[JoshK]

Good posts Steve.  The thing that puzzles me is the "turning voltage into current" explanation.  Now I haven't completely thought this through...its an impromtu post, but help me think this through...

From Kirchoff's law we know that current is preserved in a closed system.  So current out = current in.  Pot is a voltage divider so part of the current is going to ground, part is going to amp.  The primary side of a tranny has a DCR which makes me think it too acts like a voltage divider, so why would this be any different for a TVC/AVC than a pot?  I can only surmise it has to do with AC properties rather than DC properties (i.e. reactance).

[NewBuyer]

Thanks again Steve! By the way, I was asking you if you could provide a personal explanation of why the pot vs. TVC sound "different", not "better or worse". I do think that most people who compare, find TVC preamps sound superior to pots/stepped-attenuators, but that wasn't the point I was making. I'm sorry I wasn't clear in the post, my fault - I guess I just thought my implication/distinction was obvious when I was writing it - but just as obvious of course, is that you cannot read anybody's mind! 

You see, the provided explanation of how resistor-based preamps literally resist and convert some signal to heat, vs. the TVC trading voltage against current, makes perfect sense to me. But I am not an audio engineer and I don't posture myself to be an expert. I am always learning so much in this field.

My question is: Why does the pot/stepped-attenuator approach produce such a noticeably different sound result than a TVC? Obviously they are different mechanical things, operating on different principles - we all get that  - I'm just wondering if you wish to elaborate on the "why", i.e. what specifically about these different operating principles, enables them to sound so different from each other. Not trying to put you on the spot either - no worries if you prefer not to comment on these audio principles. Just asking! 

[Steve Eddy]

Good posts Steve.  The thing that puzzles me is the "turning voltage into current" explanation.  Now I haven't completely thought this through...its an impromtu post, but help me think this through...

Sure.

By the way, "turning voltage into current" is basically just their way of saying "impedance transformation."

From Kirchoff's law we know that current is preserved in a closed system.  So current out = current in.  Pot is a voltage divider so part of the current is going to ground, part is going to amp.  The primary side of a tranny has a DCR which makes me think it too acts like a voltage divider, so why would this be any different for a TVC/AVC than a pot?  I can only surmise it has to do with AC properties rather than DC properties (i.e. reactance).

Well yes, the DCR of the primary as well as the secondary limit how low the output impedance can be and do effectively act as a voltage divider with the load impedance and attenuate the signal to some degree. To what degree will depend on the winding resistances, the turns ratio, and the load impedance. But with a decent design driving an appropriate load, this attenuation is kept small compared to the attenuation provided by the TVC.

Keep in mind that the DC resistance of the primary gets reflected as the square of the turns ratio just as the output impedance of the source does, whereas the signal gets attenuated simply by the turns ratio. So if your signal is attenuated by a factor of two, the DC resistance of the primary is dropped by a factor of four.

So with respect to primary and secondary DC resistances, the TVC is at its worst case at 0dB of attenuation. Where by comparison the resistive attenuator is at its best case. Though most don't often listen with the volume cranked all the way up so it's rather moot.

Anyway, getting back to the "turning voltage to current" as I said that's another way of speaking to the impedance transformation that transformers can accomplish.

The classic example of this is the output transformer on a typical tube amp. While the tubes are run from relatively very high voltages, their weak point is that generally speaking, they can't handle as much current as say a transistor can and if you try and drive a low impedance load like an 8 ohm loudspeaker, you're not going to be able to get any power to speak of.

If you can't muster enough current directly, but you can swing a lot of volts, you can use a step-down transformer to transform the low impedance of the loudspeaker to a higher impedance that the tube can handle without current limiting.

But of course there is a price. Because the transformer is a step-down, in order to get enough voltage across the secondary and subsequently the loudspeaker in order to get the power you want, you gotta swing a lot more voltage on the secondary. Which means you have to build up a lot more voltage gain than you would otherwise have to if you had the current capacity to drive the loudspeaker directly.

The one saving grace is that as I said above, impedance gets reflected as the square of the turns ratio while the voltage gets reflected by the turns ratio so your current goes down faster than the voltage requirement goes up.

