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diy 2*100ish Watts

Mogami Cables

sasmit

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This is my diy 2 * 100W design based on the very popular LM4780, The LM4780 is setup in paralell mode here to handle 4 ohm loads and produce close to 100 watts.PCB design was done by me and fabricated by a local pcb maker.
All the electrolytics in signal path are panasonic audio grade, two 1000uf FC series on board and 10000uf FM series on the PSU board.Wima metallized polypropylene and metalfilm resistors.
 

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spirovious

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This is my diy 2 * 100W design based on the very popular LM4780, The LM4780 is setup in paralell mode here to handle 4 ohm loads and produce close to 100 watts.PCB design was done by me and fabricated by a local pcb maker.
All the electrolytics in signal path are panasonic audio grade, two 1000uf FC series on board and 10000uf FM series on the PSU board.Wima metallized polypropylene and metalfilm resistors.

Interesting.
 
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sasmit

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The psu is gonna be a regulated one using an old fashioned LM338 in a TO3 case, there will be two boards one for each rail, together these can handle 10 amps.Caps are pansonice FM for the larger resorvoir and FC series on the output of regulator
 

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sasmit

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one more look at the pcb..it's a bit dirty from soldering hasn't been cleaned. Performance is one of the best I have heard or made till date.
 

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grubyhalo

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Depends...
Nice job! Now, how 'bout clothing the amps with some nice lacquered wood and buffed metal enclosure...
 

sasmit

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working on tat :) ..I'm waiting for some larger heatsinks to arrive. I was thinking of part wood and metal chasis too...19" racking cases are the best to start with but getting that is a bit difficult ,I was even thinking of using a HTPC cabinet antec has some very nice looking models...still exploring that route .
 

sasmit

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Try Dinrack. They will ship out to you, and their bench top cases look pretty good.

The Antecs are pretty cramped and *need* fans, which you may not want. They have no ventilation on the top/bottom panel and don't work without forced airflow. I have the NSK2480 and it is an awesome HTPC case, but would not make a good enough amp case unless you change out the top and bottom panels. It's too much work.

Do you have any idea on prices for 19" racking by Dinrack ? I can't find any pricing details on their site.
 

sasmit

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Additionally, I'd worry about the Panasonic FM 10,000uF, at least Panny don't make it in that size. I'd wonder where you're getting them from. You may be referring to their tank caps, which come with other series designations.

A side note on your supply: I've built over thirty chip amps, and I did not ever like using a regulated supply. There is no improvement for the extended thermal footprint it creates - I tried a series pass and cap multiplier supplies. I would recommend you try both regulated and unregulated, and arrive at your preference.

The best improvements I've found is by keeping signal paths really, really short. I use only P2P construction now, I was using the Audiosector LM4780 PCB and kit for a very long time (~2 years) but I ended up with point-to-point wired LM3886, with the feedback resistors soldered directly to the chip pins. The sound is far superior to Peter's kit (admittedly, I haven't heard his top-end offerings). Also a few exotic components help. I use Roedersteins, Holco and Black Gate in the feedback path and the sonics are stunning. Together with a snubbered 40,000uF supply for each channel, there is no shortage of impact, resolution and separation.

And lastly, you might want to try the Class A mod. I'd be interested to hear your opinions on it. It basically involves running a small current through the output stage to bias it into Class A upto a few milliwatts. This helps with the crossover distortion and linearises the output stage at lower levels (I'm assuming you'll be doing a lot of close-range listening). A 1.5K, 10 watt resistor from the negative rail to the output should be good for 23mA, which will get you some benefits without incurring too much heat penalty. Try and keep it below 50mA if your heatsink is not up to it, and because the 4780 is two chips in the same package and so more thermally challenging.

Have fun!

Sorry for posting the wrong info..the capacitor is infact a TUP series from panasonic.

My PCB is infact very simmilar to the reference PCB from national..I could try P2P but it will get a lot messier with 4780 compared to 3886 which is easier to work with.
with a regulated supply the speaker cone movemet is relatively less compared to a normal psu ( which is a good thing I believe..may be wrong aslo :) ), I have noticed this a number of times with bass heavy tracks , the heat dissipation is considerably less compared to non regulated too.Although
I must admit as far as sound quality is concerned I didn't notice any significant difference.

I have built STK's starting from STK439 way back in 97 with unregulated psu's and enjoyed them every bit.My current listening amp is 2*TDA1514A with unregulated psu and sounds pretty good to me.
 

sasmit

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I know saying anything wrong about peter's pcb is foolish..but if you read national's application notes especially on LM4702 based Hi-fi there are quite a few ideas on pcb layout.One of the things I noticed is no-no for a groundplane type layout for audio amps. I am not too sure about it but peters design is almost like a ground plane type design.

One more surprising thing is after this app note came out, peter has started a new thread on diyaudio on LM4780 PCB which is very simmilar to mine and national's layout.I even replied to the post saying design was very simmilar to naional's reference pcb but no response from peter :eek:
 

sasmit

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And lastly, you might want to try the Class A mod. I'd be interested to hear your opinions on it. It basically involves running a small current through the output stage to bias it into Class A upto a few milliwatts. This helps with the crossover distortion and linearises the output stage at lower levels (I'm assuming you'll be doing a lot of close-range listening). A 1.5K, 10 watt resistor from the negative rail to the output should be good for 23mA, which will get you some benefits without incurring too much heat penalty. Try and keep it below 50mA if your heatsink is not up to it, and because the 4780 is two chips in the same package and so more thermally challenging.

Have fun!

I think a class AB by default works in a fashion you mentioned. All class AB designs work upto a few milliwatts in Class A to keep the crossover distortion low and then when the output devices are fully biased they become class B with each half conducting during the respective cycles of the input signal, that is how the classAB name came by.Correct me if I am wrong
 

sasmit

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you should be able to obtain them in Hyderabad..my local supplier gets them from some distributor in kokata.
 

sasmit

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Excuse the terrible soldering, this was done three years ago and I made lots of changes to the boards so a lot traces got ripped.

No the soldering can't be ignored :D ..jokin..but the joints look a bit oxidized to me.Here is my PCB layout...I know lots of comments..but I already got one set made and assembled :eek:hyeah:
 
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sasmit

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I meant in general..if I am able to get them in Bhubaneswar.. u should be able to get them there :D no offence intended..I haven't been able to go to my local supplier yet, so don't know who the actual distributor is from whom he is able to get them..
 
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