sound very low in the 15-17 click range, and others like most all of Norah Jones cd's sound much higher. I have flac files from a Minnie Driver cd that are painfully loud above click 16, so that one must have used a recording level that maxes the 2v output of the paradisea dac. It is by far the loudest of any cds I own. I purchased it online, and it was a pre-production cd, usually sent out to radio stations, and others in the recording industry prior to the general public release. Maybe the levels were modified to a lower level for the public release cds, the version I have is too loud/hot on every track.
Interesting that where I prefer the tvc (between 440mv and 800mv), the amp is getting between 30%-56% of its input sensitivity 1.44V, for any recordings that do reach 2v out of the paradisea, and much less than those %'s if 1v max out of the paradisea is the norm because of production cd levels. For my setup, the tvc is amazing for most music, however, music where I want it to be very loud/dynamic, something like jamming rock/punk (Porno for Pyros, Rage Against the Machine), or techno/electronic (Rob/white zombie), never feels like I am getting there. I recently purchased an active pre from another audiogon user, and it definitely drives the odysseys to much higher levels, and gets what I am looking for on those crazy loud rock/techno tracks, but it can't touch the sound of the tvc for just about any other music type...the overall presentation is just better when using the tvc with jazz, old R&B, country, and even unplugged rock (like Nirvana's mtv session) in this setup. Guess most music types don't need the full output of the odyssey mono extremes to be at their best. I mean who wants to hear a female vocalist, like Norah Jones, country legend like Johnny Cash, or Jazz/blues great like Ray Charles, piercing their ears? Now, Perry Farrell (PfP), or Zack de la Rocha (RAtM), things just don't sound right if they don't make your ears hurt a little
.
If max value of 1v from the paradisea dac (what was stated as maximum on most cd's), is what the tvc is getting input, then even at
0db attenuation, still only reaching about 70% of the odyssey input sensitivity. Maybe that explains why I feel like some music is under driven when using the odysseys and the tvc. I am very curious to learn more about what I am hearing with the tvc and the odyssey mono extremes, and may cross post most of the information learned here in the odyssey circle to see what users who frequent it might think. Wanted to gather a comfortable knowledge on what exactly the tvc was doing first, before tracking down its interactions with the odyssey amps. Milpai, your post has really helped, thanks again.
