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Working with the VT25920 Signal Triode
(Preliminary Data)
The VT25920 is a Thermionic Super Triode specifically designed by PAEng for voltage amplification in low voltage supply mode.
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vt25920 |
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gm |
rp |
m |
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120mA/V |
65 |
8 |
A suggested design for a low-cost high performances line preamplifier:
...or, the following minimal approach:
In both case the averaged electrical performances are depicted in this table :
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Gain(dB) |
Bandwidth(-3dB) |
Zout (W) |
THD (3.5Vrms) |
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18 |
4.5..600kHz |
110 |
.19% |
A single_ended/differential line amplifier is depicted in the next figure.
The effects of the power supply on the audio circuit is removed by the current source. As output transformer I have used a PAEng Sot-3 type unit.
PSpice Simulation Results
Harmonic Spectrum
| FOURIER
COMPONENTS OF TRANSIENT RESPONSE V(out)
DC COMPONENT = -2.574301E-03 HARMONIC FREQUENCY FOURIER NORMALIZED PHASE NORMALIZED NO (HZ) COMPONENT COMPONENT (DEG) PHASE (DEG) 1 1.000E+03 2.263E+00 1.000E+00 -1.800E+02 0.000E+00 2 2.000E+03 7.576E-03 3.348E-03 9.011E+01 2.701E+02 3 3.000E+03 1.638E-03 7.240E-04 1.798E+02 3.598E+02 4 4.000E+03 2.485E-04 1.098E-04 9.088E+01 2.709E+02 5 5.000E+03 2.771E-05 1.224E-05 -2.768E+01 1.523E+02
TOTAL HARMONIC DISTORTION = 3.427288E-01 PERCENT
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Frequency response
Current Source Audio Residuals (Fundamental @ 600mA/1kHz)
Output Impedance
PSRR
Many peoples are concerned by the use of reactive elements. A true zero caps dc amplifier is a difficult task since we are involved in the nulling of the power supply capacitors. Here the key term is c-u-r-r-e-n-t s-o-u-r-c-e.
Now, I'm experimenting with the following simple structure in a low-voltage environemt. The challenge is to create basic blocks for the design of vacuum tube amplifiers with all the advantages of Solid State (low voltage, low noise, low output impedance an so on..).
Zer0_Caps Direct Coupled Gain Stages
The Problem?
A granitic very stable temperature indipendent simple current source design.
Current to Voltage Converter for Audio DAC
Is the Cf capacitor matter of concern?
We can apply the following transform:
s-transform
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and realize a true 0_Caps I/V converter.
MM Direct Coupled Phono Stage
You can apply the above s-transform for a true capacitor_less phono stage.
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