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Can I use off the shelf 5532 Chinese stereo pre-amp modules in bridged mono mode?


New Member
I'm building prototypes for cheap conference interpreter consoles using off the shelf modules including ne5532 op-amp based pre-amplifers for both headphone preamps and mic preamps. I've got two working prototypes and am now working on cutting noise and looking to see how I can refind the design to reduce component cost and improve ease of assembly.

There is no need for stereo in the design and the conference floor input would usually be mono, as would the output for transmission to the audience. However,, in my prototypes all of the audio signal switching components, and most of the pre-amp modules I used, are stereo.

In the case of the headphone pre-amp, I have successfully used two individual mono audio signals at the input, and split the output to two independent sets of headphones (the design spec requires two headphones with their own volume control and input channel selection). Doing this means one less pre-amp is required but adds a lot of faffing about making custom cables to join and split the audio signals.

On the microphone I've just shorted together the 'left' and "right' channels on the import from the mic. This means the output is two identical audio channels but not true mono as such. Since the audio signal switching elements of the design currently carry 2 channel audio signals using three wires, the two identical signals are retained internally to the output bus connectors which are RCA pairs. Since both channels contain the same mono signal, I can take mono from any one RCA but I guess at half the potential amplitude.

I'm wondering if I can safely 'bridge' the output of the NE5532 amplifier for full power by simply joining the Left and Right channel, or will they cancel each other out or cause damage or distortion?

If I can bridge the outputs safely then I could look to use single channel switching components to potentially reduce component cost. I could also bridge the headphone preamps, using two pre-amps instead of one but with a lot less additional complication with custom cables.

The two amp modules I'm currently using (sources from AliExpress) are the XH-A902 (for the mix preamp) and the single power supply dual ne5532 pre-amplifer board (for the headphones).

I'm also keen to learn how to deal with capacitive coupling as I get a nasty hum when I touch the metal microphone case, and it is greatly attenuated when I also touch some parts of the console itself. The power supply is unearthed and always will be so earthing is a problem (is this called floating earth?).

Anyhow, that's it for now.


Well-Known Member
Most Helpful Member
You could parallel the outputs of the NE5532, though that would not give any higher signal level.

You would need to use a resistor in series with each NE5532 output to the common output point so the two amps were not "fighting" each other due to slight differences in gains from different components etc., otherwise it may distort or take excess current. That would probably cancel out any higher drive advantage.

It's not "bridging" by the way, that is when you use use two signals of opposite polarities to achieve a higher output voltage.

Re. the hum.
Use "star point" grounding for everything in your amp box, which is presumably metal?
All module 0V terminal, audio grounds and cable screens should connect to one common point by as short wires as practical, which is also grounded to the case - and no other points.
Internal screened cables should have the screen grounded at one end only.

That may mean changing to isolated phono (RCA) sockets. Phonos are not a professional grade connector and there are many far better. I personally detest the things..

What microphones and headphones are going to be used with it? None that I am aware of use phonos.

If the AC power is well away from the signal wiring and all low level cables are screened and the screens are connected to signal ground at the amplifier, there is not much you can do - proper grounding is essential. Your other option is trying different makes of power unit to see if any have less leakage, or a battery supply.

As long as the whole system is floating, the results will be unpredictable and affected by such as power wiring in the area.

That's one of the reasons most professional gear uses balanced line signals. Any hum pickup on cables is ignored as it's common mode not differential, like the wanted audio.

Nigel Goodwin

Super Moderator
Most Helpful Member
As already mentioned, paralleling isn't bridging, and wouldn't really give you any benefit (what exactly is the load you're feeding?). Actually 'bridging' opamps though is commonplace, particularly for feeding headphones, and I do so in one of our commercial projects.


Well-Known Member
Most Helpful Member
The AliExpress preamp is designed for inputs from a phone that has outputs that are about 30 times more than from a microphone. It also has no parts to power an electret microphone.
They might sell a microphone preamp module.

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