Transformer volume control 23 steps

[Dorin Bodea]

This stereo 23 steps transformer volume control is a 6th generation proprietary design. Its primary function is line level control volume but contains a high quality permalloy that you can use it also - inverting cables in the back and a short trial and error - as fixed step-up line level transformer or adaptable to DAC stages or MC step-up for moving coil cartridges! It is also small (actually the smallest I've seen), compact layout and nice looking

The basic version is a 1:1, 10k:10k, 80H@20Hz, but other transformer ratios can be made. Also balanced/unbalanced versions are possible. The logarithmic curve is according with IEC 60393-1 code 15A law. For this 1:1 version see the THD figures for 0.7Vrms at highest step (with the soundcard having about 0.0005% THD in loopback), also the frequency response 10-100kHz, these specs being of course in the same ballpark at any step.

It is neither bifilar winding nor autotransformer so therefore it has some additional isolation from various noises

Thanks, take care!

 

[nielsk]

So this is a stand alone stereo volume control with no additional components required for operation?
What will it cost for the fully balanced version?

 

[Dorin Bodea]

So this is a stand alone stereo volume control with no additional components required for operation?

Passive preamp with volume control can be a better definition, I guess

The cost for a fully balanced version can be around 700 Euro

 

[nielsk]

So this is intended for Hi Fi use, or is it intended for use in a Control Room Monitor Controller, and if so, how is it incorporated in a CRMC?

 

[Dorin Bodea]

So this is intended for Hi Fi use, or is it intended for use in a Control Room Monitor Controller, and if so, how is it incorporated in a CRMC?

It is intended for all those willing to use a transformer for volume control instead of a potentiometer, especially in Hi-Fi tube gear domain, minimalistic branch . In 1:1 version the primary has around 100Ω DC resistance while the secondary has 150Ω (decreasing with lower steps) - this can reduce noise and keep the bandwidth straight. See below a more advanced version which amplifies the signal from CD/DAC and drives directly a power tube, say, 2A3

 

[Philbo King]

This could be very handy for mastering work, where easily reproduced gain settings can greatly ease the task.

 

[Dorin Bodea]

A taper following IEC 60393-1 15A law will have 15% attenuation for 50% rotation travel, in the graph below that's somehow difficult to obtain with a simple potentiometer, both channels precisely...