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Old 22nd October 2014, 09:56 AM   #1
batty is offline batty  Australia
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Default Building a Power amp...

I have purchased and built up a couple of power amp pcbs, they require + and - 50v rails.

I have a large toroidal transformer with 2 40v secondaries and 2 25amp bridge rectifiers, I know how to put together an unregulated supply but want it regulated, anyone know of a good cct or a link to somewhere I can read about regulation.

I seem to remember 2N3055 and it's compliment were good for hi current circuits.

Thanks for reading this and any constructive help is welcome.

Cheers

Steve
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Old 22nd October 2014, 12:16 PM   #2
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40 VAC will give you roughly 54-55 V raw DC, if you want regulated supplies from that voltage, the voltage differential won't be enough for 50v regulated. For that (depending on the type of the regulator's dropout voltage), you need at least 8-10 volts difference between the input and output. Less with BJT types, more with FET-s.
Anyway, if you want to use them for power amp stages, you don't really need regulated supplies, specially with symmetrical supply ones, since their common mode PSRR (ripple rejection ratio) is rather good, there -if you really want one- you can use a simple capacitance multiplier type filter. There the drop will be around 4-5 Volts (with Darlingtons -or connected as Darlington types).
Of course all above comments are valid for a power transformer, where the secondary voltages won't drop too much under heavy load conditions.....

Last edited by dragonweed; 22nd October 2014 at 12:24 PM.
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Old 22nd October 2014, 12:38 PM   #3
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Motorola, or ONSEMI TIP 140-147 series complementary power Darlingtons are perfect for that kind of application.
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Old 22nd October 2014, 03:08 PM   #4
AndrewT is offline AndrewT  Scotland
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In my opinion you are wasting time and resources going down that regulated route.
Just buy the correct transformer and save yourself a lot of hassle.
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Old 23rd October 2014, 02:20 AM   #5
djk is offline djk
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"I seem to remember 2N3055 "

....is only rated at 60V forward biased, 30V.
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Old 23rd October 2014, 04:16 AM   #6
wg_ski is offline wg_ski  United States
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He was thinking of using 3055's as pass transistors for the regulators. Voltage ok, but beta is too low. You'd need half a dozen in parallel and another to drive them. I'd be thinking MJ11015 and its complement (30A) or MJ11032 (50A).

If you just want to lower the voltage to +/-50V, add a couple of turns around the outside with some #14 soild core THHN and wire it in series with the PRIMARY. That is, make it a higher voltage primary. Check polarity and # of turns with a light bulb in series first. When the secondary output drops (and magnetization current drops too) you've got the polarity of the extra winding right. Spread the turns evenly around the core for best performance. Do not use magnet wire for this - use the insulated stuff -- it's safer.
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Old 23rd October 2014, 06:53 AM   #7
JMFahey is online now JMFahey  Argentina
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Quote:
Originally Posted by batty View Post
I have purchased and built up a couple of power amp pcbs, they require + and - 50v rails.
I have a large toroidal transformer with 2 40v secondaries and 2 25amp bridge rectifiers, I know how to put together an unregulated supply but want it regulated, anyone know of a good cct or a link to somewhere I can read about regulation.
You don't have what it takes to regulate it down to +/-50V.

That said, you'll have raw +/- 56V or a little less, not ridiculously too much.

Post what amp you have, and specially its output transistors ... *maybe* it can work with +/- 56V

Schematic would be best.
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Old 23rd October 2014, 08:35 AM   #8
batty is offline batty  Australia
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I don't have schematic, but o/p devices are Toshiba 5200 x 3 and 1943 x3 for each channel.

Seller said the amp was good for upto around 60 volts per rail.

I may just go unregulated with a large bank of caps.
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Last edited by batty; 23rd October 2014 at 08:37 AM. Reason: more data
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Old 23rd October 2014, 04:30 PM   #9
wg_ski is offline wg_ski  United States
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RMX1450 uses three C5200/1943 pairs and +/-67 V rails and they don't blow up often. Yours will be fine with 4R loads.
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Old 23rd October 2014, 05:31 PM   #10
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Quote:
Originally Posted by wg_ski View Post
RMX1450 uses three C5200/1943 pairs and +/-67 V rails and they don't blow up often. Yours will be fine with 4R loads.
You don't overlook the voltage in the load, because in this mode of operation voltage is lower than those +/- 67Vdc (falls below +/-60Vdc). Under these conditions the voltage peak to peak on 4 Ohm load may be about ~100Vpp, which means ~35Vrms on the load; or otherwise, about 300W / 4 ohm.

@batty, GX400 may be a good alternative to your requirements:
GX400 - 400W Audio Amplifier - Made in Romania
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