Anyway, that's the gist of what they're getting at when they talk about "turning voltage to current."

se

[Steve Eddy]

Thanks again Steve! By the way, I was asking you if you could provide a personal explanation of why the pot vs. TVC sound "different", not "better or worse". I do think that most people who compare, find TVC preamps sound superior to pots/stepped-attenuators, but that wasn't the point I was making. I'm sorry I wasn't clear in the post, my fault - I guess I just thought my implication/distinction was obvious when I was writing it - but just as obvious of course, is that you cannot read anybody's mind! 

No problem! Could well have been my fault. The important thing is we're on the same page now.

You see, the provided explanation of how resistor-based preamps literally resist and convert some signal to heat, vs. the TVC trading voltage against current, makes perfect sense to me. But I am not an audio engineer and I don't posture myself to be an expert. I am always learning so much in this field.

Ultimately the point I was trying to get across in my original post is that whether a TVC or a potentiometer, signal is lost. Gone. And that whether it's lost by way of transformer action, or lost because it's sitting between the top of the potentiometer and the wiper, or as some would put it, turned into heat, makes no difference in and of itself. It's gone.

I mean, if you lose something that you're never getting back, does it matter where it's gone?

My question is: Why does the pot/stepped-attenuator approach produce such a noticeably different sound result than a TVC? Obviously they are different mechanical things, operating on different principles - we all get that  - I'm just wondering if you wish to elaborate on the "why", i.e. what specifically about these different operating principles, enables them to sound so different from each other. Not trying to put you on the spot either - no worries if you prefer not to comment on these audio principles. Just asking! 

Well, since it hasn't actually been firmly established that a TVC and a pot/stepped attenuator are in fact audibly different, asking why they are audibly different is rather putting the cart before the horse.

But setting aside the issue of sounding different, we can look at what the actual physical differences are. And there are quite a few. Some which may technically work in favor of the TVC and some against it, and some which may work in favor of the pot and some against it.

So, where to begin?

Well, for one, a TVC can provide galvanic isolation between source and load components. A pot cannot (nor can autoformer-based attenuators for that matter). A TVC can provide very high levels of common-mode noise rejection, even from an unbalanced source. A pot will not. A TVC has a high pass filter function which limits its low frequency response. A pot does not and will pass DC. A TVC has a magnetic core with hysteresis and its nonlinearities can be significant depending on signal level and frequency (increasing with increasing signal level and decreasing frequency). A pot for all intents and purposes is pretty much distortionless with regard to nonlinear distortions. A TVC presents a varying load impdance and a varying source impedance depending on position. A pot presents a constant load impedance and a varying source impedance depending on position (though again it's not quite fair to call it an impedance since it's purely resistive).

That's just a few for now. Want more?

se

[NewBuyer]

Facinating! You mean there are still more differences? That's a lot of differences you've listed, even just so far!

Yes please list more only if you wish (and have time), I'm mentally processing all of this as fast as its given and enjoying the learning process. I bet other readers are feeling the same way too. Terrific answer Steve, thanks for posting all of this! Much appreciated.

It seems like at mid and lower volumes (where perhaps most users listen?), the TVC approach provides much better output impedance to its load, and resistor approaches can do the opposite - is this right? I wonder if this could partially account for any (potential) audible differences.

Also, you mentioned the possibility of TVC non-linear frequency response and hysteresis issues - but is this truly realistic for today's well-designed TVC transformers and AVC autoformers? For example, in your posted graphs (p.18 of this post, referring to Sonic Euphoria AVC unit), it looks to me like the frequency response curve is exceptionally good for all but the very most ear-splitting volume levels - and doesn't look bad either at those loudest levels. I don't see any limiting of the low-frequency response displayed there. The same graphs seem to show this nice frequency response remains true even with very high source impedances - in fact it seems source impedances from 0 through 5000 ohms would work great with a TVC/AVC. I might be misreading the graphs - what do you think?

For instance, I am wondering if perhaps Promitheus designs their transformers to handle up to 20Vrms, specifically so that such hysteresis and frequency response issues do not occur.

I ask these questions in the spirit of a novice inquiring to an expert - so please take it as such! I really appreciate the information you are sharing.

