Compact Blameless Power Amplifier
The Compact Blameless power amplifier has been introduced to offer an economical and space-efficient Class-B amplifer that gives all the benefits of Blameless performance. It is mainly intended for use with loads that are nominally 8 Ohms but will still give excellent performance into lower impedances. If you are planning to drive 4 Ohms and below on a regular basis then the Load Invariant amplifier will give improved linearity.
- Exceptionally low distortion into a wide range of load impedances.
- Very low noise, due to innovative feedback design.
- Unique enhanced-tempco bias generator gives excellent control of the critical quiescent conditions.
- Operates to full specification over a wide range of supply voltages without modification.
F EA T U R E S
- Output devices can be either TO3P or the larger MT200 package.
- Alternate positions are provided for the input transistors (Q1,Q2 or Q101,Q102) so that devices with differing pin-outs may be used without having to cross their legs.
- Tall components have been placed so as not to obstruct screwdriver access when mounting the output devices.
- Pads and tracking for a heatsink-mounted thermistor have been included. This will connect directly to the Signal Transfer Protection PCB.
- Full overload and short-circuit protection.
- Mechanical fixing arrangements improved.
- Comprehensive project notes included. The overlay includes mechanical dimensions for machining from flat bar an aluminium block for mounting the output devices.
- Optional input bootstrapping to raise input impedance.
P C B
- The PCB is now double-sided PTH, so wire links have been eliminated.
- All transistor positions have emitter, base and collector marked on the top-print to aid fault-finding.
- Board fixing holes and pads provided for easy mounting of TO3P output devices to a heatsink.
- High-quality double-sided plated-through-hole PCB
- Gold-plated pads
- Solder mask both sides, full screen print with component values included on the silk screen to aid assembly.
- Double-thickness 2-oz copper to minimise ground resistance and voltage drops.
- Wire connection points can be either via connectors or by direct soldering.
- Fully RoHS compliant.
- Board size 140 by 100 mm overall.
S P E C I F I C A T I O N S
* The Compact Blameless Power Amplifier PCB will operate correctly, in that it gives a visually undistorted sinewave output, from supply rails of +/-5V or lower. This means that initial testing can be done at minimal risk by slowly winding up a variable mains transformer. The amplifier will not of course meet its full performance specifications at such a low voltage.
- Power output: from 25W to 100W into 8 Ohms, depending on supply voltage. Assumes adequate heatsink.
- Power supply: +/-24V to +/-45V *
- Distortion: Less than 0.0006% at 1kHz, 25W/8R. Less than 0.003% at 10kHz, 25W/8R.
- Noise out: Less than -95 dBu (22-22kHz bandwidth, RMS, source resistance 50R)
- Gain: 23 times (+27.2 dB)
- Frequency response: +/-0.1 dB, 10Hz - 20kHz
- Input impedance: 2.2k without bootstrapping, 10k with bootstrapping option
This graph shows the typical amplifier THD when running from +/-24V minimum supply rails. Performance at higher supply rails is somewhat improved.
Audio Precision SYS-2702.
80 kHz, RMS sensing