low-frequency

development:
fast or as low noise designed class-A MOS-FET-PA
fast or as low noise designed MOS-FET-PA with 150 W rms in class AB operation
low noise preamp
tube-sound with triode in signal path


fast class-A MOS-FET-PA

To drive Power-MOS-FETs without current do not exploid the possibilities of a MOS-FET. Upper critical frequency and turn-on time will be affected by the manner the MOS-FETs are driven. High-frequency circuitry is asked. We have developed a circuit, which can drive the gate capacity of the FET with more current. The driver is a combination of base-collector coupling with bipolar transistors, a current-source, which can drive fast up to 1/4 Amps. Have a look at the gate-current-schema. The fast MOS-FET-PA has to be compensated a little bit more for square-puls-operation as shown and needs 10 Ohm gate resistances to avoid gate current swinging.

It is possible to design this PA for minimum noise high-end version.

Literature: Halbleiterschaltungstechnik - Tieze/Schenk, Analoge Schaltungen - Seifart, Elektronik - Müseler/Schneider, The Art of Electronics - Horowitz/Hill

specifications with gate-current driver:specifications without gate-current driver:high-end version:

class-A

small signal bandwidth: 4 Hz - 25 MHz

gain bandwidth: 6.98 MHz

slew-rate: 770 V/us

transient overshoot: 3 %

input restisance: 43 kOhm

output resistance: 250 uOhm

gain: 11.4 dB

ueq,n = 46.8 nV/SQR(Hz) -> -111.92 dB/22 kHz/13 W

harmonic distortion: < 0.110 % / 13 W, < 0.033 % / 1 W

Po = 13/16.4/23.7 W rms at 8/6/4 Ohm

class-A

small signal bandwidth: 4 Hz - 7.3 MHz

gain bandwidth: 2.58 MHz

slew-rate: 235 V/us

transient overshoot: 39 %

input resistance: 43 kOhm

output resistance: 246 uOhm

gain: 11.4 dB

ueq,n = 46.8 nV/SQR(Hz) -> -111.92 dB/22 kHz/13 W

harmonic distortion: < 0.120 % / 13 W, < 0.042 % / 1 W

Po = 13/16.4/23.7 W rms at 8/6/4 Ohm

class-A

small signal bandwidth: 4 Hz - 4.5 MHz

gain bandwidth: 1.03 MHz

slew-rate: 66.2 V/us

transient overshoot: 3 %

input resistance: 47.8 kOhm

output resistance: 155 uOhm

gain: 11.56 dB

ueq,n = 20.7 nV/SQR(Hz) -> -120.9 dB/22 kHz/13 W

harmonic distortion: < 0.0089 % / 13 W, < 0.0171 % / 1 W

Po = 13/16.4/23.7 W rms at 8/6/4 Ohm

fast MOS-FET-PAsimple MOS-FET-PA

small signal gain:small signal gain:

slew-rate at full power with a jump:slew-rate at full power with a jump:

transient overshoot:transient overshoot:

gate-current of both MOS-FETs at a full power jump:gate-current at a full power jump:

slew-rate, transient overshoot and gate current of the MOS-FETs at 13 Wrms square-pulse-operation:slew-rate, transient overshoot and gate current of the MOS-FETs at 13 Wrms square-pulse-operation:

output at 13 Wrms square-pulse-operation (compensated):output at 13 Wrms square-pulse-operation:

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High-End-MOS-FET-PA with 150 W rms in class AB-operation

MOS-FET-PA in 150 W-Class-AB with Gate-Current-Driver for optimal square-pulse-operation. The compensation is adjusted for an transient overshoot of 3 %. Here two different versions. The differences are the quietness current of the differential amplifier and the compensation.

specifications fast version:specifications high end version:

