This is a number of designs I made.
The are not intended for beginners in electronic design.
You are supposed to have a basic understanding of electronics and knowledge of mounting and reworking double-sided PCBs.
As a minimum you should have a DVM, but preferably an oscilloscope ( 20 MHz is fine ).
Burst generator BG01.
BG01 is a simple sine-wave burst generator with a pulse/pause ratio selectable from 1:1 to 1:255.
2-channel transformer balanced input amplifier IA19.
The IA19 uses the transformers in current mode, allowing the use of very small transformers.
The input is via XLR connectors or solder terminals.
There are footprints for 2 different transformer types ( Beyer and Lundahl ).
Current load IL01.
IL01 is a dual current load designed for testing small power supplies.
The current can be set from 10 mA to 320 mA in 10 mA steps.
The voltage range is 5 V to 35 V ( limited by power dissipation ).
DC protection relay for headphones LR02.
LR02 provides protection from amplifier faults and mute during power on and power off.
Headphone amplifier for 16 Ω to 600 Ω headphones HA01.
Features include volume control, balance adjustment, 3 gain settings and power limiter.
Low-noise measurement Amplifier MA01.
This amplifier has a voltage gain of 60 dB and 75 nV noise through the audio frequency range.
Phantom Powered Pink Noise Generator NG03.
PIC based pink noise generator that fits inside an XLR plug.
It can also be built to output white noise, 320 Hz, 440 Hz or 640 Hz sine-wave.
The 440 Hz output is controlled by a crystal.
Overload indicator OI01.
Overload indicator for line level circuits.
The detection level can be set so indication occurs before the audio is clipped, making it useful for recording applications.
An integrated timer ensured a clear indication of even very short peaks.
Low-noise voltage regulator PS25.
This PSU will deliver up to ±20 V / 100 mA.
It is useful for applications where the noise or output impedance from a LM317/LM337 circuit is too high.
Universal low-power PSU PS28.
This PSU will deliver up to ±20 V / 200 mA.
It has foot-prints for a number of different voltage regulator ICs.
Phantom voltage tester PT01.
This is a small phantom voltage tester housed in a XLR plug.
Indication is with a test tone and a LED.
The tester works for P12, P24 and P48 systems.
RIAA amplifier RA12.
RA12 is a compact, single supply RIAA amplifier with very good RIAA accuracy that can be powered from the TRIG output of an AV processor.
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.
Pick-up DC current.
Gramophone VLF Output.
Pick-up Wire Colors.
RIAA equalization filter RA15.
The design is very straight-forward, easy to calculate and should be easy to trim.
Resistor color codes.
Resistor E series.
Thermally coupling two TO-92 transistors.
Reading logarithmic plots.
Simple 10 kHz square wave generator.
A simple circuit to match resistors to better than rated tolerance.
Some notes on phantom power.
Phantom supply noise.
Amplifier input capacitors.
Battery powered phantom supplies.
Microphone connector wiring.
Current load IL02.
IL02 is a low current load designed for testing small power supplies.
The current can be set from 1 mA to 64 mA in 1 mA steps.
The voltage range is 1 V to 100 V ( limited by power dissipation ).
The circuit requires an external 20 V supply.
Calculations and some Spice models for NTCs.
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