| provio |
Hello
I'm planning to build a subwoofer consisting of Peerless 12" XLS driver and Peerless 12" passive radiator. These will be placed in ~40litre box. Now I'm not sure about some things and I hope you guys could clear them out for me. Firstly are drivers meant for cars any good for home systems? That 4ohm nominal impedance would be great since I'm also building the amplifier myself. Since this is my first DIY audio project I'll probably start with easier amp (gainclone PA100 with LM3886 chips) but I need some facts will this be powerfull enough for driving this subwoofer at 8ohm load or should I buy the car version instead.. or go for bigger amp?
As for the amp, things I'm looking for are regulated psu, adjustable low-pass filter (I'll probably try Elliot's '
Eight Band Sub-Woofer Graphic Equaliser'), a subsonic filter, driver protection and volume control but more about this later. Have to decide the amp first :)
Thanks for your time and sorry about my messy english. Still learning |
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| mateo88 |
| I would say go with the 4 ohm subwoofer, because you can parallel either two lm3886's or two 3875's to get about 100 watts. With 8 ohms, you're only looking at about 50 watts, unless you bridge the chips. You may even want to see if you can find a 2 ohm subwoofer (or dual 4 ohm voice coils), that way you could parallel 4 lm3875's for about 200 watts. |
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| soundNERD |
| I would say the opposite... buy the 8-ohm and bridge two 3886s. |
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| bigmike216 |
| I say get the 4 ohm and bridge parallel some 3886's ;) |
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| yesgrey3 |
Hi provio,
I don't know if you have already read this site, but if you don't have a look:
http://linkwitzlab.com/thor-intro.htm
It's describing a subwoofer with the driver you want and it also explains lot of things. I Have used it to calculate the power needed for my subs. |
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| provio |
Hi again
Thanks for your suggestions and for the link yesgrey3, it seems to be informative.
I will probably go with 8ohm version since I have never heard a subwoofer designed for car's cabin being used in bigger room and because
the T/S parameters betweed these 2 drivers depart from each other (I would probably have to use bigger box with the car driver) and also because
of the price of course. :) I also decided to use NIGC BPA200 with DC-servo for driving the sub. I know that size isn't straightly comparable with better
sound quality and that I should start with simple GC but what the heck, I like the challenge :D
I started designing the amp on the base of AN-1192. Is it ok as it is or is there something (critical) that I should take notice of? Should I use snubbers?
Is ±30V rail voltage ok or should I use ±35V? Will 500VA transformer do the job?
I haven't found LF411ACN/LF412ACN op amps from local electronic shops (yet), so I thought of using LF411CN/LF412CN instead. Are these suitable for
the job or should I use some other chips? The datasheets give the A-versions a supply voltage value of ±22V and ±18V for normal ones.
I presume these are minumum values and I could power the chips with my rail voltage? Or do I need another psu?
I'm also having troubles finding 1N456A diodes used in the DC-servo circuit. What whould be a good low-leakage diode for replacement?
Thanks for taking your time to answer these basic questions. I appreciate your help. |
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| macboy |
| quote: | The datasheets give the A-versions a supply voltage value of ±22V and ±18V for normal ones.
I presume these are minumum values and I could power the chips with my rail voltage? Or do I need another psu?
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No, these are maximum values. You will need to provide a separate power supply for the opamps. The most common voltage to use is +/- 15 V. You can use a couple of simple 3-terminal regulators to regulate your amp rails down to +/- 15V for the opamps (see "U8" and "U9" in AN-1192; did you overlook that?). The non-"A" version of the opamps will work just fine.
