Bridged amplifiers...

[Boscoe]

I've just managed to confuse myself on this. If I had one amplifier operating normally (non bridged) and I need a +/- supply of 50V and 5A to achieve my output power. With two amps in bridged I only need +/- 25V right? But what happens to current requirements? It dosen't changed right? I'll just be using the 50V between my supply rails instead and still draw 5A? But then PS my power supply can half? Because both windings will be used at the same time at half the load if not bridged whereas the non bridged will leave one winding redundant all the time? I am right, I think I have just confused myself?

Thanks
Boscoe

[AndrewT]

50V & 5A to the load requires each amplifier to provide 25V and 5A to the half load, when bridged.

The overhead or volts lost through the system from transformer to speaker will be about the same for bridged and non bridged.

Expect that loss to be ~ 10Vdrop.
To get 50Vpk and 5Apk to the load the single amplifier needs power rails of ~+-60Vdc and 5A .
To get 50Vpk and 5Apk to the load the bridged pair of amplifiers needs power supply rails of ~+-35Vdc and 10A to the pair (5A to each).

Now look at what you have.
Both single and bridged give 156W into 8r0.
The single uses a PSU of 60V & 5A = 300W to deliver that maximum of 156W.
The bridged uses a PSU of 35V & 10A = 350W to deliver the same maximum of 156W.

Now, I ask why are you considering that solution?
The Bridged arrangement requires twice the smoothing capacitance to supply twice the current.
The Bridged arrangement requires twice the output devices to supply the same current from the pair.
The Bridged arrangement requires a slightly bigger transformer due to the lower efficiency.
The Bridged arrangement requires a larger heatsink due to doubled Ib
The Bridged arrangement requires twice as much Voltage amplifier stage resources.

For that combination of reasons, I always try to dissuade builders from adopting Bridged solutions if there is another way/s to get to the same answer.

As an educational exercise, bridging is worth investigating.

[Bensen]

If you have run the amplifier non bridged on a load of for example 8Ohm. If you than run the amp's in bridge mode, each amps "sees" a load of 4Ohm.

This means that you can put twice the power that one amp can give in 4Ohm when switched in bridge.
This then means, that the current will be the +-double througt the output stage.

I'm sorry if my explanation seems confusing.


Oh, I see Andrew was faster.

Ben

[abraxalito]

Amps have a certain saturation voltage and with bridged you have two of those voltages. So if the saturation voltage was 3V at 50V then your swing was 47V, whereas for the same amp at 25V bridged your swing becomes 44V. You can make your power supply balanced which improves the efficiency somewhat - you can have caps with double the voltage between the two supply rails - these caps have better energy storage density coz they're running at twice the voltage.

The advantage I like with bridged is ease of grounding No heavy speaker or rectifier currents need to go to ground.

[AndrewT]

Abrax.
the advantages you list are real, but are they available only to a properly designed balanced amplifier topology?
Two amplifiers joined together to form a bridged arrangement do not as far as I can see gain either of the advantages you show.

[Boscoe]

Thanks for the feed back I understand now. the reason I asked is because the amplifiers I'm looking at are the TA3020 amps from connxelectronics which give high power when bridged and so looking into it further.

Thanks
Boscoe

[abraxalito]

Originally Posted by AndrewT

the advantages you list are real, but are they available only to a properly designed balanced amplifier topology?
Two amplifiers joined together to form a bridged arrangement do not as far as I can see gain either of the advantages you show.

Yep you're right. I took it that the OP was talking about DIY amps (as in amps as components on PCBs) rather than ready-made ones (boxed with supplies). But if I'm wrong on this then sure, your point is an excellent one.

[AndrewT]

Hi,
Bridging usually gives higher power if the amplifiers and the loads suit that topology.

Higher Power does not equate to higher performance.
In fact (I really mean that phrase), bridging can cripple the performance of a pair of amplifiers if not properly designed for the intended loading.

[ingenieus]

I've got a nice big transformer in my parts bin (guess about 150VA from the size of it) but it's only 15V-0-15V. I've been thinking about using it to build a bridged amp, but it would be a lot of work and the end result would only be moderately powerful.

[AndrewT]

If toroid, add 20 or so turns.
Measure the new output voltage.
Decide if this is sufficient.
Adjust, if necessary, and then add the same number of extra turns to the other secondary.

When measuring/testing/powering up, please keep all, yes, all the winding ends captive in separate terminals of an insulated terminal block.