| odysseybmx414 |
| i am building a chipamp using the lm4730's bridge schematic in the datasheet i was just wondering if anybody else ever attemted it and has any oppinions or anything |
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| soundNERD |
If you want more power, why not try an lm3875 or lm3886.
They are much easier to use than a bridge circuit. Plus they have higher output levels, and I'm sure higher sound quality.
But if you have the parts you might as well try building out and deciding for yourself |
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| Peter Daniel |
| quote: | Originally posted by odysseybmx414
i am building a chipamp using the lm4730's bridge schematic in the datasheet i was just wondering if anybody else ever attemted it and has any oppinions or anything |
I assume you mean LM4780 bridged. This guy built it: http://www.diyaudio.com/forums/show...8699#post528699 |
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| soundNERD |
I don't know... Look on page 5 of the lm4730 datasheet, theres a bridge circuit. |
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| Peter Daniel |
| I didn't even know if they make LM4730 (as Digi Key show no link). Why use 14W amp bridged, when you can use 60W amp in stereo? |
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| odysseybmx414 |
| well i have a 15 volt 5 amp already built power supply all i gotta do is build an amp good for that power and i figured the lm4730 would be a pretty nice matchup unless anybody else has a better idea for me |
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| soundNERD |
15V single supply, +/-15V supply, or +/-7.5V supply?
If its a +/-15 supply, you should go for a lm3875 or lm3886. For a +/-7.5, go for a Texas Instruments OPA549 or 541.
If it's a 15V single supply, you should be able to use an OPA549, but I don't know how to do it. I tried building one to run off of 12VDC, and it sounded horrible, as in distorting with everything. I thought it may have been caused by low voltage, but I hooked it up to a 40VDC supply, same result. I know it can be done, though. In fact, I'll start a post on that... |
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| leadbelly |
| quote: | Originally posted by odysseybmx414
well i have a 15 volt 5 amp already built power supply all i gotta do is build an amp good for that power and i figured the lm4730 would be a pretty nice matchup unless anybody else has a better idea for me |
I think the path you are pursuing is hardly worth the time or expense. This picture shows how much power the 4730 can put into 8 ohms, as a single.
http://www.national.com/ds/LM/LM4730.pdf |
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| Stocker |
| SoundNERD don't let them get you down. Some of the most highly regarded amplifiers in the world put out single-digits of Watts, max. If this is what you want to do, listen only to those who will help you actually *do* it. |
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| soundNERD |
| quote: | Originally posted by Stocker
SoundNERD don't let them get you down. Some of the most highly regarded amplifiers in the world put out single-digits of Watts, max. If this is what you want to do, listen only to those who will help you actually *do* it. |
Yes, I know that. Like the LM3875. Only 56W but the sound is amazing and powerful, as in better than my 100W RMS x 6 Yamaha reciever (which was much more money too!!).
And I know some tube amps only produce 4 or 5 watts of power.
In general, watts means nothing to me (except in certain situations, such as comparing a 250mW 386 amp to a 56W 3875 amp. But when you see a 200W x 2 amp in a store, it can't even come close to my 56W x 2 3875 amp. |
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| odysseybmx414 |
| ok i have made my decision i am building the opa549 amp and to answer the other question, a +/-15V 5 amp supply. thanx for all u guys help tho |
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| soundNERD |
| quote: | Originally posted by odysseybmx414
ok i have made my decision i am building the opa549 amp and to answer the other question, a +/-15V 5 amp supply. thanx for all u guys help tho |
Sounds good!
I usually use the schematic provided by National Semiconductor for the LM3875, and it works well on the OPA549.
Just rememebr the Ref and I/LM pins must be tied to ground for the thing to work! I spent almost an hour before I figured that one out. |
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| odysseybmx414 |
| hey thanks for the info soundnerd u rock and one more question, how much power do u think i am going to get out of this project into 4 ohms? |
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| odysseybmx414 |
| and one more, what kind of quality is the sound? |
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| soundNERD |
I'm not quite sure, but with a +/-15V supply, that is the limit of the output voltage swing.
Running at about +/-26 or so, a single OPA549 can output 75W RMS into 4-ohm. I would guess you'd get about 50W or so RMS with a +/-15VDC supply. I'm not sure on that though.
Regarding the sound, I mostly use it for subwoofers, because of the power it can produce. Two of these in bridge (or 8 like in my next project - over 800 real RMS watts into 2 ohm :hot: :hot: ) are great for driving a sub speaker. I've heard many good things about them for full range speakers, but never personally tried it. I usually use a National Semiconductor LM3875 for normal speakers.
IF you are looking for very good sound and a lot of power, go for an OPA549, but if you want unbelievably good sound with slightly less power, go for a LM3875.
Now that I think about it, you would be better off either way with an OPA549 because the 3875 doesn't like 4-ohm. At such a low voltage, an OPA549 should be able to handle down to 2 ohms, with a large enough heatsink.
Not to confuse you by throwing more and more ideas out, but a LM3886 is another option. It's good down to 4-ohm, and has 68W RMS output power into 4-ohm, compared to 56W from the LM3875 into 8-ohm. The problem is it has a mute circuit which is a pain to use, because it is dependent on the power supply, so if you ever change the supply voltage, you have to change the resistor controlling the mute.
What are the speakers you plan to use anyway? |
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| odysseybmx414 |
| i am planning to use a 8inch sub i got it is 4 ohms 100W i dont know about the db sensitivity |
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| soundNERD |
| Oh then definately use a OPA549. I find them very good for subwoofer use. Plus they are simple to use. Besides the chip itself, only 3 resistors needed. No caps, except in the power supply. |
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| odysseybmx414 |
| can u possibly show me the schematic u are using? i have a more complicated one but would rather use one with only 3 resistors |
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| soundNERD |
Here it is, its directly from page 1 of the LM3875 datasheet.
The cap with the star next to it is not needed, and I never use it, and the other two are the power supply caps.
Remember the pinout of the 549 is different than the 3875 also |
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| odysseybmx414 |
| thank you, but what would you suggest the value of Cs |
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| soundNERD |
For most of my amps, I use two or three 2200uf capacitors plus one 0.1uf non-polarized cap per rail (positive rail and negative rail).
The best would be if you put the 0.1uf caps on the chips themselves, or the board near the amp, if you are building on a PCB. However you build it, those caps do best the closer they are to the chips.
You also do not need to use multiple caps. You can use one large cap per rail, I just use many because I got a bunch of 2200uf caps for 25 cents each. For a sub, higher capacitence per rail is better, so you may want even more than that.
Basically, the lower capacitance, the better the mids and highs will be and the weaker the bass will be, but it is the opposite as you add more capacitance. |
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