- Mounted the bias diodes and power transistors to the face plate. Note the Plexiglass transistor covers.
Leads to amp PCB are pre-installed on TO-3 transistor sockets. These leads penetrate the PCB from the solder side and are soldered to the component side. This method, combined with mounting power transistors directly to the face plate, reduces the lead length to a couple of inches. The previous version of this amp has leads routed to the component side of the PCB.
- Completed soldering components to Leach Amp V4.5 PCB's.
Component Side (note solder pads for attaching power transistor leads) -
Solder Side -
- Face plate removed, preparing to solder power transistor leads to Leach V4.5 PCB.
Left channel leads connected. They are soldered to the component side of the PCB and are just long enough to permit folding the PCB away from the face plate.
- Tested each Leach amplifier channel by removing the power supply fuses and jumping with two 110R, 1/4W resistors. Each channel shows a 2V drop across the resistors giving 18mA through each resistor. So far so good. (Note: skipped the low power PCB test. Since components were matched there should minimal DC offset).
- Leach amplifier PCB's fastened to their standoffs. Changed PCB standoffs from 3/4", shown in picture above, to 1 3/4" for improved spacing between PCB and face plate. Made standoffs with 2" machine screws and 3/16" OD x 0.014" wall x 1 3/4" long aluminum tubing (available at any hobby store). Wired face plate controls. Attached face plate to chassis base.
- Installed binding posts and Zobel bridge on rear panel.
- Attached drive head and checked clearance between HDD and face plate controls.
- Face plate with controls installed.
- Set bias current to 100mV. Compared 1.4 Vrms input sine wave to output over 20 - 20K Hz, no cross over distortion. Measured 12mV DC offset for each channel (Leach design specs less than 50mV). Sound test was excellent (subjective). No audible hum.
Amplifier Complete. Continue to PC.