[INDIA] Any DIYer made a Gainclone in India. willing to help?

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smarcher,
The idea I had of using a [INDIA] tag on the subject line was for something specific to India, ie, where to get components, where to look for raw materials. It was not intended to propogate this very typical mentality all of us Indians seem to share: groupism. I'm sure lots of people from other countries are more than happy to help you out with ideas and advice, not just the few of the members from Bharat :) So unless you have some info/query which is specific to India, please don't use the [INDIA] tag... if anything, you'll get fewer replies from others.

That aside, I believe Tarun has made a gainclone based on the LM3875. I've made a pair based on the LM3886. If memory serves me right, Ashok and a few others have made gainclones based on the Philips ICs (TDA series, I forget the part no.). What kind of specific help are you looking for?
 
Hmm
You have answered your own criticism of my using the India tag. To make a gainclone I would not need to post anything on this forum since there is so much info available on the Net. Especially with BrianGt's excellent user manual.

I used the INDIA tag exactly for the purpose of knowing what parts indians were using so as to get an idea of what is available in the local market.

Specifially, I wanted to know what capacitors (brand name) and power supply are used.

Anyways, lets not quibble since this is also a so called Indian trait.

Thanks
 
Ok, gotcha. It just wasn't that obvious from your first post what kind of info you were looking for.

Capacitors: I've used Samsung 4700uF/50V x2 (per rail) in a C-R-C form. Each cap is bypassed with a 0.1uF ceramic. The PSU is built on a PCB. You could also look for screw-terminal capacitors and build the PSU without a PCB, although this would be more expensive. I've also put 0.1uF film capacitors across the diodes in the bridge rectifier to reduce switching noise. Others have commented that this is not of much use unless there are small resistors in series with the diodes. This is not an option for me since I have used encapsulated bridges. Attached is a pic of my PSU board. From left to right, you can see the input connectors (green), bridges (black), film caps (yellow), filter caps (blue and gold), resistor (red), output connector (green), fuse holder (black) and ground connector (green). Excuse the lousy quality my webcam puts out... BTW, all these components are locally available, and have not been ordered thru any mail-order firm, etc.

Transformers: If you want to use toroidal core trafos (maybe to save space), one good source is Miracle Electronics (www.toroidal.com), they are based in B'lore and will courier transformers to wherever. Their website has an extensive catalogue, and you can email them for a quote. I've used an E-I core for both the amps I've built so far, but one which is now under construction will make use of a 25-0-25 225VA toroid core I bought from Miracle. One problem with Miracle is they are a bit expensive (I paid ~Rs. 1400 for mine, incl shipping + tax). Perhaps the Calcutta local electronics market will have cheaper transformers. For your first amp, you may want to settle for something a bit less expensive.
 

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Hi roadkill

Thanks for the detailed reply. I am a complete newbie but am really interested in this amp. I was trying to follow BrianGt's schematic. I set out to find 1500uF Panasanic FC caps but no luck. Can I use Samsung 2200uF instead? The MUR860 diodes did not look like the real thing either. I am planning to make the amp on a veroboard. I do not have a PCB source yet. There do not seem to be many DIY from this part of the world on the forum. Well, I am prepared to do the leg work and will post details of shops etc. Once again thanks for you detailed reply.
 
You need to first find out if you really need those components and how they make a difference. I for one say there is no difference, but lots of others beg to disagree. In any case, since you're a beginner, and we all make mistakes sometime, it's probably wiser to stick with cheaper components and use whatever is available. Once you get the hang of it, go ahead and splurge on Panasonic caps or whatever else is the flavour of the month.

As for diodes, there have been lots of comments about how diodes introduce switching noise. Often, capacitors are used to suppress this noise. Using a high-speed diode will only make this noise worse, and in the bargain, introduce no benefit electrically. Psycho-acoustic (more psycho than acoustic, if you ask me) effects may still exist, though.

Veroboard: problem with that is that most chip amps pins don't lie on 0.1" centres, so you'll have to carefully bend the pins.

