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This is a number of notes on different subjects.
They are not in any particular order.


Various filters for use in LT Spice.
A collection of filter sub-circuits for LT Spice:
1. order low-pass, high-pass and all-pass filters.
2. order low-pass, high-pass, all-pass, band-pass and band-reject filters.
A, B, C, D, ITU-R 468 and flat noise weighting filters.
RIAA emphasis and de-emphasis filters.
Pink-noise weighting filter.

Some notes on gramophones.
Tonearm resonance frequency.
Record modulation.
Tonearm wire.
Pick-up DC current.
Gramophone VLF Output.
Pick-up Wire Colors.
Strobo disc.

Capacitor impedance.
Electrolytic capacitor impedance.

Resistor color codes and e-series.
IEC-60757 color code abbreviations.
E3..E192 standard values.

Thermally coupling two TO-92 transistors.

Headphone sensitivity and cross-talk.
Conversion between dBSPL @ 1 mW and dBSPL @ 1 V.
Headphone cross-talk with different cabling.

Reading logarithmic plots.
How to read values from a logarithmic graph.

Some notes on phantom power.
Phantom power.
Phantom supply noise.
Amplifier input capacitors.
Battery powered phantom supplies.
Microphone connector wiring.

NTC Calculations.
Calculations and some Spice models for NTCs.

Current mode transformer input amplifier.
By using a transformer in current mode, its low frequency response can be extended considerably and its distortion can be reduced by an order of magnitude or more.

Inrush current limiters for power supplies.
Calculations for NTC inrush current limiters.

The Howland current pump basic equation.

Driving AC relays with a zero-crossing opto-triac.
Driving AC relays with a zero-crossing opto-triac is generally not a good idea, but sometimes you have no choice.

Increasing OP-AMP output current.
Boosting OP-AMP output current without additional cross-over distortion.
Current limiting is also maintained.

Some notes on filters.
Transforming cascaded 1.order filters to 2.order filter and vice versa.
Unity gain Sallen-Key bandpass filter with identical capacitor values.
Amplitude response of RIAA network.
Amplitude response of 1.order high-pass filter.
Amplitude response of 1.order high-pass filter with zero.
Amplitude response of 1.order low-pass filter.
Amplitude response of 1.order low-pass filter with zero.
Amplitude response of pink noise filter.
IEC 60268-1 filter.
Peaking frequency and amplitude for 2.order LP and HP filters.

Resistive ladder dividers.

Stereo width control.
AB-MS-AB matrix.
Stereo width control.
Headphone cross-feed circuit.
Acoustical feedback reduction for gramophones.
Hafler matrix circuit.

Comparison of Sallen-Key and State variable topology for a Linkwitz-Riley cross-over network.
Comparison of summing error and output noise for the 2 types.

Constant Directivity horn equalization.
Fixed and variable equalizer for Constant Directivity Horns.

Audio Signal Clippers.
Soft-clippers and clippers.

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