Bob Cordell Interview: Power Supplies

[Bob Cordell]

What is the best power supply design for packaging 3-amplifiers in one chassis?

I build 3-channel amplifiers in one chassis driven by a 3-way digital crossover in order to direct-drive one 3-way speaker: woofer(20-80hz); midbass(80-1.4KHz); tweeter. The driver circuit topology is identical for all three amps. The number of output transistors varies by function: 8-pairs for woofers; 4-pairs for midbass and tweeter.

I currently have a separate electronically regulated +/- 52V power supply on each amplifier driver PCB, and one large 1,500VA +/- 45V shared CRC supply common-ground shared for all output stages. The output stage is on a separate PCB screwed to the heatsink. The driver PCBs are on 1.5" stand-offs attached to the output PCB in order to isolate high output current noise and heat. This packaging also makes it easy to exchange experimental driver circuits. Heavy wire creates a common star ground on the CRC ground bus bar.

Lately I have been wondering if a separate L-C for each amplifier coming off one common rectified C would produce cleaner, more isolated sound. (common_C) + (local_LC) filtering.

What is the best power supply design for packaging 3-amplifiers in one chassis?

Hi LineSource,

What you've described here sounds very well thought-out. It is in some ways similar to what I did with my Athena active 3-1/2 way speakers described on my web site at CordellAudio.com - Home.

With the Athenas, the amplifiers were built right into the speaker enclosure. The four 125-watt MOSFET power amplifiers in each speaker shared a common power supply and, like you, I used boosted supplies for the drivers. The boosted supplies were well-filtered but not regulated to a fixed voltage.

My crossovers were analog active.

I think one large power supply is fine for driving the output stages, but that good filtering and isolation for the supplies for the drivers is a very good idea. If one wanted to go a step further, a separate large supply for the output stage of the amp driving the woofer might be a good idea.

Cheers,
Bob

 

[LevHyp]

Good afternoon Mr.Cordell,
I think the power supply has an effect to sound because it can affect the input stages current sources(that we must create current sources with very high PSRR) and increase THD.
Second source is the demanding current from capacitors, and in this case the ESR will play a major role.
And the third one, the capacitor may fail during operations ,lose the capacity and then changing the sound (because of lack of filtering ). A good quality capacitors with high inrush current capacity. Never start a power supply without a softstart. I started one without softstart and then the capacitors was at zero capacitance after second turn-on. Good day!