A friend gave me his Technics equalizer he brought from the USA here to Portugal, he told me "it should work as is" but looking at the setup and considering they use 110V in the USA compared to 220V here, I am confused.

Here is the setup as he gave it to me:

http://imgur.com/HWP2hK9

here is the schematic for the device (under the chassis there is a rotary switch to set input voltage):

http://imgur.com/w1G5IsK

Do I just need to set the module to 220V and replace the US plug with an EU plug?

What was the logic behind using the transformer to convert 220 to 110 and having the module set at 240? He told me it was working like that (I have yet to test it but the fuses are intact).

 

Do I just need to set the module to 220V and replace the US plug with an EU plug?

You also need to replace the cable, as the existing cable won’t be rated for 230V.

 

Do I just need to set the module to 220V and replace the US plug with an EU plug?

Yes. If the device had a switch to change the input voltage, you just need change it to the correct voltage and use an appropriate adapter for the plug.

The transformer you showed was a 2:1 stepdown. If you used that, you would set the device to 110VAC input.

It wouldn't convert 50Hz to 60Hz. Many US devices will operate at 50Hz.

 

What would happen if the unit was set to 240V while powered through the step down transformer (110)?

 

It might work, and it might not. The electronics would get half the power supply voltage it should, so it would distort at lower levels.
The outcome is a lot better than if it were set to 110V and connected to 230V power! That might result in the need for a new transformer.

 

What would happen if the unit was set to 240V while powered through the step down transformer (110)?

Not likely to work. US devices will operate over the typical voltage range for 120VAC; 60VAC would be outside of the normal variation.

We use 110VAC and 120VAC interchangeably because it doesn't matter with line powered devices.

 

Now that I have got the image saved and could zoom in on it, I think it actually would work.
The transformer gives 26V peak when operating at its correct voltage, which is regulated down to 15.6V using a zener and emitter follower.
With half the AC voltage, there would be 13V peak, and the emitter follower would drop 0.6V leaving about 12.4V. That's now only 20% below what it should be. Most op-amps (and I can't find any information on the SVITA75558) will work on 12.4V.
There's nothing to remove the ripple except the filtering caused by Rds of the JFET and C105, so I bet it would hum, unless the SVITA75558 has very good PSRR.
I wouldn't recommend it.

 

The reason I asked was because the previous owner told me this setup was working here in Portugal (with the 220V being converted to 110V and module set to 240V), which confused me.

Datasheet for the opamp mentions 12 to 14V input voltage, as far as I understand.
https://html.alldatasheet.com/html-pdf/31310/TOSHIBA/TA75558S/751/3/TA75558S.html

Found a service manual for the module here but i'm not familiar with this site, I cant figure out if it's downloadable:
https://www.radiomuseum.org/r/technics_stereo_frequency_equaliz_6.html