Is an autoformer (AVC) always superior to pots and resistors ?

This is an argument some of my friends made to me. AVC is always the best volume control, better than anything else such as rk50 or resistor based volume controls. Have you found this to be the case?

I am also curious why AVC is not implemented more often in high end audio preamps / integrated amps.



@j_andrews - Nice work!  I like the use of a stepped switch.  Thanks for sharing.
I wish I had the knowledge, then I would do a similar but balanced unit - very simple with one input and two parallel outputs.  The main complication would be that I have come to like having a remote and display, which would add complexity to the build.

@jmolsberg That's great, how do you like it?  What is your amp?  Do you feel the autoformers have a sound or not?  Can't wait to wrap this thing up..just need to set aside some time to inhale some soldering fumes.

@mitch2 , Yes all the Slagle autoformers would require a stepped switch as you're actually connecting to different taps on the autofomer,  As I mentioned, I purchased the most basic units which are only 16 not a lot of resolution between volume steps but I think I'll be OK with that as I usually set it and leave it alone.

At one point, he did offer some sort of collaboration with Bent where there was a remote control unit but I don't think that's available anymore.


I say the same thing to anybody who will listen, get one of Dave Slagle’s autoformers with a balance control and be done with typical resistor type volume control. If it has a sound - sign me up. I love it!


This is an argument some of my friends made to me. AVC is always the best volume control, better than anything else such as rk50 or resistor based volume controls.

@smodtactical The correct answer is 'sometimes- maybe??'.

TVCs can generate distortion which PVCs cannot. This is because if the transformer isn't loaded correctly (and being an inductor) it can 'ring', which is to say it will generate harmonics.

All coupling transformers have something called 'critical damping' wherein if you pass a square wave through it, with the correct load the square wave will be intact with minimal overshoot at the output. Loaded too heavily (output load impedance is too low) and the square wave will be rolled off (rounded corners on the square wave). Loaded too high and the square wave will overshoot and may not look like a square wave at all!

The source impedance (such as that of a CD player), the output load (the amplifier) and the turns ratio (the volume control position) all play a role.

Because of this its nearly impossible for the designer of the TVC to have the device loaded correctly at all volume control positions. You can see that it might be advantageous to have a different resistor loading the output at each position on the control, but that value will be different depending on the load that the amplifier presents to the device.

But sometimes you luck out. I wouldn't count on that though. IMO/IME you are far better off with a buffered volume control at the very least. A buffered control minimizes variables you always encounter when working with passive devices (TVC or PVC).


Hi Ralph, Not sure you noticed but the OP was asking about AVCs and not TVCs. I have read that AVCs have wider bandwidth, with less ringing, coloration, and smearing than TVCs. Here is more info about AVCs, and here is a review about an AVC preamp.

To the OP’s question, the answer would likely depend on the answer to the question, “the best at what?” In my listening experience, AVC volume controls do sound different from discrete resistor volume controls, and not necessarily better in all situations or with all types of music. Both types can be implemented as a stand-alone passive solution, or as part of a preamp with an active buffer or active gain stage, so the implementation will have a significant effect on the sound.

I have been using a discrete resistor type passive volume control with a unity-gain active buffer and so far have not found anything that sounds better to me based on stuff I have tried up to about $10K. However, I recently acquired an AVC preamp to compare with the VC/buffer set-up I have been using and since the trial is early, my only comment is that the quality of sound from each is very good but they do not sound the same.