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Power supply for headphone tube amp gives me 10-12V lower voltage comparing to the schematic (my measurements are in red for amp under load). Current under load is about 70 mA.

power supply schematic

Using simple formula : 150V * 1.414 - 2V = 210V also gives approx voltage shown in the schematic.

I even tried to do simple simulation by using www.partsim.com, and it also gives about 170V for B+ and about 210V on the first filter capacitor.

simulation

I don't know what is wrong. I've triple checked all diodes, capacitors and resistors. They are all fine, and are connected correctly. I am still missing 10-12V.

Edit : transformer data enter image description here

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  • \$\begingroup\$ WhAt is AC ripple on each stage? \$\endgroup\$ Apr 3 at 14:31
  • \$\begingroup\$ I've used two different multimeters, both shows same voltages. It is sinusoidal source, transformer primary is connected to the mains (240V/50Hz). Transformer is toroidal with 2 secondary windings of 150V, which I connected in parallel (antekinc.com/content/AS-05TC150.pdf). \$\endgroup\$
    – buggy08
    Apr 3 at 14:43
  • \$\begingroup\$ @TonyStewartSunnyskyguyEE75 : is it possible to measure AC ripple with multimeter ? \$\endgroup\$
    – buggy08
    Apr 3 at 14:44
  • \$\begingroup\$ Yes. But your filter is too lossy . What DC tinyurl.co.m/ykyl5drt . drop and AC ripple would you like in mV? \$\endgroup\$ Apr 3 at 14:59
  • \$\begingroup\$ Multimeter shows AC voltage 0.53V on the first capacitor, 0.03V on the second one, and 0.00V on the third one. \$\endgroup\$
    – buggy08
    Apr 3 at 15:00
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I will suggest an RLC filter than will only lose a couple volts. KVL indicates too much loss in DC for 80 dB 100Hz ripple attenuation. If your amp has some PSRR in the preamp you may compute that or measure it and reduce all R’s to 2.2 Ohms for now. When you come back with specs for DC drop and AC ripple, then a better sol’n is possible like an LDO or active filter.

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  • \$\begingroup\$ This power supply schematics is not my own, but is part of kit for headphone tube amp already sold in probably thousands of copies. As it is, it already sounds very good for the money. I have almost zero knowledge about electronics, so unfortunately I don't know to answer to your questions about ripple specs. All I know that I need abt. 170V DC at the output of this PS, and I currently have 159V. I've already completed this amplifier, and it sounds perfectly well, it is dead silent, even when potentiometer is turned to max (if input is not connected). \$\endgroup\$
    – buggy08
    Apr 4 at 6:03
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    \$\begingroup\$ Also there is no room in my enclosure to accommodate chokes instead of resistors. Even though I am aware this PS is not perfect, and there exists better designs, as you proposed, I am not sure I can change original power supply on the way you proposed. My only intention was to get 170V, and to try to understand why I am having 10V lower voltage then schematics shows. Yesterday I tried to put additional 270R resistor in parallel with the first one, and I've got 168V at the output. That means that if I replace both 270R with 200R resistors, I could get about 170V at the output. \$\endgroup\$
    – buggy08
    Apr 4 at 6:10
  • \$\begingroup\$ I have also measured power supply voltages without load (I took out tubes), and voltages and transformer secondary was about 155V AC in that case, and capacitors were on 209/206/203 V DC respectively, I guess it would be expected to have higher then 209V after rectifier, if AC is 155V ? At this condition (no load) there is probably no saturation at transformer, and secondary could be considered as fully sinusoidal and MM readings might be considered correct ? \$\endgroup\$
    – buggy08
    Apr 4 at 6:22

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