• Extreme Hi-End Hybrid Amplifier End PCB (two items are necessary for a stereo ampliier)
• Extreme Hi-End Hybrid Amplifier End PSU PCB

     where 

Tube model	Pd max (W)	Ri (ohm)	Va (V)	Ia (mA)	Rk (ohm)	Voltage gain (dB)	THD 30Vrms load 30K	THD 40Vrms load 30K	THD 30Vrms load 15K	THD 40Vrms load 15K
D3a triode	4.5	1900	150	24	60	37.0	0.4	0.6	0.6	0.7
EC86	2,2	5600	165	12	110	34.5	0.7	0.9	1.2	1.7
E180F triode	3.0	2700	165	15	110	33.2	0.9	1.2	1.5	1.9
6C45	7.8	1100	148	25	43	32.5	0.3	0.4	0.4	0.6
5842	4.5	1700	150	25	60	34.2	0.8	0.9	1.0	1.2
6S3PEV	3.0	5000	160	15	110	31.4	0.6	0.8	1.0	1.3

The current amplifier is a perfect Diamond Buffer used in some chip like the LH0002 and the BUF634.
This configuration has been analyzed very well in the article Bulding better buffer on Electronics World november 1992.
The same design as been used in many Audio Research amplifiers like the Audio Research D100 and the Audio Research D-400.
Also the Pioneer A-09 and the Pioneer M-6 use a Diamond Buffer on output stage but these implement dynamic current generators with some stability problems.

Advantages of this type of configuration compared to a conventional:

• compensation of Vbe non-linearities between driver and final so very low distortion without feedback
• high slew-rate and large frequency band
• temperature run-away compensation without sensors if driver and final transistors share the same heatsink
• high input impedance if driver stage use current generator (I1 & I2)
• auto protected by short circuit on output

Disadvantages of this type of configuration compared to a conventional:

• the bias current in the driver limits the current supplied to the load

It is evident that there are many benefits, but to overcome the problem of the current supplied to the load you need to study well the working points of the driver and final.

There is no trimmer for adjusting the bias so you must use exactly the transistors described in the project.
To use other types you need to make many test and in some case set R9-R12 to 1ohm or more.

This current amplifier have an input impedance near to 20Kohm and it absorbs a max peak current of 2mA also when it drive 2 ohm load at the max output level (simulated with 40Vrms on 2ohm load so 20A).

I have add a power supply regulator to eliminate any ripple coming from main capacitors after the diode bridge and it allow a soft start with these advantages:

• the capacitors near the output transistors are charged slowly so the fuse inserted before does not blow
• after switch-on the output stage should start without dc offset and it will wait the vacuum tube warm up

R1,R25                            56Kohm  1/4W  1%    or better use only R1  27K MK132 Caddock
R2,R14                            10ohm   1/2W  1%
R3,R36                            280ohm  1/4W  1%   
R26,R27                           2700ohm   2W
R34,R35                           15ohm     2W
R23,R33                           270ohm    1W
R24,R28                           5600ohm   2W
R5,R6,R7,R8,R17,R18,R19,R20       0.47ohm   5W
R15,R16                           220K    1/4W  1%
R55,R56                           2200ohm 1/4W  1%     or better use only R55 1K MK132 Caddock
R51,R52,R53,R54                   470ohm  1/4W  1%     or better use only R51 and R53 220 MK132 Caddock
R4,R13                            6800ohm   2W
R49,R50,R21,R22                   10Kohm  1/4W  1%

R29,R30,R31,R32,R41,R47,R48,R37,
R38,R39,R40,R37,R38,R39,R40,R9,
R11,R10,R12                       0ohm  (jump)

C6,C8,C9,C14                      0,47uF  63V  Wima
C1,C2,C10,C11                     100uF  25V
C3                                empty
C5                                0.1uF   100V   Vishay MKP1837
C7,C17,C4,C24,C18,C20,C25,C19     4700uF 63V Nichicon  KG  type 25x50mm
C15,C16                           1000uF 63V Panasonic or Nichicon 100°

D1,D2                             Zener 15V  1W
D3,D4                             UF4007 or 1N4007
D5,D14                            1N4007
D9,D13                            0ohm  (jump)
D8,D12,D11,D10,D6,D7              1N4148

F1,F2                             FUSE 5A FAST (with fuse holder)

U1                                2N5550 o 2N5551
U2                                2N5401

Q1,Q3,Q16,Q18                     MJE15033 (PNP)
Q2,Q4,Q14,Q17                     MJE15032 (NPN)
Q9,Q5,Q6,Q7,Q13                   NJW0281G (NPN)
Q12,Q11,Q8,Q10,Q15                NJW0302G (PNP)

IC1                               OPA134 (you can use many others single op-amp)