Class-AB

small signal bandwidth: 4 Hz - 4.2 MHz

gain bandwidth: 3 MHz

slew-rate: 600 V/us

transient overshoot: 11 %

input impedance: 48.1 kOhm

output impedance: 46.44 uOhm

gain: 18.06 dB

ueq,n = 14.32 nV/SQR(Hz) -> -123 dB/22 kHz/150 W

harmonic distortion: < 0.027 % / 150 W, 0.025 % / 1 W

Pa = 211/141/105 W RMS at 4/6/8 Ohm

Class-AB

small signal bandwidth: 4 Hz - 1.1 MHz

gain bandwidth: 500 kHz

slew-rate: 188 V/us

transient overshoot: 3 %

input impedance: 48.1 kOhm

output impedance: 12.95 uOhm

gain: 18.06 dB

ueq,n = 10.42 nV/SQR(Hz) -> -129 dB/22 kHz/150 W

harmonic distortion: < 0.033 % / 150 W, 0.0067 % / 1 W

Pa = 211/141/105 W RMS at 4/6/8 Ohm

fast MOS-FET-PAhigh-end MOS-FET-PA

small signal gain:small signal gain:

slew-rate at full power with a jump:slew-rate at full power with a jump:

slew-rate, transient overshoot and gate current of the MOS-FETs at 150 Wrms square-pulse-operation:slew-rate, transient overshoot and gate current of the MOS-FETs at 150 Wrms square-pulse-operation:

slew-rate, transient overshoot and gate current of the MOS-FETs at 150 Wrms square-pulse-operation:slew-rate, transient overshoot and gate current of the MOS-FETs at 150 Wrms square-pulse-operation:

output at 150 Wrms square-pulse-operation:output at 150 Wrms square-pulse-operation:

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low noise Preamp:

Low noise Preamp with operational amplifiers LME49990 and OPA134 from Texas Instruments. The adjustment range for treble, presence and bass are about +/- 15 dB. The necessary gain is in the first stage to reduce noise. The degenerative feedback was designed with low impedance because of noise.

specifications:

with LME49990 u. OPA134, original Texas Instruments

small signal bandwidth: 4 Hz - 7.5 MHz

power bandwidth: 4 Hz - 564 kHz

slew-rate: 15.48 V/us

input resistance: 100 kOhm

output resistance: 1140.68 Ohm

gain: 12.74 dB at 43 kOhm load

equivalente input noise voltage: 4.39 nV/SQR(Hz) --> -120.7 dB at 22 kHz bandwidth and 3.07 Veff output voltage.

harmonic distortion: 0.0058 %

Preamp:
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small signal gain:

full output at 500 kHz:

slew-rate and swing:

harmonic distortion:

equivalent input noise voltage:

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typically tubesound with triode and non-linear transformer:

Many music-lover sense the sound of natural sound and Hi-Fi-Solid-State-Amplifiers subjective "cold" and "boring". This device produces the "warm", "interesting" sound of tube amplifiers by a pentode as triode. The tube-sound results from the non-linear characteristik of the tube Ik=kx(Ust)^3/2 and of the non-linear transformer.

Input- and output voltage is in this design about 500 mVs. disturption adjustment with R6 (saturation degree 0 Ohm to 330 Ohm). With R1 (plate current 180 Ohm + 470 Ohm Poti) the anode alternate current can be adjusted. The very low-noise operational amplifier regulates the saturation degree of the tube. The THD of the 1 kHz-signal is at 2.1 mAss anode alternating current 2.33 %. with this saturation degree of the tube.

Note: A simulation with a wav-file in LTspice has shown that the result is good. [simulation output 1] [simulation output 2]

Thanks to Andreas Fecht and Alexander Bordodynov/Russia, who had some ideas for this.

specifications:

bandwidth: 30 Hz - ... Hz

input resistance: 100 kOhm

output resistance: 120 Ohm

gain: 0 .. 6.02 dB an 47 kOhm Last

>equivalente input noise voltage: 6.37 nV/SQR(Hz) --> -120.6 dB bei 22 kHz bandwidth and 1 Veff.

harmonic distortion: 1.5 % .. 14.5 %

circuit for 1 channel:

small signal gain:

in- and output signal 1 kHz, moderate adjustment:

spectum of the disturbed signal:

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