12 - 24V Pre-regulated supply from 35V rails - diyAudio
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Old 2nd December 2006, 01:05 PM   #1
Nordic is offline Nordic  South Africa
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Default 12 - 24V Pre-regulated supply from 35V rails

I worked myself into a corner on the little gainclone I started putting together for mom in law.

I have been modularly tinkering and assembling on it for the last 2 months or so.

The end result is that I kinda started running out of space, just as I decided I would like to make it an integrated amp includeing Nuuk's class A Valve Buffer. which is kinda like noteceing the nice desert at a buffet after you stuffed yourself on the main course.

There was no space for another transformer to power the lower voltage preamp, and the relay to power to amp on after delay.so I decided to try a circuit I saw about a year ago.

Rod Elliot's simple pre-regulator. He suggested it would work for dropping up to +and-70V rails to 24V after which he implemented fixed voltage regulators.

I chose to use LM317 and LM337 to give me variable supplies (not to mention the datasheet shows an extra 10db ripple rejection). In theory the supply thus have rails that are variable through a wider range than indicated above, but I like to stay within max of 10V diffirential i.e. up to 24 minus 10V. This means in theory we should never get close to the current limit for these 2 regs, with about a 5A ceiling between the 2 of them)

As far as I understand the prereg part will supply about 100mA with those transistors (biased at 20mA) per rail, which is more than enough for an opamp based buffer, and I hope for nuuk's buffer too. (work in progress short 1 transistor which I will only receive on Monday morning)

I have tested the build up pre-post reg assembly off my + and - 35V Gainclone supply, and it is the most steady output I have seen on my primitive testing equipment yet.

So I attach the neccecary schematics and board files in zip format along with some pictures....
The only thing I omitted on the files is the 10R resistor should be 1 to 2 W... the resistor is shown, just not the wattage...

Rod claims it should be cleaner than only using a regulator.
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Old 2nd December 2006, 01:08 PM   #2
Nordic is offline Nordic  South Africa
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Zipped file containing sch, brd files as well as instructions for calculating Rx.
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File Type: zip peregreg.zip (93.0 KB, 97 views)
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Old 2nd December 2006, 01:09 PM   #3
Nordic is offline Nordic  South Africa
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Hard to talk along without seeing a schematic I guess
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Old 2nd December 2006, 01:11 PM   #4
Nordic is offline Nordic  South Africa
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Remeber the text file in the zip arhcive contains importnt info!!!

SO there you go folks, an easy way to power remotes, pic and what have you inside that case off the same transformer used for your amp.

PS. the heatinks were way overkill - I'm cheap, I sawed them out af a heatsink from an ATX psu that died.
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Old 2nd December 2006, 04:50 PM   #5
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Nordic,

I am in a very similar situation. Throwing together a cheapo sub amp for my 14 year old. The Chip amp and op amp active crossover work surprisingly well but am using batteries to power the amp amp for testing.


I spent 3 hours searching on the subject (of which I am very ignorant) and came up with the same two chips you are using. Wish I had came here first!

Could I ask, what wattage pots are you using? And what if I just use the schematic on the LM337 data sheet?

Thanks!
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Old 2nd December 2006, 06:44 PM   #6
Nordic is offline Nordic  South Africa
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I threw the packets away allready... these were pretty small Bournes trimpots, 1/4W on the outside... regular ones would work just fine in that position This little board would work pretty neat for you. But hold on until monday when I can actualy listen to something powered by it...

You could use just the second part of the board with just the 2 regulators on of course or use the firts half with fixed regulators too of course...

The problem with only using LM317 etc, is that the larger the drop you achieve, the less current it can provide without overheating.
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Old 2nd December 2006, 07:15 PM   #7
Variac is offline Variac  United States
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Nice to see the holiday elves working , spreading DIY joy.....
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Old 2nd December 2006, 11:29 PM   #8
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Ok. I can wait. This is not for Christmas. Just a little side job cause I had a chip amp and an op amp to play with.

I'm fairly new to op amps also (but beginning to really like them) but I'm only using one channel. I shouldn't draw much current. And I have plenty of heat sink as I am building on the plate of a defunct plate amp.

Anyway, this is the circuit I was going to use. The simpler the better for this job.
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Old 3rd December 2006, 05:51 AM   #9
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that looks just fine
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Old 3rd December 2006, 08:16 AM   #10
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I would increase the 1 uf to 1000, unless you have a tantalum.
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