	As mention in the characteristic list at the begin of this page in this project the passive components are without compromise on any section. On vacuum tube cathode there is an Sanyo OS-CON capacitor, my choice is .... available in the Parts Connexion web store. The SANYO OS-CON is an aluminum solid capacitor with high conductive polymer or organic semiconductor electrolyte material. Due to the solid electrolyte used, OS-CON achieves low Equivalent Series Resistance (ESR), excellent noise reduction capability and frequency characteristics. Normally the capacitors with lower voltage sound better so I prefer to use a 4V   than a 16V if there is only 2V on cathode. The interstage capacitors must be of the highest possible quality because most of the sound quality depends on these. My choice is the Audyn Cap Reference classified with 11+ by Humble Homemade test but in my opinion these are much more transparent than others 12 and 13 result. As tested in the first version the anode choke give the most low distortion and the best frequency band, also the interstage transformer it more invasive so it should be used only if it is essential in the circuit as a phase shifter, see the Amplifier End. The LL1668AM/25mA with an inductance of 100H, an air gap to support a current of 25mA and a static resistance of 680ohm give a sure result. All the resistors in the current amplifier has been duplicated to use for any resistor a parallel of two components mounted with opposite direction to reduce parasitic inductance and electromagnetic flux. I learned this method many years ago by the owner and designer of a famous American factory of amplifiers and it use the same also with Solen interstage capacitors. The alternative to this method is to use Caddock MK132 with advantages. About the power supply capacitors near the output transistors there are no alternatives to the NIchicon KG capacitors because the my last experience made ​​the Amplifier End has demonstrated that these components without bypass have unsurpassed musical performance. I have used 8 x 4700uF 63V NIchicon KG capacitors for each channel so we have a great reserve of power available in a very short time. The 0.47ohm output resistances present on the emitter of final stage transistors are necessary to compensate some differences on output transistors, stabilize operating point and to merge all the outputs. In order to have no bad effects on the sound the my choice has been the MILLS MRA-5  non-Inductive wirewound resistors with 5 watt and with 1% tolerance. Using the transistors specified I have on any 0.47ohm a voltage about 0.180V so the bias current is 0.38A so 4 x 0.38A = 1.5A.

SIMULATIONS

Here all the files to simulate this circuit with LTSpice software.

• Power Diamond

• Power Diamond + PSU

Add these lines in the file C:\Program Files\LTC\lib\cmp\standard.bjt to have the transistors models:

.MODEL Qnjw0302g pnp IS=5.16751e-16 BF=114.657 NF=0.895716 VAF=50.2189 IKF=6.409 ISE=3.9641e-15 NE=4 BR=1.47167 NR=0.923324 VAR=255.567 IKR=6.34299 ISC=3.96408e-15 NC=2.82194 RB=2.66347 IRB=0.1 RBM=2.0828 RE=0.0001 RC=0.0652395 XTB=1.45322 XTI=1.08126 EG=1.05 CJE=2.14504e-09 VJE=0.4 MJE=0.376227 TF=2.16864e-09 XTF=1000 VTF=843.737 ITF=501.348 CJC=5e-10 VJC=0.95 MJC=0.251547 XCJC=1 FC=0.8 CJS=0 VJS=0.75 MJS=0.5 TR=1e-07 PTF=0 KF=0 AF=1

.MODEL Qnjw0281g npn IS=4.36849e-12 BF=98.1488 NF=1.01332 VAF=37.9046 IKF=9.71849 ISE=1e-16 NE=1.8326 BR=0.79921 NR=1.09994 VAR=339.743 IKR=5.77305 ISC=1e-16 NC=2.71592 RB=2.74892 IRB=0.33289 RBM=2.74892 RE=0.000344671 RC=0.03203 XTB=1.7742 XTI=1.12262 EG=1.20598 CJE=3.66793e-09 VJE=0.74806 MJE=0.85 TF=2.27115e-09 XTF=1000 VTF=912.955 ITF=296.602 CJC=5e-10 VJC=0.95 MJC=0.270858 XCJC=0.98254 FC=0.8 CJS=0 VJS=0.75 MJS=0.5 TR=1e-07 PTF=0 KF=0 AF=1

.MODEL Qmje15032 npn IS=3.7344e-10 BF=86.8313 NF=1.23974 VAF=31.5491 IKF=9.1678 ISE=9.2499e-12 NE=3.28127 BR=5.59346 NR=1.33161 VAR=2.1791 IKR=5.15023 ISC=4e-13 NC=4 RB=9.54492 IRB=0.1 RBM=0.1 RE=0.000568481 RC=0.0931741 XTB=0.737036 XTI=1.04983 EG=1.206 CJE=3.05969e-09 VJE=0.648491 MJE=0.352663 TF=4.94819e-09 XTF=1.50001 VTF=1.0001 ITF=0.999982 CJC=3.00108e-10 VJC=0.600021 MJC=0.40991 XCJC=0.8 FC=0.534651 CJS=0 VJS=0.75 MJS=0.5 TR=1e-07 PTF=0 KF=0 AF=1

