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Old 3rd February 2011, 09:25 AM   #1
pra3718 is offline pra3718  India
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Default Bridge/Para TDA7265

As per attached picture " Type A "

I build & listen for short time. Sound was loud but not smooth & clear. Major thing is chips was running very hot. Tda7265 is not advisable to run 4ohm in bridge configuration.

As per attached picture " Type B "

Then, I test this configuration, and I found, loudness is minimized but smooth & clear. ( Sorry I can't better describe ) Chips was running hot but not that much.

1) Is this configuration is allowed ?
2) Accept running lower impedance driver, what is the benefit ?
3) I am using 1R 1/4 watt resister. If I use 4 in parallel then is it equal to 0.25R 1 watt resister ?
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Old 3rd February 2011, 12:05 PM   #2
AndrewT is offline AndrewT  Scotland
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A bridged pair of tda7265 cannot be bridged again.
You can only use the bridging trick once to get double the power into double the impedance.

The left most diagram shows 2 sets of bridged tda7265.
This is effectively 4 amplifiers and each amplifier thinks it is driving a 2ohm load.
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Old 3rd February 2011, 12:13 PM   #3
sregor is offline sregor  United States
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Look at the schematic again. The second pair is not a bridged bridge, but a parallel bridge. It will provide less power because of the resistors and the series load.
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Old 3rd February 2011, 01:00 PM   #4
AndrewT is offline AndrewT  Scotland
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Sregor,
you are correct the rightmost is a BPA configuration.

The two 4ohm loads are in series, effectively an 8ohm loading.

Each BA is feeding current to that 8ohm load. Both BA share the current fed to the speaker and as a result each BA sees 16ohms.
The individual amplifiers inside (all 4 of them) will think they are driving an 8ohm load. This is very much different from the left most diagram where each TDA7265 thinks it is driving a 2ohm load.

But why does the rightmost diagram appear to be running hot?
He has fitted some current sharing resistors. But that is not enough.
The parallel circuit must be designed such that all the TDA7265 deliver the same current to the load.
This requires very accurate gain matching over the whole audio passband. And requires very accurate matching of output offset for all operating temperatures from a cold start up to worst case operating temperatures.

This accurate paralleling is not easy to achieve. Many parallel implementations end up overheating, because the builders do not understand the requirements nor limitations.
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Last edited by AndrewT; 3rd February 2011 at 01:02 PM.
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Old 3rd February 2011, 03:03 PM   #5
pra3718 is offline pra3718  India
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thank you.

Quote:
It will provide less power because of the resistors and the series load.
which resistors should I use ?

AndrewT, What should be your advise to less experienced builder. Should I go ahead with BPA or not ?

Still waiting answer for following questions for BPA design.

1) Accept running lower impedance driver, what is the benefit ?
2) I am using 1R 1/4 watt resister. If I use 4 in parallel then is it equal to 0.25R 1 watt resister ?
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Old 3rd February 2011, 03:56 PM   #6
AndrewT is offline AndrewT  Scotland
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Hi,
last first.
yes 4 parallel equal value resistors will be rated at resistor value/4 and power rated by lowest Pd*4.
If you mix different Pd types of the same resistance value then you don't get the full benefit of the higher power resistors.
Think of it, using P = I^2 * R
If you have 500mA passing through the single resistor then the dissipated power is 0.5^2 * 1r = 1/4Watt

Now put 4 in parallel and pass 2A through the group. The current through each resistor is the same 500mA and the power dissipated in each resistor is still 1/4W
The voltage drop across the single resistor (using V=I*R) is 0.5 1r = 0.5V
The voltage drop across the group of 4// resistors can be found from two different combinations of amperes and ohms.
Consider just one resistor of the group. It passes 500mA when the total current is 2A and the voltage drop is 0.5 * 1r = 0.5V
Now consider the group as a whole. The total current is 2A and the effective resistance is 1/4ohm (=0r25). The voltage drop is 2A * 1/4 = 1/2V = 0.5V
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Old 3rd February 2011, 03:58 PM   #7
AndrewT is offline AndrewT  Scotland
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BPA, BA & PA configurations using chipamps.
I am not a believer in any of these topologies.
I shall leave it to others to try to give a list of advantages, if they can find any !

The main reason I am against using chipamps in these types of implementations is that the peak current through the chipamp cannot properly drive the load that the builder wishes to hang on the end.
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Last edited by AndrewT; 3rd February 2011 at 04:01 PM.
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