HP Aikido Stereo 9-Pin B manual Configuring the PCB as a Headphone Amplifier, Switch Front

Page 9

8

GlassWare Audio Design

Configuring the PCB as a Headphone Amplifier

The standard Aikido is a thoroughly single-ended affair, nothing pulls while something else pushes. Unfortunately, wonderful as single-ended mode is sonically, it cannot provide the larger voltage and current swings that a push-pull output stage can. Single- ended stages can only deliver up to the idle current into a load, whereas class-A push- pull stages can deliver up to twice the idle current; and class-AB output stages can deliver many times the idle current. For a line stage, such big voltage and current swings are seldom required; headphones, on the other hand, do demand a lot more power; really, a 32-ohm load is brutally low impedance for any tube to drive. Unfortunately, a heavy idle current is needed to ensure large voltage swings into low-impedance loads.

 

 

 

 

 

 

 

 

 

 

B+

 

 

 

 

 

 

 

 

C5

 

 

 

 

 

R6

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

C6

 

 

 

 

 

 

R7

 

 

 

 

 

 

 

R9

 

 

 

C1

 

out

 

 

 

 

 

 

 

 

 

 

 

 

R4

 

 

R8

 

 

J8 (& J9)

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

C2

 

 

R15

in

R3

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

R10

 

 

 

 

R1

C11

R2

R5

C12

R11

C3

R12

R13

R14

R16

High transconductance output tubes are best for driving headphones, for example, the 6DJ8, 6H30, 12BH7, and ECC99. A coupling capacitor of at least 33µF is required when driving 300-ohm headphones; 330µF for 32-ohm headphones. Use a high-quality, small-valued bypass capacitor in C2’s position. Capacitor C3 can be bypassed by placing a small film capacitor across the leads of resistor R11.

Right HP

output

Left Line Output

Line

Mute

Headphones

Lt C2

Rt C1

Lt C1

Rt C2

Right Line Output

Left HP

Switch Front

Image 9
Contents User Guide Rev. C Overview PCB FeaturesIntroduction to the Aikido Aikido AmplifierC1 & C2 Heater Issues Filament Jumper Wire SchedulePower Supply Tube Selection Internal ShieldsCathode Resistor Values 6CG7 & 6DJ8 6CG7 & 6CG7 12AU7 & 12AU7 12AU7 & 12BH7 Configuring the PCB as a Line AmplifierSwitch Front Configuring the PCB as a Headphone AmplifierLet me know what you think AssemblyPin Aikido Schematic Rev. C Top Side PCB Mechanical Layout ECC81