Pro-ject Tube Box II power supply

[Philip A]

Hello all.

I am looking to build a new power supply for my Pro-ject Tube Box II. I am hoping that getting rid of the "wall-wort" will add a bit more musicality to my system. The problem is that it requires a 16 volt A/C power supply @ 1000ma and I am having trouble sourcing anything suitable. Thank you to everyone in advance for your help.

[!]

More details about the amp might help.

Presuming the wall wart is 16VAC @ 1000mA, what did you have in mind? Seems like the wall wart is just a transformer, maybe a film capacitor or two with the rest of the power supply circuit in the amp case. There's no expectation that substituting a different transformer will make a difference, it's the power supply circuit after the wall wart that might have room for improvement, unless they really skimped on the transformer and something higher than 1000mA would be of benefit.

If all else fails you can pop open the wall wart and reuse the transformer and add some filtering in a new case.

Also your profile doesn't seem to have any location info, so people won't know where to suggest purchasing anything.

[Minion]

! is absolutly correct ...... a different transformer will make little to no differance in the sound ....... Adding more/better DC filtering inside the unit it"s self would be the only option .....

[!]

Just saw the PDF short-spec sheet for the Tube Box II, consumes only 410mA @ 16VAC, higher current transformer isn't needed.

[Philip A]

Thank you ! and Minion. Sorry, I should have added a bit more information. It is a phono pre-amp that I am looking to mod. Pro-ject Audio seems to run all their products on 16VAC. I also have one of their turn-tables and their speed box controler. I do find that there is some noticeable hum with their product which is why I started the post. I will look into better filtering. I like the idea of using the transformer from the original wall-wart. Any suggestions on circuit configurations would be appreciated. I am from Whitby Ontario Canada and will update my profile soon. Thank you again.

Philip.

[!]

Is there hum only when the source is supplying an audio signal, or is there hum also with source plugged in but no signal? Is there hum when there is no source plugged in?

Look at what the power supply subcircuit is doing inside the preamp.

See whether it is just rectifying and filtering to make a single voltage rail, or if it is splitting it into a positive and negative voltage rail via voltage doubler circuit (plus ground between them).

If it is only producing a single rail, you could temporarily test with a known clean alternate power source that is DC to see if the hum goes away. Perhaps it is easier to vaguely describe this than to convey what I mean without seeing the circuit or schematic for it.

The question in my mind is whether the hum comes from poor design in general, a degradation or defect from some part like dried out or defective capacitors, leaky diode or transistor, OR whether the design is working as good as it can and needs improved to remove the rest of the noise, OR if this noise is not caused by inadequate or malfunctional power supply and filtering at all.

Another thing you can do is measure the power rail(s) after the last filter stage to see if you get a significant level of fluctuating DC or AC voltage measurement.

Reusing the original transformer would basically just mean putting a film capacitor or two after it (around 0.047uF and 0.47uF, 25V+ possibly?) and a standard AC line filter module in front of it. Random example of AC line filter (I don't know who makes the best or most cost effective vs what's available in Canada):
Digi-Key - CCM1772-ND (Manufacturer - 15SRB1-Z)

Otherwise it's a matter of knowing what circuit is used in the preamp for power and what lengths you are willing to go to, and additionally how much voltage margin there is.

If there is enough margin you could cut trace(s) or remove some component to add jumper wires or pins for an add-on regulation subcircuit. If there is not enough voltage margin, or enough space since according to the spec'd you might have a couple watts or more heat needing addt'l space for heatsink(s) too, then you might be able to replace the entire power supply subcircuit with an external power supply but all details of the circuit must be known to effectively and safely (no pre-amp risk) implement it. With external power supply you open up options for a difference transformer too, perhaps it is easier to find one that is 18VAC instead of 16VAC for example then after regulation your voltage can still be down at the original desired level.

Schematics or high-resolution top-down and bottom-up shots of the PCB with the power circuit might help.

[Philip A]

Thank you again for the all you input "!". I will test a few of your suggestions this weekend. I think it may be a case of the wrong cartridge/arm combo. I have switched from an Ortofon 2M Red to a Clearaudio Aurum Beta MK2 on my Pro-ject RPM 1.3 turntable. When played through my modded Jolida JD-9A phono stage the Beta MK2 seemed to be under damped. Although it was smother sounding, the lack of a subsonic filter in the Jolida made me switch back to the Tube Box II. I have upgraded the tubes in the Tube Box II to Tung-sol 12AX7 Gold pins, and am looking to either mod the Tube Box II or possibly add a subsonic filter to the Jolida. The Tube Box II would require a new case if modded and as you have suggested an external PSU.

[advpcb]

Hi

[Philip A]

Hello "!". Thank you for the Digi-Key link. I will attempt to construct a PSU using the Digi-key AC line filter and a 16VAC power supply that I have left over from my old BBE processor. Thanks again for your help!

[gosserd]

Were you able to solve your Tube Box II hum issue? I have had the same problem from day one. I like the unit, but I'm about to move on from it.