TVC Sound

I'm fortunate, at the moment, to have the use of an MFA TVC (silver) version. These have been the subject of much discussion both here and elsewhere and I have been keen to have 1st hand experience of what they can do.

The first point to make is that I quite like the sound of it. It definitely doesn't squash dynamics in the way that stepped attenuators made with resistors do. It is also very nicely made externally and internally with the possible exception of the rather nasty, gold coloured, impact moulded plastic knobs. I have used it with several valve power amplifiers but predominantly with some home made 845 pushpull amplifiers which (as a result of having no feedback) are rather sensitive at their inputs and which as a result, do not often lend themselves to use with active pre-amps (unless they are very quiet)

I have gained the impression from some here that the quality of these transformers were such that conventional active line stages were almost rendered redundant.

I'd beg to differ. The TVC does have a distinctive sound particularly in the way it modifies the timbres of certain instruments. I have heard better, more natural sounding, active linestages although not perhaps at this price level.

I thought I'd have a look at what it actually does.

There are effectively 24 different transformers in each channel. You can select between them to set your preferred level. The behaviour of each is different.

The transformers ring (electrically) quite alot. This happens less where the attenuation is less. At the first few positions on the switch (where it is likely to be used) it is quite excessive.

Putting a square wave through the transformer is quite revealing and highlights resonances that are occurring above the audio band. You might say that you don't listen to square waves but how any component amplifies them is very instructive as to how it will handle the harmonics of real musical instruments

I enclose an image of the TVC at position 37 reproducing a 4KHz square wave.



I imagine variations in the output impedance of the different sources which might be used will affect the behaviour of the TVC as does different load impedances. I would be looking at adding some kind of zobel network across the output to control the resonances with the particular source and load I was using.

The conclusion I draw from this is that if you hear one of these and don't get on with it, it isn't necessary to blame yourself or your ancillary equipment. Like many items of equipment, the transformers aren't entirely accurate and give just one version of the truth. I like some of what it does but I find certain active preamplifiers preferable in a number of ways.

Just my tuppenceworth

 

Very informative Murray thanks

 

At what frequency do you guesstimate the ringing to occur? It looks like it comes at a fairly low frequency, possibly inside the audio band. What voltage did you use?

 

Hi,

Hmmm, this does not look what I measured (or ideed what Martin Colloms measured). I'm most concerened that there seem to two distinctly seperate resonance frequencies. One of them seems to be at less than 60KHz (estimated).

Can you (did you) reliably exclude that possibility of interactions with your measurement setup?

Ciao T

 

this attenuated square wave is about 300mV in amplitude

sweeping with a sine wave the 3 dB down point seems to be at about 38K but there is a very large resonance at about 43K and the next large one isn't until about 150K

Moving to a different level of attenuation shifts these resonances around and the shape of the ringing square wave is entirely different. I would suggest that the sound is different as well. At near to maximum volume (minimum attenuation) the square wave is at its best with minimal ringing but none of the amps I have can be used anywhere near those settings with CD as a source.

The +6dB boost switch improves things aswell. presumably less attenuation going on.

 

I have just been playing with a pair of TX102 into a pair of SMPS powered 3875 gainclones ,I wasnt sure it was turned on it was so quiet ,compared to a NAIM rig.I havent got a selector yet so the volume is selected by crocodile clip 30db attenuation is about right for casual listening .The clarity is awesome, now for casing it up,selector etc.

 

But by activating the switch the there will be greater attenuation at any given volume point compared to when the switch is not activated. It will be all the more difficult to reach maximum volume (minimum attenuation).

 

By activating the switch, the output at any given setting is greater therefore the TVC is attenuating less. The square wave shape at that particular setting is improved. I must look at how the shape when using the +6dB switch is, compared with when the volume control is advanced to give an equivalent output. My suspicion is that the +6dB shape is always better as the transformer is doing less transforming.

Looking at the output at the first few volume control settings (near maximum attenuation) the resonances are quite excessive. Besides the 42KHz one and the 152KHz one there is another at just over 100KHz.

From the experiences I've had with output transformers the HF response should just die away steadily. You don't even want flat plateaux in this decay never mind huge peaks!

It doesn't surprise me that people find these things very detailed if harmonic content is being thrust forward unnaturally. (particularly by the 42KHz resonance) I was listening to it at low levels last night and it does give an odd presentation of strings, piano tone and brass.

I would hesitate to recommend it to anyone using power amps with high input sensitivity for this reason.

