[milpai]

Hi All,

I have the Ref C-Core and want to get a new power amp. I am not too technical when it comes to gear. Should the "input sensitivity" of an amp be on higher side (> 1.0mV) or on lower side (< 1.0mV) for the TVC+AMP to sound great?
Currently my integrated amp that is being used as a power amp has input sensitivity of 770mV and I have to go from (click) 0 to 12 for the sound to be at moderate level in my 12X14 listening room.

Thanks

[Brown]

The lower the better. Below 1 mv is desirable. TVCs are at their best when connected to an amp with very low input sensitivity. Further use cables under two meters. even though the TVC has been tested to use up to 5 meters I found that shorter sounds better.   

[milpai]

Thanks for the reply Brown.
So does it mean that a stereo power amp that I plan to buy, which has input impedance of 22KOhms and sensitivity of 2.0V and power output of 110X2 at8Ohms will be unsuitable for my TVC?

[Brown]

its not the best choice. The input sensitivity is too high. Under 1mv is recomended TVCs are NOT for all amps IMO. Now where they really shine is with SET [ Single Ended Triode ]  amps.
   I am sure many buyers have had good results with other amps. What I am saying is to pull every last bit of performance from a TVC  SET amp with low input sensitivity is the ticket.
    Be prepared to maybe reconsider your CDP. The TVC WILL give you 100% of the character of such. So in your CDP up to the challenge of the transparency of the TVC.
    Again TVCs are NOT for all systems but when your system is receptive then by all means GET ONE.

[guest48077]

My Amps are 1mv. I am using the same same TVC that you are looking into. I am getting very good results. I love them

[milpai]

Brown,
My CDP is pretty good. It is a Marantz SA-8260. I do not want to go the tubes route. Just out of curiosity - what is the input sensitivity on these SETs that you are mentioning? My current NAD has input sensitivity of 770mV. But I believe it lacks the "current" that the Quads would sing with.

Undertowogt,
I did not get the details on your amp. I am looking at the Parasound A21 or The Odyssey Stratos for my Quad 21L which are 88dB with 6 Ohm nominal impedance.

[guest48077]

[quote author=milpai link=topic=71162.msg666196#msg666196 date=1252000888

Undertowogt,
I did not get the details on your amp. I am looking at the Parasound A21 or The Odyssey Stratos for my Quad 21L which are 88dB with 6 Ohm nominal impedance.
[/quote]

I have POWERED MONITORS for now. Yorkville YSMp1's they are a VERY good affordable near field studio monitors.........$500 a pair.

The specs are:
10k ohms Input Impedance
1Vrms Input Sensitivity.

I have the dual mono TVC with 1 XLR input and 2 XLR outputs. I made a DIY PASSIVE RCA switch box with 8 inputs and one output....this output goes to the TVC input.

Doing it this way I saved money on the TVC as I only ordered it with one input. I also now have 8 inputs instead of 3 or 4. This is a route you may want to explore if you are just a little handy with a soldering iron...............See my pictures for Clarification.

[Brown]

Brown,
My CDP is pretty good. It is a Marantz SA-8260. I do not want to go the tubes route. Just out of curiosity - what is the input sensitivity on these SETs that you are mentioning? My current NAD has input sensitivity of 770mV. But I believe it lacks the "current" that the Quads would sing with.

Undertowogt,
I did not get the details on your amp. I am looking at the Parasound A21 or The Odyssey Stratos for my Quad 21L which are 88dB with 6 Ohm nominal impedance.

   They are .6 mv. Please let me say again that TVCs will work well with a higher input sensitivity [ no higher than 1mv is recco]. IMO when one uses am amp with the lower senitivity it will give better results.
    Both amps are good choices. So if you can audition them in YOUR system your ears will tell the tale.   

[milpai]

I hope to select the amps within a few days if all goes well

[Brown]

I hope to select the amps within a few days if all goes well

 Good luck.

[milpai]

I hope to select the amps within a few days if all goes well

 Good luck.

