HDRP200 High speed very low distortion singleton power amplifier

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hey Ricardo,

You have a very nice design, I love how you decided to use a common emitter stage loaded with a CCS to keep the even harmonics as part of the IPS's sound signature.

Have you tried to cascode DN2540 with a low noise Jfet?
I used DN2540 a lot in my tube gear and I have noticed that by itself it does not make a good sounding CCS.

Some links that could be useful:
CCS: not everything that glitters is gold (Part I) – Bartola(R) Valves
Mini CCS – Bartola(R) Valves
Flexible CCS board prototype – Bartola(R) Valves
Tracing (MOS)FETs to be used in the gyrator PCB – Bartola(R) Valves

Best regards,
Silviu Savu
 
hey Ricardo,

You have a very nice design, I love how you decided to use a common emitter stage loaded with a CCS to keep the even harmonics as part of the IPS's sound signature.

Have you tried to cascode DN2540 with a low noise Jfet?
I used DN2540 a lot in my tube gear and I have noticed that by itself it does not make a good sounding CCS.

Some links that could be useful:
CCS: not everything that glitters is gold (Part I) – Bartola(R) Valves
Mini CCS – Bartola(R) Valves
Flexible CCS board prototype – Bartola(R) Valves
Tracing (MOS)FETs to be used in the gyrator PCB – Bartola(R) Valves

Best regards,
Silviu Savu

I did simulate a cascoded CCS but was unsure of the resulting current stability.
Would you please suggest a suitable jfet for this purpose ?
 
Circuit description:

IPS
Q1 – KSC1845 NPN – Input transistor running @ 540uA

IPS CCS
Q5 – BC560C PNP (Controlling bjt)
Q4 – BC560C PNP (Stiff bjt)
R29 – 100 ohm (Base stopper to avoid instability in the CCS)
R28 – 1k2 ohm (Current setting resistor)
R27 – 15kohm + R32 – 15kohm (current setting resistors for the CCS controlling bjt)
C21 – 47u (Filter for R27 R32 current setting resistors for the CCS controlling bjt)

IPS BIAS
R5 – 32k4 ohm + R31 – 2kohm // 1k trimmer (voltage divider provides base bias voltage for Q1)
R4 – 32k4 ohm (voltage injector – places Bias on Q1 base)
C3 – 470u (Bias circuit filer / stabiliser)
Q7 – KSC1845 NPN (connected as a transdiode “base collector shorted” is there for anti drift purposes as it is thermally bonded to Q1)

TIS (VAS)
Q2 – BC556B PNP (Beta helper… this EF shields the TIS transistor increasing the circuit input impedance and total beta)
Q3 – 2SA1381C PNP (TIS transistor provides current to voltage conversion)
C24 – 25pF (Miller compensation capacitor ” CDOM ”)
R11 – 11 ohm (TIS emitter degeneration)
R10 – 220 ohm (beta helper emitter resistor)
R12 – 12k ohm (power limiter for the beta helper bjt)

TIS CCS Boostrap
R15 – 1k5 ohm (-Rail boostrap resistor)
C7 – 330uF (Bootstrap capacitor connected to the output)
M5 – DN2540 (N-Channel Depletion-Mode Vertical DMOS FET connected as floating CCS)
R34 – 330 ohm (base stopper for DN2540)
R24 – 82 ohm (sets the CCS current used as TIS idling)

OPS
M1 – M2 – Lateral NMOS ECW20N20-S
M2 – M4 – Lateral PMOS ECW20P20-S
R17 – R18 – 270 ohm (NMOS gate stopper)
R19 – R20 – 180 ohm (PMOS gate stopper)
R25 – R26 – 0.2 ohm (NMOS emitter resistor)
OPS BIAS
R13 – 120 ohm // R30 – 1kohm trimmer (uses TIS standing current to set bias on the output lateral mosfets)
C9 – 47u (helps turnoff output devices)

FEEDBACK Circuit
R8 – 1k8 ohm (series feedback resistor)
R9 – 68 ohm (shunt feedback resistor)
R33 – 100 ohm (shields Q1 emitter from the action of C4)
C4 - 22pF (Lead compensation capacitor)
C5 – 2200uF (nuls feddback at DC so Gain is unity at DC)

INPUT CIRCUIT
C14 – 22nF (connected between signal GND and chassis, filters input RCA and lowers sensitivity to EMI)
R1 – 220k ohm (input RCA load)
R3 – 1k ohm (input low pass filer set to 720kHz with C2)
C2 – 220pF (input low pass filter)
C1 – 10uF (Input DC blocking capacitor)
R2 – 5 ohm (lifts signal GND from power supply GND reducing hum)
D7 – D8 – 1N4148 (closes circuit around R2 for high current protection in case of fault)

MOSFET GATE PROTECTION
D1 – MURS320 (Clamps the bootstrap and so limits output devices Gate Source voltage to below 4 volts in case of overvoltage at the input)
 

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I made the 5 transistor version with LF353 servo 25 years ago for car stereo.
performance is excellent until it clips, then the rails stick noticeably.
Mine was all reverse transistors, 2N5401 x2 2N5551x 1 and IRF530 , IRF9530.
PNP vas versus NPN vas may be better