can someone help me with this Power-supply question?

Hi Forum. I'm new here. I just occasionally need some help on electronic topics...

I'm a Pro-musician, but always had a weak side for electronics too.
Lately I got my hands dirty on "renovating" some old mixing-desks, and learned a lot of new things.
(also - some bad experiences).

Now, I have this old H|H-desk standing here, but the original ("dual-coil") transformer is dead.
Normally it is has a rotary-switch on the back to select the voltage. (110 / 220 V).
Since I don't need that, I'm thinking to simply remove it.
Also - I happen to have a rather nice Single-coil transformer that I that I would like to put in instead.

Now, since I really don't know the rules of POWER-SUPPLIES, and how they are "installed" correctly, I just wanted someone that knows things
to give me blessings for my project.


It's really nothing wild, I think.
- but then again, I could be wildly mistaken!

I'll try to explain the givens:


Desk has a 2-coil transf. (??) 1A
- it has 4 pins on one coil, and 3 pins on the other.
(See schematics).

The one I've bought has 4 pins;
0 / 220V / 0 / 24V
// Primary: 220V - 0,2 A
Second. 24V - 1,3 A

CAN I replace the old (malfunctioning)one with this one?

Please try to explain for me the DOs and DON'Ts if there are some, since I want to learn...

Thanks.

The original transformer's two primary windings are 110V each. For use on 110V mains they are connected in parallel. On 240V, in series.
Its secondary winding is a centre-tapped, 18 - 0 -18V, which conveniently allows the two output voltages, pos and neg.

The transformer you want to use does not have a centre-tapped secondary so you can't obtain both pos and neg 15V outputs. You would need an additional transformer.

The output from the secondary is regulated down to a +15, 0, -15 DC bipolar supply. This is easy with the center tap.

To make your single 24V secondary work will require some trickery.

A) Since its peaks reach +17V and -17V, there is a slim chance it can be made to output +14, 0, -14.



You can only do this if your appliance draws small current. You must determine whether 13 or 14V is adequate for your appliance.

B) Or if you need upwards of 1A output at +15V and -15V, then you will need to add some kind of voltage multiplier to step up the output.

- > Syncopator

Dear,
this was indeed a nice answer. Precise and very quick.
thanks a lot!

Could you maybe even give me a hint what kind of transformer I should look for, as a exchange?
I really think that the old transformer is a bit too small for it's "duties".
It's a 16-channel desk, and as I have ... well - "heard" - it's good to have "more" power than actually necessary...(dunno about the facts here though).


As I wrote; it doesn't need to be a switchable (110V) transformer anymore.
220/230 would be fine for me...
I also wouldn't mind to spend a little more on quality... if it's worth it.

any ideas?

- - - Updated - - -

-> BradtheRad

- - - Updated - - -

:roll:

ok.

thanks.
I think the desk should have at least it's 15V.
it's a 16ch. version, which was the biggest version build of the series, and I think that the power-supply was the same for all versions, and most probable, thus, developed
to just deliver power enough for the biggest version (16ch.). I wouldn't try to go lower here.
Actually - I'd would rather in contrary, like to "beef it up" a bit... since I believe it would "sound better" with more ... "headroom".
(Now please - don't get me wrong here: - I don't believe in this esoteric mumbo-jumbo that costs a lot of money...
but I believe that it -logically- would be better to have plenty of power, so that all parts can work properly...
Like a Ferrari - that also drives VERY well in a SLOW speed; even if that is a complete waste of money...).
Please don't hesitate to correct me here - if that is a wrong idea.

Maybe you could even give me a hint to what kind of transormer-replacement I should be looking for?
- I'm really a novice in this field. Please excuse...

Thanks a lot for help.

R4Dt said:

Could you maybe even give me a hint what kind of transformer I should look for, as a exchange?

Click to expand...

Look for a transformer with a 110 or 115V primary, and a 18-0-18V or 20-0-20V secondary.

The VA (power) rating should be similar to that of the original. The only way to guarantee that is to take measurements of the original's lamination stack; width, height and thickness, and get some idea of the windings' physical measurements too.

Then choose a transfomer which is similar in size, or better, slightly larger in pysical size than the original.

The logic behind this is that all reasonably well designed transformers with the same VA rating will be approximately the same physical size.

Yes, it might be difficult to find dimensions from on-line catalogues, but some stockists do mention them. And any who don't should answer relevant questions.

Yes, if you can get an exchange, then an 18-0-18 is what you need (in agreement with Syncopator).

My post #3 was in case you were committed to going with the single 24v secondary.

I should add that it does not appear possible to carry out my suggestion B. A voltage multiplier will need to draw greater current than 1.3 A. Your transformer would most likely overheat.

I'm not sure that you get what I mean.
(or maybe I don't get what you mean... hehe)

I'll try a second time to UL the schematics:

As far as I believe (and that might be completely wrong) I shouldn't think too much about exact Voltage... since I have the regulators, right?
There should be +/- taps, for sure, but - I think it should be 24-0-24 (and not 18-0-18) Volts. No?

I'm a little bit confused about the Amperes, though...
(can't find where I got this 1A from. will look again tomorrow).

In this kind of build; are there ANY differences concerning Quality?? - like; different parts, or even the transformer?
CAN a transformer be .. well "bad"? - (or are there simply some minimum requirements...).

- - - Updated - - -

What I don't really get is how the transformer can take 110 AND 220 V (??) - and then transform it to ... whatever.
Maybe I SHOULD read about it a bit.
- somehow I find it intriguingly fascinating, all this... haha!

R4Dt said:

There should be +/- taps, for sure, but - I think it should be 24-0-24 (and not 18-0-18) Volts. No?

Click to expand...

An 18-0-18 will produce sine waves with peaks at 24V. The nomenclature is a convention though it may appear misleading.

The peaks show up on your schematic as 24 and -24V. But your appliance probably draws this down to about 18, 19, 20V, according to current demand.

In this kind of build; are there ANY differences concerning Quality?? - like; different parts, or even the transformer?
CAN a transformer be .. well "bad"? - (or are there simply some minimum requirements...).
...
What I don't really get is how the transformer can take 110 AND 220 V (??) - and then transform it to ... whatever

Click to expand...

You can only trust that the dealer would rather carry merchandise from a reliable vendor, than risk having unhappy customers return items. Same for the manufacturer.

When you install it in your equipment, you'll be wise to verify that it holds its volt level for the full current output. And that it doesn't overheat.

It's also important that you get a transformer intended for 50Hz if that is your AC frequency. Do not get one made for 60 Hz and plug it into 50 Hz. It will overheat.

The 110/220 switch is a clever way to hook together two primary coils in two different ways. The unit can be used anywhere in the world. Alert: Bad things might happen if you set it to 110V and plug it into 220V.