The Signal Transfer Amplifier Power Supply

The Signal Transfer amplifier power supply provides a high-current power supply for powering two of our amplifiers, combined with regulated +/-17V supplies for powering op-amp circuitry such as: The Low-Noise Balanced Input Card, or The Amplifier and Loudspeaker Protection Card The main high-current power supply is a simple and thoroughly dependable unregulated supply of beautiful simplicity which maximises efficiency and reliability, and allows the instanteous delivery of power as required. All the power amplifiers produced by The Signal Tranfer Company have inherently high supply-rail rejection and simply do not need the complexity of regulated supply rails to give an extremely good noise and hum performance. PCB0014: £28:50 each

The layout of a power supply PCB to minimise hum and ripple is an art all of its own. With this design, approved by Douglas Self, you can be sure you have the optimal solution. It can supply between +20V (for a low-output Trimodal amplifier in Class-A) or up to +45V for the other power amplifiers we produce. The normal reservoir capacitor fit is two 10,000 uF 50V capacitors in parallel, giving a total of 20,000 uF, but other capacitor sizes with the same terminal spacing (10 mm) can be used if preferred.

The power supply PCB is fitted with positions for a comprehensive set of standard high-quality connectors that make wiring up an amplifier system very straightforward. Full instructions are supplied with the PCB.

F E A T U R E S

• Main AC input by push-on connectors for enhanced reliability
• The main bridge rectifier may be soldered directly to the PCB, so it is in contact with the chassis beneath, or may be mounted on a separate heatsink and connected with flying leads, as shown in the picture
• The main bridge rectifier is fitted with multiple snubber capacitors to prevent the generation of HF noise
• The main supply rails have multiple HF filtering capacitors to prevent any noise reaching the output
• Two fuses in AC input circuit protect the transformer secondaries against accidental sort-circuits
  
• The +/-17V supplies are fully protected against short-circuit, over-temperature, and decoupling capacitors trying to discharge themselves back in to the supply when the AC power is removed
• 5532 opamps can be damaged if one supply rail fails, so a mutual shut-down system ensures that if one rail collapses, perhaps due to an accidental short-circuit, the other rail also switches off at once and the opamps are kept completely safe
• If the main supply voltages are between +/-24V and +/-20V, the +/-17V supplies can draw their input directly from this by adding two links on the PCB, saving the cost of a separate transformer.
• The +/-17V bridge rectifier is fitted with multiple snubber capacitors to prevent the generation of HF noise

S P E C I F I C A T I O N S

• Main supply output voltage: +20V to +45V, depending on transformer secondary voltage
• Main supply output: 5 Amps continuous. Assumes adequate heatsink for bridge rectifier
• Main supply ripple: 1.75V pk-to-pk at 5 Amps continuous output current (using 2 x 10,000 uF)
• +/-17V supply output: 500 mA continuous
• +/-17V supply ripple and noise: less than -80 dBu, measurement bandwidth 22 - 22 kHz

C O N N E C T O R S

• PL1, 2, 3, 4: Push-on connectors for main AC input
• PL5: Left channel amplifier main DC out (V+, 0, V-)
• PL6: Right channel amplifier main DC out (V+, 0, V-)
• PL7: DC and AC power out to Protection Card
• PL8: Shutdown input. Signal is passed on to Protection Card, which opens muting relays
• PL9: +/-17V,0V out to Left Balanced Input Card
• PL10: +/-17V,0V out to Right Low-Noise Balanced Input Card
• P11: +/-17V to Power On indicator (LED will require series resistor)
• P12: AC input for +/-17V supplies