[Steve Eddy]

Facinating! You mean there are still more differences? That's a lot of differences you've listed, even just so far!

BUT WAIT! THERE'S MORE! IF YOU BUY NOW...

Yeah, there are a few more, but that covered most of it and the most significant differences.

Yes please list more only if you wish (and have time), I'm mentally processing all of this as fast as its given and enjoying the learning process. I bet other readers are feeling the same way too. Terrific answer Steve, thanks for posting all of this! Much appreciated.

You're welcome. I'll come up with a few more tomorrow.

It seems like at mid and lower volumes (where perhaps most users listen?), the TVC approach provides much better output impedance to its load, and resistor approaches can do the opposite - is this right? I wonder if this could partially account for any (potential) audible differences.

Pretty much, yup. As for audibility, while it's certainly possible to have a high enough output impedance coupled to enough cable capacitance that the high frequency rolloff could be unarguably audible, I can't rightly say where the actual limit may be.

Also, you mentioned the possibility of TVC non-linear frequency response and hysteresis issues - but is this truly realistic for today's well-designed TVC transformers and AVC autoformers?

Well, it's certainly real. As for realistic, that rather puts me in the position of trying to make judgements as to actual audiblity and "sound different" which I wished to put aside and just discuss the basic material and functional differences between a TVC and a pot/stepped attenuator.

For example, in your posted graphs (p.18 of this post, referring to Sonic Euphoria AVC unit), it looks to me like the frequency response curve is exceptionally good for all but the very most ear-splitting volume levels - and doesn't look bad either at those loudest levels. I don't see any limiting of the low-frequency response displayed there.

What I meant by limited low frequency response was simply that the response drops as you approach 0 Hz versus a pot which is flat down to DC. A good transformer driven from a reasonably low source impedance will usually have a low frequency cutoff (-3dB) around a few Hz or less. The Stereophile graph cuts off at 10Hz and only shows a rolloff of a dB or two.

And again, I wanted to set aside any issues of "sounds different."

The same graphs seem to show this nice frequency response remains true even with very high source impedances - in fact it seems source impedances from 0 through 5000 ohms would work great with a TVC/AVC. I might be misreading the graphs - what do you think?

I think you may be misreading something. None of the graphs show frequency response with it driven from 0 through 5,000 ohms. As far as I'm aware, John was driving it with the lowest output impedance from his AP rig which I believe is under 1 ohm so that would be what the frequency response graph represents. Low frequency response (and distortion) will increase as the source impedance increases.

For instance, I am wondering if perhaps Promitheus designs their transformers to handle up to 20Vrms, specifically so that such hysteresis and frequency response issues do not occur.

I wouldn't presume to try and second guess their design choices. But let me just say that transformer design is a delicate balance between many different factors most all of which have consequences for the other. Want a higher primary inductance so you can have a much lower low frequency response? Sure, let's add a bunch more turns. Whoops! We've lost some high frequency response because of the added winding capacitance due to the added turns.

I ask these questions in the spirit of a novice inquiring to an expert - so please take it as such! I really appreciate the information you are sharing.

You're welcome, and thank you for the kind words. Though please don't consider me an expert. While I know a fair amount about transformers, to consider me an expert on them would take away from those who truly are experts. Those who know all the ins and outs, all the compromises, and all the various techniques to minimize those compromises to produce transformers of the best quality. Those are the real experts.

se

[NewBuyer]

Well said Steve! Thanks again for the helpful information. I'll probably ask you a question or two in the future too if that's OK, as I think that I will always be learning in this hobby. That's part of the fun for me.

What I can say for certain is, this Promitheus TVC sounds truly incredible in my rig. The only other preamp I've ever heard approach this level of "good" to me in my system was no preamp at all (figure of speech) - the Shotgun Stepped Attenuators by Scott Endler of Endler Audio. They are 4k shunt design and attach directly to the amp inputs, and are thus relieved from the usual cable load capacitance issues. They are only $40 apiece! Sound is better than actives I've auditioned up to the $2500 mark.

