I'm trying to figure out if I can "bridge" two channels of the SAME chip amp to increase output power. The device in question is the TDA7575B. It has 2 channels. The inputs are differential type. Can I somehow wire these two channels together to drive one 4 ohm sub? Thank you in advance!
That chip, each output is already "two outputs bridged".
Bridging bridged outputs does not make sense.
Even paralleling the outputs (not in the datasheet and possibly risky) would not significantly increase the power output for 4 Ohms.
If 17 Watts in 4 ohms is not enough, use something higher than 13V power.
You "could" get a car subwoofer with two 4-ohm coils, and approach 34 Watts. Double power is NOT double-loud, and often disappointing. You should be looking to 60W systems.
Bridging bridged outputs does not make sense.
Even paralleling the outputs (not in the datasheet and possibly risky) would not significantly increase the power output for 4 Ohms.
If 17 Watts in 4 ohms is not enough, use something higher than 13V power.
You "could" get a car subwoofer with two 4-ohm coils, and approach 34 Watts. Double power is NOT double-loud, and often disappointing. You should be looking to 60W systems.
Doubling cone area is a very effective way to gain "thud". Two 4-ohm woofers would load-up that amp and be a satisfying gain in boom. Does mean a double-size box.
Thanks for your response.
The subs are factory subs in special enclosure in the car in the floor under the seat so they can't be easily replaced or altered. And since it's the car I can't increase the voltage without adding some kind of boost converter.
The original amp chip is rated at 70W / 4 ohms single channel. Anyone know of a good equivalent? Has to have differential input.
The subs are factory subs in special enclosure in the car in the floor under the seat so they can't be easily replaced or altered. And since it's the car I can't increase the voltage without adding some kind of boost converter.
The original amp chip is rated at 70W / 4 ohms single channel. Anyone know of a good equivalent? Has to have differential input.
You can combine multiple chip-amps' contributions using an output transformer to get more power. But I'm not sure if you can tolerate the bulk or weight of a transformer in an automobile application.
What do you know about the subwoofers? I've seen OEM under the seat subs that had an oddball impedance like 1.6 ohms. This was driven by a bridged digital amp, with differential input. In fact, all OEM subs I've seen have been driven by a bridged digital amp with differential input.
So don't assume that the subs are 4 ohms. Also,you can drive a single ended input amplifier with one leg of the differential signal. You will pay a noise penalty but it might be inconsequential with a subwoofer.
Measure the DC resistance of the subs and add 15% to get an idea of their actual impedance. If they're 2 ohms or below, you can find a cheap digital amp that can deliver at least 60 watts to each sub.
So don't assume that the subs are 4 ohms. Also,you can drive a single ended input amplifier with one leg of the differential signal. You will pay a noise penalty but it might be inconsequential with a subwoofer.
Measure the DC resistance of the subs and add 15% to get an idea of their actual impedance. If they're 2 ohms or below, you can find a cheap digital amp that can deliver at least 60 watts to each sub.
> chip is rated at 70W / 4 ohms single channel.
Read the specs carefully.
http://www.st.com/content/ccc/resou...df/jcr:content/translations/en.CD00175174.pdf
The "70 Watt" number is for 2 Ohms, and further has a footnote which turns out to say "saturated SQUARE wave output".
The SINE output is 37W in 2 Ohms or 22W in 4 Ohms. The 22W number is essentially my 17W number except they use the awful high voltage "14.4V" to take the reading. Modern cars and their low-maint batteries run closer to 13V. I don't even like 14.5V on my tractor's batt.
Electrically, what it gives is all you can do with your existing impedance and battery voltage. The next step IS boosted power supply or different woofers of silly low impedance.
> The subs are factory subs
I would expect these speakers are designed FOR the power you already have. Power handling (voice coil area and cone excursion) is *expensive*. Car makers have to make every part as good as it needs to be, and NO gooder, or they will go broke.
The next step after a good factory car-sound IS to go to the boom shop and buy the big finned boxes and dedicated car subwoofers. I fought this in my Honda, was starting to go for two 12" woofs firing through the back seat armrest hole, but it all got too messy for me.
Read the specs carefully.
http://www.st.com/content/ccc/resou...df/jcr:content/translations/en.CD00175174.pdf
The "70 Watt" number is for 2 Ohms, and further has a footnote which turns out to say "saturated SQUARE wave output".
The SINE output is 37W in 2 Ohms or 22W in 4 Ohms. The 22W number is essentially my 17W number except they use the awful high voltage "14.4V" to take the reading. Modern cars and their low-maint batteries run closer to 13V. I don't even like 14.5V on my tractor's batt.
Electrically, what it gives is all you can do with your existing impedance and battery voltage. The next step IS boosted power supply or different woofers of silly low impedance.
> The subs are factory subs
I would expect these speakers are designed FOR the power you already have. Power handling (voice coil area and cone excursion) is *expensive*. Car makers have to make every part as good as it needs to be, and NO gooder, or they will go broke.
The next step after a good factory car-sound IS to go to the boom shop and buy the big finned boxes and dedicated car subwoofers. I fought this in my Honda, was starting to go for two 12" woofs firing through the back seat armrest hole, but it all got too messy for me.
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So I measured the resistance. Its too much work to get to the speaker itself so I disconnected it's wires on the amplifier and measured it there. It reads 2.7ohms.im assuming it's a 4ohm speaker. Also done some reaserch online, most people who have this car also claim its a 4 ohm.
