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Can someone explaing phrasing on Switching Supplies for me?
MUFF WIGGLER Forum Index -> General Gear  
Author Can someone explaing phrasing on Switching Supplies for me?
EPTC
Hey everyone - Looked for this in search and couldn't find a definite thread on LABELING on the back of Switching Supplies. Hopefully someone can answer this question:

I have a 1970s mixer that runs off of 8 C-sized 1.5v batteries, for a total of 12v to operate (or 8 x 1.5v) It also has an optional power cable input.

In research, I've found the current era SONY MPA-AC1 switching supply works with this mixer to generate the 12v needed. On the brick itself, here's the labeling:

SONY supply
Input: 100v-240v ~ 0.75A-0.4A
50-60 Hz
Output: 12V === 3A
(then the normal diagram polarity icons for the adapter, which i do totally understand)

So I was going to buy an after market equivalent to the Sony MPA-AC1 but also notice at home that I have a DVE Switching Supply. It's almost identical to specs to the Sony, with exception of what I've marked in bold:

DVE Supply
Input: 100-240v 1.2A
50/60 Hz
Output: 12v === 3A
(polarity icons match identically)

So the question: Is the DVE safe to use? If they both output an identical 12v what does Input mean? I basically want to provide exactly the right power to this device, and see I have this spare switching supply that matches except for Input.

I found this link that suggests both are identical for use, just the Input rating on the Sony is for more global market use, possibly? https://www.apartmenttherapy.com/deciphering-the-power-label-on-your-a c-adapters-168405

Thanks as always. Hopefully this is a useful conversation.
ranix
The DVE seems to use more input power (power in watts = volts * amps, amps is current) to produce the same output power. https://en.wikipedia.org/wiki/Watt

This probably means it is less efficient than the Sony supply and produces more waste heat.

The Sony supply specifies both the minimum and maximum current it looks like. Since it can work at lower voltages (100v) or higher voltages (240v) the amount of current it draws when at a lower voltage is higher, 0.75A. When the input voltage is higher it pulls less current, 0.4A, because the input voltage is higher. The DVE supply is probably just specifying the max current it will draw at max load.

The DVE is probably safe to use but it will run hotter than the Sony supply, which is probably a better power supply. By this I mean the DVE power supply brick itself will be physically warmer to the touch than the Sony power supply.

Different types of power supplies have different behavior when they fail or when a device pulls less current than the power supply expects. It's possible for a power supply to provide higher voltage than advertised when its load is low. It's also possible for it to produce *much* higher voltage when it fails, depending on how it's designed. If your DVE power supply is old and has been in a box for 20 years you might want to toss it and get a new one with similar specs. If it's reasonably new and in good condition I wouldn't worry about it.

Power supplies can also be dirtier or cleaner than others. They produce DC but with a little bit of ripple in it. It's "dirtier" if the peak-to-peak voltage in the ripple is higher, and if there's more harmonic content, and "cleaner" if there's less. I have a couple computers that run poorly with some 12V power supplies and well with others. This is rarely a problem for me when using equipment other than computers.
EPTC
ranix: Thank you!!

So it looks like you're suggesting the DVE will run hotter (to the touch) and be less efficient in draw but is spec'd similarly to the 12v output needed?

I might want to try the supply on the mixer and if it doesn't add any hum to the audio (or other erratic effect) then commit to getting a proper Sony adapter. As the mixer is designed to run on batteries, I expect response to erratic power is built in, partly, as a set of 8 C batteries obviously lose potency unevenly over time.

Your generous and informed response is really appreciated!
ranix
Yeah there's usually a voltage regulator inside the device that can handle a little droop. You're right, that is how it handles voltage droop as your batteries deplete. I think that plan sounds fine. I might not even bother getting another supply. I do use cheap power bricks myself sometimes but I also keep all my equipment on power strips I can turn off when not in use. I don't like leaving AC adapters plugged in and powered on when I'm not around.

I don't think it will run much hotter, it might not even be noticeable. Maybe 1 or 2 degrees? It gets spread out in the case. I'm not sure that the cheap supply will run hotter, it's just that's my best educated guess as to what will happen based on the information available. I'd bet it would be like 1 or 2 degrees celsius hotter if you measured it with an ir thermometer or infrared camera.

There's some other wigglers around who care more about power supplies than I do and might share their wisdom too.
JimY
If the AC input voltage includes the supply used in your country, then you only need to worry about the DC output voltage, current and polarity.

For use with audio equipment, you should avoid supplies that say "For office equipment only" or "ITE only" or similar variations on the label. It means the DC output contains noise that might be troublesome.

