B1 Power Supply Options

[Beftus]

From the manual: "A regulated supply is better, but the circuit is pretty good at ignoring noise on the supply and minor fluctuations."

The large caps are for filtering PSU noise and to be able to cope with an unregulated PSU. At least, that's my interpretation of what Nelson wrote. I don't think Nelson envisioned what you're proposing. That's why Nelson wrote that "the value of C1 and C2 is not critical, and you can use as low as 1000µF". With C1=1000µF and R1=1ohm you get a first order low-pass filter @ 159Hz. Not a filter value that's very good at filtering mains hum.

You are of course free to hook up the outputs of the MUR860 diode bridge to the B1. Please report back your experiences. We, myself included, might even learn something useful!

Note that Nelson sold his commercial B1 with a SMPS to provide the B1 with some juice.

Your gainclone might have a higher PSRR...

[R-K Rønningstad]

Originally Posted by LucasAdamson

I am looking to power up my B1 now as it's all soldered up.

The board not a Pass Labs, but a clone. It has a shared section consisting of 2x 15,000uF caps, a diode, led and resistors before the gain stages, as in the Pass schematic. Isn't this stuff the tail end of a power supply?

Could I simply use a small toroidal transformer and a MUR860 diode rectifier I have spare to supply 18v DC to the unit? Would that be sensible?

There is/was a B1 clone at ebay. I wonder, is that NP approved, or..?

[LucasAdamson]

Originally Posted by R-K Rønningstad

There is/was a B1 clone at ebay. I wonder, is that NP approved, or..?

Yeah, I feel a bit bad about that. I asked for a recommendation for a buffer design/kit here on diyAudio, and was advised to buy a "B1 board off ebay for peanuts". I looked it up and it looked real quality for $10, so I bought it right away. I wasn't even aware at the time that I could have bought from Nelson Pass for almost the exact same cost. Had I known I certainly would have bought from Passlabs.

Lucas

[R-K Rønningstad]

Buy another PCB from Nelson as a compensation, and use that B1 in another room or something. That will make you feel better!

[sharpi31]

Would it be worth trying a high capacitance unregulated supply? I was thinking about 45000uF after the rectifier, then 1 ohm followed by 30000uF for C1?

As you might have guessed, I have plenty spare 15000uF caps to play with :-)

What would be the strengths and weaknesses compared to a standard LM317 regulated supply?

[AndrewT]

Originally Posted by sharpi31

Would it be worth trying a high capacitance unregulated supply? I was thinking about 45000uF after the rectifier, then 1 ohm followed by 30000uF for C1?

As you might have guessed, I have plenty spare 15000uF caps to play with :-)

What would be the strengths and weaknesses compared to a standard LM317 regulated supply?

Pass suggests an unregulated supply for the B1. He specifies 30mF for the final/only stage of smoothing.

I would be tempted to try 10uF X1 or X2 across the transformer primary, then 30mF after the rectifier, and finally two 1r0 resistors, each feeding 30mF to individual channels of B1. Gosh, 90mF for a buffer!!

[R-K Rønningstad]

The only thing is that the voltage at the B1 rail will vary with varying mains. If you use e.g. a 317 type regulator you will fix the voltage at 18 Volts DC or whatever.

[sharpi31]

Thanks both for the feedback. I'm building a new B1 at the moment and will follow Andrew's advice.

I have a transformer with 15Vac secondary, so I should get 21.21V with normal mains voltage. This sits nicely in then middle of the 18-24V range, so fluctuations in mains voltage shouldn't be too much of an issue.

I remember reading an argument against using a regulated supply with zero feedback gain stage... can't remember the exact reasons.

[johnm]

Hi folks.

Hoping someone here can help with selecting an appropriate transformer for the B1. My head's in a spin with the varieties of PSU options available i.e. transformers with 0-18V secondaries, or 18-0-18V CT versions. Full wave/half wave/bridge rectifiers etc.

Basically I have a Peter Daniel PSU board which I'm re-using from a past project. I also have an LM317T which I'll use with a 240R/5K adjustable resistor to get the required output, which I've decided will be 24V (the max. voltage Mr Pass mentions in the build PDF).

Is it best to use a CT 18-0-18v transformer with just two MUR860 (I have four of these) diodes, or a 0-18V transformer and four MUR860s? A bit of help to aid this layman would be most greatfully accepted

Thank you,

- John

[KatieandDad]

I'm using 9-0-9 30Va toroid + WOO1 bridge + 4700uF + 2R2 + 4700uF

Someone suggested running B1 at 22V so I'v got a straightforward LM317 reducing the 25V from the CRC down to 22V. But to be perfectly honest it runs silently and perfectly at 25V from my basic PSU.

Nelson's original B1 only used a Wall-Brick and the on-board 15000uF 1R0 15000uF gets rid of any noise.

I wouldn't recommend an SMPS wall brick.