The TVC and the Shotgun Attenuators do sound different from each other, but I could easily live very happily with either of these options in my system. Who knows, I might go back and forth with them in the future, but right now I am really enjoying the Promitheus TVC, what an incredible sounding preamp! This audio hobby is extremely fun. 

Edit Yes I must be interpreting those graphs differently from you somehow... I see a pair of graphs that you posted on p.18 of this thread, regarding the Sonic Euphoria AVC - one showing frequency response at various source impedances, another showing frequency response with various volume settings. In the bottom graph, frequency response at various volume settings shows that the frequency response is excellent even at the loudest volumes, but actually improves as the volume level is decreased to mid and low levels. Knowing the tester was using a <1k source impedance to produce all the curves in that particular graph is helpful. In the top graph, we see the frequency response for various source impedances (from bottom to top at 100k, 10k, 5k and 1k). Looking at the 10k, 5k, and 1k graphs, we see a clear convergence pattern that implies that source impedances of 5k and less (perhaps even up to 10k and less) maintain the excellent frequency response pattern, with slight improvements occurring as source impedance decreases. Visually this pattern implies continued expected improvement as source impedance reduces past the lowest tested impedance of 1k. At least with the TVC I have, this matches my ears as well when feeding the TVC from a Burson Buffer. These graphs do seem very explanatory to me, but I could of course be missing something...

[PromitheusAudio]

Steve
Thanks for helping to explain more about tvcs and the standard pot. You have been a great help

On our dac release i expect to release the solid state output-dac in a months type. There will a couple of sample units that will be send out to gauge the sound of dac. I planing to have 2-3 beta testers to let us know their personnel views.

On the reference tvc, is where better parts are used. Also a few more mechanical improvements that would help out

The power energizer is something that we have been making for awhile but did not put it up on webpage.

Oliver's posting on the 7.5m cable is very interesting as it shows the tvc can tackle some serious interconnect lenghts

[GHM]

Steve
Thanks for helping to explain more about tvcs and the standard pot. You have been a great help

On our dac release i expect to release the solid state output-dac in a months type. There will a couple of sample units that will be send out to gauge the sound of dac. I planing to have 2-3 beta testers to let us know their personnel views.

On the reference tvc, is where better parts are used. Also a few more mechanical improvements that would help out

The power energizer is something that we have been making for awhile but did not put it up on webpage.

Oliver's posting on the 7.5m cable is very interesting as it shows the tvc can tackle some serious interconnect lenghts

Hey Nick.. I would love to hear this new Dac and how in compares to my Audio Sector NOS Dac. aa  Put me on the lottery list of available ears.These are very exciting times in deed!

Yes Steve aka Guru  has definitely filled in some gaps for me. Thanks Newbuyer for the great questions!

[Steve Eddy]

Well said Steve! Thanks again for the helpful information. I'll probably ask you a question or two in the future too if that's OK, as I think that I will always be learning in this hobby. That's part of the fun for me.

Sorry, your Question Quota has been exceeded. All further questions will be billed at $9.95 per question. PayPal only. 

What I can say for certain is, this Promitheus TVC sounds truly incredible in my rig.

Coolness! 

And that's really what it's all about. We can sit here and talk about specs and numbers and how this works versus how that works, but at the end of the day, all that really matters is does it give me pleasure and enjoyment? If it does, that's all that need be said.

The only other preamp I've ever heard approach this level of "good" to me in my system was no preamp at all (figure of speech) - the Shotgun Stepped Attenuators by Scott Endler of Endler Audio. They are 4k shunt design and attach directly to the amp inputs, and are thus relieved from the usual cable load capacitance issues. They are only $40 apiece! Sound is better than actives I've auditioned up to the $2500 mark.

The TVC and the Shotgun Attenuators do sound different from each other, but I could easily live very happily with either of these options in my system. Who knows, I might go back and forth with them in the future, but right now I am really enjoying the Promitheus TVC, what an incredible sounding preamp! This audio hobby is extremely fun. 

All I can say to that is that I'm always pleased to see someone having fun. Can never have too much of that.

se

[Steve Eddy]

Steve
Thanks for helping to explain more about tvcs and the standard pot. You have been a great help

You're welcome.

