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Old 21st January 2004, 08:04 AM   #21
vossie is offline vossie  Israel
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Try stephan@vortech.co.za
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Old 21st January 2004, 10:52 AM   #22
Shaun is offline Shaun  South Africa
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Hi, Stephan

Thermal stability is not an issue with this amp. It runs rather cool, being a (almost) class B design. But even when I had the output biased to 100mA, the drivers hardly got warm. Even driven hard, the drivers hardly manage a blush. It's a brilliantly simple and effective configuration: the fact that the devices that undergo the largest changes in temperature (o/p transistors) are not critical to output stage stability.

So much for thermal stability of the output stage...

This amp is not dc coupled, though, and the dc gain is unity, so that dc drift is not an issue here. However, in my PCB layout, I did provide for the possibility of dc coupling. The differential pair and current mirrors are placed close to each other, face-to-face, respectively. So, after gain-matching them, they may be mechanically/thermally coupled. This should prevent any possiblilty of thermal drift.

As for the next meeting venue, I'll only get to see the contact person this evening.

I'll email you the schematic.
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Old 21st January 2004, 08:09 PM   #23
Shannon is offline Shannon  South Africa
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Default Local Component Suppliers & Knowledge Base

Stuart,

Thanks for the info. I'll contact them this week to check prices.

I think the online idea is good. I have some webspace that I've never really used over the last few years. However, it would need to be static for now.
I'll put a basic one together and post the link when its ready.

I want to include the following:
-Heatsinks,
-Pots (stereo conductive plastic eg Bourns, Vishay etc)
-Lateral Mosfets eg 2SK1058/2SJ169
-Complementary Power Transistors eg 2SC3281/2SA1302, MJ15003/MJ15004
-Chokes (used to be an RF engineer working in Highveld Techno Park - can't remember the company - that would wind this )
-dials (access to milling machine eg engineering companies)
-Faceplates (eg http://brian.darg.net) - aluminium

etc
Anyone with info on suppliers for the above (including approx pricing) and anything else you want to include, please post it or email.
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Old 22nd January 2004, 07:32 AM   #24
Shaun is offline Shaun  South Africa
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Hello from sunny South Africa
OK, found the prices of some transformers from W. Gardner & Son:

400VA: R310.50
225VA: R240.50

Plus (optional)-
Vacuum impregnation: R15/R10 resp
Dipping: R20/R20 resp

Heatsinks
Mantech have a nice 200mm heatsink, which can be ordered to your length. It is not anodised.

Transistors
Beware counterfeit transistors. I'd rather buy from ON Semi directly, but MOQ is 25 pieces.

Communica should be able to supply chokes and mains filters
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Old 22nd January 2004, 07:54 AM   #25
DieterD is offline DieterD
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Wow, at last a few more South Africans.

My interest mainly high power amps, (son's a DJ) Presntly building a TO3 version of the ESP P68 300 watt amp.

I bought TO3 MJ15022/3 from Candy Electronic in Durban, about R 14.00 each, however the first lot tried blew when tested on my revised amp, now Ive gotta figure out if I messed up or if they are fakes. Weird actually, the amp worked fine with only two outputs full voltage, I then fitted the new trannied on a big heatsink, three per side, amp worked but on testing at high volume blew, and took the drivers with. I think I should opne the trannies and have a look inside before I carry on.

We build our own speaker boxes, and scrounge old rack mountable amp boxes from local music shops, but it all looks rather tatty and a database of good South African suppliers would be very handy. I will start getting all my previous suppliers detaisl together and will mail to whever wants them.

Proudly South African
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Old 22nd January 2004, 08:05 AM   #26
Shaun is offline Shaun  South Africa
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Default Fakes

Hi, DieterD

Check this http://www.massey.ac.nz/~jcmarsha/fakes/ and the links on the page.
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Old 22nd January 2004, 09:36 AM   #27
DieterD is offline DieterD
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Yeh, seen that,
Funny story, I first built 2 P68s using 2SC3281 and 2SA1302's salvaged from a dead Sammick amp, worked well so I decided to build two more. I ordered parts from Protech in Durban, was quoted about R 20 per pair, so I bought 8 pair. (They dont stock anymore!!)

After a while, and after reading that article I was convinced they must be fake. I built the amps anyway and my son now uses that one more than the other cause it runs cooler. Had absoluely no hassles, so they must have been genuine despite the price.

Anyone know where I can get equivalent TO3P "flatpacks" to the above in RSA, I have converted the P68 to take metal trannies but Rods design and board are really good and I would prefer to build them as designed.

DieterD
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Old 22nd January 2004, 12:44 PM   #28
Shaun is offline Shaun  South Africa
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Hello from sunny South Africa
Default Get free samples!

You can order up to 10 samples of each of different parts from ON Semi - for free!
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Old 23rd January 2004, 05:05 AM   #29
DieterD is offline DieterD
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Default Free Samples

Thats cool, but at the rate my sons need amps that will last me two weeks.
I have just discovered I have been supplied fake MJ15022/3's from Candy Electronics in Durban, do any of the South Africans out there know where I can get "proper" ones in RSA, I need about 30 odd to build a new mobile DJ rig.

Any ideas?

DieterD
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Old 23rd January 2004, 05:23 AM   #30
Shaun is offline Shaun  South Africa
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Hello from sunny South Africa
DieterD

Shannon wrote above:

Quote:
With regards to components, Avnett Kopp seems to be the only supplier carrying some of the popular semiconductors used in these designs eg MJ15003/MJ15004 etc.
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