Powering an SF-2

[jazzyvee]

I use an SF-2 in my rack and because the psu cable is flimsy compared to a mains supply cable and has been broken once, i am currently having thoughts about options to do away with the wall wart and have a mod done to my DS-5 which will have an output socket on the back to power the sf-2 via a similar socket to its own. That way i could use a short cable between the units and have less risk of damage or cable being pulled out.


There is a lot of space in the Ds-5 to do this. So my question is, would it be ok to take a feed from the DC +/- 18vdc output that goes to the bass in some way to get +18v and connect that to a socket for plugging in the Sf2 or is there a better way to get that output without affecting the performance of the bass or Sf-2.
If its an easy thing to do, i could do it myself with guidance on where to tap off the power or i can take it to an electronics service guy and get them to do it.
what do you think.?
It might be a good for alembic to offer a mod like this as an optional extra for series bass buyers who have, or are thinking of getting an Sf-2

[JimmyJ]

Hey Jazzyvee,

A couple thoughts...  The SF-2 looks like it needs between 10.5 - 17VDC and doesn't draw much current.  But the DS-5 puts out more like +/- 18VDC.  So even one "leg" of the DS-5 might be too much voltage, and I probably wouldn't want to run anything else off of only one side of the PSU because that might effect the bass.

There are DC-DC converter chips which you may be able to use to bring the DS-5's 36VDC down to say 15VDC, but that's getting complicated and there's very little room for additional components or even a tiny power output jack in the DS-5. 

You could do it with a 2nd box, 5-pin in, tap and convert the power, 5-pin thru, dc out for the SF-2....  But that feels unnecessarily complicated and you're probably better off just using the "wall wart" supply and securing that small wire...

Jimmy J

[xlrogue6]

Non-regulated wall warts (like the one you've most likely got for your SF2) put out a few volts more than their stated voltage, 18 volts shouldn't be an issue. The real question is whether the DS5 has sufficient current capacity to drive your SF2 along with your bass.

[jazzyvee]

Good points from you both. Jimmy J , i should have said DS-5R as that has more room inside. What about a separate ac to dc circuit inside that is tapped off the mains side at 240v ac so would not affect the power supply going to  the bass. Im going to investigate this a little further.

[JimmyJ]

Ah yes, the DS-5R does have some space!  Almost enough to fit the "wart" inside, or a smaller version...  The only thing about that is you'd need to be careful not to introduce any hum sources near the audio signal wires, which are unshielded in there.

Maybe it is the simple answer and you could run it off of only the + leg of the PSU without causing any trouble.  That's a question for Mica / Ron.  A tiny power jack on the back of the DS-5R with a short jumper to the SF-2 would be pretty slick!

Jimmy J

[Picure]

Would it be possible to add an extra power outlet plug to the back of the DS5R where you can plug a short cable wall wart for the SF2? This would be like the old Fender Bassman amps with the extra power outlet socket.

[JimmyJ]

That's another possibility.  But I can tell you (from experience) that drilling holes in these cases is hard enough but trying to cut a square or other shaped mounting hole is a real pain.  (Is there even a 240v power outlet that can fit in a single rack space?)  Plus you would then need to figure out a way to secure the wart to the back of the DS-5R so it wouldn't fall out every time you moved the rack...

I think we should ask Mica to pass along these 2 questions to Ron: 
#1. What would happen if we used only +18 and ground (0) from a DS-5R to power an SF-2?  Would that throw the +/- 18 volt supply into an "unbalanced" state and effect the bass?  If so ...
#2. What about tapping off the full swing of 36VDC, passing it through a DC-DC chip to step it down to 15V, and running the SF-2 from that?  But would that "-18 becoming ground" cause a problem between the two boxes?

My brain is full of cobwebs so I'm enjoying this exercise.  Makes me feel young.  HA!

Jimmy J

[xlrogue6]

Using the +18 side of the DS5R would only pull that rail down if it lacks sufficient current capacity to drive the bass and the SF2 simultaneously. If it's got that, should be easy to add something like the Switchcraft 712A to the rear panel of the DS5R.

[jazzyvee]

Cheers Kent, I will see if I can find a source of that socket in the UK in anticipation of that option working,

[keith_h]

The deciding factor is the transformer and bridge rectifier current ratings in the DS5R. I haven't looked inside mine for a long time but seem to recall seeing the diodes were 1N4001, 1N4003 on in that family. These have a maximum current draw rating of 1 amp. I'm not sure what the transformer is but the schematic calls out 100 mA minimum. In the SF2 FAQ Mica says the SF2 draws 50 - 55 mA (depending upon voltage). I don't know what the Series current draw is but given the 100mA minimum I would guess is is somewhere between 50 and 100 mA but might be more with LED's.

So before cutting any wires you should determine the current rating of the installed transformer and rectifier diodes to see if they have sufficient capacity. I would also measure the current draw of the bass with the LEDs on and full volume to get an idea of what it is. Or maybe Mica will chime in and answer the current draw questions.