# Question - How do I power this vintage Memory Man?



## Prosonic (Apr 28, 2009)

Hi, 

I have a question about powering a vintage Memory Man and I know there are some people who know a thing or two about pedals around here! Here are some pictures of what I'm working with...








































It seems like the paper sticker on the side says it takes a 24v power supply with the weird Electro Harmonics plug end (like the one for the holy grail?), but I'm not 100% sure and I don't want to accidentally fry this pedal! There's also an opening at the back of the pedal where the input/output jacks are that looks like it might have been for a permanently attached power cord. Not sure about that either. Does anyone know anything about this? I'd love to get it up and running!

Thanks,
Norman


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## bzrkrage (Mar 20, 2011)

Check out these guys, they may know a thing or two.
EHX.com | Vintage EHX | Electro-Harmonix Forums
or this guy.
Electro-Harmonix Memory Man - Solid State Echo / Analog Delay Line | DiscoFreq's Effects Database
(Try this one first):bow:

Hope this help.


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## Milkman (Feb 2, 2006)

bzrkrage said:


> Check out these guys, they may know a thing or two.
> EHX.com | Vintage EHX | Electro-Harmonix Forums
> or this guy.
> Electro-Harmonix Memory Man - Solid State Echo / Analog Delay Line | DiscoFreq's Effects Database
> ...


I'm sure it did.

GC is such a great site for getting help for stuff like this.

Nice pedal by the way. I had one from around 1978 or 1979. Mine was a Deluxe Memory Man. I think I used batteries (lots of them if I'm remembering correctly).

The chorus is actually quite nice.

Have fun.


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## mhammer (Nov 30, 2007)

I just returned an EHX Polychorus I repaired earlier this evening, and it has the identical sticker. Internally, it converts what the adaptor provides down to 15VDC, and the DMM is no different. The regulator needs at least 2v more at its input than it puts out in order to perform properly. As long as you have a17VAC input you'll be fine


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## Prosonic (Apr 28, 2009)

mhammer said:


> I just returned an EHX Polychorus I repaired earlier this evening, and it has the identical sticker. Internally, it converts what the adaptor provides down to 15VDC, and the DMM is no different. The regulator needs at least 2v more at its input than it puts out in order to perform properly. As long as you have a17VAC input you'll be fine


Hi mhammer, 

Thanks for the info! I'm pretty clueless as to the details of powering pedals. What kind of adapter would I need?


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## mhammer (Nov 30, 2007)

The sticker specifies 24VAC. Unlike a DC output adaptor, where one contact is positive and the other negative, the two contacts coming off a wallwart that puts out AC are entirely interchangeable. The good part is that you don't have to pay attention to the polarity of the plug. All you need to have is the right kind of plug, which I gather is a mini-phone type, not unlike earphones.

The Polychorus I repaired *was* being used with a mammoth 24V transformer that supplied enough current to power a 20W amplifier. I did my buddy a favour and replaced it with a small wallwart that was spec'd at 18VAC/350ma. Works like a charm for his Polychorus, and would do the same for your MM.

A few tidbits about power supplies and circuits and design rationales...

Circuits will draw only as much current as they will need, so whether one uses a 100ma unit, a 350ma unit, or a 2A unit, the Memory Man (and Polychorus) is only going to draw something like 25-40ma out of that, tops. That modest current draw makes it amenable to running off a pair of 9v batteries in series (to produce 18V) and some early Electric Mistress units did just that. However, the current draw is big enough that even a decent alkaline is not going to last a long time, and the cost of new batteries adds up.

So, EHX opted for a wall-derived power supply. In some units, there was a transformer, and a power cord to the wall. However, transformers can induce hum in audio circuits or wires near them, and it's not like there is wads of real estate in those boxes to physically isolate the transformer from the circuitry and audio wires (to jacks, switches, and pots). So, what a number of manufacturers did was to move the power source outside the effect chassis, and connect it with a jack/plug.

There are two basic ways to provide external power to a chassis. Both ways will ultimately culminate in the 120VAC from the wall being converted into something that mimics (as much as possible) a DC battery of one or more specific voltages for use by the effect circuit. Wall AC has to be converted, massaged, coaxed, into the DC that the circuit needs. The transformer steps the 120VAC down to something in the range required by the pedal. 

The extra critical element is what is referred to as *regulation*; the smoothing out of AC and production of one or more DC voltages that have as little wiggle (commonly known as "ripple", as in teeny waves left over from bigger waves) as possible and needed. 

That latter part is important. Circuits vary in how tolerant they are of ripple, so supplies vary in terms of how much they pay attention to it. Not all wallwarts that say "9VDC/300ma" on the outside provide the same degree of smoothing/regulation, and all too often players will say "I'm getting an annoying hum from such and such a pedal. What's wrong with it?". The problem is _not_ the pedal. It's the fact they are using a wallwart that meets the absolute bare minimum criteria for "regulation", says nothing on the black plastic to differentiate it from better adaptors, and is sealed so you can't look inside it to determine if it contains the sort of parts to _provide_ that regulation. This is why many pedal manufacturers insist that you use THEIR adaptors. It's not that others will not do what theirs do. It's that the majority of customers will be in no position to tell whether any given adaptor they have purchased will provide suitably hum-free performance, _unless_ the adaptor manufacturer has assured it.

The circuitry required to do the regulation, unlike the transformer, does not induce hum in things nearby. It can also be fairly compact, and the parts pretty darn cheap. So, it is the manufacturer's choice to either have the regulation circuitry _built into _the wallwart, such that the wallwart puts out regulated *DC*, or provide the regulation and smoothing inside the effect itself, and simply feed *AC* to that circuitry _from outside_ the chassis. If it should happen that the effect circuit itself needs several different supply voltages for different aspects of the circuit (e.g., one voltage for the delay chip/s, another for any other audio chips, etc.), then there is greater likelihood the manufacturer will elect to simply feed the effect with an AC voltage, and let the regulation circuitry inside the box do the heavy lifting, if only because a wallwart supplying more than one DC voltage (e.g., ground, plus 5VDC plus 12VDC) would have to have at least 3 wires.

It IS possible to find replacements for any proprietary wallwarts provided by, or insisted upon, by a manufacturer. But, all other things being equal, finding a suitable replacement for an AC supply (which doesn't have to provide ANY regulation) is easier than finding a DC supply that provides the needed regulation. So, wisely, EHX elected to use an external AC supply (keep the hum away from the effect), and do the regulation_ inside _the pedal, where it can live up to the criteria you need.

As noted in my earlier post, the regulation circuitry takes a somewhat higher input voltage (i.e., bigger than it really needs, but much less than the full 120V) and whittles that down to a precise, stable supply voltage. And, like a sculptor, that circuitry likes to start out with a bit more - and a certain minimum amount more - than it needs. 24VAC will assure that the minimum is met, but 18, 20, 22, and 26VAC would also meet the criteria. Is 24V "best"? Looking at the regulation schematic, it doesn't seem like it. So, if you happened to find an 18VAC/60ma wallwart in a pawnshop, the chances are damn good it would do the trick. If you found 24V/100ma that would give you confidence.

Just be sure to plug the wallwart into the pedal before you plug the wallwart into the wall! The sparks people see with the mini phone-plugs when they don't follow that sequence can be a little disarming!


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## greco (Jul 15, 2007)

Mark...Each time you write this power supply information, it becomes closer to a dissertation. 
And....each time, I read it with the same enthusiasm and enjoyment.

Cheers

Dave


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## mhammer (Nov 30, 2007)

Thank you sir. Much appreciated.


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