Old gear can be expected to have power smoothing capacitors that are past their best, especially if they've been unused for long periods. These are the "electrolytic" capacitors. Anyway, this means the unit won't remove power supply ripple noise as well as it once did. Techs who restore old gear, usually replace all of those capacitors with modern equivalents as a matter of course.
EPTC
Nice to hear all of that, JimY! - Especially the part about labeling, thank you! - The DVE didn't work at all, but the unit is clean and sailing with batteries presently. I have an order on a SONY supply, got one for under $10 so figure I'll check it out, too.

I'm a little amazed at how clean and clear this Sony mixer sounds. Obviously cared for, or maybe never even used. It's one of their 6 channel stereo mixers intended for broadcasting radio/TV field work in the 70s and can power any mix of six mics, six turntables (!), or 6 line inputs. Seller indicated it wasn't tested so the cost was barely above shipping for thing. If it wasn't functional, I was expecting it to be a visual piece if anything. I was over the moon when I put in batteries and pressed power on, as it sounds as clear and new as if I just received it new, no crackle on any slider, switch, or pot! It even has a calibration tone generator that's sounds amazingly nice. I do wonder if the batteries add to its clear sound, actually.

JimY wrote:
If the AC input voltage includes the supply used in your country, then you only need to worry about the DC output voltage, current and polarity.


Huh, so simple! Not sure if there's any jumper inside to set the DC plug to work or not (I need to get a service manual) but The DVI didn't power the unit on at all, which I'm thankful for if it wasn't the right fit. I know the Sony adapter should work, anecdotally. Fine to keep using with batteries, too, just that might become expensive as it's immediately a great mixer for listening to and working with. On to the Sony!
JimY
The thing about batteries is that they are also capacitors so don't need as much help getting noise out of the system and of course, don't have any AC supply ripple either, so just because it works well on battery, don't mean it's good for an AC adapter.
calaveras
Nobody mentioned amperage?
The difference in efficiency shouldn't be much of a concern, it's a fairly low amount of power.
What is more important is the amount of current draw.
Quote:

Input: 100v-240v ~ 0.75A-0.4A
50-60 Hz
Output: 12V === 3A

DVE Supply
Input: 100-240v 1.2A
50/60 Hz
Output: 12v === 3A

You will notice they both output the same amperage range,
with the DVE requiring 1.2 amps of mains current to provide the same output power that the Sony does with .75A.
Not a huge difference.
However, I'd be paying attention to the amperage demand of the device you are powering.
You said it uses 8 C cells at 1.5V each to provide 12V. If all that was important was 12 volts, they could get by on 8 AAA batteries. But they didn't because presumably the mixer wants more current than AAA cells can provide (or provide for a reasonable amount of time)

I'd check the labeling on the mixer to see if anywhere it says 12v at 1 amp or similar. Might need to find a manual?

Amps are not like volts though. Most are aware that you don't want to overvolt. Dont put a 12v power supply on something that demands 9v and expect it to work.
However with amperage the opposite is true. You are almost always going to be fine exceeding the rated amperage. All that does is provide for excess current capacity. If your mixer draws 1 amp at 12v. Using a 2 amp power supply will mean that it only has to run at half capacity to provide power. Well within it's operating range, and likely to run cool around the clock.
Think of it like having a bigger gas tank, or more torque.

I've only heard of one case where the opposite is true. A pedal made by a well known company had a flaw that it would get into thermal runaway if you gave it a power supply rated for more than a fifth of an ampere.
But that is generally very rare.
JimY
Well, I did mention current although assumed we all know that it's measured in amps.
And that lets me bang on about capacitors again. As they age, they can either get more resistive and not smooth the ripples or go leaky and waste current, shorting it to earth, or explode and make a fine mess that is just as nasty as the gunk from a leaking battery.
The following is a pretty good explanation, which isn't trying to sell you some audiophile stuff.
http://gigapod.free.fr/re-cap.html
EPTC
calaveras wrote:
You said it uses 8 C cells at 1.5V each to provide 12V. If all that was important was 12 volts, they could get by on 8 AAA batteries.


Really interesting observation, thank you for that!

