High rail voltage and strong are different.
I would hope in the interests of clarity, he would say high rail voltage, if high rail voltage is what he meant.
But strong is ambiguous, in an electrical sense.
Precious McKenzie is strong. Kevlar, when defined by stress to weight ratio, is strong.
I would hope in the interests of clarity, he would say high rail voltage, if high rail voltage is what he meant.
But strong is ambiguous, in an electrical sense.
Precious McKenzie is strong. Kevlar, when defined by stress to weight ratio, is strong.
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in practice, bridging only gives you 2x the power and not 4x theoretical....you need to double up the power traffo in order to get a 4x power
I don't understand this "rule". In practical terms with a given load (8 ohm speaker) and a given supply voltage (12 volts) you'll get more power out of a BTL than with a non-bridged amp.
You probably won't be able to run a 2 ohm load on that BTL, or even a 4 ohm to fully double the 8 ohm rating, but you still get more power with your 8 ohm speakers because of the larger voltage swing, right?
You probably won't be able to run a 2 ohm load on that BTL, or even a 4 ohm to fully double the 8 ohm rating, but you still get more power with your 8 ohm speakers because of the larger voltage swing, right?
No it won't.
One does not get double the amperes when one halves the load impedance.
Bridging doubles the voltage swing, but only if the load impedance seen by each half of the bridged pair remains the same as it was.
If you keep the same load impedance for the bridged amplifiers as was fitted to the single amplifier then you won't get the doubled voltage and thus won't get the doubled current and won't get the quadrupled power.
Further if the amplifier is specified for a particular load impedance range and one bridges the amplifiers and now asks that pair of amplifiers to drive a lower impedance load that is outside the recommended range then there can be consequences.
The doubled power into twice the load impedance rule works, every time.
One does not get double the amperes when one halves the load impedance.
Bridging doubles the voltage swing, but only if the load impedance seen by each half of the bridged pair remains the same as it was.
If you keep the same load impedance for the bridged amplifiers as was fitted to the single amplifier then you won't get the doubled voltage and thus won't get the doubled current and won't get the quadrupled power.
Further if the amplifier is specified for a particular load impedance range and one bridges the amplifiers and now asks that pair of amplifiers to drive a lower impedance load that is outside the recommended range then there can be consequences.
The doubled power into twice the load impedance rule works, every time.
because you can use your own experiments to find that it is correct.
Whereas if you experiment with a pair of amplifiers to prove the 4times power you will find it is incorrect.
You don't have to believe me. Just prove it to your self.
Just as a reminder of the sense of the "rule" and the nonsense of the 4times power.
The bridged pair of amplifiers delivers a total output power that exactly equals the total output power of the two single amplifiers. Whereas the bridged amplifier cannot magic an extra 100% of output power from the ether.
The bridged pair of amplifiers delivers a total output power that exactly equals the total output power of the two single amplifiers. Whereas the bridged amplifier cannot magic an extra 100% of output power from the ether.
Andrew, please have a look at the spec for the QSC RMX series. It's a good illustration of what is possible in bridged mode. Ultimately current is limited, of course - and that limits the power. That's been mentioned often in this thread.
But if you can't change the load, bridged mode gives you more power and more headroom.
But if you can't change the load, bridged mode gives you more power and more headroom.
Pano,
I downloaded the QSC link.
I see 12 pairs of power figures quoted in there that show the doubled power into twice the load impedance for 11 of the pairs. There is one pair that do not meet the "rule".
I cannot see any power pairs that show a quadrupled power.
It seems that the QSC link does prove the "rule" without even doing the experiments, provided that the QSC figures are correctly stated.
I downloaded the QSC link.
I see 12 pairs of power figures quoted in there that show the doubled power into twice the load impedance for 11 of the pairs. There is one pair that do not meet the "rule".
I cannot see any power pairs that show a quadrupled power.
It seems that the QSC link does prove the "rule" without even doing the experiments, provided that the QSC figures are correctly stated.
You can double up the transformers if you wish.
The double power into twice the load impedance still rules.
Now take a single power amplifier.
It is rated at 100W into 4r0 and can reliably drive 4ohm speaker. It has it's own PSU. As an aside it will probably deliver ~60W into 8r0 and drive an 8ohm speaker 24/7 for a year and never overheat.
Now take a second identical amplifier again with it's own PSU.
Bridge this pair of amplifiers. You will get a 200W into 8r0 amplifier that is capable of drive an 8ohm speaker reliably.
What you will not get is a 400W into 4r0 amplifier and it is not specified to drive a 4ohms speaker reliably. Add on two extra PSUs, for your doubled up transformers giving a total of 4 PSUs for your bridged amplifier and it still won't be specified for driving a 4ohm speaker reliably.
