Test Gear
Here you’ll find several jigs and utilities I’ve designed to make laboratory life easier.
OpAmp Test Jig
Coming soon—in the meantime you can check the pictures.
OpAmp DC Gain/DC Gain Linearity Tester
DC_gain_linearity_tester_r1.pdf
DC_gain_linearity_tester_r1_PCB.pdf
A test jig to test the DC gain and the DC gain linearity of an opamp. Feed input with low-frequency triangle wave (about 10 Hz usually works well) and connect outputs to oscilloscope in XY mode. The peak-to-peak X-axis reading divided by the peak-to-peak Y-axis reading multiplied by the sensitivity range setting (JP1–JP4) gives the DC gain. Use JP5 and JP6 to reduce wideband noise, JP7–JP9 for offset trimming and JP10–JP13 for output loading. The additional ±15 V power supply is only needed for main supply voltages below about ±12 V
100x Laboratory Preamplifier
A simple unbalanced 100x/40 dB preamp to extend the vertical sensitivity of typical oscilloscopes, powered from two 9 V batteries—helpful for trimming CMRR and checking for hum problems. Output is filtered (with a first-order high pass filter and second order Butterworth low pass filter) for an equivalent noise bandwidth of 20 Hz to 20 kHz. This will clean up the oscilloscope trace, uncover low-level signals within the audio band and aid for rough noise measurements. Special care has been given to the power supply rejection ratio of the amplifier. The bootstrapped cascode and special compensation capacitor connection as well as the JFET current sources do greatly improve things in comparison to standard circuitry.
70 dB Low Noise Amplifier
Untested low noise amplifier based on paralleling several amplifiers. Probably better than −140 dBu EIN (for 20 kHz bandwidth and shorted input) with a full 16 channel version.
Transistor Test Jig
Allows measurement of hFE of a single transistor and Vbe matching of a transistor pair at a wide range of collector currents. Given careful realisation, Vbe matching measurement resolution is about 100 μV at 0.5 mA collector current. A volt meter with 10 μV resolution is recommended to allow accurate hFE measurements of high gain transistors at low collector currents.
Source Impedance Switch
source_impedance_switch_r1.pdf
A simple jig to provide various source impedances for noise measurement and stability tests. In addition to this, a switch allows the measurement of phantom power ripple noise and hum contribution—to simulate China-grade microphones the current drawn (about 10 mA total) is non-equal for the two legs. Use a well-shielded and -grounded enclosure for this jig.
Resources
thd_analyzer.pdf
Excellent article by Bob Cordell on THD+N analyser design.
JFET Jig1.pdf
Simple JFET measurement jig by Fred Forssell.
Terms Of Use
The designs described on these pages are not commercial in any way. This means that I do not sell PCBs, kits, or anything like that. It also means that any for-profit use of the information on these pages is strictly prohibited—you may not sell PCBs, kits (neither partial, nor complete) or finished (or unfinished) units of the designs on this site, without the express written consent of Samuel Groner/SG-Acoustics.
Disclaimer
Notice that all information, schematics, layouts etc. are supplied as is, and that I can in no way be held responsible for its accurateness, functionality or even safety. Samuel Groner/SG-Acoustics shall not be responsible and disclaims all liability for any loss, liability, damage (whether direct or consequential) or expense of any nature whatsoever, which may be suffered as a result of, or which may be attributable, directly or indirectly, to the use of or reliance upon any information, links or service provided through this website.