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My LM3875 based chipamp!
http://diyaudioprojects.com/Forum/viewtopic.php?f=10&t=24
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Author:  dmc [ 18 Aug 2008, 06:52 ]
Post subject:  Re: My LM3875 based chipamp!

hi gmilitano,
thanks your suggestions, anyway can i use 160VA(250V, 50Hz) with 2A? :confused:

Author:  Gio [ 18 Aug 2008, 07:03 ]
Post subject:  Re: My LM3875 based chipamp!

If your mains voltage is 250V and the transformer 160VA, a 1A filter would be sufficient. If your mains voltage is 120V, you will need a 2A filter.

Author:  mwhouston [ 28 Aug 2008, 19:01 ]
Post subject:  Re: My LM3875 based chipamp!

dmc wrote:
bsgd wrote:
Well this is my LM3875 based chip amp!

It's basically a copy of Mark's LM3875 gainclone chip amp.
I used 6800uF caps instead of the 10000uFs and also used an ALPS black beauty as volume pot.
The tranny I got from an old YAMAHA active subwoofer.

This is a great project for anyone willing to get into audio DIY. It's pretty straight forward to build and there's no high voltage to get you into trouble ;) .


i'm interest this amp too, but i dont know how many ampere EMI filter it is.
it is 2A? :headphones:


All the power amps I have built up to the last two valve amps I have used cheap power filters. It is a good idea and I'm sure does help with RFI clean-up. Also they are easy to install. I think if you can fit them in the case and you don't mind the extra work to mount them, go for it. As I said they can only help.

Another even easier way to help with real basic power filtering is to pass all active, neutral and earth wires, inside the case, through ferrite cores. Even heavy mains wire can be passed two or three times through a large ferrite core. An even more lazy versions of this is to pass your earth wire only two or three times through a ferrite choke (core). So not the active and neutral just the earth.

I earth all my chassis when the device has mains connected (and fuse the active). This stops RF being spread into the chassis which can radiate from the metal case into more sensitive components or if your signal earth and power earth are one, helps stop RF being mixed with the signal. These are very simple steps to take to reduce RF in the audio path and it DOES improve the sound.

Author:  bsgd [ 02 Sep 2008, 06:44 ]
Post subject:  Re: My LM3875 based chipamp!

Right now I'm also using ferrite chokes everywhere in my projects (I finally managed to get some around here). They do help.
In this LM3875 project I didnt use any ferrite chokes or EMI filters cause I didnt have a single one on hand (you see, I live in Brazil and to get those parts I need to buy them from US). What I do use is just a 470nF/275vac X2 certified cap at the power input (sometimes, if I can get hold of a small choke I use it too for an LC filter).

Author:  dmc [ 09 Sep 2008, 07:12 ]
Post subject:  Re: My LM3875 based chipamp!

gmilitano wrote:
If your mains voltage is 250V and the transformer 160VA, a 1A filter would be sufficient. If your mains voltage is 120V, you will need a 2A filter.



:up: thx gmilitano.. :) ;)

Author:  dmc [ 10 Sep 2008, 08:57 ]
Post subject:  Re: My LM3875 based chipamp!

actually how do we choose a capacitor value in this kit?
some using 10,000uF, 6,500uF and 1500uF?:confused:

Author:  dmc [ 10 Sep 2008, 09:31 ]
Post subject:  Re: My LM3875 based chipamp!

and is it necessary we use the 160 AV transformer?can i change to lower rate? :confused: :worried:

Author:  RiGuy [ 10 Sep 2008, 09:45 ]
Post subject:  Re: My LM3875 based chipamp!

The big toroid is pretty necessary. Everyone is using a minimum of 80VA on each channel and up to 400VA. You have to oversize to get punch and sustained bass. I built the LM3886 and its similar to the LM3875. I use 100uf on the chip and 144kuf on the power supply. There is an explanation of how to select size on the datasheet for the LM3875 but on this forum there are several LM3875 projects.
For instance
http://diyaudioprojects.com/Chip/Synerg ... Gainclone/
The more capacitance you put on the power supply the more you can make up for the smaller toroid to sustain long bass and punch it up. Want some cheap electrolytics with big power for this? Go to http://www.apexjr.com and find the 12,000uf caps for 1.99US each. You could mount those on the chip if you wanted, but I think you put the big inexpensive caps in the PS and snub them as Mark did in that project. Then snub your rectifiers as well. The put high quality lower capacitance caps on the chip. Many use 100uf Panasonic FC caps from digikey. You can use that brand for the rest of the caps on the chip as well and the performance per dollar is high compared to other brands that cost less/more. You also get away with making a very small amp that way and maybe you make the big power supply separate so you could use it to run other amps that run on similar voltage.
My suggestion would be to go medium on the toroid unless you can find a cheapie on ebay for like 300-600VA. Try to get at least 250VA but dont be discouraged if 180 is all you come up with. You can crutch it with a big bank of those cheap caps. How much caps do you need? Well at least this is something you can EASILY pop more caps into for taste. Start with ~20,000uf per rail if you are going small and high quality on the chip.
Ri

http://www.apexjr.com/capacitorsR.html#Radials

Author:  dmc [ 10 Sep 2008, 11:36 ]
Post subject:  Re: My LM3875 based chipamp!

RiGuy wrote:
The big toroid is pretty necessary. Everyone is using a minimum of 80VA on each channel and up to 400VA. You have to oversize to get punch and sustained bass. I built the LM3886 and its similar to the LM3875. I use 100uf on the chip and 144kuf on the power supply. There is an explanation of how to select size on the datasheet for the LM3875 but on this forum there are several LM3875 projects.
For instance
http://diyaudioprojects.com/Chip/Synerg ... Gainclone/
The more capacitance you put on the power supply the more you can make up for the smaller toroid to sustain long bass and punch it up. Want some cheap electrolytics with big power for this? Go to http://www.apexjr.com and find the 12,000uf caps for 1.99US each. You could mount those on the chip if you wanted, but I think you put the big inexpensive caps in the PS and snub them as Mark did in that project. Then snub your rectifiers as well. The put high quality lower capacitance caps on the chip. Many use 100uf Panasonic FC caps from digikey. You can use that brand for the rest of the caps on the chip as well and the performance per dollar is high compared to other brands that cost less/more. You also get away with making a very small amp that way and maybe you make the big power supply separate so you could use it to run other amps that run on similar voltage.
My suggestion would be to go medium on the toroid unless you can find a cheapie on ebay for like 300-600VA. Try to get at least 250VA but dont be discouraged if 180 is all you come up with. You can crutch it with a big bank of those cheap caps. How much caps do you need? Well at least this is something you can EASILY pop more caps into for taste. Start with ~20,000uf per rail if you are going small and high quality on the chip.
Ri

http://www.apexjr.com/capacitorsR.html#Radials




Woo :shock: :shock: ....unexpected capacitor act important role here..
thanks buddy make me get shock... :D
then i will get some 20,000uf for the power supply, and 100uf for the chip. :mrgreen:

Author:  RiGuy [ 10 Sep 2008, 11:48 ]
Post subject:  Re: My LM3875 based chipamp!

And remember those caps for the PS can be any size and just string them along in a capacitor bank til you get the right amount of capacitance. Make sure you get a good voltage rating for the caps. For the LM3875 if you stick to 50V or more you are going to be fine.
What was shocking?
Ri

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