The algebra is clear: Pout = E^2 * load resistance, where E=output voltage.
Double output voltage, in same load, is 4* power. Do you understand this?
As I said, the amp now has to deliver double the current: instead that the other side of the speaker load is at ground, it is now at the OTHER amp output which is the same voltage as THIS amp but on 'the other side of ground'. Since current = voltage / load resistance, and the voltage across the load is now double, the amps have to deliver double current, so it is 'as if' they see half the load resistance. So before bridging check that your amp can handle half the load of what you intend to use. If you want to use an 8 ohms speaker, make sure the amps can handle 4 ohms. If you want to use 4 ohms speakers, make sure your amps can handle 2 ohms.
BTW Your speakers are now 'floating' and not connected to ground, is that clear?
BTW2 Andrew has pointed out that when you bridge the amp, because it 'sees' half the load, it most probably cannot give out the same max output voltage than unbridged, so the output power doesn't quite quadruple. Instead of 4*150W you may get 'only' 550W. But that depends on the power supply.
jd
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nooooooooo ....Output volts is x2 so is nominal load shared across the two amps
I'd keep this simple at first and just do the one amp and work forward from there.
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Look, draw it out. No bridging, you have x volts output on one side of the speaker, other side is at ground. With bridge, you have still x volts on one side of the speaker, but now you have -x on other side of the speaker. So, total voltage across speaker is 2x.
jd
HI,
I am very glad that ur interested in my small project ....... in the bias config even if the wiperpot goes open still the bias hold on few mA higher than the original selected because i originally designed the circuit with the 2 diodes in place then I thought that
by put in transistor and a trimmer i can control the bias then why not ............ so even if the wiper pot goes open I don;t think the o/p will blow up neways i am very unexperienced considered to u so always do pont out my mistakes......
i am the uploading the sim pictures feel free to point out any form modification
WIPER OPEN
An externally hosted image should be here but it was not working when we last tested it.
WIPER OK
An externally hosted image should be here but it was not working when we last tested it.
regards
sekhar
You changed the load from 4 ohms to 8 ohms. That halved the power again.
25V in 4 ohms = 156
50V in 4 ohms = 635
jd
Bias and Bridging solutions
I quit using adjustable bias years ago. Try a string of Schottky diodes to bring up the bias. Attach to a power transistor or on heat sink very near transistor. Extremely reliable! Going to be probably 6 or 7 Schottky diodes in series. Of course regular silicone diodes may be used in the string on a very limited basis for different bias values and low value resistor (less than 5 ohms).
If you use amp in bridge mode operate second channel as a unity gain inverter of the first channels output. I mean unity also and not 0.995 or 1.005 times- I mean 1.000. Here, a small pot in series with resistor can be very useful for trimming gain to 1.000. Sound will be much better when trimmed to unity, much better!
I quit using adjustable bias years ago. Try a string of Schottky diodes to bring up the bias. Attach to a power transistor or on heat sink very near transistor. Extremely reliable! Going to be probably 6 or 7 Schottky diodes in series. Of course regular silicone diodes may be used in the string on a very limited basis for different bias values and low value resistor (less than 5 ohms).
If you use amp in bridge mode operate second channel as a unity gain inverter of the first channels output. I mean unity also and not 0.995 or 1.005 times- I mean 1.000. Here, a small pot in series with resistor can be very useful for trimming gain to 1.000. Sound will be much better when trimmed to unity, much better!
Original design was pretty good
I liked your original design except use complementary pair output stage and no gain on the output stage so it is emitter follower. I do not like gain in output stage unless load is well defined because gain there places load into the gain circuit. This means it is feedback only making circuit work. Circuit will not work with load without feedback because gain is not stable. I like amplifier to work without feedback first. Then proper feedback can only make it better.
I liked your original design except use complementary pair output stage and no gain on the output stage so it is emitter follower. I do not like gain in output stage unless load is well defined because gain there places load into the gain circuit. This means it is feedback only making circuit work. Circuit will not work with load without feedback because gain is not stable. I like amplifier to work without feedback first. Then proper feedback can only make it better.
hey sumaudioguy,
I am nt quit familiar with the type of bias setting ur recommending kindly help me understand is it in this manner that the diodes r supposed to sit on the main heat sink so that when the transistors heat up the conductivity of the diodes reduce and in turn they reduce the bias of the output transistors.....correct if iam wrong I have placed a ciruit kindly look at it and tell me is it done right or wrong .......& which schottky diode to use which one is most commonly avaiable ............
And bout using the 2nd amp at unity gain ........... how i am supposed to do it plz give a block diagram with the component values and tell me how does it work better than a normal bridge config,
REgards
Sekhar
I am nt quit familiar with the type of bias setting ur recommending kindly help me understand is it in this manner that the diodes r supposed to sit on the main heat sink so that when the transistors heat up the conductivity of the diodes reduce and in turn they reduce the bias of the output transistors.....correct if iam wrong I have placed a ciruit kindly look at it and tell me is it done right or wrong .......& which schottky diode to use which one is most commonly avaiable ............
And bout using the 2nd amp at unity gain ........... how i am supposed to do it plz give a block diagram with the component values and tell me how does it work better than a normal bridge config,
REgards
Sekhar
forgot the circuit
An externally hosted image should be here but it was not working when we last tested it.
let's suppose you have a pair of 150W into 4r0 amplifiers and you also have a 500W peak capability 86dB/W @ 1m speaker that is 8ohms.
Use the existing amps or go and buy a new one?
Using the existing amp (~90W into 8r0) driving the speaker you can get ~97dB @ 2.5m
Bridge a pair (~300W into 8r0) and you can increase the maximum SPL to ~102dB @ 2.5m.
That is 5dB extra. It has cost next to nothing.
Note that 300W is NOT 4times 90W These figures are for a 4ohm capable amp that drops 0.8dBV when changing from 8r0 to 4r0. Some amps will be more than 0.8dBV and some less than 0.8dBV. Most of my amps are in the region of -0.3dBV to -0.6dBV going from 8r0 to 4r0 and I don't have any 4ohm speakers.
Use the existing amps or go and buy a new one?
Using the existing amp (~90W into 8r0) driving the speaker you can get ~97dB @ 2.5m
Bridge a pair (~300W into 8r0) and you can increase the maximum SPL to ~102dB @ 2.5m.
That is 5dB extra. It has cost next to nothing.
Note that 300W is NOT 4times 90W These figures are for a 4ohm capable amp that drops 0.8dBV when changing from 8r0 to 4r0. Some amps will be more than 0.8dBV and some less than 0.8dBV. Most of my amps are in the region of -0.3dBV to -0.6dBV going from 8r0 to 4r0 and I don't have any 4ohm speakers.
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