Power supply – HP Aikido Stereo 9-Pin PCB User Manual

Page 6

GlassWare Audio Design

Heater

300k

100k

1/2W

B+

300k

100k

1/2W

B+

0.1µF

250V

0.1µF

250V

100
100

Alternatively, you might experiment with floating the

heater power supply, by “grounding” the heater power

supply via only a 0.1µF film or ceramic capacitor. The

capacitor will charge up through the leakage current

between heater and cathodes. Not only is this method

cheap, it is often quite effective in reducing hum.

Power Supply

The power supply is external to the Aikido PCB and can be mounted in, or outside,

the chassis that houses the PCB. The optimal power supply voltage depends on the

tubes used. For example, 6GM8s (ECC86) can be used with a low 24V power supply,

while 6FQ7s work better with a 250-300V B-plus voltage. The sky is not the limit here,

as the heater-to-cathode voltage sets an upward limit of about 400V.

The genius of the Aikido circuit is found in both its low distortion and great PSRR

figure. Nonetheless, a good power supply helps (there is a practical limit to how large a

power-supply noise signal can be nulled). I recommend you use at least a solid, choke-

filtered tube or fast-diode rectified power supply. If you insist on going the cheap

route, try the circuit below, as it yields a lot of performance for little money. FRED

rectifiers are expensive, but make an excellent upgrade to the lowly 1N4007.

All Diodes = 1N4007
All Resistors = 1 ohm 1/2W

.01µF
1KV

100mA
high-DCR

B+