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Old 2nd September 2011, 04:10 AM   #61
trevmar is offline trevmar  United States
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Quote:
Originally Posted by rickedd46 View Post
My speakers are 3 ohms and I'm looking to parallel bridge a pair of these per channel. What's the recommended resistor values and wattage I should use?
Where were you contemplating putting these resistors? Each module of the L20D is capable of driving 3 ohms, but they have a maximum average output current capability of about 6 amps (at 70C). That would mean approx (6 / 1.414) x (6 / 1.414) x 3 = 54watts maximum into 3 ohms, and you would want to keep the supply voltage at a minimum, say 50-0-50 volts or so, (so as to reduce dissipation in the IRFI4020). Is 54 watts enough for you?

There may be amplifiers more suitable for that 3 ohm load. Have you looked at the T2, T3 and T4 from HifimeDIY? Unfortunately their website seems to be down at this moment. But there are plenty of discussion threads here on diyAudio
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Old 2nd September 2011, 04:13 AM   #62
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Originally Posted by 454Casull View Post
What's the PSRR on this amp?
Anyone?
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Old 2nd September 2011, 04:20 AM   #63
trevmar is offline trevmar  United States
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Originally Posted by 454Casull View Post
PSRR Anyone?
Below is the PSRR graph from the reference design data sheet " iraudamp7s.pdf "
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Old 2nd September 2011, 04:24 AM   #64
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Cool, thanks.
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Old 2nd September 2011, 02:47 PM   #65
ljm_ljm is offline ljm_ljm  China
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Quote:
Originally Posted by rickedd46 View Post
Hello,

My speakers are 3 ohms and I'm looking to parallel bridge a pair of these per channel. What's the recommended resistor values and wattage I should use?

Thanks.
We can not violate the principle of Ohm's law.

L20D in the case of 8 ohms (about +-63V DC) power can output 200W, 5A approximate.

However, in 4 European time, to achieve the same power, the current takes about to 7A, the voltage only need about +-50V.

The BTL can not increase the output current, which can increase the output voltage.

I suggest you reduce the transformer voltage, and improve the current transformer.

With L15D or L15DX2, since they are original in IRAUDAMP7S-150. In the case of 4 ohms 250W power output (+-50V)
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Old 2nd September 2011, 02:59 PM   #66
ljm_ljm is offline ljm_ljm  China
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Originally Posted by trevmar View Post
Where were you contemplating putting these resistors? Each module of the L20D is capable of driving 3 ohms, but they have a maximum average output current capability of about 6 amps (at 70C). That would mean approx (6 / 1.414) x (6 / 1.414) x 3 = 54watts maximum into 3 ohms, and you would want to keep the supply voltage at a minimum, say 50-0-50 volts or so, (so as to reduce dissipation in the IRFI4020). Is 54 watts enough for you?

There may be amplifiers more suitable for that 3 ohm load. Have you looked at the T2, T3 and T4 from HifimeDIY? Unfortunately their website seems to be down at this moment. But there are plenty of discussion threads here on diyAudio
.
Very correct

Lower impedance, the same power needs of a larger current, which has a huge MOSFET ID requirements, and output inductor are also a great test.

But it needs the power supply voltage also reduces the requirements.

In fact the most important thing is we know we need power.
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Old 2nd September 2011, 06:53 PM   #67
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Quote:
Originally Posted by trevmar View Post
Where were you contemplating putting these resistors? Each module of the L20D is capable of driving 3 ohms, but they have a maximum average output current capability of about 6 amps (at 70C). That would mean approx (6 / 1.414) x (6 / 1.414) x 3 = 54watts maximum into 3 ohms, and you would want to keep the supply voltage at a minimum, say 50-0-50 volts or so, (so as to reduce dissipation in the IRFI4020). Is 54 watts enough for you?

There may be amplifiers more suitable for that 3 ohm load. Have you looked at the T2, T3 and T4 from HifimeDIY? Unfortunately their website seems to be down at this moment. But there are plenty of discussion threads here on diyAudio
.
Thanks for replying.

I'm thinking about tying 2 outputs per channel with resistors. I have a +/-70V PS from a Soundcraftsmen PM860 (8.5A). It provides plenty of current. I have run a pair of PM860s bridged at 4 ohms pushing subwoofers at a party without problems.

I don't have a +/-50V PS.
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Old 2nd September 2011, 07:56 PM   #68
trevmar is offline trevmar  United States
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Originally Posted by rickedd46 View Post
I'm thinking about tying 2 outputs per channel with resistors. I have a +/-70V PS from a Soundcraftsmen PM860 (8.5A). It provides plenty of current.
Whatever amplifier module you choose will have significant excess heat dissipation from such a high supply. The L20D should be able to handle it OK, but few of the others will.

Ljm_ljm warned the inductor might saturate, but the 1D17A-220M inductor (clone) used in the L20D is capable of handling 6 Amps average, from a heat perspective, while its peak (saturating) current is way higher, at about 15A.

So the key element is the output transistor, the IRFI4020-117.
If it is a clear day, and the wind is blowing in the right direction, and you keep the heatsink really cool, this part is rated at 9 Amps continuous, 36 Amps peak. The 9 average amps falls to 6 Amps as the transistor heats to 100 degrees C. If you decide to push the L20D to its limits, you will get about 120W continuously out of each module.

I guess it is possible to bridge two modules using high-power resistors, but, as a designer, this is not something I would want to do. There are many complex issues involved, including feedback loop stability.

The first thing I would do is measure the actual impedance of the load (subwoofer?). I most cases it will be higher than 3 ohms around the enclosure resonances, which is where most of the power probably lies. If this is the case then one L20D will be able to safely drive the 120W average level, with occasional peaks easily reaching 250W.

Note: YMMV - Your mileage may vary - I haven't tested the L20D below 4 ohms.
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Old 2nd September 2011, 11:25 PM   #69
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Thanks trevmar,

I'm ok with dissipation. I'm actually pulling the output board from the amplifier which is fan cooled and dropping these in. I got to figure how insert the temperature sensing transistors into the L20D heat sinks. I will follow your advise and use one per channel and see what I get.
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Old 3rd September 2011, 01:47 AM   #70
ljm_ljm is offline ljm_ljm  China
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Add a small fan active ventilation devices, reducing the MOSFET and the inductor temperature, you can get more power margin range.

This is a very simple way, can be installed on top of the radiator, while reducing the heat sink MOSFET, and the inductor temperature.

But may bring some fan noise.
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