I think the concept of the TVC is an interesting one but I'm not convinced whether it can be executed in an entirely satisfactory way. I'd be interested to hear one from the likes of Tamura, Hashimoto or Tango.

My main interest was to see whether it would be worth incorporating them within an amplifier. Given it's performance at low levels I'm not sure I will try this now.

 

Hi,

That does not sound like the current generation 102, it does sound more like a MKI, even though that had it's resonance at 60KHz, not 43KHz. Thing is, very few MKI where made and non should have found their way into Music First Audio Gear.

Ciao T

 

Ah so when did Mk1 change to Mk2? What were the differences? What mechanism could have brought one of these Mk1 units to be in a relatively recent preamp?

 

A quality control problem?

 

I don't know whether this pic helps date it.




here's a 1K square wave via the MFA with the volume full up (no attenuation). Pretty good. Not much use though. Output way too high.



Heres a 1K square wave via the MFA at the volume setting one click above full attenuation (ie 52)



not very good considering its only 1K


Here's the 4K square wave at position 37 (slightly higher than where I've been using it) I'd say this is poor really.



All of these are into 220K from a 600 ohm generator.


Thorsten, I presume you and MC didn't just test this at minimal attenuation?

 

ouch, that is rather poor.

 

Hi,

Not really, it's the transformer insides that decide.

Not at minimal, but I did test in 10db steps downwards.

I'll test my own unit again when I get time, hopefully this week.

This bugs me, as th MKII & MKIII transformers are NOT SUPPOSED to do this and the ones I measured did not do this.

Markus may be right though, it may be QC and there is always the (small) chance that someone loaded up by mistake the MKI program on the winding machine, which would be a major bummer.

Ciao T

 

I've now heard a TVC three times (inc Thorsten's own with him present) and on each occaision the improvement in clarity over active stages has been noticeable. Layering within the mix is easier to hear and there is a reduction in glare and grain.

But.....

I also hear a reduction in pace and dynamcs. Music lacks a little drive and attack compared to a decent active stage, though the TVC is still better than a passive pot or attenuator.

Interesting to see the measurements at different settings. I heard a TVC recently at BBV's with Simon and we all commented that the sound was different (dynamically) at different setting. We could only make assumptions as to the cause.

It seems from my (ltd) experience that TVC's can sound very good indeed but are pretty system dependent. For example my tube phono stage won't drive a TVC at all yet will work into even quite low (5k) non inductive loads. Remember that the TVC presents an inductive load and not all sources will be happy driving it.

 

I think that was due to the croc clips we were using in the end. When we took more care the problem dissapeared. With my phono the TVC seemed to give more pace and drive than the active pre - using the S&B cores. However my tvc is driving a pair of crossovers across 20cm of low cap cable. Its a shame we couldnt use your tube phono with the tvc to really nail down what was happening.

 

There doesn't appear to be any Serial Number on this unit. How does a customer know which of the 3(!) versions he's got?

I had the opportunity recently to listen to these particular power amps with a Kondo M77 linestage driving them. Fun as the TVC is (at higher levels) it really isn't playing the same game as that pre-amp. Unfortunately I'm not lucky enough to have 20 odd grand to drop on one of those but was hoping this might be a little closer than it is.

I think I shall be persevering with the home made active stages for the time being.

 

Hi Nick,

Welcome back

Yes, it was all a bit 'hit n miss' that day, but we can't escape the fact that each attenuation setting changes the system bandwidth and possibly the distortion levels if those scope results are any indication. Too many variables there for me 'cos I like to know what I'm hearing and why

I'd say that if you like what the TVC does then you need to build a system around it, one which mitigates the side effects.

I have a nagging voice in my head that te TVC is a complex solution to a simple problem and there are much bigger fish to fry when solving the problems of music reproduction.

 

Hi,

All Silver versions had Audio Note Silver RCA's, so that is the way you tell them apart. The Silver versions always tended to be "one off - on request" units.

There where only two versions of the Copper, you can tell them apart by the RCA Sockets, the later version has the much worse sounding "standard Hi-End" version (Hexagonal flange visible), instead of the original "low metal" versions I had specified (which have a vestigal round flange) that the dealers kept bitching about.

So with the switch to customised MKIII TX-102's came a change in RCA Sockets.

Non of the versions of the TX-102 used in Music First Passive Preamps should measure quite like yours.

Ciao T

 

It is rather good isn't it? Thanks for the insight Murray, I was starting to think I was going mad thinking the TVC wasn't the last word in preamps. Now I have some understanding of why I might have preferred anumber of active units. The M77 does sometimes appear on AG if you have a spare £10K!