| quote: | | Is ±30V rail voltage ok or should I use ±35V? Will 500VA transformer do the job? |
For an 8 ohm load, go for +/- 35 V rails. That is just about the ideal voltage to maximize output power into 8 ohms. 500 VA will do just fine; even 300 VA or so would be adequate. Don't forget that when choosing a transformer, the AC voltage must be 71% of the desired DC voltage. So for +/- 35 VDC rails, you need a transformer with either dual 24 VAC to 25 VAC outputs, or a single 48 VAC to 50 VAC centre-tapped (often called simply "50 VCT") output. Dual secondaries give you more flexibility in how you build your power supply, since you can wire them up to be centre-tapped or leave them separate or even parallel them (if you only need one output not two). |
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| provio |
| quote: | Originally posted by macboy
No, these are maximum values. You will need to provide a separate power supply for the opamps. The most common voltage to use is +/- 15 V. You can use a couple of simple 3-terminal regulators to regulate your amp rails down to +/- 15V for the opamps (see "U8" and "U9" in AN-1192; did you overlook that?). |
Yup I somehow missed that part. Thanks for clearing this out.
| quote: | Originally posted by macboy
Don't forget that when choosing a transformer, the AC voltage must be 71% of the desired DC voltage. So for +/- 35 VDC rails, you need a transformer with either dual 24 VAC to 25 VAC outputs, or a single 48 VAC to 50 VAC |
I'm going to use linear regulators so do I need to worry about AC output, as LM338 is capable of "+40V, -0.3V input/output differential"? If my VDC secondaries are 38Vrms, I could theoretically drop the voltage to 15V with these chips right? Although that could get a little :hot: |
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| Nuuk |
| quote: | | If my VDC secondaries are 38Vrms, I could theoretically drop the voltage to 15V with these chips right? Although that could get a little |
That's right and you are closer to the ice cap than me so don't add to the global warming! ;) I wouldn't want to drop more than 10 volts through the LM338 unless you use some serious heatsinks! :att'n: |
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| Yoghourt |
| quote: | Originally posted by provio
I also decided to use NIGC BPA200 with DC-servo for driving the sub.
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bpa200 in national application note both uses inverted and non-inverted configurations. Instead of having 2 different configurations driven by the same signal, you can drive symetrically and use only 1 configuration. Example: signal to first NIGC and inverted signal to second NIGC. It's simpler (parts selection, same PCB for both legs of bridge), probably better, and surely easier to set up.| quote: | I haven't found LF411ACN/LF412ACN op amps from local electronic shops (yet), so I thought of using LF411CN/LF412CN instead. Are these suitable for
the job or should I use some other chips? |
LF412 is ok for the DC-servo. For the buffer, you can use whatever opamp you like: opa2134, OP275, etc...
| quote: | | I'm also having troubles finding 1N456A diodes used in the DC-servo circuit. What whould be a good low-leakage diode for replacement? |
From my experience, 1n4148 is a good starter for the job. I've read that one of the best low leakage diode is...a cheap transistor! Simply take a low cost NPN transistor, and tie base to collector.
Alas, I learned this trick after having bought a bunch of low leakage diodes bas45a.
Thanks for taking your time to answer these basic questions. I appreciate your help. [/B][/QUOTE] |
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| macboy |
| quote: | Originally posted by Nuuk
... I wouldn't want to drop more than 10 volts through the LM338 unless you use some serious heatsinks! :att'n: |
Ah, but don't forget that the only thing that these regs are powering is a couple opamps, not the power amps. With only a few mA of current flowing through them, you can easily drop the voltage 10 V or 20 V or 30 V and still probably get away with using no heatsinks at all! I rarely use heatsinks on my pre-amp regulators, and even sometimes use those little TO-92 case, 100 mA regulators (e.g. 78L12). |
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| Nuuk |
| quote: | | Ah, but don't forget that the only thing that these regs are powering is a couple opamps, not the power amps. |
Yes you are right. I thought they were for powering the power amp chips. I don't use heatsinks on any of my pre-amp/buffer regs either! ;) |
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| provio |
| quote: | Originally posted by macboy
Ah, but don't forget that the only thing that these regs are powering is a couple opamps, not the power amps. |
This is getting a little confusing :D
I meant to use LM338s for regulating the whole amp, LM3886s included. I would then use LM7xL15s to drop the voltage from ±35V rails for opamps. Is this even reasonable or should I just build normal unregulated PSU?
