We want
Because of these various requirements, it has been decided in a rather early stage to build 3 sections.
All DAC members experienced before that power supplies may affect the sonic performance of audio systems. Therefor a neutral and stable power supply was required for this project.
Most regulated power supplies heavily rely on feedback systems. Since feedback mechanisms are not yet fully understood by most designers, we have been very careful applying those. Since the DAC chips (PCM63) are rather friendly towards the supply (+/-5 V +/- 10%), no rigid stabilisation was required. Therefor we searched for passive supplies, which behaved stable enough under varying load and / or temperature. Dynamic variations of the load, above the cut-off frequency of the transistors, could be dealt with by applying capacitors close to the PCM63s.
The basis for such power supply could simply be a reference, followed by a source or emitter follower, to reduce output impedance a little. In this search we found the circuit diagram of the Audio Note DAC-3, which basically resembled what we where looking for. We decided to adapt this circuit as it sounded very fine.
We choose for Schottky barier diodes as they do not suffer from majority charge cariers storage and therefor do not generate that much RF, followed by pi-style filtering, to get rid of bot 100 Hz riple as well as RF noise. Traditional zener diodes were taken as reference, folowed by a tripple-emitter follower.
The final circuit consists of a center tapped mains transformer (T1), that supplies a greatz style rectifier. Both positive and negative voltages are buffered by C5 and C6, and smoothly filtered by R1/C7 and R2/C8.
Zener diodes D5 and D6 are fed by resistors R3 and R4, from the voltages across C7/C8. As a result 2 stabilised voltages of 8,2 V appear. In series with R3 a LED is added as a visual indicator.
Both zener voltages are filtered and slightly attenuated by networks R5/R6/C9 an R8/R7/C10. The resulting voltages are fed to the bases of both Q1L and Q4L. These transistors form the input pair of super emitter followers Q1-3 and Q4-6. All emitters are loaded rather heavily (all 470W ), to linearise the transfer to the outputs. Ofcourse both left and right channels are separated to minimise crosstalk in the analogue domain.
We needed roughly filtered voltages of about +/- 10 V. Regulating would foolw later-on, by applying traditional voltage regulators
Passive rectification and filtering has been chosen. LM317/337 style regulators have been applied on the digital board, close to the various digital circuits. Dynamic variations of all loads could be filtered by applying capacitors close to all digital circuitry.
We again choose for Schottky barier diodes, followed by pi-style filtering, to get rid of bot 100 Hz riple as well as RF noise.
Again a center tapped transformer (T2) has been taken to suply rectifier diodes D5-8. Both voltages are buffered by C15 and C16, and smoothly filtered by R9/C17 and R10/C18. Lateron stabilisation takes place on the digital board
Again, most among you may have experienced that also tube power supplies affect the sonic character of certain gain stages. A neutral sounding power supply was required for this project.
We went passive again. The final tube gain stage does not require that much current, and also current swing was low. Asd a result passive supplies are possible.
This power supply consists of transformer, tube rectification and passive filtering by cascaded stage, to reduce the ripple.
The mains transformer has 3 secundary windings
The high voltage winding supplies a 6X4 rectifier, as it is able to supply more than enough. The first filter capacitor (C1) smoothes the voltage as that contains lots of 100 Hz ripple. A choke (L1) and second capacitor (C2) act as a second filtering stage. The voltage across C2 supplies 2 equal stage consisting of R10/C10 and R20/C20, both being close to the tune stage as current is required there.
The 6x4 rectifier heater is supplied by the second winding. The heater voltage is related to the cathode by R1, to keep cathode heater voltages low.
The third winding (0-8) supplies a Schottky diode based rectifier. The voltage is smoothed and regulated to supplie the heater of the E88CC based gain stage. The + of the 6,3 V is connected to ground. As a result the heater voltage is always below the cathode, which extends tube life.
The final circuit for the high voltage section consists of a center tapped mains transformer (T1), that supplies a greatz style rectifier. Both positive and negative voltages are buffered by C5 and C6, and smoothly filtered by R1/C7 and R2/C8.
The heater voltage regulator is based on a traditional LM317 style concept, U1, R3/4 and C3/5/6
Copyright © 2001, Marc Heijligers and the DAC group - All rights reserved.