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Old 27th October 2007, 03:38 PM   #11
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The TDA7294 high-efficiency circuit is actually a Class-G output stage with dual rail pairs, a low pair at +/- 20V and a high pair at +/- 40V. It is worth reading and understanding Class-G operation before attempting this circuit. Douglas Self's book has a chapter and example discrete bipolar circuit for Class-G operation, but the principles are the same here.

The basic TDA7294 circuit (non-bridged) is simple and reliable - there are numerous tweaks to it in various gainclone threads on this forum. I would strongly recommend it as an excellent first DIY amplifier project.

The TDA7294 is available at Modern Electronics (off S.P. Road) for Rs.85, and the basic circuit PCB is available at Om Electronics for Rs.20. You'll need two each for dual-channel (stereo) operation.

The entire assembled module is also available for Rs.180, but I'd advise buying the bare PCB, IC, passives, etc. and assembling it - this allows the use of premium capacitors, components, etc.

A well-designed discrete solid-state amp like the Symasym, Leach, Aleph, GEM, AKSA, JLH, SoZ, DoZ or derivatives can easily outperform anything else, but the quality of components, careful matching, assembly, testing and tweaking are mandatory.

Chipamps/hybrid modules can give reasonable results without expending as much effort, but for best results, a similar process of iterative tweaking is recommended.

For Bass/Treble adjustment, I'd suggest using a stock passive Baxendall tone control. These are available as stock populated PCBs with all components, dual-ganged pots, etc. already installed at Pooja Electronics (off S.P. Road).
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Old 28th October 2007, 12:09 PM   #12
Paswa is offline Paswa  India
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I live near kolkata, west bengal. Some really good circuit's PCB are not available here. Is there any PCB supplier in India that ships PCB via mail courier ?
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Old 29th October 2007, 01:13 PM   #13
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When buying components, such as capacitors, which brands are considered as premium? The same goes for transformers.

Thanks,

Nitin.
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Old 29th October 2007, 02:37 PM   #14
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In electrolytic capacitors: Elna, Panasonic, Nippon Chemicon, Rubycon, Nichicon, Sanyo. Specific series have specific properties - some are good in the signal path, some only for supply filtering and bypass. They're not always available in the desired values. The premium types like Cerafine, Black Gates, Silmic IIs, etc are pretty much unobtainium, and are likely to be counterfeits. I've found Panasonic FC (which is the best inexpensive electrolytic for just about any audio application) and FJ from time to time. Elna ROS can be hard to find, except some occasional surplus items. Elna RJH and RJ4 show up from time to time, and they're OK for supply filtering/bypass.

In polypropylene: Wima - hard to find.

In film/mylar: Vishay, Philips are OK.

In most other types: brand doesn't really matter. Silver Mica is preferred for some small values related to compensation/stability. Ceramics are to avoided in the signal path.

Toroidal transformers: Salzer, Miracle (both are made to order)

E-I transformers: brand probably doesn't matter as long as it meets specs.

Metal film resistors: Dale, Vishay is OK - any 1% tolerance type should be OK. Carbon-film should be avoided unless that value is unavailable in metal film.

Transistors: Toshiba, Panasonic, Hitachi, NEC, ON Semi, Philips, SG. Transistors and ICs are very heavily counterfeited, especially power, driver and high-voltage types. Never buy in quantity unless you're sure that you've got a genuine item.

RCA connectors: Neutrik gold-plated (only the male connectors are available at S.P.Road for making the external line-level cables).
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Old 29th October 2007, 03:30 PM   #15
Paswa is offline Paswa  India
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as like maplin.com, velleman.com etc, is there any geniune electronics goods and parts supplier/retailer chain in India ?
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Old 29th October 2007, 03:47 PM   #16
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They are there in Bangalore, but you may have to pay through your nose or buy in quantity. RS Components will sell retail quantities, but marked up hugely. Arrow and Future Electronics are wholesale distributors, and will only sell in volume. You probably can't economically build DIY prototypes with parts sourced this way.

For DIY, you best bets are the traditional electronics bazaars like Ritchie Street, Lamington Road, S.P. Road, etc., where you can buy single-unit quantities of parts with only a small markup to wholesale.
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