Thanks. Looking to the Parasound A21. Seems like an upgrade from my current amp - at a good price.

[jmck407]

The lower the better. Below 1 mv is desirable. TVCs are at their best when connected to an amp with very low input sensitivity. Further use cables under two meters. even though the TVC has been tested to use up to 5 meters I found that shorter sounds better.

Brown,

I have been struggling to understand what amps match best with a TVC and why.  Could you (or anybody else) give some details on why a TVC performs best with an amp of very low input sensitivity, below 1mv?  My knowledge on this topic is limited, and a guess might be that the low input sensitivity allows the tvc to be able to give the amp a voltage well above it's spot of maximum gain (input sensitivity of the amp?) thus doing what most active pre-amps achieve with gain.  But this could be entirely wrong.

The TVC seems to work quite well in my system using Solid State amps, and a tube DAC. The only times I feel the tvc is not a good fit is when I want very loud/dynamic sound for rock, or electronic type tracks.   Bumping the tvc below 20%  voltage step down (80% of max on volume knobs) causes things to get pretty ugly.  I have tried to figure out why the tvc works well with the amps for most other music (jazz, blues, country, etc..) when it's input sensitivity is well above the desired 1mv.  Below is one such attempt:

I currently have a Paradisea DAC Rev 1 http://dhost.info/mhdtlab/P3.htm (outputs 2.0, this is a rev 3 but I think the output Voltage stayed the same) to a promitheus rev4 TVC connected to a pr. of Odyssey mono extremes.   I can't seem to find where Klaus has stated the input sensitivity of the Odyssey mono extremes, but in this link, they are calculated at 1.44V http://www.audiocircle.com/index.php?topic=3275.msg27024#msg27024 , and Kluas does not dispute the calculations. 

From Nick's TVC FAQ http://www.promitheusaudio.com/tvcfaq.htm my understanding of what the TVC does is attenuate the input voltage with 0 clicks on the volume knob/transformer being about full attenuation (about 0V),and maximum clicks (on my ref4 tvc 22) at about 2.0V when inputting the paradisea to the tvc.  Also as you increase the clicks from minimum, the output impedance of the tvc goes upward.

If the numbers are correct for input sensitivity of the Odyssey amps, then at about 72% of max, the TVC would be sending a voltage equal to the input sensitivity of the amps (2v from DAC x .72).   And that is about where I  have the volume knobs at on the TVC with that setup, 72% of 22 is about 16.  Most tracks sound best between 15 and 17 clicks on the tvc volume knobs.

For the same DAC, and the rev4 tvc, the minimum you could step the 2V of the DAC down at one click of the volume knob would be 2000/22=91mv...assuming each click attenuates equally.   Does that mean that any amp with an input sensitivity below 100mv, you would be at or above the input sensitivity at 1 or two clicks on the volume knob?  Is the extra "head room" on the volume knob (another 20 clicks, versus the 6 of for my odyssesy monos) what makes the low input sensitivity amps desirable for the TVC's?  Would the extra "head room" help get things loud for rock/electronic music without it sounding messy?

I have also read where people have said that if you have a high gain amp, then that overcomes the undesirable high input sensitivity values when used with a passive pre.  Maybe this is why things sound o.k. to me with the Odyssey monos with most music.

Brown or anybody else please comment to let me know if I am way off on understanding things, or close.

