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Just wondering, since the regulator can have under an ohm of impedance, if big capacitors are still required after it. Maybe a small one under 1uf to prevent oscillations, but the regulator itself can cope with the amp demand, no?
At least i guess the values can be reduced, eg a 4uF where a 40uf would have been needed without regulation?
TIA!
Joris
Follow Ups:
The important question is, what is the magnitude of AC (signal) current going through the power supply? For example, in a single ended amplifier the output signal current loop includes the power supply. So for example if the signal through the tube varies from zero to 120mA, then the power supply must handle that range of current even though the average current is 60mA. If the regulator won't retain regulation through that range then the AC current can go through a capacitor after the regulator - but the capacitor impedance must be lower than that of the regulator if it is to absorb more than half of the current.
Push-pull is more complicated, especially Class AB or B. Highly linear tubes in deep Class A won't have much AC current in the power supply, while Class B will have the full peak output current.
Listen and determine for yourself. Most active regulators are non linear, and so, I have BY EAR used up to 120 uF after them. Forget about all you read and model, and design by ear as to amount. Then YOU will know !!
Have fun, I used to regulate, double regulate everything.
Jeff Medwin
What kind of regulator? What voltage? Some regulators - e.g., gas tube regulators - should not be loaded with more than 1 ufd of capacitance. From your question, you must be referring to a solid state regulator. If its output impedance is only 1 Ohm, you don't need any capacitance beyond what is necessary to prevent the regulator from oscillating.
That said, you need to know the frequency characteristics of the regulator (output impedance versus frequency).
Hello,
Yes it is solid state. I have no means of measuring impedance vs frequency, maybe i can have an approximation in spice.
Thanks for you answer.
SPICE is an excellent way to look at output Z over frequency, assuming all the models are available. I've SPICED some of our very low noise regulators where I work, and the results closely agree with measurements.
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Buy Chinese. Bury freedom.
Available free online from Linear Technology Corp. You'll need to invest some time in learning the program, but it's worth the effort. Once the circuit is built, I analyze output Z by attaching a sine generator to the output through a resistor. Attenuation across the resistor is inversely proportional to output Z.
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Buy Chinese. Bury freedom.
Edits: 08/21/14
I am familiar with LTSpice, but still at hobbyist level. I appreciate those analysis tricks.
Regards,
Joris
Even a 100uF cap exhibits about 80 ohms Xc at 20 Hz. If the regulator really represents 1 ohm resistive (and that value extends well beyond the audible passband), you shouldn't need much capacitance.
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Buy Chinese. Bury freedom.
Thank you for your answer.
John Camille used only a small .056uF teflon after his tubed regulator described in sound practice, hence my question. Still I might put a couple uFs just by habit :-)
Be careful, some regs will oscillate with only a few uF. Let us know the application and how it all sounds when you're done!
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Buy Chinese. Bury freedom.
The application is for a SET electrostatic headphone amp. Current draw about 130mA, B+ somewhere around 350V. I started designing the circuit with a RIAA stage in mind but changed plans.
Here's the schematic.
Of course the final C is the case in point, simulating with .056uF did not show significant change.
Thanks for your comments! I'll let you know how it turns out.
Joris
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