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Hi-End DAC tube output stage        
August
2016 - now

INTRODUCTION

This is a full differential balanced output stage designed by me many years ago for an Italian company.
The main features are simplicity, very good sonic performances and perfect instrumental measurements.
This circuit can also receive in input un-balanced signal and convert this to balanced so is perfect also like a pre-amplifier.
It can be used with many DAC chip with voltage differential outputs like CS4396, CS4398, WM8741, ES9018, ES9038PRO.

SCHEMATIC

Here the schematic of the output stage excluding power supply and output relay section

This is the complete schematic of the output stage including power supply and output relay section (click to enlarge).

R31,R32,R33,R34,R19,R20,R21,R22     22K 1/4W 1%
R66,R67,R68,R69,R70,R71,R72,R73     2K2 1/4W 1%
R10,R11,R13,R14,R27,R28,R29,R30     470 1/4W 1%
R43,R44,R53,R54,R45,R46,R59,R60    100K 1/4W 1%
R2                                 150K 3W
R1                                  18K 2W
R4,R5                               10K 1/4W 1%
R7                                   1K 1/4W 5%
R74                                 47K 1/4W 5%
R9                                  100 1/4W 5%
R64                                  1K 1/4W 1%
R61,R62                             4K7 1/4W 5%
R63                                 5K6 1/4W 1%
R65                                220K 1/4W 1%
R3                                 470K 1/4W 1%
R6,R8                                 1   3W 5%
R11,R16,R17,R18,R25,R26,R23,R24    100K   1W 1%
R47,R48                             100 1/4W 1%
R35,R36,R37,R55,R56,R56             33K   2W 5%
R39,R40,R41,R49,R50,R51             33K   2W 5%  (are necessary if you use balanced out)
R12                                 100      trimmer 20 turns, to set to obtain 12.6V

C1                               33uF 400V
C4,C5,C8                         220uF 25V
C10,C2                           100uF 400V
C3,C7                            1000uF 25V
CY1,CY2,CY3,CY4                  10nF 440VAC  RS 335-066
COUT1,2,3,4                      2.2uF 400V MKP
CPOWER1,2,3,4                    33uF 400V MKP Solen
B1                               4A or 6A 100V diode bridge
D1,D2,D3,D10,D11                 1N40007
D5,D9                            Zener 10V 1W
D4,D6,D7,D8                      UF5406
Q2                               2N2905A
Q1,Q3                            IRF840
Q4,Q5,Q6,Q7                      IRF820 (only Q5 and Q5 are necessary if you don't use balanced out)
IC1                              LM1086
V1,V2                            ECC82 or 12AU7

J12,J5,J6,J7,J15,J16,J3,J4,J1,J11,J8             RS 718-7987

In the anodic power supply section there is a choke to create a CLC filter in order to reduce all noise, I suggest a valid choke with 10H min, max Rdc 600ohm and a gap to support 70mA min DC current.

 

PCB

This pcb is available on Ebay shop jims_audio.

MEASUREMENTS

Output stage max distortion 0.01% at 4Vrms output and 10Kohm load.

Output stage frequency response 20Hz-20KHz at 0dB.

DAC ES9038PRO + this output stage max distortion 0.0047% at 3Vrms output.

DAC ES9038PRO + this output stage max distortion 0.035% at 13Vrms output.

DAC ES9038PRO + this output stage frequency response 20Hz-20KHz at 0dB.

 

PHOTOS

Here the details of heatsink with the contact to create a ground connection. 

       

Here the details of vacuum tubes filament connections.

     

Output stage

DAC9038PRO + this output stage