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Old 28th January 2003, 04:34 PM   #1
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Question General Bridge/parallel considerations

I theory any number of identical amplifiers can be connected in parallel to drive the same load to achive more power than a single unit can. My question is, because in the real world identical amplifiers doesn't exist, wich is the general way to compensate this small diferences?. What I'm trying to do is to combine power amp ICs in bridge/parallel configuration to get more power and keep things relatively simple. Thanks!
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Old 18th November 2006, 02:38 PM   #2
gni is offline gni  United States
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Default Parallel Amps

Amp paralleling is all most amplifier do internally with special circuits
so all the output transistors work in harmony. Don't hook up two
Amplifiers in parallel . . .it would be bad. No simple way to increase
power except by careful planning and layout of circuits designed to
amplify and distribute the current.

Chris
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Old 18th November 2006, 08:56 PM   #3
K-amps is offline K-amps  United States
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I wanted to do this on a Forte Model 3 amp. Asked Nelson and he suggested paralell bridge the output stages. He said tie the input and output and watch out for DC offset.

I asked him if the gain of the 2 channels differed and caused issues... he didnt reply... but he did say to tie the two OP stages with a 0.1 resistor.

My approach was to feed both channel OP stages from one channel's drivers.
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Old 18th November 2006, 11:42 PM   #4
gni is offline gni  United States
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Default Parallel Amps

Some sort of resistor or network should be employed to prevent
the output transistors from killing each other. . .I understood this
to be putting two different but similar amps in parallel. . . something
that will fry the output transistors of one amp or the other. . . interally
anything goes. . . as long as it is designed correctly

Chris
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Old 19th November 2006, 02:24 AM   #5
K-amps is offline K-amps  United States
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Sure thing...

To me if the driver is common, it is like one big OP stage, after all every output still has the ER's in series.

It is when you join 2 separate amps that it gets hairy..
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Old 19th November 2006, 04:23 AM   #6
lndm is offline lndm  Australia
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With regards to parallel amps.

Beware of any difference between the amps, not just DC offset. There is noise and interference. I've killed amps instantly trying to do this. It is inelegant at best, in my opinion.

What do you hope to achieve? You'll get the same output power unless the amp was under much stress before in which case I feel you should try a better match for your speakers instead. If you are driving two speakers from one amp you should use them separately. The halved Zo is not worth this particular effort in my opinion.
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Old 19th November 2006, 06:20 AM   #7
ilimzn is offline ilimzn  Croatia
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There is a whole subforum here called 'Chip amps' where this exact topic is discussed in much more detail, based mostly on an application mote by National Semiconductor (for the LM3886).
Unless you would like a more general discussion?
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Old 19th November 2006, 10:29 AM   #8
K-amps is offline K-amps  United States
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Quote:
Originally posted by lndm
With regards to parallel amps.

Beware of any difference between the amps, not just DC offset. There is noise and interference. I've killed amps instantly trying to do this. It is inelegant at best, in my opinion.

What do you hope to achieve? You'll get the same output power unless the amp was under much stress before in which case I feel you should try a better match for your speakers instead. If you are driving two speakers from one amp you should use them separately. The halved Zo is not worth this particular effort in my opinion.

Appreciate the sentiments...

My application is 3 bass drivers in parallel with DCR or around 2-2.5 ohms. I'll need 3 amps to do that plus 3 runs of cable plus 3 runs of passive networks, plus the cost of the other amps... Life is so simple.
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Old 19th November 2006, 10:41 AM   #9
AndrewT is offline AndrewT  Scotland
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Default Re: General Bridge/parallel considerations

Quote:
Originally posted by luisma1972
combine power amp ICs in bridge/parallel configuration to get more power

Quote:
Originally posted by K-amps
tie the input and output and watch out for DC offset.

if the gain of the 2 channels differed ......he did say to tie the two OP stages with a 0.1 resistor.

My approach was to feed both channel OP stages from one channel's drivers.

Kamps approach is paralleled output stage and completely different from paralleling chipamps to allow lower impedance loads to be driven.

Have a look at the datasheets from a selection of manufacturers. Some are very helpfull with guidance on paralleling and bridge parallel for more power.

ps there is another chipamp thread running on exactly this question.

It appears your search button is not working properly.
__________________
regards Andrew T.
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Old 19th November 2006, 10:54 AM   #10
K-amps is offline K-amps  United States
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I reckon it has been discussed before: but whats better using one driver to drive 8 OP devices or 2 drivers running 4 each?

As far as sonic preference goes, I prefer non-parallelled approach, however from a pure current delivery standpoint would 1 or 2 drivers be better:

Keep in mind with more OP devices running on their high Hfe area, the need for beta droop on the driver is reduced...
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