Chip amps used in "push pull"

[ChrisA]

I'm new to these chip amps. I have some experience with vacuum tubes. Maybe this is common and someone can point me to a schematic or two. I need about 100 watts of power. So I think why not use two chip amps working 180 out of phase, one amp drives the positive speaker lead wire the other drives the negative speaker wire. So, I'd run the input (if it's not already a "balanced" source from say, an XLR cable) to a phase inverter (or an audio coupling transformer) and then to two 50W amps.

What I'm looking to build is a bass guitar amp. I would build four of the above (eight chips total) and each push/pull pair would drive one 10 inch speaker in a four speaker cabinet.

[Tekko]

What you mean here is a bridged amp, this already exist so its nothing new, you can get four times the power doing this but remember that the amps will see only half the speakers impedance.

If two amplifiers in bridge mode share a 4ohm load, each amp will see 2 ohms, or 4 ohms if its a 8 ohm speaker.

This is important to remember or you´ll blow up the amps, or atleast run them very hot which will eventually make them fail, and when they do they till also kill your speaker.

I suggest you check the bpa300 thread, its about a 300 watt bridge amplifier using i think six LM3886.

[paulb]

Also called BTL for Bridge Tied Load.

[ChrisA]

That BTL amp is a "Bridged" amp. I'm looking for "push/pull"

In a bridged amp you simply sum together several amps by wiring them in parallel.

In a push pull design one amp drives each speaker lead.

The difference is kind of like wiring the amps in series or in parallel.

Here is the simplest example of a push/pull design I can find.
http://www.drtube.com/schematics/hiwatt/hwpwr50w.gif
Notice the two triodes are 180 degrees out of phase. In a solid state design you don't need the transformer and can drive the speaker's voice coil directly. What I'm thinking of is roughly replacing each of the triodes with a cheap chip amp part.

I'm asking if anyone has seen this done

[leadbelly]

Originally posted by ChrisA
In a bridged amp you simply sum together several amps by wiring them in parallel.

In a push pull design one amp drives each speaker lead.

Your definition of a bridged amp is incorrect. The previous respondents are correct. Search on "bridged".

[AndrewT]

Hi,
look up the National datasheets and application notes for their range of chipamps.

They give examples of single, bridged (BA100), paralleled (PA100) and bridge/paralleled (BPA200).
They also give the design procedures and component values.

The idea of 4amplifiers, each dedicated to a single driver is good.
Each driver in it's own volume would be better. This would allow for a failed/shut down amplifier or blown speaker. The remaining three would keep operating.
One failed driver in a 4way cabinet will probably not sound nice.

Make sure all your drivers you intend to power from bridged chipamps are really 8ohm. Design each channel of the amplifier to drive 4ohms and 2r0. The 2r0 loading is not as severe as driving a real 4ohm speaker. I would consider a 1r4 load as a good test for a 4ohm amplifier.

[analog_sa]

Originally posted by leadbelly


Your definition of a bridged amp is incorrect.

Or his idea of push-pull for that matter.

[Circlotron]

Originally posted by AndrewT
The idea of 4amplifiers, each dedicated to a single driver is good.
Each driver in it's own volume would be better.

If you separate the cabinet into 4 compartments it will make the whole box be MUCH better braced as well. Each driver sees only 1/4 of the total volume anyway, so nothing much changes as far as each driver is concerned.

4 amps --> 4 drivers

[star882]

At that power level, digital would be lighter and cheaper. Since you're dealing with an analog input, a hybrid digital is the way to go, unless you're also using DSP in which case a pure digital can also be used.

There are premade modules that do exactly what you want.
http://www.coldamp.com/opencms/openc...078/index.html

Here's an article on the theory of Delta Sigma conversion which is what's used in many pure and hybrid digital amplifiers:
http://www.beis.de/Elektronik/DeltaS...eltaSigma.html
Note that in practice, it works better to have two Delta Sigma stages running in parallel, with the same clock signal but with one signal inverted by 180 degrees, so the carrier more or less gets cancelled out leading to lower losses at low signal levels. (The design of a Delta Sigma digital amplifier, especially the pure digitals, is very involved and it is not recommended for a beginner to design one. There are chips that integrate the Delta Sigma modulators and for some, even the power stages in one easy to use package.)

[Tekko]

Do NOT reccommend coldamp, its just a buncha trash. i´ve had complaints from chat friends about coldamp products going unstable and blowing up. I´d reccommend proven modules like hypex ucd or even better modules from huygens audio in china, not some expensive useless junk from coldamp.