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I have to design a PSRR test fixture with a 2.4KHz signal imposed on a dc power supply. I can do it using a bias tee at rf but the size of the components at audio confound me. The application is a Sample and Hold Amplifier Test Fixture. I would like to stay away from transformers and/or large inductors since I probably have to wind them. Any suggestions welcomed.

micropt
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    My suggestion is that your justification for not using wound components makes no sense; if you can buy the parts for a sample and hold amplifier then you can buy a small transformer. – Andy aka Jan 30 '17 at 14:31
  • depending on your current needs, you can just use an amplifier with some offset – Vladimir Cravero Jan 30 '17 at 14:40
  • More specs on voltage and current please. Perhaps a power opamp would work for you? – George Herold Jan 30 '17 at 15:24
  • define and list all measurements to be made. Rise time, droop, C value thus Z source , sample time etc. No need to use inductors at these low f. – Tony Stewart EE75 Jan 30 '17 at 16:19
  • AndyAKa I would buy a transformer if I knew what to look for in specs. – micropt Jan 30 '17 at 19:02
  • Also the supply is 15 Volts, 55mA. I don't have the IC yet; it is a redesigned SHA which was obsoleted but now I have to test. I have to measure the entire gamut of parameters but I have a budget to buy parts for the fixture. – micropt Jan 30 '17 at 19:04

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Your audio bias-T is more difficult than radio-frequency bias-T, because the DC and AC sources contain frequency components not far removed. This situation requires much more careful design of the AC and DC power sources.
Power supplies most often expect that current will always flow one way. Current is expected to flow out to the load, and not backward (into the supply). Backward current flow is a possibility where a 2.4 kHz signal source is added to DC supply and Device-Under-Test (DUT). To absorb any backward-flowing current, a big swamping capacitor might be added to power supply output:

schematic

simulate this circuit – Schematic created using CircuitLab It is quite possible that DUT contains capacitance between its DC power input and power return. The parallel impedance of DC supply plus swamping capacitor should be very much smaller than DUT internal capacitance. In addition, the AC source must have a low output impedance to drive DUT capacitive load. The AC source might be required to have a low output impedance at much higher frequencies as well, if DUT draws transient currents - a likely possibility for some sample-and-hold circuits. AndyAka's suggestion of a step-down audio transformer is a good solution for a low-impedance AC source. A small transformer can likely cope with DC current flowing through its small number of turns on its low-impedance winding.
If DC plus peak AC current requirements are reasonably low, a power op-amp might be used to combine DC and AC sources. Output impedance can be quite low in the audio frequency range, but some op-amps become unstable when presented with capacitive loads. Try to measure peak current requirements of your DUT before approaching design decisions.

glen_geek
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