Ross Flanger Power question

[alteredsounds]

Got a nice red old Ross Flanger that I'd like to have on my pedalboard but it has a mains cable terminating in a US 3-prong plug.  Am I right in guessing that the transformer inside drops the ac to either 18 or 9 vold dc?  In which case I could wire in a boss style socket and just bypass the main cable and transformer?

Cheers,
Nick

[Mark Hammer]

The answer might be yes to those questions, but it might be no also.  In general, Ross stuff tends to be very similar to MXR.  I don't know why, it just is.  If the flanger has an SAD-1024 in it, then it will be able to tolerate up to 15v as a supply voltage.  Any onboard transformer would have onboard regulation to assure that supply voltage.  If you plug a DC wallwart into the flanger to bypass the onboard transformer, then you would need to be able to assure the regulation circuit on board is appropriate  to produce the desired outcome.  If the planned-on wallwart is AC, then you need to use some on-board regulation and be able to assure that the supply voltage is appropriate.

So, in theory you can use a variety of AC or DC wallwarts to bypass the onboard transformer, but there is more to it than just plugging one in.

[alteredsounds]

Thanks for the info Mark.  I know some companies made the 'Deluxe' models mains powered as it was an attraction to having assosiated battery problems and I'm guessing this is prob the case with the Ross.  I was hoping to take the power of my powerbrick which has one 18v and the multiple 9v's.  Any more info would be gladly accepted.

Cheers,
Nick,

[Mark Hammer]

Tell us about the power supply.  For instance, are there any 3-pin regulators on it, like an LM7812 or 7815?

[alteredsounds]

Finally got round to looking at it!  The power cord goes to a small transformer on the board and then off to resistors and caps.  It does have a SAD-1024 onboard.  15v is a kinda awkward figure I guess because I can get either18v or 9v out of my powerbrick.

Any ideas welcomed, I really want it on my board but not running off the mains cable especially because it is 110v (US) and I'm in the UK, I have a stepdown transformer but it isnt practicale to take to gigs for one pedal.  If I could get a boss-style socket on it and do it from a regular power-suppply that would rock!

Cheers,
Nick,

[Mark Hammer]

The 3-pin regulators that will help you provide a stable 15vdc to the board need to see at least 2v more on their input than they are delivering on the output.  Consequently, you should be able to make a little adaptor box with a 15v regulator (LM78x15) plus indicator led, smoothing cap, and input/output jacks that you can feed +18vdc (assuming it is a stable 18v) and downregulate that to 15v for purposes of feeding the Ross. remember that the regulator always needs to see a rectified DC (or close to it) input anyways.  It has absolutely no "idea" if the 18v seen at its input is the product of a transformer, cap and a couple of diodes, or the product of a complicated switching regulator, or even batteries for that matter.  All that really matters to that regulator is that it's more than 17vdc....and that it's going to the right pin on the regulator!

The advantage of having such an adaptor box is that you can use it with a variety of power bricks putting out more than 17v, and still be able to use the same power brick for other purposes that require 9 or 18v.

[alteredsounds]

Thanks loads Mark!  I kinda see where you're coming from on parts but also have to admit to being largely pretty lost.  Can I break it down into my 'idiot' way of thinking being:

Remove the Transformer
Connect a small board that will drop the 18v to 15v
Connect this to where the transformer was going

Am I miles off, would LM78X15 do the voltage reduction and what kinda cap would I need to do the smoothing?

Much Appreciated,
Cheers,
Nick,

[Mark Hammer]

The idea is to simply bypass the onboard transformer, and feed the 15vdc from the regulator to wherever the 15v would be distributed from on the flanger board.  There will be some point where the existing on-board circuit normally supplies 15v to everything.  Chances are pretty good it will be something near the biggest cap on the board.  The same way the regulator doesn't "know" the DC at its input is coming from another regulated supply, the chips on the board don't "know" the 15vdc is coming from something situated outside the chassis.

So...

To make a standard 3-pin 15v regulator "work", first you look at the datasheet.  Here's one:  http://www.fairchildsemi.com/ds/LM%2FLM7818.pdf

On page 18 and 21 you can see the "no frills" version of such a chip in action.  DC omes in and DC comes out, with small value caps on both input and output.  Seems to good to be true, but its true.  The regulator CAN be mounted inside the Ross unit in some fashion, but you may end up with more flexible and re-usable things if the regulation is done off-board.  Your choice, ultimately.  No harm in retaining the smoothing cap (which I assume will be at least 470uf) on the Ross board.

[alteredsounds]

Thanks once again Mark!  There is a BLOODY massive 470uf cap just up from the transformer, so my power source would connect up to the + and - of this cap as an entry to the board?

[Mark Hammer]

In theory, yes.  But what you need to do to verify this is to see if the + side of the cap is tied to all the V+ points of the chips, ether directly or through small value (e.g., <1k) resistors.

[alteredsounds]

I owe you a pint mate

[alteredsounds]

Prob a dumb question but........ the only place I can find the LM78x15 (rhselectronics) just has LM78 listed, is this the same thing?

Cheers,
Nick,

[Mark Hammer]

There are two categories (usually) of 3-pin regulators.  One is the same size/shape as a "normal" FET or bipolar transistor and can safely regulate up to 100ma.  The other is the same size/shape as a power transistor (complete with heatsink) and can safely handle up to 1A.  The both have numbers that start with LM78, but end in different numbers depending on the voltage and current rating.  So, an LM78x05 will regulate at 5vdc but depending on which letter occupies the spot of the 'x', it might be a 100ma rating or 1a rating.  A LM79x05 will provide the same regulated output voltage as the 79 version, except negative (i.e., one is for +5v, the other for -5v).  Again, look through the datasheet for the series.  Some of what's there will be mumbo jumbo to novices, certainly, but look at it long and hard enough and you'll start to see the pattern.

You certainly do NOT want an LM78.  As you can see here - http://www.national.com/pf/LM/LM78.html - it is a completely different beast.

Never be afraid to type the part number and 'pdf' (e.g., 'LM7815 pdf') into Google.  You will usually be able to find the datasheet (they're all in pdf form).

[alteredsounds]

The LM7815's finally turned-up!  Am I right in thinking that this is the option I require:

FIGURE 8. Fixed Output Regulator on page 18 http://www.fairchildsemi.com/ds/LM%2FLM7818.pdf

With the 0.33uf on the Input and 0.1 on the output is that 15v? Also, the diagram seems to join the in and out to earth or a i am reading it wrong (likely!).

Sorry to be asking again, any help much appreciated.

Cheers,
Nick,

[Mark Hammer]

The input and output pins are AC coupled to ground/earth through the capacitors you mentioned.  Feed that input pin at least 17vdc and you will see sweet stable 15vdc on the output pin.

[nbabmf]

I'm bumping this thread because it is relevant to what is sitting on my bench right now!

I have a red Ross Flanger whose transformer has kicked the bucket.  I suppose I could just feed, say, 18VDC to the regulator by way of a DC power supply, or even charge pump it up with a MAX1044, but I'd like to try to source a replacement transformer first.  I have no idea what I'm looking for though!  The transformer is stamped with "245 1005826".