There actually are plenty of folks from India here, but all seem to be mysteriously silent... *shrug*
 
HI roadkill

Can you if possible post detailed parts list. I will be using LM3875 chips. I am not too keen on the kit route. Would like to try doing it myself. It is quite interesting roaming in the market trying to collect parts. ;-)

What caps do you suggest?

TIA

Sudeep
 
Guys, you are in a different league altogether. I used paypal. The kit comes in parts & customs is not usually bothered about this. They have bigger fish to catch.

Abidr,

Point taken. The kit route does not justify the DIY spirit. However, I find it difficult to learn electronics. I prefer to go the kit route. I am more inclined towards DIY speakers which I have made my own & have spent a lot of time doing . 3-way active.

Roadkill,

Yes, I did a quick visit of the market here in Blr & I know the parts put together cost about 200/- Did you design your own pcb ? Why don't we do a high-power bridge/parallel/b-p ?
 
Hi, I'd be happy to design a PCB based on National's BPA200 or BPA100, but these are for LM3886, not LM3875. I believe they are the same except for one pin which on the 3886 is V+ and on the 3875 is an NC. And yes, I made my own PCB, which I've posted here.

Then again, Abid has already said he's willing to release his designs. You can print the foil patterns onto paper with a laser printer and give it in at Om Electronics, SP road for a single-sided PCB. It's cheaper to make a PCB for one amp, and ask him for multiple copies of the board.

Detailed parts list:
it's straight out of the 3886 datasheet. I've used metal film resistors (1% tolerance. Gain setting resistors were sorted for matching value), film capacitors for HF bypass, ceramics for RF rejection, Samsung electrolytics (470u/50V) for local (on-board bypass, not to be confused with the bypass caps on the PSU). I also used Relimate connectors for signal and Phoenix-type moving cage wire terminations for speaker connection and power input. The PCB is tiny, it's just 1.7" by 1.7". As I've already mentioned, I'm not a believer in capacitor sound. At least, not for the filter caps. Just to be sure, I bought some Elna For Audio caps (10000 uF/71V) to use in an amp (gainclone) I built for a friend... no difference.

Sunil,
I know most ppl believe the chip amps dont sound good. I for one think they sound great... perhaps maybe even a little too great to waste on a sub. For a sub, you can get away with using a regular class B or AB amp with relatively cheap output transistors, biased at a point which will give a bit of distortion but keeping them cool. That's what I've done, anyway: a dual P3A bridged. I use some transistors labelled with "2SA1302" etc, but I'm pretty sure they're fake. So far, no fireworks, no problems. Been using this amp every day for the past 3 months.

One thing about using Brian's PCBs: my oh my they look good! Compared to the (relatively) crappy looking PCBs we get here, they're awesome.
 
Diy means doing everything ourselves & knowing/learning the art of electronics. Calcutta, Mumbai, Delhi, Banglore & Chennai hv excellent component shops. Beside IC's, u can get very wide range of condensors now. Initially not knowing the source is a problem but better to look for shops in ur own city. Knowing this takes lot of time but it is a long term proposal for serious DIY. If u still need help, lot of friends r here to help.
Mahendra Palesha
 
Thanks.

Thanks Roadkill,
I will check that out.
I can't find any 10kuF 71 V caps in Chennai. There are lots of 50V and 100V caps. Even 75V and 63V are not easy to find. The few 63 V caps I found are made by strange companies. I suspect that they may be Chinese. The ( blue) 100V computer grade ones look very dusty. I wonder if they are pretty old and taken off the shelves from other countries. It says Sprague on them.
Cheers,
Ashok.
 
Why the fixation on 71 V anyway? If 50V is too low, use a 100V cap. They're only a little bigger/expensive.

BTW, Amar Radio has Alcon make computer-type capacitors, both with screw terminals and with solderable lugs. I bought the lug kind for Rs. 120 each (10000uF, 63V). These are brand new, and I can vouch for Alcon caps being good: I have a 17 year old Alcon cap whose value is within spec.
 
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