About snubbers, is the resistor+capacitor combo supposed to be placed before capacitors between V+/- and GND? What about between V+ and V-? Is there any good schematic or picture showing how this should be done? |
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| macboy |
| quote: | Originally posted by provio
This is getting a little confusing :D
I meant to use LM338s for regulating the whole amp, LM3886s included. I would then use LM7xL15s to drop the voltage from ±35V rails for opamps. Is this even reasonable or should I just build normal unregulated PSU? |
No, it is not resonable to expect a single pair of 5 A regulators to power four LM3886's. If you used a pair of regulators per LM3886, that would work. But why? Regulated supplies are (IMHO) overrated, and in this specific case, where you are building a subwoofer amp, they are totally and completely unnecessary. The only function they could serve is as space heaters. Save your money.
(Consider this as an intellectual exercise - the regulators can handle up to 5 A, so if you were able to use them at that maximum level, the maximum current through your 4 ohm load is 5 A. The RMS current will be 3.54 A (for a sinewave). Then RMS Power, P = I^2 * R = 50 W. So with a single pair LM338's regulating your power supply rails, the maximum power you can get out of any amp of any topology is 50 W RMS (into 4 ohms). This is a limit imposed by your power supply. If you use really big caps on the output of the regulators to smooth out the current requirements from the regulators, you may be able to get 5 A average (or RMS) out of them. Then power would be 100 W in to 4 ohms, but that's really stretching it. And that's assuming that you do not have to derate the output current capability of the regulators for any reason, including Vin - Vout being too high, excessive temperature due to inadequate heatsinking, etc.) |
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| provio |
| quote: | Originally posted by macboy
No, it is not resonable to expect a single pair of 5 A regulators to power four LM3886's. |
Yes I was actually thinking of using 2 or more regs per rail. This would still probably be cheaper than buying 80000uF worth of capacitors.
Here (in the attached image) is part of my schematic which is based on AN-1192. What do you guys think, is there something I should change? Would 0,09R be better than 0,11R for Ro? Should I use capacitors at LF412N's suppy pins?
If I will use carlosfm's unregulated PSU design, is it ok to just add 20000uF per rail or should I change something else? |
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| rmpmla |
| quote: | Originally posted by provio
Hello
I'm planning to build a subwoofer consisting of Peerless 12" XLS driver and Peerless 12" passive radiator. These will be placed in ~40litre box. Now I'm not sure about some things and I hope you guys could clear them out for me. Firstly are drivers meant for cars any good for home systems? That 4ohm nominal impedance would be great since I'm also building the amplifier myself. Since this is my first DIY audio project I'll probably start with easier amp (gainclone PA100 with LM3886 chips) but I need some facts will this be powerfull enough for driving this subwoofer at 8ohm load or should I buy the car version instead.. or go for bigger amp?
As for the amp, things I'm looking for are regulated psu, adjustable low-pass filter (I'll probably try Elliot's '
Eight Band Sub-Woofer Graphic Equaliser'), a subsonic filter, driver protection and volume control but more about this later. Have to decide the amp first :)
Thanks for your time and sorry about my messy english. Still learning |
You can also consider the OPA549 or 541 in parallel-bridge using 4 ohm driver. If you can get it for samples then that would be a good start. i fried lot of chip amps before making one work :)
here is my sub using a OPA 549 in para-bridge with Rod elliot's EAS filter and a cheap 15" car subwoofer. |
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| Gcollier |
Hello all, I have also been thinking about putting together a sub amp to replace y current underpowered unit. My plan is to use a pair of bridged non-inverted OPA541's. The bridging will be accomplished with a DRV134 similar to Digi's design. I have attached my first draft of a PCB. The plan is to use two of these and mount the bridging board in between. Obviously the caps on board are a bit small for a sub, there will be a pair of 6800uF caps on the PSU board. I'm going to try unregulated first as I would like to keep it as simple as possible. I really don't need a filter of any sort as I am using this with an HT preamp that has a sub out, If I do add one I'll likely just use an adjustable active lowpass filter with an OPA134...cheap and simple.