Good luck with your 6 Moons review!

se

[NewBuyer]

Sorry, your Question Quota has been exceeded. All further questions will be billed at $9.95 per question. PayPal only. 

You should raise your prices Steve! We're getting spoiled around here.

[Steve Eddy]

You should raise your prices Steve! We're getting spoiled around here.

You're right. And I've always hated that stupid .95 and .99 thing. We'll just make it an even $2.00.

se

[gooberdude]

Just a reminder to anyone who is thinking about ordering the promitheus tvc, definitely spend extra $ on the CMC rca's that are now listed on nicholas' site.  They supposedly sound much, much better than stock, and are a good deal at $25 per pair.   I ordered my tvc with 3 of the 5 inputs with them, and one set of the outputs - getting the 5th input added only cost $5!  If you look at the pictures, the CMC's appear to be nicely made.   I'm assuming that most, if not all, of the reviews on this TVC have been done with stock rca's....   

I ordered mine a while back, anxiously awaiting its arrival.  malaysia takes a week off next week, i should have it 1st week of Novemeber and i'll put my thoughts down soon thereafter.

Nicholas is to be commended for his efforts as of late. i think he's been swamped with orders, but he still e-mails every few days to let me know of improvements, new products, DIY OB speakers and Room Lense's & what not.  I have a feeling his gear is gonna get better & better going forth, quite exciting.

Is anyone using the wood box TVC in an urban area?  i live downtown chicago in a large bldg, just wondering if anyone has had emi/rfi issues...    I have a sheet of ERS cloth ready to go just in case.  Every time i've used the stuff it seems to have done more harm than good though.

matt     

[Steve Eddy]

Is anyone using the wood box TVC in an urban area?  i live downtown chicago in a large bldg, just wondering if anyone has had emi/rfi issues...

Well, I'm not in downtown Chicago and I don't own the Promitheus TVC, but Sacramento's rather large and urban and I've used lots of transformers including "nude" unshielded ones and I haven't had any problems using all wood enclosures. And with transformers, when there are problems, it's usually from the low frequency magnetic fields being produced by your own equipment.

se

[NewBuyer]

Just a reminder to anyone who is thinking about ordering the promitheus tvc, definitely spend extra $ on the CMC rca's that are now listed on nicholas' site.  They supposedly sound much, much better than stock...

Is anyone using the wood box TVC in an urban area?  i live downtown chicago in a large bldg, just wondering if anyone has had emi/rfi issues...    I have a sheet of ERS cloth ready to go just in case.  Every time i've used the stuff it seems to have done more harm than good though.

matt     

Thanks for the info Matt! Just wondering, where did you hear that the CMC Pure Silver RCA sockets sound so much better than the stock? Why would this be true, is there anything wrong with the stock RCA's (are they disappointing at voltage conduction or something like that)?

About emi/rfi, I have only had a hum problem on a used input if I had put another component directly on top of the TVC, and even then, only if that component also contained a strong emi-emitting power transformer.


By the way, I wonder if PaulFolbrecht ever received his aluminum TVC, and/or the wooden interim unit? I've been wondering how his aluminum version will sound. I was looking at one of the previous ebay TVC auctions, where Nicholas said the wooden chassis was best-sounding:

(from ebay):
Q: "Hi, can you do the TVC in a brushed or polished aluminum chassis?"
A: "Yes we can supply the TVC in polished aluminum chasis however, the sound is not so good. Some how the wood brings out the best in the tvc. Also the sound has been tuned to the tvc."

[gooberdude]

thanks steve.    i cringe at the thought of sticking ers cloth inside the tvc.
how come the folk and the speak in this forum (audiocircle) is soooo much nicer and calmer than aa?