The double power into twice the load impedance still rules.
Now take a single power amplifier.
It is rated at 100W into 4r0 and can reliably drive 4ohm speaker. It has it's own PSU. As an aside it will probably deliver ~60W into 8r0 and drive an 8ohm speaker 24/7 for a year and never overheat.
Now take a second identical amplifier again with it's own PSU.
Bridge this pair of amplifiers. You will get a 200W into 8r0 amplifier that is capable of drive an 8ohm speaker reliably.
What you will not get is a 400W into 4r0 amplifier and it is not specified to drive a 4ohms speaker reliably. Add on two extra PSUs, for your doubled up transformers giving a total of 4 PSUs for your bridged amplifier and it still won't be specified for driving a 4ohm speaker reliably.
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We must not be looking at the same figures, then. Just for example, see the 4 ohm power for the RMX 1450. In Stereo mode it's given as as 450W and in bridged mode 1400W (EIA). That's 3 times the power into the same load. If the power supply could deliver more current, it could be 4X.
I agree, current is ultimately limited to what your power supply can deliver. In a stereo amp run bridged, you now have a power supply that was designed for 2 channels supplying one. That helps. None the less, effective voltage available is now doubled. The power supply has to be able to keep up. But that is not a limit of BTL, that's the power supply current.
I agree, current is ultimately limited to what your power supply can deliver. In a stereo amp run bridged, you now have a power supply that was designed for 2 channels supplying one. That helps. None the less, effective voltage available is now doubled. The power supply has to be able to keep up. But that is not a limit of BTL, that's the power supply current.
From the one figure quoted, it appears that we are reading the same data.
That data supports the doubled into twice rule.
That same data does not support the quadrupled version of the rule.
I wish I knew how to import that table and pick out all the 12 pairs of power data, 11 of which support the doubled rule.
And show that 4times is NEVER achieved.
That data supports the doubled into twice rule.
That same data does not support the quadrupled version of the rule.
I wish I knew how to import that table and pick out all the 12 pairs of power data, 11 of which support the doubled rule.
And show that 4times is NEVER achieved.
Perhaps you are confusing voltage and current? A BTL delivers twice the voltage to the load. 2x voltage into the same load means 4X the power. Simple, verifiable, and old news. It's Ohm's law. Basta.
Now, on the practical side, is the power supply up to the task? Are the output transistors and the heat-sinks big enough? Not always, but they could be designed to be up to the task of the extra power. The reason we don't see the bridged ratings of commercial amps hitting 4X the power of non-bridged mode is simply the limitation of the power supply, output devices and heat sinks. You don't want to burn up the amp, and you might running 4X the power..
But an amp that was designed for BTL only could have enough power supply, enough heat-sink, big enough output devices. If it did, then it would have 4X the power of an un-bridged amp running off the same PSU voltage. There are a lot of low voltage (5V, 12V) amps designed that way. They use BTL mode to squeeze the most they can out of the limited voltage, and then size the components appropriately for the power.
There are two parts to the answer, both important.
Now, on the practical side, is the power supply up to the task? Are the output transistors and the heat-sinks big enough? Not always, but they could be designed to be up to the task of the extra power. The reason we don't see the bridged ratings of commercial amps hitting 4X the power of non-bridged mode is simply the limitation of the power supply, output devices and heat sinks. You don't want to burn up the amp, and you might running 4X the power..
But an amp that was designed for BTL only could have enough power supply, enough heat-sink, big enough output devices. If it did, then it would have 4X the power of an un-bridged amp running off the same PSU voltage. There are a lot of low voltage (5V, 12V) amps designed that way. They use BTL mode to squeeze the most they can out of the limited voltage, and then size the components appropriately for the power.
There are two parts to the answer, both important.
the reason why AndrewT keeps on insisting that 4x power is unrealizeable is because of the power traffo limitations of the 2 channel amp...
say a 2 channel amp is rated at 100 watts at 8ohms....
now if you bridge them, they will see 4 ohm loads each...
the amplifier rails therefore sags such that the output voltage is lesser, thus no 4x
the 4x power can be realised if the rails can be held to be same as that for the 8ohm case...
in automotive, the 12volt rails is held constant because of the battery, thus a 5watt chip when bridged can produce 20 watts of power...
i hope i made myself clear.....basta....
say a 2 channel amp is rated at 100 watts at 8ohms....
now if you bridge them, they will see 4 ohm loads each...
the amplifier rails therefore sags such that the output voltage is lesser, thus no 4x
the 4x power can be realised if the rails can be held to be same as that for the 8ohm case...
in automotive, the 12volt rails is held constant because of the battery, thus a 5watt chip when bridged can produce 20 watts of power...
i hope i made myself clear.....basta....
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