John Linsley-Hood Revisited - diyAudio
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Old 30th July 2014, 04:20 PM   #1
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Default John Linsley-Hood Revisited

Decided to build a couple of Class A Amps.to the John Linsley-Hood design after reading "The Class A Amplifier Site",now hosted by Rod Elliott on his "Elliott Sound Products" web site for the umpteenth time,incorporating some features suggested by contributors and with more modern audio transistors.
Starting with a 12-0-12v transformer to supply approx.+&- 16V to the output stage,I added a Voltage doubler (4 X1N4007 diodes,2X 470uF 25V and 1X1,000uF 35V electrolytics).to supply a LM317L voltage regulator,programmed for 25V.
One contributor to TCAAS felt that a true Constant Current drive to the driver transistor,rather than the usual "Boot-strap"gave better results.A second LM317L was configured as a CCS(100R pot + 18R) to provide the load for the 2SC3421.
A 10K pot+22K took the +25V to the junction of the feedback resistor and it's decoupling capacitor,to provide output offset, by injecting a small current into the emitter of the BC556 transistor.This capacitor should be shunted with a 1uF polyprop.
Transistor line-up:
BC556, 2SC3421, 2X 2SC5200.
Both Rod Elliott and Graham Maynard (see his GEM Amps.) warn to be on the look out for counterfeit Toshiba transistors.
The only problem was the amount of heat.Being a Class A a considerable amount of heatsink is required but the resulting sound is outstanding.Well worth the effort!
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Old 31st July 2014, 02:55 AM   #2
kimbo is offline kimbo  Australia
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Pretty pictures please!
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