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Old 3rd September 2004, 05:26 PM   #11
MikeB is offline MikeB  Germany
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hi eva,
As the amp is bridged, it can put out double the voltage, so:
18-3 = 15 *2 -> 30 make 112watt into 4 ohm...
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Old 3rd September 2004, 05:43 PM   #12
Eva is offline Eva  Spain
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True, but I was talking about supply sagging. Most simple 18V supplies tend to drop to 12V with load so in order to get 18V under load the no-load voltage should be higher
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Old 3rd September 2004, 10:56 PM   #13
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Default The Radio Amateus power supplies can be good to you

Normally they used 17 plus 17 volts AC, heavy rectifiers and heavy output transistors, most of those supplies are designed to hold continuosly 200 watts, supplying 13.8 volts.

Internal DC Voltage is around 24 Volts DC that goes to stabilizer and series regulation 2n3055 units.... each one holding 30 watts of heat normally.

I think one of that can be good to you, as i can see you normally use low voltage in your amplifiers...you can adjust internally to 18 Volts.... it will give you the same 200 watts....11 amperes easy in this case.... and the transistors will be cold...because the 24 volts will drop a lot...you will have 2 or 3 volts over transistors.

Almost all those supplies uses series regulation, with one error transistor in the output, with a trimpot in the center of output voltage divider and some darlington connections to the parallelled 2N3055.

I think this can be very usefull to you...your dream supply!

regards,

Carlos
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Old 4th September 2004, 07:24 AM   #14
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Quote:
Originally posted by Eva
For a unregulated supply I would use the highest supply voltage supported by the IC to account for sagging
Eva,
Going by your advise, I've decided to invest in a 18-0-18V, 5A Transformer. No-load voltage should work to about +-24V, i.e. 2V greater than ic's absolute maximum of +-22V. Hope this is OK. The next lower voltage transformer available is only 12-0-12, 5A.

The same schematic was published in another article in elektor, but this time with a power supply of 12-0-12, 7A transformer. No special regulation but 22,000 MFD *2 caps. This could be a typo - not sure. The author claims it can deliver 200W .

The original schematic was designed for public address systems which can operate on 12V car batteries.

Carlos, Is that your son?
Radio amateur supply ....sounds expensive, but would certainly be my dream supply.
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Old 4th September 2004, 10:24 AM   #15
MikeB is offline MikeB  Germany
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Quote:
Originally posted by Eva
True, but I was talking about supply sagging. Most simple 18V supplies tend to drop to 12V with load so in order to get 18V under load the no-load voltage should be higher
Ah, sorry...
But these are very poor psu's aren't they ? Internal resistance of 0.66ohms...
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Old 4th September 2004, 05:41 PM   #16
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Default Rosham, thank you the attention, the little girl

Is my last daughter (hehe, maybe...not sure!), i have four beautifull girls, and my Spanish beauty, my wife.
As Arabic people, i have my own "harém", and i am proud of that.

Only girls here.... also a Maid...this is wonderfull!

Larissa Rapela is her name...now with Spain Passport, will to go Orenz Barbadannes, where the family started.

by

Carlos
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Old 4th September 2004, 06:36 PM   #17
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It seems to me that a very important point has been missed. The opamps in the schematic given in post#1 are TDA2030 chip amps from Philips, and the schematic shows a method of extracting more power out of them. The reason +/-18v is used is that this is the maximum supply voltage for these chips. An 18v-0-18v transformer will blow them up.
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Old 5th September 2004, 02:45 AM   #18
Eva is offline Eva  Spain
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18-0-18V transformers tend to produce +-27V after rectification with no load since those 18V are rated at full load instead of no load

+-22V at idle may be OK for this IC but +-27V may be too high for most units, altough some units may survive. In case of blown ICs an easy solution is to add turns to the transformer in order to reduce those 18-0-18V to 14-0-14V or add some kind of regulation
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Old 5th September 2004, 11:17 AM   #19
johnnyx is offline johnnyx  United Kingdom
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18v-0-18v is the absolute maximum for the TDA2030 chip.

The LM1875 is pin - compatible with the TDA2030, the same PCB can be used for both, and it will work fine with the 18v - 0 - 18v transformer. It has better performance too. The circuit may need some changes, because the quiescent current will be different, but it's capable of more power.
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Old 5th September 2004, 03:23 PM   #20
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Actually I'm using TDA 2030A . This has a max supply is +-22 , as compared to +-18 of TDA 2030. Anyway I've decided to get down to 12-0-12V transformer. While testing, found the chip tends to get too hot under excess voltage. You guys are right. The chip wont hold.

Carlos...4 kids and a beautiful wife....a very happy family indeed!!
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