I was planning to use a 3886 setup for car audio use, and was wondering what voltage would give best performance. I can't seem to find a pattern on output power vs input voltage when ya bridge/parallel the setup.
The amp will be 2 channel, with one inverted with reverse polarity, so it could be used for either stereo or a single sub channel bridged.
I'll probably use 3 chips per channel, and can't decide where to go between 35v which is recommended in that BPA200/PAR100 guide for 2 chips into 4 ohm, or up towards 42v which is what they used for the 4 chip bridged.
I've read that around 45volts is about the max they can do, so i could even try that, but i think it would be overkill.
The amp will be 2 channel, with one inverted with reverse polarity, so it could be used for either stereo or a single sub channel bridged.
I'll probably use 3 chips per channel, and can't decide where to go between 35v which is recommended in that BPA200/PAR100 guide for 2 chips into 4 ohm, or up towards 42v which is what they used for the 4 chip bridged.
I've read that around 45volts is about the max they can do, so i could even try that, but i think it would be overkill.
I've made an excel speardsheet where you put in supply voltage and max power dissipation per chip (around 30w into 8 ohms for normal applications) and you get power into 8, 4 and lowest ohm and number of chips needed for both parallell and bridged configuration. Check it out and see if tou have any help from it.
How do you get the voltage you need from a car?
How do you get the voltage you need from a car?
I'll use a SMPS through a toriod to get the rails, but it means i only get one pair of positive and negative, so yeah, have to decide on voltage.
What voltage
Immo_G
How are you going to have 3 chipos per. channel if you go for the bridged/parallel version.......you need at leat four or maybe you mean 6 in total ??
To the question about what voltage. My expirence say that you should only go past the 35 V if you REALLY NEED it.
You can also look at it form an other side, i.e. the idle power disipation.
Let say you go for the bridged/parellel verison with 4 chips. Each chip have a idle current of 50-80 mA. Let just say 50 to 60 mA to be nice. This means that you have a idle currnet of around 200 to 240 mA.
Using the +/- 35 V you have a idle dissipation of 70 x 0,2 = 14 W.
or 70 x 0,24 = 16.8 W.
Let's say that you are "unlucky" and have four chips with a idle current fo 80 mA and you go for the +/- 44 V (mac. voltage). You then have 88 x 0,32 = 28,16 W idle !?!?!?!
30 W in idle is not directly scary, but in my book it is stil so high that you have to give it an extra thought.
So you have to ask your self. How do I get all this heat away from the chips ??.....................................
I am not too familiar with car-stereo, but it seems like most car-speakers are farely low impedance to take advance of the high current/low voltage present in a car.
If you go for a bridged version, just remember that each part of the bridge only "see" half the impedance.
So if you put on a 4 ohm speaker, each part in driving a 2 ohm load. (and THAT will for sure NOT be possible if you are using the +/- 44 V unless you have a serious number of chips in parallel !!)
It is up to you what way to go, but I hope my comment have given you some "inspiration".
Thomas (maker of DAS MODUL)
Immo_G
How are you going to have 3 chipos per. channel if you go for the bridged/parallel version.......you need at leat four or maybe you mean 6 in total ??
To the question about what voltage. My expirence say that you should only go past the 35 V if you REALLY NEED it.
You can also look at it form an other side, i.e. the idle power disipation.
Let say you go for the bridged/parellel verison with 4 chips. Each chip have a idle current of 50-80 mA. Let just say 50 to 60 mA to be nice. This means that you have a idle currnet of around 200 to 240 mA.
Using the +/- 35 V you have a idle dissipation of 70 x 0,2 = 14 W.
or 70 x 0,24 = 16.8 W.
Let's say that you are "unlucky" and have four chips with a idle current fo 80 mA and you go for the +/- 44 V (mac. voltage). You then have 88 x 0,32 = 28,16 W idle !?!?!?!
30 W in idle is not directly scary, but in my book it is stil so high that you have to give it an extra thought.
So you have to ask your self. How do I get all this heat away from the chips ??.....................................
I am not too familiar with car-stereo, but it seems like most car-speakers are farely low impedance to take advance of the high current/low voltage present in a car.
If you go for a bridged version, just remember that each part of the bridge only "see" half the impedance.
So if you put on a 4 ohm speaker, each part in driving a 2 ohm load. (and THAT will for sure NOT be possible if you are using the +/- 44 V unless you have a serious number of chips in parallel !!)
It is up to you what way to go, but I hope my comment have given you some "inspiration".
Thomas (maker of DAS MODUL)
Yeah what i intended by 3 chips per chan, was to have 2 channels, running 3 chips in parallel on each, with the option of bridging both together into 1 higher powered channel.
I wanted to go 3, to give a tad more overhead if needed, and also to spread out the heat dissipation. Also when bridged , the load might not stay above 4 ohms the whole time, and i wanted some safety there.
I hadn't considered the idle current issue, i'll probably have this amp fan cooled anyway, so 30 watts isn't an issue.
I might try ~ 35 volt area, to give a nice mix, though i'll do some more research on what sorta output i'll be needing, no point having 150 watts per chan if i only use 20
I wanted to go 3, to give a tad more overhead if needed, and also to spread out the heat dissipation. Also when bridged , the load might not stay above 4 ohms the whole time, and i wanted some safety there.
I hadn't considered the idle current issue, i'll probably have this amp fan cooled anyway, so 30 watts isn't an issue.
I might try ~ 35 volt area, to give a nice mix, though i'll do some more research on what sorta output i'll be needing, no point having 150 watts per chan if i only use 20
Hello to all, this is my first post here, but I've been interested in building my own amp for car use. I was wondering how did you step the car voltage up that high. Is it a simple circuit that I can construct. Please forgive my ignorance, I know a little about electronics, but notices I said a "little".
I run bridged LM3886s at 42V in one of my amps.
It took LOTS of time/effort to work out how to cool the buggers at that voltage.
I found that mica or silicone-rubber insulation pads were the biggest problem. They were generating too much of a temp drop and causing the ICs to overheat.
In the end i didnt use any insulation and made the heatsinks live.
Was worth it though, the amp does 220W RMS into 8Ohms before clipping.
The amp is about 3yrs old now and still going strong at that voltage.
It took LOTS of time/effort to work out how to cool the buggers at that voltage.
I found that mica or silicone-rubber insulation pads were the biggest problem. They were generating too much of a temp drop and causing the ICs to overheat.
In the end i didnt use any insulation and made the heatsinks live.
Was worth it though, the amp does 220W RMS into 8Ohms before clipping.
The amp is about 3yrs old now and still going strong at that voltage.
Yeah i've heard the cheap insulators are a joke, and that the isolated 3886's just can't do the power without overheating.
Live heatsinks is tempting for my use, except that as a car amp, it'll be in a car boot, and stuff could roll against it, as I was going to use long heatsinks as the sides of the amp. Also the sinks would be used for the PSU mosfets, though i could isolate them, anyone know if this could cause some bad crosstalk?
I'll probably go with 35 volts, or whatever close to that works out as a nice multiple of the 12-14v (36-42v maybe).
Now i just gotta find some sg3524's here in aus to get started.
Live heatsinks is tempting for my use, except that as a car amp, it'll be in a car boot, and stuff could roll against it, as I was going to use long heatsinks as the sides of the amp. Also the sinks would be used for the PSU mosfets, though i could isolate them, anyone know if this could cause some bad crosstalk?
I'll probably go with 35 volts, or whatever close to that works out as a nice multiple of the 12-14v (36-42v maybe).
Now i just gotta find some sg3524's here in aus to get started.
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