Think it through again....
Although the amp has an instantaneous peak output power capability of 135W \ \ (V x A).
The LM3886 is a high-performance audio power amplifier
capable of delivering 68W of continuous average power to a
4Ω load and 38W into 8Ω with 0.1% THD+N from
20Hz–20kHz.
Exceeding these ratings distortion and linearity qnd reliability goes out the window...
Although the amp has an instantaneous peak output power capability of 135W \ \ (V x A).
The LM3886 is a high-performance audio power amplifier
capable of delivering 68W of continuous average power to a
4Ω load and 38W into 8Ω with 0.1% THD+N from
20Hz–20kHz.
Exceeding these ratings distortion and linearity qnd reliability goes out the window...
And thinking about it yet again, examine the end result.
Every time you double the power, you get 3db more from the speakers.
Every time you increase the power by 10 times, the human ear perceives double the volume.
Why not try specs, and then do what you'd like? In my opinion, you need to start with a recommended baseline first, and then go in a particular "direction" towards what you'd like to change/improve.
Since it sounds like you're bound to buy two transformers anyway, why not do it on purpose? You could make one design on LM3886T (lower voltage), and you could make another on LM3875T using the higher voltage you're wishing for, with the more tolerant chip.
I think that would cover the bases, get you unstuck, and you'd have more fun. 😉
Every time you double the power, you get 3db more from the speakers.
Every time you increase the power by 10 times, the human ear perceives double the volume.
Why not try specs, and then do what you'd like? In my opinion, you need to start with a recommended baseline first, and then go in a particular "direction" towards what you'd like to change/improve.
Since it sounds like you're bound to buy two transformers anyway, why not do it on purpose? You could make one design on LM3886T (lower voltage), and you could make another on LM3875T using the higher voltage you're wishing for, with the more tolerant chip.
I think that would cover the bases, get you unstuck, and you'd have more fun. 😉
good call danielwritesbac, I'm sitting here stressing an extra 50watts (which is like 15% of my total power anyways, which would never be missed once built). So I'm gunna go middle road, get a 24Vac toroid (35VDC per rail) and live with that. If I really need more power, and I'm thinking my design can handle it, I'll run a lower load. I'm using this amp to run a 8ft tall line array housing 24 3" drivers per channel. I'll try wiring them up in a series/parallel config to equal 8ohms (or as close as I can get it, havent ran the numbers yet) for now. but with 24 drivers, you can arrange the wiring configuration around to equal all kinds of different resistances. If I want more power, rewire the drivers to equal 6ohms, maybe 4ohms if the chips can handle it. Like I said up a few posts, to get more current up the voltage, or lower your load. And because once I buy these xformers, I really dont wunna go back out and drop another $200 just to up my volts a few. So dropping the load should allow more current.
The reason for the questions is more learning for me. I ask, review peoples answers, and it helps me understand dos/donts and allows me to learn more about speak/amp design. Thanks to everyone to has helped me with this!
The reason for the questions is more learning for me. I ask, review peoples answers, and it helps me understand dos/donts and allows me to learn more about speak/amp design. Thanks to everyone to has helped me with this!
Sounds great, except that I would probably pay $2 for an audio grade EI core at a thrift store or garage sale (plus free heatsinks, scads of resistors and maybe even score some epoxy caps too). Those that are already in older electronics are usually super quality. 😉
I have 2 good quality torrid transformers. They are 15vac 3amp for each of the 2 secondaries. Will they work for this amp? earlier in this thread it is posted . that 18 v at 1.48 amp would work for a 4 ohm load. I have 2 gainclones that have el transformers that hum real loud. They have has 19 volt secondaries. I want to swap my quiet torrid will it work? Thanks phil
dual 15V will work, but you get slightly less power
Try it out. Also, add more capacitors to the rails to lower the hum
Try it out. Also, add more capacitors to the rails to lower the hum
transformer that hums
thanks I will swap out the transformer. the sound is too loud during quiet spots in a movie.
thanks I will swap out the transformer. the sound is too loud during quiet spots in a movie.
philiparcario said:
Hi Phil! The humming is usually a ground thing. Well, some transformers hum from inside themselves (not from speakers). Otherwise, its probably a ground loop.
I think the first thing to try is a 22k resistor in parallel with the amplifier input (if it doesn't have a potentiometer).
Next up is to duplicate test-bench conditions. That's having the ground lines "each to its own" for input, speaker, and power--and they never meet again.
And, grounds are never more than 1/4" away from "their" hot partners, although closer (point blank range) or "zip tied" is even better. Gosh, that sounds like fun. 😉
I'm thinking that they probably won't hum on the test bench, and then you can spot the difference.
For stereo amplifiers with Center tap transfomers, the cables need to be the same length for both, and chassis ground comes from the power supply with just one wire, not from the amplifiers. Some potentiometers are already the chassis ground (metal to metal contact beween amplifier enclosure and signal ground).
