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Old 26th February 2012, 07:08 PM   #31
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Random question , i plan to have 2 channels, each one being 2 of the circuits bridged to get around 600 watt max per channel. If i wanted could i bridge it again to 1200 ish with no problems? for use on single high power subs ect
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Old 26th February 2012, 08:34 PM   #32
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Quote:
Originally Posted by Volperossa View Post
Random question , i plan to have 2 channels, each one being 2 of the circuits bridged to get around 600 watt max per channel. If i wanted could i bridge it again to 1200 ish with no problems? for use on single high power subs ect
No you can't, every AMP that is not in BTL can only be bridged one time, would be awesome if you could bridge it again thou.

But the TDA7294 gives out some serious watt's in 4-8Ohm when bridged, TDA7293 will of course give even more since it will take 10V +/- more, a DUAL SET Transistors pr AMP and then bridge them (TDA7293) and you can achieve up to 1500W (MAX) in 8 Ohm, and 2500W - 3000W (MAX) in 4 Ohm.
This will of course require some SERIOUS POWER at the input side, 8 Ohm you can do with a 1000VA 2x40V Ring-Transformer and of course a GOOD amount of capacitors >50,000uF
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Old 28th February 2012, 06:30 PM   #33
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The most you can get out of any amplifier(a little less due to the voltage drop across the output devices) with +/- 50v supply rails into 8 ohms is 156.2 watts.
Into 4 ohms this is 312.4 watts.

Therefore in a bridged (BTL) configuration this becomes 624.8 watts into 8 ohms.
At this level each transistor has to supply 17.675 amps to the load.

Lets assume for the above example that the rails are +/- 55volts (although this is over what the power opamp is rated for)and the output voltage was +/- 50v, then each transistor has to dissipate (55-50) volts*(17.675) amps= 88.375 watts per output device.

Although this is well below the power rating of the transistor, 17.675 amps is over the rated maximum current handling of 15 amps for the transistors.

Therefore it is suggested that two pairs should be used in each leg of the amplifier as well as a single one running into 4 ohms to be within the safe limits of the output devices.

In order to run this amp Bridged (BTL) into 4 ohms at 1025.6 watts, or, a single amp at 2 ohms at 624.8 watts a minimum of 4 pairs of output devices should be used on each TDA729X power opamp.

It is possible you could get more power, But Only, By using a lower impedance load and to do this you would either have to double the output pairs again or use a Paralleling technique as commonly done with chip amps and at this point stability problems could become an issue.

I do plan on getting the parts to try one of these and put it to some rigorous tests, sometime this summer though.

This technique is used to boost the current output of opamps and I have seen it used in small to medium powered amplifiers as well and headphone amps, But never one with this power capability configuration.

Cheers !!!

jer

P.S. It is very interesting and is a configuration that I myself had thought about for many years using a LM383 and a 2N3055 and 2N2955 but never got around to trying it.
National semiconductor has documented this type of amp using a LM377 and a pair of complimentary transistors in the 15 to 20 watt range back in the late 70's and early 80's.

Last edited by geraldfryjr; 28th February 2012 at 06:54 PM.
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Old 28th February 2012, 08:35 PM   #34
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Hehe think i was a little tired when i wrote that post, thanks for the correction.

Now the numbers with an input of 55V +/- on the TDA7293 (again using some simple voltage regulator input can be just under 60V, my TDA7294 is actually running 50V!!! and has been for 3+ years)

With 55V you can achieve:
---------- Normal --- Bridged
8 Ohm = 189W -- 756W
4 Ohm = 378W -- 1512W
2 Ohm = 756W -- 3024W
1 Ohm = 1512W -- 6048W
NOTE: If you use 1x Pair of transistors you will be limited to about 600W, so just to be "safe" go by the "formula" of 500W pr transistor pair, so if you want > 500W in 2 Ohm use 2x Pair Transistors, Now for Bridged power of 1000W 4Ohm you can just use 1x Pair Transistors pr AMP
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Old 28th February 2012, 09:58 PM   #35
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Yes, Very Good!

I couldn't remember off hand which chip was the higher voltage one ,TDA7293. he,he

Most would probably not push them that hard, But, I know me !!!
2.7 amps over spec is not that bad especially for occasional peaks.
But, I personally would feel more safe with the added outputs.
I am currently running my DC300a on a 1.6 ohm load and it gets quite hot at times even though its heatsink leaves much to be desired!

Keep up the Great Work and Keep on DIYin' !!!!



jer
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Old 16th March 2012, 06:13 AM   #36
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I have recently got ahold of a pair of 260va 22v transformers. How would this work under 22v? too low for this setup? im hoping i can get around 200 watt from each transformer
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Old 16th March 2012, 07:33 AM   #37
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What kind of output impedance are you planing on using?

jer
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Old 16th March 2012, 07:37 AM   #38
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22v (transformer voltage rms before rectification not including semiconductor losses) into 4 ohms would get you 121 Watts.

jer
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Old 16th March 2012, 03:20 PM   #39
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121. is that in rms?
cause i could live with that!
But is thats Max then ... amazing amount of disapointment here since it come from a amp that claims to be able to push 240 max
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Old 16th March 2012, 11:41 PM   #40
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well the watts are pretty much tied to the volts, especially if you are using 8Ohm, but if you make a bridged AMP you can get around 480W (200W+RMS) at 22V, this is of course if you use a Transformer that puts out 22V-0V-22V or 2x22V AC
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