Reactive output attenuator schematic?

[LeftyStrat]

I want to build an amp where the only volume control is an attenuator. Anyone got schematics?

[cdemike]

Because of the impedance issues that come with any L-pad setup, I'm not convinced it's possible to present a consistent reactive load to an output transformer while maintaining continuously variable volume control as opposed to stepped settings (e.g., as with the JohnH attenuator). However, a dummy load feeding a re-amp device like a Fryette Power Station wouldn't have any of those impedance issues since the output transformer is connected to a consistent reactive load. That allows isolation of the varying impedance associated with the volume control through a comparatively high-impedance volume control that is in parallel with the reactive load. I considered making something similar to this a while back and drew up this schematic:


I ended up just making a variation on a plain M2 JohnH attenuator, but this was the thread related to that project: https://ampgarage.com/forum/viewtopic.p ... er#p477597

[Snicksound]

I want to build an amp where the only volume control is an attenuator. Anyone got schematics?

You're asking for the magic bullet that everyone has been chasing for many years.

The best we've got is, as someone else pointed, a reactive load feeding a clean power amp with a proper volume control. Like the Fryette Power Station, the Two Notes Torpedo Reload II and the Boss Waza Tube Expande.

There are reactive loads that also have variable attenuation, but it's usually stepped attenuation (e.g. UA Ox Box, Two Notes Captor X) and never 100% transparent. Each notch has its own colour.

Of all the things I've mentionned, only the Captor X is sort of affordable, but it's kind of flawed as an attenuator: there's only two notches (-20dB and -38dB) and it's far from transparent. It's better as a load (no speakers connected).

Fully variable reactive load would require scaling capacitance, inductance and resistance all in perfect harmony. It's so complex it just doesn't make financial sense compared to a load+amp.

If you want an amp that has that as the Master Volume, look into power scaling instead, via VVR (variable voltage reduction). This has been done on some commercial amps (e.g. Fender Bassbreaker 45). There are kits.