On amplifier kits, the power ground for Center tap transfo, hooks up to the kit's terminal for CG (chassis ground).
Then again, the torroid probably works best for monoblocks, while the EI is really good for stereo amp.
P.S. Thanks for your help earlier with my speakers. For me, they're much more difficult than amplifiers. 😉
P.P.S. For some reason, I always think of the first thing last. Anyway, first try might be to plug tv, sub, and everything into just one "power strip" before connecting to the wall outlet. A related test is to plug just a battery power CD player into the amplifiers (one amplifier at a time) and see if the hum is gone.
MotoMan_Yz400 said:
Yes (I object).
Remember that each chipamp can only deliver a certain maximum average power. You have to keep the chipamps within their SOA (Safe Operating Area). And you will WANT to keep them within their low-THD (Total Harmonic Distortion) operating area.
To get more power, with the same load, you would add parallel chipamps to get more current, and also raise the VA rating (but NOT the voltage!) of your transformer (or maybe add parallel identical transformers, in a pinch).
And if you lower the load impedance to get more power, you would need to LOWER the transformer voltage, and probably raise its VA rating (unless it was already large-enough).
You REALLY need to download and carefully read AN-1192 from national.com , after downloading and reading the datasheet for the chipamps, and then download the spreadsheet they have for calculating this stuff automatically.
Well as ohms law states, if you voltage and load stays the same, so does your current. If I'm running a single chip in it's safe range, adding more wont increase the power output. The only thing that will happen is the heat from one chip will now be spread across to chips, making both chips run cooler (each chip is sharing the load current effectively reducing produced heat in one chip).
Now with that said, how would you increase your setup so each chip is producing the same heat as a single one? well you load isnt going to change, so to up the current (which makes a chip hot) you must up the voltage. Here I'll try to do this with numbers.
(this is going to be number ran assuming the chip is in a steady on state)
if I have 30VDC per rail in an 8 ohm load, thats 3.75amps running through a single chip (in a single chip amp). If I were to parallel the chips up so now I have 2 chips performing the same function as 1 (using it to help with heat) then that means each chip is taking half of the current so thats now 1.875amps each. Ok well if one chip can handle 3.75 amps safely, and now I'm currently only running 1.875amps, then each chip is not being ran at it's full potential. So to equal the 3.75amps per chip (7.5amps between both) I can up the voltage or lower the load. Well my load is staying the same, so the voltage now needs to be upped to 60VDC to keep each chip at their peek potential current.
Now I'm excluding a few things, just trying to get the jist of my thought out there. Gootee, sounds like you disagree with my thinking. Could you help and explain where I'm flawed? I'm not an expert on this, so I basically running off of what I learned and general properties of electricity. Theres most likely something that I'm missing here that I just dont see.
MotoMan_Yz400 said:
That all seems to sound reasonable. But there is an error:
When you run two amplifiers in parallel, with one load, each amplifier sees twice the actual load resistance. If you run N amplifiers in parallel, each amplifier sees N times the actual load resistance.
For 2 bridged amplifiers, each amplifier only sees 1/2 of the actual load impedance.
That all changes, when you bridge AND parallel them. See AN-1192.
At any rate, to make it easy, see Table 1, on page 4 of AN-1192.PDF, from http://www.national.com . It gives the maximum recommended power supply voltages for 100-Watt bridged and 100-Watt paralleled amps, and for 200-Watt bridged & paralleled, for loads from 2 Ohms to 16 Ohms.
Tom G. is this true?.
When you run two amplifiers in parallel, with one load, each amplifier sees twice the actual load resistance. If you run N amplifiers in parallel, each amplifier sees N times the actual load resistance.
When you run two amplifiers in parallel, with one load, each amplifier sees twice the actual load resistance. If you run N amplifiers in parallel, each amplifier sees N times the actual load resistance.
Ohms law applied to amperage?
Translated to midwest (where I live) that's a question of. . .
How would you rather start your car?:
1) A double-size 12v battery.
2) A 24v battery.
Either will start it, but only one is unharmful.
Back on topic, as I see it, what you're supposed to do is use more chips + more amperage for more power. 😉
Limits on voltage apply no matter how many parts there are, because no individual part should be pushed over its rating.
Past this point, you're talking series wiring, which doesn't have the desired effect of increasing power output. . .
Thus, any application designed to increase power output needs to observe voltage ratings corresponding to advisable safe limits for individual parts, plus an additional load safety margin for any bucking of the output. Ohms law + circular logic. Anyone dizzy yet? 😉 Its basically the guidelines in National Semiconductor Application Note #1192 for bridge parallel amplifiers. 😉
Translated to midwest (where I live) that's a question of. . .
How would you rather start your car?:
1) A double-size 12v battery.
2) A 24v battery.
Either will start it, but only one is unharmful.
Back on topic, as I see it, what you're supposed to do is use more chips + more amperage for more power. 😉
Limits on voltage apply no matter how many parts there are, because no individual part should be pushed over its rating.
