04-03-2017, 12:43 PM
In 1961, Dinsdale showed a single germanium transistor RIAA input stage for use with a moving magnet and crystal cartridges, tape EQ and flat http://69.195.158.203/Archive-Wireless-W...961-12.pdf . Of course transistors were new fangled devices back then and were very expensive, so there was a powerful incentive to minimise the number of them in the circuit.
The old two-transistor RIAA stage stage was also originally devised by Dinsdale in 1965 http://69.195.158.203/Archive-Wireless-W...965-01.pdf had both a DC feedback path to stabilise the operating point, and an AC path to set the gain at 1kHz and apply RIAA correction, and a bootstrapped first transistor. Used OC44's. The performance of that can be made quite acceptable using silicon transistors, adding an emitter follower buffer to drive the RIAA network, changing the bias conditions to ensure symmetric clipping, and upping the supply voltage (typically <0.01% distortion).
But like Mark said - thank goodness for op-amps! Although they used to be expensive; when I built the Texan back in the early 70's, 741 and 748 op-amps were 60p each (about £6 in today's money). Forking out the equivalent of £36 for six opamps was a big deal for a 16 year old.
The old two-transistor RIAA stage stage was also originally devised by Dinsdale in 1965 http://69.195.158.203/Archive-Wireless-W...965-01.pdf had both a DC feedback path to stabilise the operating point, and an AC path to set the gain at 1kHz and apply RIAA correction, and a bootstrapped first transistor. Used OC44's. The performance of that can be made quite acceptable using silicon transistors, adding an emitter follower buffer to drive the RIAA network, changing the bias conditions to ensure symmetric clipping, and upping the supply voltage (typically <0.01% distortion).
But like Mark said - thank goodness for op-amps! Although they used to be expensive; when I built the Texan back in the early 70's, 741 and 748 op-amps were 60p each (about £6 in today's money). Forking out the equivalent of £36 for six opamps was a big deal for a 16 year old.
