Switching 230 Volt Transformer to 120 Volt


I picked up this small PA Mixer from ebay that the seller claimed that would work on 120 volts eventhough the mixer is from denmark.

The mixer works however, the voltage stamp on the back of the mixer says 230 volts. :xeye:

I switched the power transformer with an old cassette deck transformer lying around doing nothing. Both offering similiar sizing. To my surprise the mixer was getting half the voltage all along and, now works perfect. :angel:

Perfect in the sense of no buzz (As if it's not grounded) when interacting with other components and more power to drive.

Only one problem... The Transformer gets hot within 30 minutes.
Seeing that I never mess with the caps I'm wondering if it's the root of the problem.

The caps in the mixer is 16v 450 uf and, the transformer on the tapedeck had 25v 1000uf capacitors.

I've read numerous articles about having a transformer too small for caps but not a Transformer higher than the caps.

As I type I have a muffin fan blowing cool air across the Transformer. I'm looking at a way to remedy this problem.

AndrewT said:
sounds like you haven't much of a clue about using mains electricity safely.
Get help before you injure someone.

I do. However, we are talking about a device that offers a different voltage from where I reside. So, there is a big possibly that the cycles are different as well.

Maybe I should just get a step up transformer and not focus on this very much. The unit offers only a half an amp fuse so, we are not talking big power here.

AndrewT said:
your answer and what it does not say, tells me you need help.
Go get assistance before you or someone gets injured.

Well that's why I came here for.... Assistance. All you need to do is ask the question(s) and I'll be happy look on the PC board and tell you. If it was a matter of upgrading the caps, or rectifier I would be willing to do so.

I'll just get a step up Transformer and, use it to boost the voltage on the original Transformer. The unit requires no more than 1 amp to stabilize. So one of those Trisonic 50 Watt 120 to 220 volt Step-Up Transformers will be more than plenty with no ill effects.

Thanks anyway.
Best to find the correct transformer to begin with than to use step up or down interfaces = which could add noise, reduce system quality.

From what you post above, I would guess that the mixer uses +/- 9 volts DC or even just + 9 VDC, thus the 16 VDC rating on the mixer caps.

The heat from your alternate transformer is probably because it just is not big enough ... an anemic, low wattage transformer will run hot under load.

Do you have the manual ? ... Or a schematic ??
" ... This is the information I was looking for. ... Here's the manual but it is not in english. ... I'm heading out the door so I'll post back later. ..."

1) Yes!! This mixer is definitely worth "saving" = a keeper as they say! ... my nephew would like to have it ...

2) From the pdf file manual: Note that the back panel silkscreen printing indicates a wide range of input AC voltages from ~ 100 VAC to ~ 250 VAC in four variations. IMPORTANT: This may indicate that B]the internal power supply may be of the switching variety[/B] and actually may optionally be plugged into any household outlet from 120 VAC through and inclusive 250 VAC. ... ALTHOUGH there may be some switching arrangement internally that would allow semi-permanent setting of the operating voltage to something "fixed".

If this were mine, I would simply have replaced the power cord for use with 120 VAC and left the internal parts and wiring alone until I had a schematic to work with. ;)[
TheMG & FastEddy thanks for your input.

Well, let me tell you why I created this contraption. When I got the Mixer and powered it up, all of the signal LED indicators lit up and, remained on.

Being an audio guy, I know audio signal indicators shouldn't be illuminated if there is no signal passing through the channels. Nevertheless, the mixer functioned and I was happy. The output wasn't loud as I expected but, I just figured it was the nature of the beast.

A Month later I was chasing an excessive buzz and, it led right back to the mixer. When I pulled the plug out of the socket, the buzz would vanish. However, once Iplugged it back in, the buzz reappeared. :dodgy:

Seeing the back of the mixer had a little dot on the 230 Volt chart and, not the 120 I figured it was getting low voltage.

This is when I decided to use an alternative Transformer. Once I switched Transformers, all the signal indicators would remain off and, only light up if you are feeding the channel a signal. :smash:

Anyway, I purchased a Step-Up Transformer today and, reinstalled the original transformer. Feeding the mixer 220 Volts all the signal indicators respond correctly, no buzz issues, and, the mixer's output offers a better drive. :angel:
" ... Seeing the back of the mixer had a little dot on the 230 Volt chart and, not the 120 I figured it was getting low voltage. ... This is when I decided to use an alternative Transformer. ..."

Without the schematic or some info printed on the circuit board, you probably did not notice how to change the internal jumpers (or wiring connections) to set the power supply up for operation on 120 VAC ... I would bet this is easy or at least painless. :eek: