MachMat Schalmei I
If you have comments, suggestions, going to use this design please let me know!
I'll try to explain why I made all choices, if anything isn't clear or an error from me (quite well possible), please
let me know.
Click here for the amplifier.
Click here for the powersupply.
Notes:
- First stage has extra powersupply filtering (12K with 10 uF) because this stage will determine almost all hum and sound
quality of the turntable. I use the 5751 paralleled because it's a very good low noise tube designed for this type of
purpose. Other tubes can be used like the 7025 or the ECC808, with small circuit changes. I used the tube paralleled
because I have better output impedance to drive the filter circuit after it and less noise. Also I still can make a
balanced input when going to MC in the future.
- The high frequency correction is between the first and second stage. Calculations can be made by:
1/(2*pi*2140 Hz)=Rtot*C, where Rtot is the drivingstage's output impedance plus the filterresistor value.
- The second stage is directly coupled to the first to eliminate another capacitor in the signal.
- The second stage drives the low frequency correction circuit. This correction is quite complicated, to make some good
calculations I derived the formulas. The third stage buffers
this filter and gives the last amplification to get the right signal level.
- The final tube buffers the volume control and drives the cables to the amplifiers.
- Except for the input tube all tubes are directly heated triodes. This of course needs extra care for the heather supply.
All supllies will be stabilised to be sure no hum gets in the signal. Directly heated triodes are outstanding lineairity
tubes, very nice for these low signals...
©MachMat 1998. For comments or questions please mail.