FAQ for transformer volume control

 

Impedance and the TVC

On the source of 100R assume (phonopreamp/CDP) and input impedance of 47 K of power amp

 

say source output impedance of 100R of your Phono preamp

A TVC  are basically step down transformer like a valve trans what they do is they step down voltage but you gain in current drive.

Best part is that output impedance also drops by the factor of squared.

 A TVC will have change in output impedance depending on the volume setting that you are playing with.

A formula for output impedance

output impedance after TVC  = output impedance (before TVC) /((Vin/Vout)squared) at 10%. At 1 volt from cdp(assume) out of 0.1volt after TVC Output impedance = 100R /((1/0.1) squared)

                             = 100/(10)*(10)

                             = 1 R

So at 10% volume your output impedance has drop to 1R.

At 50% At 1 volt, out 0.5 volt TVC (this should be loud) Output impedance = 100R/((1/0.5)squared)

                            = 100 /4

                            = 25 R

At 80% At 1 volt out 0.8 volt after TVC ( ear blasting ) Output impedance = 100R / ((1/0.8) Squared)

                             = 100/1.56

                             = 64 R

In short all TVC have step-down effects which can be seen very easily after this calculation. Also take note all tvc users has always this to say that they do not need to turn up the volume to get the details and the bass to come out. This is very clearly seen in the 10% ratio where the output impedance is so low that every single nuance, detail, bass present themselves very easy.

 

Unlike resistive elements where the output impedance is set by the resistive element (potentiometer or step attenuator form with resistors) i.e. 10K pot will have an output impedance of 5K , 50 K pot will have an output impedance of 25K. A TVC output impedance is always calculate from the equipment source, and is always lower than the source output impedance.

 

 

Why use a TVC versus high quality potentiometer.

Most people find that the TVC sounds significantly better than even the best potentiometer or stepped attenuator.

 

And it's not a subtle difference; most people report that the TVC has such an open, deep and low bass, effortless sound that they would not consider going back to a resistive device.

 

Exactly why they sound better is because one impedance issues mention above and the fact that the TVC doesn't attenuate by wasting energy.

The Tvc is like the gear box in the car. If you need to drive at a slow steady speed which method would you choose:

(1) leave the transmission in high gear and apply the brakes to keep from going too fast, (which how a resistive device works)

(2) downshift into a lower gear that will allow the car to go the desired speed with minimum effort ( which how the TVC works)

 

THE TVC is essentially an electronic gearbox that operates without wasting significant energy. Potentiometers and stepped attenuators adjust the signal level by literally turning the excess signal into heat. On the other hand, when A TVC is adjusted for low volume level it actually makes things easier for the source, much like a low gear makes things easy for your car engine.

 

 

Driving 2 Amps with the TVC