Power supply for a active summing block.
I had been posting about a problem with my car amp and sub in Loudspeakers forum "My almost finished sub" , and the thread went to deep into amplifier so I start a new thread here to ask u guys about the non speakers stuff.
Ok, the following picture is the summing block I am going to build. However, how do I build a power supply for it to use in a car, and how do I determine what gain I want? I used some info form my CHy Moy headphone amp knowledge to draw this, so I am not sure will this work for car audio. Plz give me some advices.
All you have to do is make a voltage divider with two equal resistors, filter them with capacitors, and use the node where they join as your reference voltage.
(See the attached scan)
Choose identical resistor values that draw significantly more current than the IC's you are using, so the referance voltage will be stable. I usually used 100 ohms, but values as high as 1k could be reasonable for a low current IC. 100 ohms will be sufficient to easily run a couple of quad amps. Be sure the power rating for the resistor is adequate for the current it will draw.
A more precise supply can be made using op amps to derive the reference, but they will have to handle the supply current through their outputs. Besides, there's really no need to complicate things for this type of job.
This supply will leave a DC component in the output signal, simply use a decoupling capacitor in series with the output of the last IC to eliminate that.
You can use a transistor or relay in front of the divider to switch the supply on/off with the remote lead.
As far as the summing circuit goes, I've always been more comfortable summing into the inverted input because of it's virtual ground characteristic. Without the benefit of test equipment to verify performance, I feel this is the best way to ensure other impedances are influencing the circuit as little as possible.
I have been known to be wrong.
If you choose to use the inverted method, simply use an inverting follower for your output buffer. You can use that for your gain stage as well, if you want gain. I would suggest minimal gain ( no more than 2 or so) because you don't want to approach the 6 volt rails you created with the supply above.
By the way, nice job with the Dremel tool. Is that MDF you cut with that thing? You really should invest in a cheap jigsaw to save yourself some effort!
The headunits RCA ground is grounded (maybe via a 1k resistor, maybe not) to the car body, would this interfere with your circuit?
If you know the input impedance of your amp, use it for R in the formula:
to determine the subsonic filter frequency. If the one output is driving two inputs of the amp, that would be:
The reference (shown as ground in those drawings) is NOT grounded (not in car audio). The drawings are a little misleading. In the case of (a) or (b), it wouldn't matter. But in (c) it would short circuit the negative supply rail. The only thing connected to the reference are the connections to ground on the schematic you're using for the summing block.
Just connect the shield for the output RCA's to the input RCA's shield.
Notice on the drawing (c) isn't using batteries for a DC supply, it's using rectified AC. Therefore the capacitor on the input.
I'll have to look back at the schematic to be sure it's strictly a buffer...
dont u think the next config willgive u better resolts ?
These are really handy for quick wood work
Handheld scroll saw at loewes. They can be had for $20-$40, and are pretty handy...takes a steady hand though ;)
Sorry for skipped on day of post. I recieved my amp yesterday, and I took my time on gaming after my 3rd chemistry test. So I'm back again, and I need to do a little shopping for installing the amp and try the bridge mode first. Also, I am not really sure how the sub out will act like, if it comes out to be the same signals from left and right then everything will be fine. Then I just need to connect it to the amp and drive sub seperatly. However, if this is really true, I can also change this block to a true buffer or blanced line output device. So the posts here are still useful for this application, and keep posting. Then I will test the sub outs later when I am installing my amp.
Car: 96 Red Honda Civic Coupe
HU: Kenwood KDC-MPV5205 MP3/CD reciever:
- Preout Level/load (During Disc Play):
2000 mV /10 kOhm
- Preout impedance:
< 600 Ohm
Amp: Blaupunkt PA2150 Class T Amplifier
1.RMS output power : bridged (4Ohm) @ 1.0% THD
= Min power in any channel 480 Wrms.
2.RMS output power : non-bridged (2Ohm) @ 1.0% THD
= Min power in any channel 180 Wrms.
3.@ Rated power, bridged mode - 51 Amps
4.@ Rated power, non-bridged mode - 32 Amps
5.@ 33% rated power, non-bridged mode - 11 Amps
6.@ 10% rated power, non-bridged mode - 5 Amps
7.@ idle - 1.5 Amps
8.@ Rated power, non-bridged
Average Value for all channels >100db
Test conditions: Loads 4Ohm resistive in all modes unless noted, voltage=13.8 Volts DC.
Input impendance - 10k ohms
Input signal voltage control range - 0.3-6.0 vrms
Trigger line current draw - @20mA
Subwoofer driver: JBL LC-S1200W
Recommended Amplifier Power Range: 12-200W
Frequency Response: 40Hz¡V500Hz
Mounting Depth: 5" (127mm)
Cut-out Diameter: 10-3/4" (273mm)
Thiele and Small Parameters
Nominal Impedance: 4 Ohms
Revc: 3.45 Ohms
Vas: 124 Liters
Enclosure Volume 1.25 cu. ft. (35.88 Liters)
Enclosure Volume 1.75 cu. ft. (49.54 Liters)
Port Diameter 4" (101.6mm)
Port Length 10-3/4" (273mm)
Sealed-Chamber Volume 1.25 cu. ft. (35.88 Liters)
Vented-Chamber Volume 1 cu. ft. (28.31 Liters)
Port Diameter 4" (101.6mm)
Port Length 6" (152.4mm)
I think this will be more than enough details for you to answer my following questions regarding to your post. I had been reading different car audio site lately, and I found one extermely useful. So I understand I can get power supply form the circaret(spelling) lighter, or seting up a distrobution block from batt + voltage for this purpose. What is the differences and advantage on these ways? For the gain calculation, I think I will set the final summing block output voltage not more than 5. Since My amp max is 6 vrms, I think <5v will be save and the sound will be pretty decent. Am I right? And how can I calculate the final voltage which coming out from the active summing block with a voltage follower? I will redraw the sch, so this question can leave it by now.
So is it not a good idea to turn on everything at the same time with the remote power from the reciever?
Is it because the pop it created by the rush of the voltage flow?
I want to test the bridged mode and drive the sub in series to see how its work, and the package came with a high line level adapter, should I use it? Do you guys use normal RCA 2 males-2 males too? Or should I leave it for the summing block since its lead the female leads are wires only (easy assemble for PCB).
instead of the resistor network and get a much better power supply
I'm kinda jumping in, in the middle here, but why does this need to be active? :confused:
L/R summing is as simple as 2 resistors. Of course adding phase switches is a whole different matter, but won't your sub amp have phase and if not, why don't you just swap the polarity of the speaker?
What you are doing is very simple.
The way you are doing it is not. :whazzat:
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