Pleiades ECC83 ECC82 RIAA MM preamplifier

 At your risk. Take all safety precautions. Dangerous voltage present. Protect also your precious hearing.

This is a revisited preamplifier made before 2000. Many mistakes are now been corrected, such as RIAA filter, removing cathode bypass capacitors, leaving only resistors in order to reduce gain and possibility of overload. 47pF or even 220pF has been removed from input assuming that phono cable itself may be of the order of 47pF.

Topology, circuit description for 1 channel.

Capacitor couples MM cartridge (the potential at grid is -200mV, so there is grid current that would flow to the cartridge for better or worse and the capacitor stops it), to grid of first half of ECC83. Cathode resistor is 1KOhms. Anode resistor is 100K. Coupling capacitor from anode to RIAA filter (see Heathkit AA-32 schematic) consisting of 220K, 22K, 15pF. Then 5pF for the HF (a series capacitor should possibly be included to stop reducing treble for ever).

Then another stage of half ECC83 with 1M at grid to ground, 100K at anode. 1K at cathode. Coupling capacitor from anode to 1M potentiometer.

Final stage is an ECC82 used as SRPP (series regulated push pull, see The Tube Amp Cookbook - Allen Wright), resistors used are of the order of 560 Ohms. High voltage 2.2uF capacitor at output.

The 2 channel preamplifier when fed by a Shure 75ED Encore cartridge can feed Sennheiser HD580 headphones to a high level of big sound.

Voltage supply is of the order of 140V, decoupled with 10K resistors and capacitors for each stage. Anode potential is of the order of 65V.

Power consumption is of the order of 30W!

So encouraged by the great sound while listening to Rocky Soundtrack LP, In the Burning Heart - Survivor, (Skyfall-Adele CD with inverse RIAA Lipshitz, Jung network, strings sounded so real), it is decided to create a similar electron tube amp with very low power consumption and loser even noise using DC90 electron tubes and the final stage being an ordinary anode follower with output transformer to lower the impedance without negative feedback. See previous, next posts.

It is amazing how electron tubes give this big sound. How do they do it?

Reference:

https://sound-au.com/p80-Inverse-RIAA.pdf