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Cristi 14th January 2010 04:52 AM

Class D Audio Amplifiers
Discussions about class D audio amplifiers from Connexelectronic

Kjeldsen 14th January 2010 01:08 PM

Hi Cristi,
I have ordered some NXD TDA8950 boards from you. While I'm waiting for the boards to land i Denmark, I'm, looking for the rigth transformator. What will you recommend - minimum and optimum?

I'm looking at 2x25 volt 200 VA minimum per 2 channel board.

Cristi 15th January 2010 09:04 AM

Hi Brian

the proper transformer for TDA8950 amplifiers must provide an ac voltage in range of 2x22V to 2x26V and at least 4A, and if possible 5-6A to provide enouch current to the amplifier when is used with low load impendance. the one which you have chosen seems within the specs, with minimal power.
an alternative is to use a SMPS, lightweight and with regulated output voltage. Connexelectronic
the price is similar with a mains transformer

Kjeldsen 15th January 2010 09:26 AM


Kjeldsen 20th January 2010 11:03 AM

Input pins:
I'm not quite sure what to do with the middle pin (pin 3). I have read the instructions.
Maybe you could make at drawing on how to cable the module.

Something like this

fb 21st January 2010 01:59 AM


with the TDA892xV2 boards, TDA8920TH IC, bridged into 8ohms:

- is it possible to get the full 135W output (or close) using +19dBU balanced input signal?

- is the BIPS board required to allow the use of balanced input signal?

- is it reasonable to run 2x such modules off the one 250W (400W peak) SMPS that you sell? (Music signal only)


Cristi 22nd January 2010 03:29 PM


pin 3 of the TDA89xx amplifier is the Mode pin. when the voltage on this pin is 0, the amplifier is muted and in stang by. when the voltage is about 2-3 V the amplifier is in Mute mode and when the voltage is >4V the amplifier is working normally. please read the manual of the v1 for more details. they share the same schematic, just the layout is different.


+19dB is much higher level than the amplifier requires and you need an attenuator to reduce to the proper level.
for full balanced input you can use either BIPS or modify the amplifier, the ic already has balanced input, but is not used and connected to GND.
the smps can provide the peak power for 2 modules if you use one for low and one for mid-hi freq. it might need to add some extra capacitors.

Kjeldsen 22nd January 2010 05:59 PM

I have read the manual, and know about the voltages, but do I need to supply 4 volts to the pin? I thought the board would work with just one normal 25-0-25 volt transformator?

Cristi 23rd January 2010 11:23 AM

The board has a simple regulator with zenner diode which provide this voltage. by default, the amplifier is unmuted. when you connect the pin 3 to GND the amp will mute.

Kjeldsen 25th January 2010 06:53 AM


Originally Posted by Cristi (
The board has a simple regulator with zenner diode which provide this voltage. by default, the amplifier is unmuted. when you connect the pin 3 to GND the amp will mute.

Thanks, thats what I hoped for.

Next question. The NXD chip and the rectifier bridge is not the samme hight. When I'm using the mounting holes on the same heatsink, then there is a hight difference and I'm afraid that the NXD chip will not have full contact. The NXD chip is the lower one, and therefor som downforce should be applied to the screws, for the chip to get full contact.

Is this a problem, or can I go forward with both chip and rectifier bridge on the same heatsink?

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