Hi all,
I have 3 pcb board left of a hybrid amplifier project, based on a revisitation I made from the YAHA headphone amplifier.
The main difference from it is that I preferred not to use the grid leak bias (tending to the positive region of Vg) but the classical cathode bias running tha amp at 24Vdc, through a simple LM7824 on B+ of the ECC82. The tube filaments too are fed with Vdc, from a CRC filter. The transformer is a toroidal one 12VAC and at least 20VA, I found this one doesn't offer magnetic coupling (and then zero hum) respect to a EI core transformer, that takes more space too. The PSU is made up of two units, one of which is double the other with a FW rectifier going to ECC82 plates.
A mention is deserved to the opamp, it should be able to bear >60/70mA of output current: so I deem the choice can be NJM4556, NJM4580 or NJM2114. The latter I have to say is very good (though with lesser current of the prevoius ones) but good soundstage and dynamics.
If someone's interested to the boards otherwise I appreciate some opinion about the circuit. As little implementation I also thought to use as alternative to Ra a CCS based on a constant current J-fet or LM334...I know it's a simple project, but for the overal cost of components is a fine sounding little amp.
I have 3 pcb board left of a hybrid amplifier project, based on a revisitation I made from the YAHA headphone amplifier.
The main difference from it is that I preferred not to use the grid leak bias (tending to the positive region of Vg) but the classical cathode bias running tha amp at 24Vdc, through a simple LM7824 on B+ of the ECC82. The tube filaments too are fed with Vdc, from a CRC filter. The transformer is a toroidal one 12VAC and at least 20VA, I found this one doesn't offer magnetic coupling (and then zero hum) respect to a EI core transformer, that takes more space too. The PSU is made up of two units, one of which is double the other with a FW rectifier going to ECC82 plates.
A mention is deserved to the opamp, it should be able to bear >60/70mA of output current: so I deem the choice can be NJM4556, NJM4580 or NJM2114. The latter I have to say is very good (though with lesser current of the prevoius ones) but good soundstage and dynamics.
If someone's interested to the boards otherwise I appreciate some opinion about the circuit. As little implementation I also thought to use as alternative to Ra a CCS based on a constant current J-fet or LM334...I know it's a simple project, but for the overal cost of components is a fine sounding little amp.
