Power Supply for EAR 834P with optional EZ81 tube rectification

It’s been a good long while since I explained rather wordily and colorfully, which decision process led me to buy a chinese copy oft he EAR 834P as my phono preamp – but since then, not much has changed in the marketplace. There are several ready built versions of this amp on aliexpress, but most oft hem are about as nice to have in your living room as a burning portable toilet. Trust me on this, I have tried them, so you don’t have to. There is a new clone of the Klimo D phono pre, but that’s about it. The EAR 834P, when done well, is still an excellent RIAA amplifier, which can take it up with some of the biggest names in the business. If I had to advise you on a new phono preamp today, I’d point you to that copycat EAR again – except, of course, if you can solder.

I wouldn’t change the type of amplifier, mind you, I’d only build it myself. For several years now there has been a surprisingly well made chinese PCB for an EAR 834P clone available. If you build it with the compentents supplied, you acchieve nothing, however, but to waste many precious hours of your free time. But if you use that opportunity to put in some good components, you’re already a good part of the way towards your goal. Luckily there is an excellent and extraordinarily recommendable thread on the LencoHeaven Forum, which lovingly details the building and most recommended parts. The real Achilles‘ heel of this board is the power supply, though (which luckily comes perforated for easy removal). The regulation circuit utilized is honestly quite ghastly. A new power supply was desperately needed. There is not nothing out there, per se, but there was no obvious and easily available answer to my problem. So be it. I’m a man, and I too have an axe. And so I decided that I would cook up my own circuit board. So why don’t also build in the option for tube rectification? No, it’s definitly not necessary, but it makes you feel warm and fuzzy inside. And ain’t that what Hifi’s all about.

I definitively did not reinvent the wheel here. The amplifier as well as the heater supply got a very usual linear power supply, which solves the problem of filtering by throwing material at it. For your troubles, you get a very good, stable and reliable solution. The most important thing for me was, that the resulting PCB boards would be freely available, so everyone could just download them and have the board manufactured, whereever one might be on this here planet. A part list and an clearly laid out schematic should make it as easy to replicate as possible. I want to save you the troubles I’ve had with this issue.

The circuit is tried and tested in several builds and works flawlessly. The only little caveat, which I have to adress, is the fact that the power supply of the amplifier is not regulated, meaning: The input voltage is not flexible, if you want to keep the same output voltage (which you obviously want). So, if you’re using a different transformer, you have to adjust the filter resistors. Same applies if you want to change the load, for example, if you want for both channels to have their own seperate power supply. Or if you want to use it for a different preamplifer, which is completely possible. How to adjust those values is explained in detail down below.

Here is the schematic:

Here are the files for the PCBs:
This one has the amp and heater supply on one board and this one is just the amplifier supply alone. Here you find a picture of the parts on the PCB.

Here ist he parts list:
For tube rectification: Sec: 275V-0-275V 30mA, 6,3V 1,5A, 6,3V 1,5A (3A, if two rectifier tubes are to be used)
For solid state rectification: Sec: 275V 30mA, 6,3V 1,5 A

For tube rectification: EZ81 tube (My choice: Tesla 6CA4)
For solid state rectification: 4x Schottky Diodes (Ideal Part: QSpeed Diode LXA03T600) + 4x 100nF/250V MKP Capacitor

1x 47uF 630V MKP Capacitor
3x 120uF 500V Elko Capacitor
1x 10H 1666R Choke (Hammond 154E)
2x 11 kOhm 5W MOX or Wirewound Resistors (or whichever filter resistors you need)
1x 47uF 100V MKP Capacitor
1x 18K 3W MOX or Wirewound Resistor
1x 68K 4,5W MOX or Wirewound Resistor
4x Schottky Diodes (z.B. SB560)
4x 100nF/250V MKP Capacitor
2x 220uF 25V Elko Capacitor
1x 10000uF 35V Elko Capacitor
1x LT1084CT#PBF Voltage Regulator
1x 215R 1/2W Precision Metal Film Resistor
1x 845R 1/2W Precision Metal Film Resistor
1x 10uF 25V Tantal Capacitor
1x 4700uF 25V Elko Capacitor
3x 0,1uF 63V MKP Capacitor
1x 220R 3W Potentiometer

Guide to adjusting filter resistor values:
The filter resistors determine the voltage coming out of the power supply. The higher the values, the lower the voltage. I already determined that with a transformer with 275V output voltage, the resistors have got to have 11 kOhm, if you’re using only one power supply for both channels, and 22 kOhm, if you want to use a seperate power supply for each channel. If you have to adjust the resistors, you should use the PSU Designer II. Here is my PSU Designer file, with which you can work. The important fact here is, that you have to use a load of 68k for the entire amplifier or 34k for a single channel. If you change the input voltage, just adjust the values so that the voltage across the load resistor stays the same as it is in my basic plan. Should you want to use this supply with a different amplifier, be advised that the last filter in the PSU Designer file is on the main board and needs to be eliminated. Obviously, the target voltage is propably different and most likely also the load. How to calculate all of this is much to extensive for this article, however.

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