All active 300B Rev 3
All active 300B Rev 2
All active 300B

Pentode/Mosfet Cascode CCS Rev 3

Here is a more comprehensive guide to setting up the Pentode/mosfet cascode CCS. I hope it helps.

Pentode/Mosfet Cascode CCS setup information

New! Pentode/mosfet cascode CCS

Having listened to the Pentode CCS for a couple of months I was really happy with the sonic performance. I was not happy with the noise performance though. In the output stage it didn't matter. In the driver stage it added a small amount of hiss. In the line stage it was still not too bad. You had to be within a foot of the speaker to hear the hiss. My speakers are 100db/watt so it really wasn't that bad. My anal side got the best of me though. After staring at the circuit and poking at it allot I finally figured out the noise situation. In the Pentode CCS the voltage reference has about 1mv broad band noise on the reference terminal. If you take the resistance of the current set resistor and compare it to the plate resistance of the tube it is connected to we have a large noise gain. The new Pentode/mosfet cascode CCS (P/MCCCS ) is designed to get around this problem. First the voltage reference is much higher. Then there is a filter after the reference that reduces the noise down into the microvolt range. With a clean higher voltage reference you can use a much higher value of current set resistor. This does 2 things, it reduces the noise on the reference and reduces the noise gain of the circuit. The new circuit is about 20db quieter referenced to 5Vrms output on the line stage than the PCCS. It has noise performance that is a couple of dB quieter than the C4S I have been using as a reference. The output impedance is 11.5 Meg ohms! This translates into >60db power supply isolation. 

All the technical stuff is great but how does it sound? It resolves even more low level detail than the PCCS but keeps the trait of not sounding bright or edgy. The back ground sounds are much more vivid and the sound of cymbals being tapped with the drum stick are amazing. I installed a pair of them in my 26 line stage in place of the C4S's. The switching arrangement is still setup so now we can compare the two  pentode CCS's. The difference between the original PCCS and the P/MCCCS is as much of a change as there was going from the C4S to the PCCS. You only switch back and forth a couple of times then the switch doesn't move again. When you go from the P/MCCCS to the PCCS the sound stage seems to collapse and get more 2 dimensional. 
 Pentode/Mosfet Cascode CCS Rev2 
 Pentode/Mosfet Cascode CCS

Worksheet for Pentode CCS
 Pentode CCS worksheet

Schematics for the Pentode CCS active plate loads
 6BQ5 active plate load
 39-44 6.3ma CCS
 6AU8 6ma CCS

The C4S current source shown in several schematics on this page was designed by the late John "Buddha" Camille. It is available in kit form with a great manual from Bottlehead corporation. Bottleheads website

Schematics for the battery filament 26 preamp. It has been quite a journey over the last year starting with choke loading and progressing through the different CCS's.

26 Battery Biased Mosfet CCS linestage with shunt reg
26 Hybrid Pentode Mosfet Cascode CCS loaded preamp
26 Pentode CCS loaded preamp
26 C4S Preamp
26 Choke loaded preamp
Power supply
Battery charger
Relay Controller

Schematic for the All active loaded 45. Credit goes to Voltsecond for the design of the Big C4S on the output stage.
 All C4S loaded parafeed 45 amp

Schematic for the battery powered 31 parafeed amp
 Battery powered DHT parafeed amp

Schematic for the C4S loaded 56/76 preamp
56/76 C4S preamp

This crossover network is for my 3 way Electrovoice system that consists of a SP 15 Woofer, 8HD diffraction horn with 1824 driver for Midrange and a T350 Tweeter. System is right at 100db/watt and an easy 16-20 ohm load.
Electrovoice_3way_xover

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