G. |
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| soundNERD |
That looks really good! It looks like you designed it in Eagle using a copper pour. If you don't mind telling me, how do you do that? I've been trying to do copper pour for a long time and could never figure out how to.
Thanks! |
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| Gcollier |
| quote: | Originally posted by soundNERD
That looks really good! It looks like you designed it in Eagle using a copper pour. If you don't mind telling me, how do you do that? I've been trying to do copper pour for a long time and could never figure out how to.
Thanks! |
To do a copper pour in eagle you use the polygon tool (not the rectangel tool).
1. Place your components and connect them with the signal tool.
2. Use the Name tool to name the signals.
3. Draw your "copper pour" area with the polygon tool.
4. Use the Name tool to name the polygon the same as the signal you want to attach it to.
5. Use the change tool to adjust things like isolation, and thermals etc.
Good luck |
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| rmpmla |
| quote: | Originally posted by Gcollier
Hello all, I have also been thinking about putting together a sub amp to replace y current underpowered unit. My plan is to use a pair of bridged non-inverted OPA541's. The bridging will be accomplished with a DRV134 similar to Digi's design. I have attached my first draft of a PCB. The plan is to use two of these and mount the bridging board in between. Obviously the caps on board are a bit small for a sub, there will be a pair of 6800uF caps on the PSU board. I'm going to try unregulated first as I would like to keep it as simple as possible. I really don't need a filter of any sort as I am using this with an HT preamp that has a sub out, If I do add one I'll likely just use an adjustable active lowpass filter with an OPA134...cheap and simple.
G. |
Nice PCB layout :). if you have some OPA 549 spares, i would go for this coz it has more power than the OPA541. Yup, i also use the DRV134 for the bridging. the low pass filter i use is fixed though quite simple and easy to build.
The sub i built is unregulated with a pair of 30,000uF caps. I can post the internals if its okay |
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| Gcollier |
| quote: | Originally posted by rmpmla
Nice PCB layout :). if you have some OPA 549 spares, i would go for this coz it has more power than the OPA541. Yup, i also use the DRV134 for the bridging. the low pass filter i use is fixed though quite simple and easy to build.
The sub i built is unregulated with a pair of 30,000uF caps. I can post the internals if its okay |
I'd luv to see the internals |
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| rmpmla |
| quote: | Originally posted by Gcollier
I'd luv to see the internals |
here it is before installation unto the enclosure. |
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| rmpmla |
| i used a connector from a busted PSU for PC. this make it easy to dis/connect the gainclone amp from the power supply and subwoofer in case of troubleshooting or repair. |
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| officeboy |
Once you are done with the amp part of your project, you may want to have a little look at this.
I ran into problems putting together a crossover that was simple and adjustable and had some documentation. So I stripped parts and ideas from a few different websites and put this together.
http://www.diyaudio.com/forums/show...&threadid=33067
Use it or don’t, but if you read it you may learn a little something about putting together a crossover for a sub (or you may not…) I tried to document my learning about things as I went along.
And you may be surprised at the output of your sub. My 2 lm3886's can shake the whole damn house. |
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| Gcollier |
| quote: | Originally posted by officeboy
Once you are done with the amp part of your project, you may want to have a little look at this.
I ran into problems putting together a crossover that was simple and adjustable and had some documentation. So I stripped parts and ideas from a few different websites and put this together.
http://www.diyaudio.com/forums/show...&threadid=33067
Use it or don’t, but if you read it you may learn a little something about putting together a crossover for a sub (or you may not…) I tried to document my learning about things as I went along.
And you may be surprised at the output of your sub. My 2 lm3886's can shake the whole damn house. |
TI has a very good and simple filter design white paper and software on their website. I haven't actually built anything with it yet, but the actual circuts look easy enough. |
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| soundNERD |
I never have made a variable crossover. Instead I use WinISD Pro Alpha and use the 2nd order active lowpass filter calculator.
I've had no problems yet, and every crossover I've made seems to work perfectly fine.
