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Very cheap SMPS to power gainclones and other audio amps.
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Author:  delta67 [ 11 Aug 2017, 07:51 ]
Post subject:  Very cheap SMPS to power gainclones and other audio amps.

The debate around SMPS vs Iron cored transformers in powering HI-FI audio amplifiers seems to end in favour of the switching power supplies !!

Here is an interesting example about such a debate:
https://electronics.stackexchange.com/q ... wer-supply


And here is a praiseful review of an SMPS powered gainclone:
http://www.decdun.me.uk/gainclonesmps.html
Another one from the inventor of the gainclone himself (Thanks Mike for the precious gift to the audio community) :
http://www.dogbreath.de/Audiodigit/Audiodigit.html

You are convinced? If NO leave NOW, this thread is not for you.

Fore those who are interested I’ll show you how to modify a PC AT or ATX power supply to get symmetric output from +/-12V to +/-24V @ some Amperes (this depends on the power of the PS).

We need a PS with center tapped output transformer and a TL494, or clone ( KA7500, KIA494...), control IC. But other PSs can also be used I think.

Some facts (please correct me if I’m wrong):
- We can get up to 24V from the +/-12V rails by changing a single resistor.
- The limitation of the -12V rail is due to the used “small” rectifiers only. If we change them with “big” ones we can sink as much amperes as from the +12V rail.

There is many tutorials on the web showing how to mode a PC PS to get 13.8V. I recommend understanding this step first.
http://electronics.pl7.de/power-supplie ... v-dc-20-a/

and more links here:
http://www.f8eho.net/content/alimentations

What we need to do?
1- Change the output of +/-12V rails to the value we want.
2- Change the “small” diodes in the -12V rail by “big” ones.
3- Omit the +5V and +3.3V rails.

The final circuit which we must do is shown in the attachments.

- For L1 and L2 wind some turns of 1mm copper wire on the yellow toroidal core.
- L3 and L4 are the +12V rail inductors (you can salvage from another PS).
- 1000uF Capacitors must be rated at about 20% more than the needed V value .
- The rectifying diodes must have 50V @ 10A or more.

Choose R1, R2 values to get the needed V.

A much simpler way for rectifying and filtering is shown in the following link. Despite a simple alternance rectification and a basic filtering the author claims that the PS works very well:

http://www.astuces-pratiques.fr/electro ... 00w-a-500w

Author:  gofar99 [ 11 Aug 2017, 21:51 ]
Post subject:  Re: Very cheap SMPS to power gainclones and other audio amps

Hi, I use SMPS all the time. They are just fine. I have seen the mods for using PC power supplies but they are often larger than what I am powering. With ones from several companies quite inexpensive I just buy what I need.

Good listening
Bruce

Author:  delta67 [ 12 Aug 2017, 04:29 ]
Post subject:  Re: Very cheap SMPS to power gainclones and other audio amps

Thanks gofar99 for the feedback.
Yes, the PC power supplies are "large", literally and figuratively, with relativelly big boxes and high power.
The advantage are cheap and we can find them everywhere. You live in the USA, so you can buy any thing you need, but think about those guys in the 3rd world !!
By using a moded PC PS you have double satisfaction, the joy of DIY and the fonctionnality.
How your amp sounds with the SMPS?

Author:  M. Gregg [ 12 Aug 2017, 06:22 ]
Post subject:  Re: Very cheap SMPS to power gainclones and other audio amps

I use a charge pump in my Aikido line stage.

This was trying to see what I could drive off a laptop PSU for fun.
There was no real reason to do this except I wanted to just power it from a laptop PSU using only DC into the preamp.
I used a charge pump to generate 350v and fed this into a Maida regulator. (low current) Feeding two ECC88 and two EM80.
Because of the SRPP and heater lift voltages using the same supply as the B+ I used a DC to DC converter to isolate the heaters.
The simple filter (pic) helps chop off the noise..
I have never powered a power section off SMPS but I like the line stage.
This wasn't to reduce cost just wanted to see if it worked for fun.
Some people on the net have used nixie tube B+ circuits to good effect.

Regards
M. Gregg

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