Past this point, you're talking series wiring, which doesn't have the desired effect of increasing power output. . .
Thus, any application designed to increase power output needs to observe voltage ratings corresponding to advisable safe limits for individual parts, plus an additional load safety margin for any bucking of the output. Ohms law + circular logic. Anyone dizzy yet? 😉 Its basically the guidelines in National Semiconductor Application Note #1192 for bridge parallel amplifiers. 😉
Speedskater said:
Hi Speedskater,
I'm very glad that you asked. You don't have to take my word for it. And I really don't mind. In FACT, I actually hope that no one will! (PLEASE NOTE that the following is not directed at you, personally, by the way. I just want to try to alert everyone to the readily-available resources. ;-)
To wit:
Everyone who has not yet done so, PLEASE, download AN-1192.pdf (entitled 'Overture Series High Power Solutions'), by simply right-clicking on the following link and then selecting 'Save Target As' from the pop-up menu (assuming you're using Windows etc):
http://www.national.com/an/AN/AN-1192.pdf
If you don't have the free Adobe Acrobat PDF-Viewer, go to http://www.adobe.com and download and install it.
Then (to get this out of the way, first), just to corroborate the statements I made about the load impedance seen by paralleled and bridged amplifiers, look at AN-1192.pdf:
1. Page 3, right-hand side, 1st paragraph of section 4.3 (bridged)
2. Page 4, left-hand side, 3rd paragraph of section 4.4 (parallel)
But hey! It "might be a good idea" to also read the REST of it, at least, that is, if you're AT ALL interested in designing or building any type of chipamp-based amplifier!
Also, if you have not already done so, please download the following:
http://www.national.com/ds.cgi/LM/LM3886.pdf
http://www.national.com/ds.cgi/LM/LM3875.pdf
http://www.national.com/ds.cgi/LM/LM1875.pdf
http://www.national.com/ds.cgi/LM/LM4780.pdf
And there are EVEN MORE(!), just like those, at http://www.national.com , with a complete list of ALL of the 'Overture'-series chipamps available for free at:
http://www.national.com/products/catalog.do .
And hey! WOW!!! If you want *** FREE SAMPLES *** of any of those chipamp chips (Fresh, clean, pure, genuine ones! Delivered directly to your door, in milliseconds! As many as you want! [Well, not quite.]), just go to http://www.national.com and type a chip's model number into the 'Top Secret Decoder Ring' search box on the national.com homepage!
BUT, WHILE you're there, DO check out all of the other extremely-valuable and rare, hard-to-find, NOS, genuine "Application Notes" (with free ACTUAL schematics!), which are available ONLY to the truly-dedicated, intrepid explorers among you, and are actually (gasp!) free for the downloading, AND all of the other amazing 'Top Secret' documents that you might dare to try to ferret-out, and even the free(!) software tools they have there.
Hurry! Don't miss out! Not available in stores! (Your mileage may vary. Not responsible for accidents. Offer void where prohibited.)
Well according to paper AN-1192, it shows I had the right thinking. However, I was alittle ambitious on my numbers. According to the Maximum Power Supply Voltage chart (Table.1) It should that in an 8 ohm load with a bridge (2 chip) design the max rail voltage is 28VDC. And if you were to parallel/bridge (same config, just 2 chips per leg rather than one) it allows you to up the voltage to 37VDC. So by increasing the number of chips per leg, you can run higher voltages, equaling higher output currents. According the the LM3886 Data sheet, the maximum rated voltage is 84VDC. So theoretically you could used a bridge/parallel design with a whole mess of chips, running at the maximum rating of 84VDC, and could push almost a 900watts! (but that would be a BIG heat sink to get rid of all that heat)
MotoMan_Yz400 said:
That sounds right. But remember that, before, we were only talking about the paralleling of amps (IIRC), which is very different than paralleling AND bridging, when figuring power and rail voltages, etc.
Anyway, now you are right, I think, because when using both paralleling AND bridging at the same time, the 1/N (bridged) and N (paralleled) factors for the load that each amp sees can cancel each other, and the whole multi-amplfier assembly can then be treated sort of like a single amp, at least for power and voltage calculation purposes, meaning that simply raising the rail voltages is then a way to increase output power, as you said. At least I THINK that's right.
900W might be nice. But as far as the heatsinks go, no matter how many chipamps were paralleled and bridged, you would be able to just use about the same size heatsink, on each chip, that you would use for a single-chipamp setup, since no single chipamp would be pushed beyond the normal limits. With 900 total watts. You might end up with a fairly-good room heater, though. 🙂
Speedskater said:
Hi Kevin,
That's great. I glad if I was able to provide even a little bit of help, toward that.
"Puzzle it out' is really a perfectly-apt expression, here. This stuff can sometimes be quite puzzling, especially at first. I'm still just learning (always).
'So much great stuff to try to learn; so little time.'
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