I got my hands on some TDA1562Q amps, will give them a try...
I got my hands on some TDA1562Q amps, will give them a try...
the maximum output from an amplifier is very roughly one third of the supply voltage when driving a high impedance load.
That gives you a maximum of 4Vac from a 12Vdc supply.
If you bridge a pair of amplifiers you can get a doubling of output voltage, but each amplifier has to be rated for half the load impedance.
Now apply a 4ohms load to that bridged amplifier. Each half amplifier has to drive 2ohms. The maximum output voltage may be 60% of the high impedance output.
So the bridged result is 4V*60% *2 = ~4.8Vac into 4ohms i.e. 5.8W (most manufacturers claim 6W into 4ohms for sensible no clipping and low distortion).
If you allow 10% distortion which implies severe clipping, then you may see claimed outputs of around 10W to 12W from 12Vdc. If the 2ohms loading per half amplifier allows 70% of the maximum then the output increases to ~8W into 4ohms when fed from 12Vdc.
That is all you can get out of a bridged car amp fed with 12Vdc. Pure science and no magic.
If you want/need more power, then you have to feed the amplifiers with more voltage.
That gives you a maximum of 4Vac from a 12Vdc supply.
If you bridge a pair of amplifiers you can get a doubling of output voltage, but each amplifier has to be rated for half the load impedance.
Now apply a 4ohms load to that bridged amplifier. Each half amplifier has to drive 2ohms. The maximum output voltage may be 60% of the high impedance output.
So the bridged result is 4V*60% *2 = ~4.8Vac into 4ohms i.e. 5.8W (most manufacturers claim 6W into 4ohms for sensible no clipping and low distortion).
If you allow 10% distortion which implies severe clipping, then you may see claimed outputs of around 10W to 12W from 12Vdc. If the 2ohms loading per half amplifier allows 70% of the maximum then the output increases to ~8W into 4ohms when fed from 12Vdc.
That is all you can get out of a bridged car amp fed with 12Vdc. Pure science and no magic.
If you want/need more power, then you have to feed the amplifiers with more voltage.
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Math is real-good up to here.
> 70% of the maximum then ... ~8W into 4ohms when fed from 12Vdc
"70%" is a fair value for arbitrary power voltage design. It is easier to allow some sag than to optimize for a lower voltage.
In car-sound we can not (readily) change supply voltage. Most good car-sound amp chips show near 1V loss, far less than the 70% sag we see in wall-power work.
The "12V" battery is 12.6V resting and reliably 13V-14V when the engine is running, the most common play condition. Historically higher voltage were used. "14.4V" somehow became engrained in car-sound tests. While that is awful high for modern low-water batteries, that is a number you see.
And while I use "one third" all the time, the true value of 1/2.828 is nearer 0.35.
Take 14.4V assumed battery voltage. Deduct 1V for chip loss, 13.4V. 4.7V Sine RMS. Double for bridge. 9.5V Sine RMS. In 4 Ohms, this really can be 22 Watts just below clipping.
A lesser class of chips omits boot-strapping (or full complementary power process), loses 2V-3V, makes 16W at clipping.
For marketing, everybody cites 10% THD (which is significant clipping) for another 20% more Marketing Power.
In real cars (without hot-rod electric systems) the regulator aims well below 14V so the battery does not bubble, the wire to the radio is thin-gauge, and you may well dip to 12V on the booms. About 12W in 4 Ohms.
As you say, bridging a bridge is NOT possible without an isolated battery, and NO amount of little tinkers will make much of a difference. Running fat B and G cables directly to 1F cap and amp may gain a fat dB. Anything past a good factory radio does "feed the amplifiers with more voltage" from a step-up converter. You can buy whole 1,000W (OK, 750 true W) finned-boxes far cheaper than you can buy part of the parts.
> 70% of the maximum then ... ~8W into 4ohms when fed from 12Vdc
"70%" is a fair value for arbitrary power voltage design. It is easier to allow some sag than to optimize for a lower voltage.
In car-sound we can not (readily) change supply voltage. Most good car-sound amp chips show near 1V loss, far less than the 70% sag we see in wall-power work.
The "12V" battery is 12.6V resting and reliably 13V-14V when the engine is running, the most common play condition. Historically higher voltage were used. "14.4V" somehow became engrained in car-sound tests. While that is awful high for modern low-water batteries, that is a number you see.
And while I use "one third" all the time, the true value of 1/2.828 is nearer 0.35.
Take 14.4V assumed battery voltage. Deduct 1V for chip loss, 13.4V. 4.7V Sine RMS. Double for bridge. 9.5V Sine RMS. In 4 Ohms, this really can be 22 Watts just below clipping.
A lesser class of chips omits boot-strapping (or full complementary power process), loses 2V-3V, makes 16W at clipping.
For marketing, everybody cites 10% THD (which is significant clipping) for another 20% more Marketing Power.
In real cars (without hot-rod electric systems) the regulator aims well below 14V so the battery does not bubble, the wire to the radio is thin-gauge, and you may well dip to 12V on the booms. About 12W in 4 Ohms.
As you say, bridging a bridge is NOT possible without an isolated battery, and NO amount of little tinkers will make much of a difference. Running fat B and G cables directly to 1F cap and amp may gain a fat dB. Anything past a good factory radio does "feed the amplifiers with more voltage" from a step-up converter. You can buy whole 1,000W (OK, 750 true W) finned-boxes far cheaper than you can buy part of the parts.
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