You should be able to make a variable crossover with it, though. Just choose a capacitor value, then figure the resistor values needed for the lowest cutoff freq. and the highest cutoff freq. Then find a potentiometer to match those requirements. |
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| soundNERD |
| quote: | Originally posted by Gcollier
To do a copper pour in eagle you use the polygon tool (not the rectangel tool).
1. Place your components and connect them with the signal tool.
2. Use the Name tool to name the signals.
3. Draw your "copper pour" area with the polygon tool.
4. Use the Name tool to name the polygon the same as the signal you want to attach it to.
5. Use the change tool to adjust things like isolation, and thermals etc.
Good luck |
Thanks. I tried that But I cannot get it to work. It works perfectly when I draw the polygon and then name them both the same thing, but once I save and close Eagle, if I open it back up, the copper pour is gone and it's just back to the original bright blue lines I drew to make the polygon, but it's not filled in.
Also, it often doesn't turn bright blue when I do the copper pour. Instead I use the polygon tool, make the drawing, and when I close the design, it should turn bright blue and stay there once I click out of it, but sometimes it doesn't. And the only way to fix that is to exit and re-start Eagle.
Any ideas on why this is happening? I have Version 4.13r1 if that matters. What version are you using? I think this may be a glitch or something in this version. |
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| Gcollier |
| quote: | Originally posted by soundNERD
Thanks. I tried that But I cannot get it to work. It works perfectly when I draw the polygon and then name them both the same thing, but once I save and close Eagle, if I open it back up, the copper pour is gone and it's just back to the original bright blue lines I drew to make the polygon, but it's not filled in.
Also, it often doesn't turn bright blue when I do the copper pour. Instead I use the polygon tool, make the drawing, and when I close the design, it should turn bright blue and stay there once I click out of it, but sometimes it doesn't. And the only way to fix that is to exit and re-start Eagle.
Any ideas on why this is happening? I have Version 4.13r1 if that matters. What version are you using? I think this may be a glitch or something in this version. |
Ok this is an easy one...click the "ratsnest" button and it will restore your polygon. :D |
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| soundNERD |
Thanks!! It works perfectly now! My boards are going to look so great now
Here is the first one I have made. Does this look like a good design? It's for the LM1876TF chip (going in a small 2.1 system - 3875 for 56W into the sub, 1876 for 20W x 2 into the satellites). |
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| provio |
Hi again
Recently I have been busy but now have spare time to continue this project. After thinking this over again, I decided to use OPA549s in inverting configuration without dc-servos and split the signal with DRV134. I'm a little lost again and hope you guys could clear some things out.
Firstly, I'm not totally sure how to handle dc offset. Is it the best way to use a trimmer on chip's positive input (Rb)? How is this value calculated? I thought that Rb=Ri*Rf/(Ri+Rf) but someone (on some thread which I cant find right now :D) suggested to use a trimmer with value way over this.
Also, how is the DC blocking cap (Ci) before Ri calculated? What about the one (Cin) before DRV134? Is it even needed? Would it be better to use polyprop. rather than electrolytic caps here?
In the final version I'll probably use smaller value resistors and smaller gain (10 or so). Please tell if there is anything I should add/remove.
Thanks |
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| provio |
As I seek for knowledge, more questions keep coming up, so please bear with me :D
How much gain can I use with OPA549 for subwoofer use before it negatively affects sound quality? I found out that bandwith at -3dB should be atleast 100kHz to avoid rolloff effects but this was considering full sonic range. A gain of 20 would give 45kHz bandwith. Is this too low for a subwoofer?
Will decoupling caps (Ci) result in different frequency response on both sides of bridge? Should these be omited and only use Cin before DRV134? If I use polypropylene caps on the signal path, would it be benefitical to bypass them with larger electrolytics in hope of better bass response?
If I understood correctly, these RC-networks (Cin&Rin, Ci&Ri) also act as high-pass filters. I have checked different schematics and all of them have the cutoff point around 7Hz. Wouldn't it be more practical to have this higher (around 15-20Hz) so that no subsonic filter is needed? |
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