| DonoMan |
This is probably a stupid question, but here goes...
I want to make a linkwitz transform circuit for a sub in my car. I have no problem getting the circuit designed with the spreadsheet. But the problem is that I only have a +12v supply and the signal is AC. Linkwitz transform amplifies DC, so if I just put a 6v bias, I should get 12v out. Is there a simple way to handle this that I'm just not noticing, or do I want a 12v to -12v inverter, or what? |
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| richie00boy |
Sorry but you have completely the wrong idea about the power supply and also about what the Linkwitz Transform does.
What you need is a split supply of something like +/-12V. Have a look on the ESP website for how to make a negative rail using a 555 timer. |
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| DonoMan |
| Er... I was exactly asking if that's what I should do. And I didn't even say what I think a linkwitz transform is for, but it DOES happen to amplify DC. |
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| richie00boy |
Er... you talked about having a 12v power supply then the signal being AC. That to me said you were getting confused. Then you said about putting 6v bias on and getting 12v out. This would only happen if the gain of your Linkwitz Transform was 2, unlikely.
Sorry just commenting on what I saw. You have your answer anyway. |
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| janneman |
| quote: | Originally posted by richie00boy
Er... you talked about having a 12v power supply then the signal being AC. That to me said you were getting confused. Then you said about putting 6v bias on and getting 12v out. This would only happen if the gain of your Linkwitz Transform was 2, unlikely.
Sorry just commenting on what I saw. You have your answer anyway. |
I don't know what a Linkwitz Transform is (cross over filter?) but I guess what he needs is power for some kind of opamp circuit from his 12V battery. Normally that is done by biasing the opamp circuitry at midpoint (here 6V) and then capacitively coupling the signal.
However, without an actual circuit this discussion can go on and on without getting anywhere. Where's the circuit?
Jan Didden |
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| DonoMan |
| I thought it was pretty clear, but never mind, I'll just use a 12v to -12v converter |
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| richie00boy |
| You can make a pseudo rail by biasing at the midpoint, but with the possibility of the supply dropping to maybe 10v occasionally it may cause the op-amp to latch to one of the supply extremes. It also offers very little headroom, and the LT with large DC gain needs headroom. |
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| DonoMan |
I got a message from someone saying that LT isn't as useful for a car, so I figured I'd explain why I'm using one.
I have a Camaro, my sub box is a "stealth box" in the corner of the back hatch, about .6cuft, sealed. I'm using an Eclipse SW8200 which likes a lot of volume. Gives a severe hump at 64Hz and rolls off early. LT is an absolute necessity in this case. |
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| mikee55 |
Just my 2 pence worth. I used a Linkwitz Transform from the Linkwitz site in my car. Basicaly I used the 2 opamp circuit after a 24 db lowpass filter. I wasn't able at that time to measure my driver so I used the same component values that Mr Linkwitz used. I also used some variable resistors instead of fixed so I could see what happened when I tried to tune the system.
The circiut was fed to my Alpine Bass Engine amp. It is a 2 ohm stable amp that bridged and fed a 4ohm SPLX 12" driver, ( this driver has now been measured and is Transformed nicely, thankyou richie000boy). I put the driver in a 40 litre box as per Mr Linkwitz's Thor and powered the circuit straight from the inside of the amp. Most car amps I found so far have a high voltage split rail supply for the amplifier and the bridge/crossover circuits that use op-amps have a low voltage supply. Any multimeter should help you find +/- 15 volts or so or Mr Rod Elliott of Elliott Sound Products has a nice simple 555 ic power inverter as per richie000boy's suggestion, I did before I dived into my amp for its supply.
Even though a Linkwitz Transform isn't ideal for car use as some say, I found it enjoyable only because I get a buzz the lower the bass goes. The cone flapped madly and I often had distortion but I didn't care.
Cheers mikee55 |
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