TVC preamps: good or bad?

I currently have Promitheus Audio Reference C-core TVC and I can confirm that this unit is extremely transparent and extremely quiet. Soundstage definition and resolution is the best I've heard in any system at any price. Each instrument has its own well defined space. Dynamic contrast is top notch. This TVC doesn't have the midrange magic that tubes provide, but it gets pretty close.

This is the top-of-the-line TVC that Promitheus Audio makes, so I don't know how their other units compare to this one. From what I've read, these TVCs don't work well on systems where there is not enough gain. I don't have that problem at all. The sound is already too loud if I pass the 1 o'clock mark.

Regards,

iSanchez

As far as I know resistors also introduce colorations. TVC is just most transparent and neutral preamp solution I have ever tested. It lets you hear everything that your other components will allow. It doesn`t add any warm or cold colorations. If other components sound good it will sound good and if other components sound bad it will sound bad. It is dead neutral. I usually don`t go very deep about different technical theory's. I just listen and keep what sounds best. If sound matters most there are no cons with TVC. I am pretty sure that a good TVC can stand against any preamp prize no object. It seems that this is just superior technical solution. Just don`t place it near power amp because hum may appear. I suggest you to find some balanced Promitheus TVC. With balanced connections there will not any hum problem. These usually go for some $500 used and you can sell it at same prize if you dont`t like it.

Thank you everyone for your responses. I think that Unsound has rephrased my question very well. I am hoping that someone with more technical knowledge will come along and shed some light on the subject.

I have heard a passive TVC pre in my system and I was not impressed. But I know better than to generalize a single bad experience to the technology as a whole.

BTW, I am not looking to buy a TVC preamp ... so please don't email me with offers to sell me one :)

What was the system setting when you tried the TVC?

TVCs can be considerably more neutral than many active line stages. But not **all** line stages!

A lot depends on how careful the design of the TVC actually is. The issues of TVCs are: bandwidth, hysteresis loss (introducing a loss of low level detail) and ringing (introducing brightness).

The advantage of a TVC is of course no noise and circuit simplicity. If designed properly, ringing attributes can be reduced, but one should note: in order to do this, the TVC has to have a loading resistance that is different for every volume control position. The reason for this is that the TVC must present an amenable load to the sources (DAC, phono preamp etc.) while at the same time being able to change the turns ratio. This is usually accomplished by having the multiple taps of the transformer on the secondary side, selected by the switch. Without an appropriate loading resistor for each position, the TVC will express the inter-winding capacitances rather than the actual turns ratios. Most designers set up an approximate loading resistance, but this ignores the ringing issue, which can only be addressed by a different loading resistor for each tap. With only one loading resistance, the bandwidth and ringing issues will be different with each volume control position. It is likely that many have found that there is a particular volume position that seems to sound the 'best' as a result.

To date I've seen no TVCs that pay attention to this issue. Anyone who has worked with audio transformers will realize how important this is.

Even with proper loading, hysteresis losses inside the core of the device will rob the signal of low level detail in much the same way that push-pull output transformers in a tube amp will (part of the reason SETs have made such a comeback in the last 20 years).

It is a testament to how bad some line stages are that TVCs often outperform them. Circuit simplicity is a good thing in audio (less places for the signal to get messed up) and TVCs are not only simple, but can provide gain and impedance control of the output if designed properly.

Despite this a **properly** designed line section can easily trump the best TVCs. This is a good example of getting what you pay for.