Newbuyer, regarding the new silver rca's, nicholas had them on hand when i ordered the tvc
& i inquired into upgrades.  at the time he hadn't compared them to the stock rca's,
but a few weeks later he wrote to say his dealer A-B tested them & there was an improvement. 
if interested, nick will sell you pairs of these.  i bought an extra pair & plan to put them on my amp.  they are right in line w/vampires & other good rca's, in terms of price.  considering noone has reviewed the tvc with them, i doubt you have anything to worry about (see the 24 pages here!)

on the site he's now listing a hot rod version of the tvc.  there's gonna be a few versions of the design going forth, i'd bet my left foot.    this may be something we're all re-ordering in a year or 2...

tonight i just received a 2nd pair of paul speltz's anti-IC's w/eichmanns.  been listening to vinyl through an all speltz cable system for the 1st time tonight...i'm thoroughly satisfied with his stuff, especially for the $.   this new set is heavier than the previous, larger diam copper cables.    I've been sharing a mapleshade clearview ic betw tt & cdp for months.  removing the clearview & putting the orig anti-ic betw my phono & pre yielded huge improvements, and the anti-ic is about 4 hrs burned-in...     

no affiliation whatsoever

matt

[NewBuyer]

Ok, I'm just going to come right out and ask this (possibly ignorant)question:

Why would RCA's made out of silver, be any better sounding than RCA's made out of the usual materials (copper, nickel, gold-plating, etc etc)?

Thanks to anyone who wants to help me understand this... (and others reading here too hopefully)...

[GHM]

how come the folk and the speak in this forum (audiocircle) is soooo much nicer and calmer than aa?

Hey Matt..seems too me people on this site actually take the time to judge equipment on its sound and not make assumptions based on the price tag. Plus the people here are just plain down to earth folks that love audio and enjoy sharing their experiences with others. I also notice the group here thinks outside of the box..not weighted down by audio hype and big name brand gear. Definitely my preferred site with a terrific bunch of folks!

Ok, I'm just going to come right out and ask this (possibly ignorant)question:

Why would RCA's made out of silver, be any better sounding than RCA's made out of the usual materials (copper, nickel, gold-plating, etc etc)?

Thanks to anyone who wants to help me understand this... (and others reading here too hopefully)...

Newbuyer the only time I experienced a significant change in sound with connectors. Is when I was modifying my Maggies and replaced the nickel plated jumpers with solid copper. What I got was a fuller sound. The edge I was hearing with the nickel was also gone. The nickel had a metallic cold sound to it that I hadn't notice until the change. Not sure if going to solid copper or silver RCAs would make such a drastic change with this unit though.

You could always buy a set of solid copper vampire inputs or something similar from Soniccraft if you're here in the states and solder them in or get someone to do it for you. I thought about going this route. I haven't made a decision though.

By the way I did buy a pair of Vampire CM2FCB(solid copper gold plated) to go in my custom battery powered integrated.

[gooberdude]

I have never compared the sound of rca connectors, so i'm in no way qualified to chime in about the differences. 

I did, however, just replace the stock speaker binding posts on both my '92 Thiel loudpseakers w/eichmann cablepods.   No joke - my speakers sound quite different now.  Much, much smoother & the bass is really tight, not boomy.  from top-to-bottm it seems like more music is coming from the speakers now....like something was holding back the signal before.  imaging, tonality...the whole shebang

I'm going to have a set of 'pods' and the CMC rca's installed on my '92 Muse 100 amp too...kinda hoping hoping there's synergy with this new set-up & that the new connectors 'wake up' my amp similar to my speaker experience.   

So, in terms of age and design, i do think new connectors of a good design may outperform the old stuff...but again i'm just going by my recent experience.  According to the repair guy who installed them, the cablepods sounded so good he's making them stock on the speaker line he makes. www.vanlspeakerworks.com    He's been using $140 per set WBT posts for years, but thinks the 'pods' sound much better and for $90 less a set.   i'm a big fan of all the eichmann products i own.

regarding if one metal sounds difft/better than the other - i'm a bit skeptical about that!    But, i do have oyaide wall outlets and male/female plugs which are all supposed to jive together due to the types of metal used in the plating & what not...i dunno BUT my gear sure sounds great now. 
high end ac wall outlets have to be about the best $100 or less tweak going....

I just joined the circle, been checking out old threads all week.  I haven't read one fight or derogatory put-down yet....ac is civilized!    i really, really like being here.

Now, how do i get the smiley faces in this text?   when i click on one it does something like this>   

or maybe the graphic is added once i post this?   newbie issue!   please diregard if cute little yellow dude's are here when i post this.                 

matt