Currently it has eight alkaline C's inside as I had a pack on the shelf, but I tested it with a parallel battery holder for 8 AAA lithiums and it worked great. These are wondeful for making single lithium AAA into an equivalent alkaline C: https://www.amazon.com/gp/product/B00OUM1KKI/ref=ox_sc_act_title_5?smi d=A2Y9R0VEAYJBWE&psc=1 - Very useful for flashlights and other C-sized gear, you just have to be mindful of the adapter fitting the housing as its diameter is a little wider than a normal C. Do you mean capacity on a C vs a AAA? You're right that they're both 1.5v, I'm not sure on what necessitates a C vs AAA in design (maybe it was longevity? They claim it will give 12 hours of use on a full set, for daily broadcast use that's maybe the design for C's)

(there's also a converter for D cells with AA's - great way to make use of lithium where there isn't a D or C lithium yet available)

If the adapter in the mail doesn't work then I'm going to continue with batteries, thinking the capacitor JimY describes might be dead; also might be a jumper so looking forward to finding a service manual. It's the MX-650 for anyone who might have one. Thanks, all!
EPTC
JimY wrote:
The following is a pretty good explanation, which isn't trying to sell you some audiophile stuff.
http://gigapod.free.fr/re-cap.html


Thanks for this, Jim! - Interesting point about 'Service Life' being 20-25 years. They mention that's different than 'Shelf Life' so if this is possibly an unused or lightly used device I wonder how needed a recapping would be presently, as its used Service Life might still be young? I'm really charmed by the distinctive sound of the mixer and would hate to lose that through servicing it to remove the present components.
JimY
I agree to an "if it ain't broke, don't fix it" policy. The point I want to make is that those capacitors do a lot to reduce noise & ripple from an AC power supply so if you have trouble finding a quiet one, you know the trouble could actually be in the mixer.
With something that hasn't been switched on much over the years, it's worth persevering for a while (providing it isn't making horrible noises and smoke!). Those capacitors can revive if left "soaking" with the power on for several hours. The chemical electrolyte in them "forms" under the applied voltage, repeating a process that's done when they are first made in the factory. "it sounded better after warming up" is not a myth!
Blairio
JimY wrote:
I agree to an "if it ain't broke, don't fix it" policy. The point I want to make is that those capacitors do a lot to reduce noise & ripple from an AC power supply so if you have trouble finding a quiet one, you know the trouble could actually be in the mixer.


I picked up a Korg MS10 synth a few years back and gave it to a trusted local tech for a lookover and a service. The first thing he did was replace the mains smoothing capacitors. He explained that not only do they let line noise through as they fail, they also cease protecting downstream circuits from dangerous voltage fluctuations. It wasn't an expensive service, and the (now) 38 year old synth sounds as good as new.
EPTC
Just a postscript for anyone following on the Sony MX-650

Sony power supply arrived today - and I don't know who did what on the previous listing I'd seen using the SONY MPA-AC1 but it has a center pin in the adapter - which definitely doesn't work with the mixer (it has its own center pin)

So it's to batteries for me - I don't want to play with this stuff much - Might try to source one of the original Sony adapters from the 1970s - It seems that whichever MX-650 that was fitted to work with the MPA-AC1 must have been customized to have a center pin AC.

In my spare time waiting for the adapter to arrive I did find a small power brick Everglow supply here (http://www.emtcompany.com/everglow-abu120030-ac-power-supply-charger- adapter/101326370.html) that did power on the mixer! (others had not) - but man the noise was terrible! I heard a lot more than hum, it was static and noise on top of the signal. Removed it immediately.

With batteries it is whisper quiet!

Still loving the mixer. Happy to commit to it being battery powered.
EPTC
So the Everglow adapter actually being able to work SOMEWHAT got me curious about the original supply for this. Closest manual reference I can find online is for the MX-14 which has the same specs. It lists this for battery or AC power:



That's a blurry image but the reference is for the Sony AC-12 to work for these. Any guess on why the Everglow worked but the DVI did not? They're both random adapters found around the house. The Everglow is a small power wart and was impossibly noisy. A quick google finds this to be what the original Sony AC-12 looks like.



Are these old supplies worth using? I'm inclined to not try, of course. Just a fun bit of trivia in figuring this out.

The MX-14 seems to be identical the MX-650, minus a few L/R pan pots and the calibration tone generator. This manual suggests about 45 hours from a fresh set of 8 C cells, so that's not that expensive. I'll be curious to see how long AAA lithiums run the thing once I swap them out with the C's currently inside.
JimY
Those DC "barrel" power plugs are deceptive. There are a few different sizes of outside diameter, inner pin and length that appear very similar, but don't quite match. This can be worse in old equipment where the spring contacts in the connector are worn out or very badly tarnished. Of course, you also have to get the polarity right. Centre pin positive is probably the most common but you need to be certain. Some equipment has some kind of protection built in against a reverse polarity supply, but not all.

I've had good results with generic switching supply of the kind used for laptops, and there are some very inexpensive ones, but you might have to be prepared to replace the connector, either in the equipment or the supply to ensure a proper connection.
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