Thanks,

John

[milpai]

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:

----------------------------------------------------------------------------------------------------------------------------------
When your amplifier manufacturer indicates the input sensitivity of your amplifier is 1V, what he is telling you is that it takes only a 1V input signal in order to drive that amp to its maximum volume level.  If you were to increase the amplifier input to a value in excess of 1V, the result would be a distorted signal from the output of the amplifier (also referred to as ?clipping?) and likely damage to your speakers.  As a result, you will get the full range of possible volume levels out of your audio system when operating with an amplifier input voltage that never exceeds 1V.  This is an important point in that a lot of audiophiles think an amplifier will always provide a certain fixed amount of gain such that any input signal will automatically be amplified by a certain factor.  This sort of logic leads people to think they can increase the ?headroom? of their audio system by, for example, buying an active preamp that offers a higher amount of gain.  This is flawed logic, and it is simply not true.  Once the input signal to your amplifier reaches the voltage level specified as the input sensitivity, any extra voltage gain above that level that is available from your source components and preamp is of no use to the amplifier.  To send a signal to your amp with a voltage level that exceeds the input sensitivity will only cause distortion, clipping, and damage to the system.  (You would immediately know that something is wrong, leading you to lunge for the volume knob in order to turn down the volume.)

 

Since your CD player has an output voltage of 2.2V, you will need to reduce or ?attenuate? the output signal from the CD player in order for that signal to be compatible with the 1V specified input sensitivity your amplifier.  That is where the TVC comes into play.  The sole purpose of the TVC is to reduce or ?attenuate? the signal from your source components so that the signal passed along to the amplifier is compatible with its specified input voltage and results in a decibel level that is right for the listener.  In your case, the TVC will need to reduce the output signal from the CD player by about 50% even if you want your amplifier to play at its maximum power output level.

 

Now, to get more specific about what your TVC does in order to achieve this reduction or ?attenuation? of the input signal, each of your two TVC boxes contains a transformer.  The purpose of a transformer is to alter the voltage and amperage characteristics of an electrical signal.  A transformer can either ?step up? or ?step down? the voltage level of an electrical signal.  As a result, you will often see transformers referred to as ?step-up? or ?step-down? transformers.  It is also possible for a transformer to pass the electrical signal through in an unaltered manner so that the voltage and amperage values are the same at the input and output of the transformer.  However, in this case, the transformer is serving no obvious purpose and appears to be just an unnecessary piece of equipment in the signal path.  When a transformer increases the voltage level of an electrical signal, the amperage level of that signal is decreased by a corresponding amount.  Similarly, when a transformer decreases the voltage level of an electrical signal, the amperage level of that signal is increased by a corresponding amount.  The total power or ?wattage? of the signal is always preserved (except for a minor amount of loss of energy due to heat and noise caused by the inherent inefficiency of even a well-designed transformer).  Since volts x amps = watts, you can see how the relationship works here.

 

With that as background, your TVC is inherently a step-down transformer with a range of settings on the volume knob that equate to different levels of attenuation for the music signal.  When the volume knob is turned all the way clockwise to the maximum setting, the transformer is applying no attenuation to the signal.  As a result, with the TVC in this setting, the 2.2V signal from your CD player is passed along to the amplifier in an unaltered form and your amplifier sees an input signal of 2.2V as if the TVC were not in the signal path at all.  Of course, with an amplifier that has an input sensitivity of only 1V, this would have disastrous results given that you would be significantly overdriving your amplifier.  Damage to your speakers and/or amplifier would likely result.

 

As a result, the TVC is a very necessary component in this situation.  The TVC will need to reduce the signal to a voltage level that does not exceed 1V in order to operate within the performance limits of your amplifier.

 

Now, the topic of which setting on the volume knob is the ?right one? is a bit trickier.  The attenuation of the voltage level of an electrical signal is measured in decibels (dB).  I believe that most of the standard-version Promitheus TVCs offer -54dB of attenuation.  (Upon request, Nicholas can customize the range of attenuation for you; however, I believe the standard versions of his TVCs all offer -54dB of attenuation.)  Nicholas uses 24-pole switches for his volume knobs, meaning that you have 24 different settings that allow you to dial in 24 different levels of attenuation.  I believe the lowest setting (volume knob turned counterclockwise to the first position) equates to -56dB of attenuation, and the highest setting (knob turned clockwise to the 24th and last position) equates to zero attenuation.  Starting with the volume knob at the highest (24th) position, each counterclockwise click of the knob dials in an additional -2dB of attenuation.  Once you reach the 12?oclock setting on the dial, the incremental level of attenuation increases to -3dB for the last ten counterclockwise clicks of the volume knob.  As a result, I believe the 24 different volume settings are as follows for a typical Promitheus TVC:

