lm4780 in parallel any help very much appreciated - diyAudio
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Old 28th May 2014, 07:38 AM   #1
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Default lm4780 in parallel any help very much appreciated

hi there I have a few question's about the audio sector lm4780 amp in parallel ... I have searched and searched but cannot seem just quite what I'm looking for.

1. does anybody have any or direct me to where I can find hi-res photos (top and bottom) preferably with the 10000uf cap implemented on the ps

2. can someone clarify which are the correct components (on audio sector) as the parts list differs from the schematic

3.could someone explain why on the data sheet for the lm4780, the parallel example, uses 1 of the input resistor is 54.4k and the other is something like 49.6k now, I know that it's to do with offset and the balancing the two halves of the chip out but why does the audio sector use 2 x 22k

4.how much precision is needed 1% or 0.1% especially for the 680r resistor, have got 0.1% for everything else , but just cannot find a 680r resistor at 0.1%

In all haste, I have realised that trying run it as a parallel, is probably not the best way to go for noobs. but no-oneachieved anything by giving up at the first hurdle

hopefully you guys and girls can help , many thanks in advance ( I'm sure the answers will help out a lot of noobs like me, that are in the same position)
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Old 28th May 2014, 07:55 AM   #2
sangram is offline sangram  India
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The 680 value is not critical, you can use 1k which I anyway prefer.

Here is one pic, but those are 4700uF. Can confirm that 10kuf also fit fine. Scroll down a few posts

Balanced power amplifier
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Old 28th May 2014, 08:45 AM   #3
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thank you for your quick reply , Its a shame it's not clearer , but thanks for the info , every bit helps, cheers

Last edited by rosco122; 28th May 2014 at 08:59 AM. Reason: mis-spelling and poor grammar
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Old 28th May 2014, 12:48 PM   #4
sangram is offline sangram  India
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Sorry, that was from a cellphone camera.

Note that the caps, specially big ones, foul with the bolts fixing the chip to the sink. Since I use straight screwdrivers and Philips head bolts, I had to put them on the back of the board. If you use allen bolts and a right-angled key, this is not necessary to do.

I don't know what changes have happened over the last seven years, but the 22k resistors are for input and feedback, there are some 220 ohm units for adding in series with the input, and the bigger Panasonic ones are for the zobel - if supplied.

The small 10uF FC caps go on the PS board, and the large ones on the amp board. Additional buffer is highly recommended.

I am looking at the parallel amplifier schematic on the TI datasheet - April 2013 version - and there is a shared input resistor, and the feedback values are the same for both channels. Don't know where you saw different values?

Last edited by sangram; 28th May 2014 at 12:51 PM.
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Old 28th May 2014, 01:36 PM   #5
Einric is offline Einric  United States
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Default My Parallel AudioSector 4780

Here are the best shot I have to show any detail.
I can take some additional pictures at a later time.
The build guide that Peter provides should tell you everything you need to know.
If you have more specific questions please let me know, I will help however I can.
Attached Images
File Type: jpg Power Supply Finished.JPG (920.9 KB, 173 views)
File Type: jpg 4780 Under.JPG (707.2 KB, 163 views)
File Type: jpg Layout.jpg (703.4 KB, 158 views)
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Old 28th May 2014, 02:04 PM   #6
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thank you very much, it was actually the audio sector lm4780 in parallel pics I was after ..... obviously just one p/s board and I can just make out that the R0 is solder underneath gives this away as stereo but thanks I'm sure this will help someone though ......I may ask peter ( probably the best person in the world to ask) if he has some hi-res photo's of the top and bottom of completed boards ( both of parallel and stereo of his lm4780's

a nice clear picture of what were supposed to be shooting for would help out a great deal .....you know, not just placement but metal film or carbon or what type caps , poly or alu.....
anyway thanks to your good self and to everyone
for their help
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Old 28th May 2014, 02:20 PM   #7
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hi there Sangram it is on the nat semi data sheet, i was a bit wrong here the input resistor for the left amp is 47k and ri for the right amp is 4.7k and rf1 is 46.4k and rf2 is 51.1k. I would have thought you would want to have a close a match a possible on both amps (with my very limited knowledge) or unless that's part of the circuit to actually create a defined amount of off set to create a *null offset circuit ( if thats the correct term)
I don't think I have enough posts to post a link but its in all the nat semi lm4780 data sheets in the parallel example
thanks for all your help
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Old 28th May 2014, 04:19 PM   #8
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hi there sangran I have found the parallel schematic hahahah like a moron, I was looking at the bridged version not the parallel

I'm beginning to see my errors thanks for your help
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Old 28th May 2014, 05:09 PM   #9
sangram is offline sangram  India
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Thank heavens. BTW use the TI versions, they are more recent and have a wee bit more information than the original NS ones, and also are annotated and hyperlinked. Very helpful indeed: LM4780 | Mid/High-Power Amplifier | Speaker Amplifier and Modulator | Description & parametrics

Bridged would have different values because one is used in inverting mode.
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Old 29th May 2014, 03:26 PM   #10
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Default lm4780 parallel components

hello everyone , I just asked peter for some photos so hopefully he or i will be able to post some pics ..if peters not to busy.

Now in this spirit of this thread can anyone on you brilliant people give us newbs the minimum voltage ratings and wattage ratings you would go for .....for these on the Audiosector lm4780 board again im sure this would hel[ newbs like myself .....and please explain why? so we can learn!
for R1/R2 I'm guessing 1/2 watt and up?
for R3/R5 I'M guessing 1/2 watt and up?
R0/R4 I'm guessing 1/2 watt and up?
Now R8/R9 I have 0.1R rated 3 watts wire wound powers ...thoughts?
RM the 10k SMD ...AGAIN 1/2WATT smd but in smd is quite hard to find , now I know I can just use a flattened through-hole ?
R7 I have 2r7 at 7 watts wire wound ...suggestions
Cz 0.1uf or 100nf if you prefer ... I have 1% at 100v again suggestions please
now which resistor set is critical ......for accuracy 1% or 0.1% and which can we get away with being just 1%

I'm hoping this thread will give us newbs a better understanding of the components and why they are used ....so please explain as though you are explainig it to newb and not stephen hawking, thank you diy audio members for all your help ....you will earn your place in heaven, paradise, valhalla or that big components storage box in the sky for this

thanks rosco_leuven
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