.MODEL Qmje15033 pnp IS=7.51228e-10 BF=134.35 NF=1.25737 VAF=12.5778 IKF=1.88497 ISE=7.74267e-12 NE=3.34528 BR=5.14173 NR=1.47488 VAR=1.4505 IKR=7.47186 ISC=3.25e-13 NC=4 RB=4.37743 IRB=0.1 RBM=0.1 RE=0.000332989 RC=0.381218 XTB=0.223027 XTI=1 EG=1.05 CJE=3.06005e-09 VJE=0.64838 MJE=0.352991 TF=4.78203e-09 XTF=1.50001 VTF=1.00006 ITF=0.999988 CJC=3.00101e-10 VJC=0.600019 MJC=0.409916 XCJC=0.8 FC=0.534975 CJS=0 VJS=0.75 MJS=0.5 TR=1e-07 PTF=0 KF=0 AF=1
 

POWER SUPPLY FOR THE CURRENT AMPLIFIER

The power supply for the current amplifier use two 500VA toroidal transformers. The good power supply transformers for audio should have an electromagnetic flux 20% lower than normal (14000 gauss instead of 17000). I have used a rectifier module based on four ON Semi MBR40250 Schottky diode to create a full wave bridge rectifier. Here a good description of the benefits derived from the use of Schottky diodes in audio amplifier. The same diodes as been used in my Amplifier End but you can start to assemble this project also with a common diode bridge like the IRF 36MB60.   After the diode bridge there are a pair of 10000uF 63V (size: 50x80mm) capacitors to create a first soft rectification. Here you can use any normal capacitor like Kendeil, BHC, Sprague because these are not on the signal path. As explained in the simulation before using larger capacitors does not bring us benefits. The my choice is 36V-0-36V transformers to get about 100W on 8ohm. You could increase the voltage of the transformers to have more output power but keep attention to the capacitor voltage and to the hot to dissipate on heatsinks.  About the capacitors near the output transistors (on pcb) use only Nichicon KG as specified in the list  8 x 4700uF 63V KG (size 25x50mm) per each channel.

POWER SUPPLY FOR THE VOLTAGE AMPLIFIER

To get the max sonic performances the my choice is a slow turn on power supply for the filaments using a common LM317 or LM350 and a virtual battery operation power supply for the anodic with a power mosfet.

For this power supply I have used the R-CORE model R26-90 got on Ebay shop with primaries 2 x 115v and the secondaries 0-165v(0.2A) and 2 x 0-9v (1.1A).

R6,R8                 1ohm     2W R74                   47Kohm   1/4W  R7                    1Kohm    1/4W R9                    220ohm   1/4W R12                   100ohm multi-turn R4,R5                 10Kohm   1/4W  1% R3                    470Kohm  1/4W  1% R1                    39K      2W R2                    100K     3W CY1,CY2,CY3,CY4       10nF   400V C2                    150uF  400V C1                    33uF   400V US10,US11             56uF   400V Solen MKP C3,C7                 2200uF 25V C4,C5,C6              220uF  16V D4,D6,D7,D8           UF5408 D1,D2,D3              1N4007 D5,D9                 zener 10V 1W B1                    diode bridge  4A 100V IC1                   LM350 or LM317 Q1,Q3                 IRF840 Q2                    2N2904

• pcb for this release

• pcb dual mono or single

MEASUREMENTS

Follows the distortion analysis of the complete amplifier on 8ohm load,  obviously until 30V this is the distortion of vacuum tube voltage stage because the current amplifier have a distortion value 10 or 20 times less and only after 27 volts rms it goes into clipping zone for the supply voltage limitated by project.   On 4 ohm load the plot is very similar.

CABINET

• File with the position of the 16 x 3mm holes to fix transitors

PHOTOS & CONSTRUCTION DETAILS

1) set the variac to about + 2v and -2V dc to check that the heatsink is not connected to these tensions
2) control the voltage after the regulators these should rise slowly in a few seconds
3) set the variac to + 15V and -15V to verify that the output voltage goes to zero volts dc
4) set the variac and -20V to + 20c to verify that the voltagee across the resistance from 0.47ohm is almost equal among all the transistors (0.05V - 0,06V)
5) set the variac at the final voltage

SOFT START - PUSH BUTTON - PROTECTION  (see the relative page)

POWER SUPPLY SWITCH

Vandal Resistant  Push Button Switches RS Stock No. 174-6381 Manufacturer Apem Manufacturers Part No. AV021003C900 The panel cut out  is 22mm, the same of noval socket, so this is the ideal choice for the 10mm front panel because you can use the same cutter.

 

TOTAL COST

It is possible to find some components at lower cost, in red the most important for the final result

description	unit price	quantity	total (euro)
D3a	25	2	50
Solen 56uF 250V	20	2	40
HI-Fi2000 chassie with machining (about)	300	1	300
500VA transformers	100	2	200
30VA transfomers	40	1	40
10000uF 63V	15	4	60
4700uF 63V KG	6	16	96
transistor	36	2	72
LL1668/AM	230	2	460
Audyn Cap Reference 2.2uF	40	2	80
other	100	1	100
DACT	150	1	150
			1648