[SOLVED] What transformer to use?

[jure8479]

What transformer to use for TDA2050 audio power amp?

Hi,

I have recently built an audio power amplifier with TDA2050.
The project found on this web site originally uses three TDA2030 integrated amps: Circuit Power audio Amplifier with TDA2030 2.1. Following some advice in the comments, I simply replaced the TDA2030s with TDA2050s.

Since I lack experience in audio amps in general and their power supply setup, I would like your opinion on what transformer to use.
I was thinking of using laminated core 2x15V 10VA. Should I use a toroidal transformer instead?

Happy 2014

 

[godfreyl]

They recommend a transformer rated at +-12V, 3A, which seems sensible. That works out to 72VA.

You can increase the transformer voltage to +- 15V, but then the current rating should be increased proportionately as well, which leads to a rating of about 100VA.

If you're not going to run the amp continuously at full power then you could safely reduce that to maybe 50VA. 10VA is definately too low though.

You can use a toroidal or an EI core transformer. Either would be fine.

 

[crutschow]

Toroidal transformers are more expensive but have a smaller external magnetic field so are less likely to induce hum into the adjacent audio circuits. If you can keep the power transformer well away from the audio circuits then a laminated core transformer should be fine.

 

[jure8479]

Toroidal transformers are more expensive but have a smaller external magnetic field so are less likely to induce hum into the adjacent audio circuits. If you can keep the power transformer well away from the audio circuits then a laminated core transformer should be fine.

In your opinion, what distance would be "well away"? Would 15-20 cm be enough?

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Thank you both for your help.

- - - Updated - - -

Does the transformer need to have two secondary windings (and why)?
I connected a used 50VA transformer with a single 12V secondary winding to the amp, and it seemingly works ok.

 

[crutschow]

15-20 cm should be enough to minimize magnetic coupling. In particular, keep the sensitive amplifier input connections away from the transformer.

If you only need a single voltage supply then you only need one winding on the transformer output.

 

[godfreyl]

Does the transformer need to have two secondary windings (and why)?
I connected a used 50VA transformer with a single 12V secondary winding to the amp, and it seemingly works ok.

You need a dual-rail supply (positive and negative voltage). The pic below shows the wiring options for dual and single secondary. If it's working then presumably you got that right.

The main disadvantage of using a single secondary is that you get double the ripple voltage on the output. If that's a problem, you can fix it by doubling the size of the capacitors.

Looking at it the other way around - the advantage of dual secondaries is you can use half the capacitance for the same amount of ripple.

Also, with a single secondary the ripple on the output is at 50Hz/60Hz, whereas with a dual secondary the ripple is at 100Hz/120Hz. But that's not an advantage either way.

 

[jure8479]

I will try to get a dual secondary toroidal transformer for the amplifier.
Everyone, thank you for your help.