 

Position 1 (lowest volume setting) -56dB

Position 2 -53dB

Position 3 -50dB

Position 4 -47dB

Position 5 -44dB

Position 6 -41dB

Position 7 -38dB

Position 8 -35dB

Position 9 -32dB

Position 10 -29dB

Position 11 -26dB

Position 12 -24dB

Position 13 -22dB

Position 14 -20dB

Position 15 -18dB

Position 16 -16dB

Position 17 -14dB

Position 18 -12dB

Position 19 -10dB

Position 20 -8dB

Position 21 -6dB

Position 22 -4dB

Position 23 -2dB

Position 24 (highest volume setting) 0dB

 

Now comes the tricky math.  To calculate the extent to which the input signal from your CD player is attenuated by your TVC, take the number of decibels of attenuation, divide by two and plug the result (x) into the following equation: 1/ (10^(x/10)).  For example, when the volume knob for my living room TVC is in position 17 (-14dB, which is around the 2 o?clock setting), divide the 14dB of attenuation by 2 to produce a value of 7.  We then calculate the denominator of the equation: 10^(7/10) = 10^0.7 = 5.012.  This means that 14dB of signal gain is equal to roughly five times the voltage level, and -14dB of signal attenuation is equal to 1/5 the input voltage level.  So -14dB of attenuation means we are reducing the voltage level of the input signal by 80%.  As a result, if the input signal to my TVC is a 2V signal, the TVC will pass along only 1/5 or 20% of that signal to the amplifier, which means my amplifier will see an input voltage of 0.4V or 400mV.

This brings up an interesting point in that the input sensitivity of my amplifier is specified as 250mV.  So, on the surface, since 400mV is in excess of the 250mV input sensitivity, it would appear that I would be driving my amplifier beyond its limits with the volume knob dialed up to the -14dB setting.  However, it is important to note that the output voltage specification on a source component represents the maximum output level when playing a disc that is recorded at the very highest possible recording level.  Nearly all CDs are recorded at a level where the musical peaks never reach the maximum signal level that can be recorded on the disc.  As a result, very few discs will ever result in your CD player outputting its full 2V potential even when playing the loudest passages of music on that disc.  In fact, most discs will have peak levels that never go much above 1V.  Thus, you will find that the volume setting on your TVC tends to be about 6dB higher than would be implied by a full 2V output signal.

[Derockster]

Hey guys just want to say this is great stuff,helps me to understand what my TVC is doing or more so not doing.Would be great if we could get some input from the creator of this great product.Regards derockster

[jmck407]

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.

[milpai]

John,
Sorry, could not get to you earlier. By 1V sensitivity, I mean the sensitivity of the power amp. For eg. the Parasound A21 has Input sensitivity of 1V. That means 1V is required for Parasound A21 to put out the full 250Watts.

Your calculation is correct. But please read to the previous post. My friend calculated 1/5 based on the formula 1/10^(7/10) = 1/10^0.7 = 1/5.012 which is approximately 1/5. What he means is that one-fifth of the output from CDP will be sent to power amp. My CDP outputs 2V and 1/5th of that is 400mV (0.4V). So your calculation when interpretted properly should say, of your CDP's 2.0 volts only 1/500th will be sent to the amp which is 4mv (0.004V).

Looking at layman's (like mine) view it would mean that if I position the TVC know to 12 (of the available 24), the input signal from the CDP will be divided to 1/2 thus achieving 1V. But this is incorrect. And again for the explanation, here is the explanation that I got from my friend (John, we both owe him a big thanks dude!!):

------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
If you run through the math outlined at the bottom of the last post, you will see that the 12 o'clock position on the volume knob (position 12) corresponds to voltage attenuation of -24dB.  This equates to a 94% reduction in the voltage level of the input signal, which means a 2V signal would be reduced to only about 120mV.  (Given that your CD player will be outputting peak voltage levels closer to 1V when playing most CDs, the actual peak voltage level seen by your amplifier would more likely be in the range of 60mV.)

