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RE: power supply vs sound?

Posted by TimeConstant on February 23, 2015 at 10:55:30

In Reply to: power supply vs sound? posted by vinnie2 on February 23, 2015 at 05:35:57:

Maybe this post will answer one aspect of your question.

I had asked myself this very same question, whether changes in Power Supply configuration would render an audible difference, so I did something about it years back and created a tube rectified Preamp with a switched Regulated and Un-Regulated filter section.

To this day I still enjoy this Preamplifier, although the motorized volume control stopped working :(

My DIY effort was a bit odd, as I started with an old NOS military potted power transformer with some unusual secondary voltages.
After some brainstorming and a few calculations I came up with a design that used dual 12X4 rectifiers.

The preamp circuit was Aikido 6SN7 based with the PC board stuffed for a +300VDC supply, and a floating 6.3 Volts AC supply for the four 6SN7 tubes.

The rectifier filaments were connected to a 10 VAC secondary winding to light up the two 12X4 filaments, as the primary was 115VAC and the capacity was 3 amps, the filaments settled in at 11.5 VAC when the section was loaded.

What makes this Preamp unique was the implementation of a 3P3T toggle switch to switch between a CLCRC supply that used a series resistor and series shunt OC2 gas regulators or a simple CLCRC Regulated supply with a resistor.

At the flip of a switch I can go from a OC2 Regulated +300V Supply to an plain un-Regulated 290-310 VDC supply (depends on where the 120VAC mains is on any particular day or moment).

The sound of the Aikido Preamp changes dramatically when I switch between Regulated and Un-Regulated, and not only I can hear the difference, but my fellow music lovers who have enjoyed this Preamp have heard a difference.

The differenced in sound?

Un-Regulated sounds softer, rounder, much more ambience with less defined lower registers. It sounds much more like music to me, but not as good when I play aggressive source material like Rock or Techno Pop. Classical music is wonderful as well as the softer smooth Jazz genres.

Gas OC2 regulation sounds much more robust and pushed forward, with better overall definition and attack though the uppers have less bloom and air around the notes. Speech is more intelligible when watching DVD movies in the OC2 Regulated mode but my 53 old ears can’t speak much more to this as my hearing is not as good anymore.

So I can say that the same base Power Supply with regulation added can sound different when switched between two power supply sections that each have a different series DC dropping resistor value and a pair of series OC2 Gas regulated tubes.

The different series dropping resistors are necessary to compensate for the extra current draw from the HV secondary winding when I flip on the OC2's.

This also may have something to do with the Preamp amp sounding tighter or stiffer when regulated, but also the noise floor is not a dark or quiet as it is when I flip the regulators out of the circuit. Likely has to do with the regulators having some noise performance drawbacks.

My gut feeling has always been that most all Tube Power Amps don't use or have regulated B+ hence they will really benefit from a Choke input power supply design, but this is just a loose opinion from having experimented with Choke input type HV power supplies, I really need to build a Power Amp that implements real HV regulation to see what the effects are on the sound. This can become expensive with Tubes and a design effort with Solid State regulators.

Somehow I think that part of the clique tube amp sound comes from the general implementation of Un-regulated B+ and smaller size caps with Tube Rectifiers.

My ears seem to prefer Diode Rectifiers on Power Amps as punchier sounding than tube rectifiers.

Using large value power supply capacitors in my experience helps stiffen up the sound.

My DIY Dynaco ST-35 uses 200uF/200uF and a 80uF at the end, definitely helps the sound I get more depth than with the stock Dynaco values.

But crazy large supply Caps don't seem to help past a certain point, of course not with tube rectifiers that have limits. Diodes must handle the inrush better.

Attached is my diagram.... great question, I hope to have addressed some aspects here.

This post is made possible by the generous support of people like you and our sponsors:

Analog Engineering Associates

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