To achieve a 50% reduction in the input signal, you need attenuation of only -6dB, which is between the 4 o?clock and 5 o?clock positions on the volume knob.  This means, with a CD player rated at 2V of output voltage and an amplifier with input sensitivity of 1V, you will most likely be operating your TVC turned up well beyond the 12 o?clock position.

The issue with an amp with low input sensitivity (high value in the range of 2.0V) is, you wind up running the TVC with almost no voltage attenuation applied to the output signal from your source components.  This means the TVC is not allowed to ?work its magic? by increasing the current and lowering the output impedance for the signal it sends to your amplifier.  This invites potential problems with frequency response roll-off and/or compression of dynamics.

------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------

Again, whatever info is in between the 2 lines is from an online friend, and I will not take any credit for it. I can only thank him much 

[trebejo]

John,
Sorry, could not get to you earlier. By 1V sensitivity, I mean the sensitivity of the power amp. For eg. the Parasound A21 has Input sensitivity of 1V. That means 1V is required for Parasound A21 to put out the full 250Watts.

No, hold on, that's not right. There are two ways to talk about an amplifier's input sensitivity. The first is the way that you are thinking of it, i.e. as the input voltage required to achieve maximum output.

The second way is the way that Parasound is doing it: it correlates an output signal to an input signal. In the case of the A21 (and the A23, I might add), the signal gets amplified by a factor of 28.28, as it goes from 1V to 28.28 V. However, I doubt that 28.28V is the same as 125W across 8 ohms.

It's probably easier to talk about the gain--I don't know why Nicholas does not talk about that instead of the input sensitivity.

So anyway, the A21 has a gain of 20*(log(28.28/1)) = 29db, which is typical or maybe a little high. HOWEVER, note that that is across its xlr inputs! Since the xlr voltage is usually twice the rca voltage, you get a bonus of 6db compared to what other amps might spec.

So if the CD/DAC/whatever has xlr outputs at 4V, then the TVC will pass those 4v through to the amp and you'll get an extra 6db (which, I think, means an extra three clicks on the dial). The parasound manual also says something about the sensitivity for the rca inputs, but I am not sure how to interpret it so if you are not using xlr, you may want to ask them about it.

With xlr, it looks like a nice amp to pair up with the TVC (as does the A23). An SS amp will typically give you around 28db of gain on its rca inputs, and all bets are off about its xlr inputs (since many amps are not truly differential even if they have xlr inputs). So if you can get 35db, it sounds like a good match.

[milpai]

trebejo, I am not sure what you mentioned is correct. I got the Parasound A21 over the weekend and pretty much like the combination. I am still at the 11-12 o'clock position for my normal listening. BTW, not all CDPs output twice as much voltage through XLRs. Carys and Marantz do that but I don't think Sony does that.

Soundwise, the new amp did not impress me when I FIRST switched it on. I let it burn-in for about 10 hours. The amp has started to open up. There is a sense of natural sound to the saxaphone that I had not heard in the NAD. My bass also has some definition now. I will not call it night-n-day difference when compared to the NAD. But for me it is worth it. I think it is at the low and high listening volumes that this amp makes a difference. The resolution is not lost at these levels. With the NAD at high volumes, I would quickly turn it down as the resolution would be lost. At lower volumes, the amp lost a bit of upperend frequencies. Though I like the new amp, the NAD was no slouch.

But the Parasound A21 and Promitheus TVC are a great match.

[trebejo]

Good for you, milpai! It's nice to find a good amp.

You can try the xlr vs. rca experiment with that amp, and see if the volume knob remains in the same position for the same loudness. You can also contact Parasound, they will be able to tell you about the difference.