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-   -   Major Noob question about powersupplies. (http://www.diyaudio.com/forums/chip-amps/18259-major-noob-question-about-powersupplies.html)

Hybrid fourdoor 27th July 2003 10:26 AM

Major Noob question about powersupplies.
 
Lets say you guys recommend a 24V transformer for a GC. At Parts Express they sell a 25V torrid...now heres the question...in order to hook up a stereo pair of GC circuits do I hook them both up to the same output wires, or are there mulitple taps comming off of the transformer that each have 25V?

And also can I power both chips off of one 25V supply, so long as they, collectevly, don't draw more current than the supply can handle (3A or 5A in the case of these torrids).

Also would one of the Velleman PS kits such as the one Parts Express sells that has 1.5-35V @ 1A be suitable to power a GC...using one PS per channel. I don't know how much current a Gain Clone draws so I didn't know if that was a powerfull enough supply.


Sorry for the Noob questions....maybe there are others that watch this forum that don't know this stuff too. :rolleyes:

Hybrid fourdoor 27th July 2003 10:35 AM

Ok with the kit mentioned above I would still have to buy a transformer to convert 120V AC down to 24V AC right?

Maybe someone could just point me how to make a PS for these things....it looks like a transformer....some IC's and some caps and thats it.

SY 27th July 2003 12:55 PM

Let me give a somewhat generic answer. Some people will use a transformer with a single secondary (centertapped assumed) to make a single bipolar supply, then use it to drive both channels. Some people will use a transformer with dual secondaries (each ct) to make two sets of bipolar supplies and run one to each channel separately. Or even use two separate transformers to make separate supplies for each channel. All of these schemes will work, at various cost and performance levels.

Is this what you're asking?

Nuuk 27th July 2003 12:56 PM

I think that your questions may be answered HERE

(although I apologise for the 'lack of content' ;)

S.C 28th July 2003 01:06 AM

What is the effect on sound when we using One PS or Two PSs to power two channels?:scratch: Will it sound better and louder if we use two separate one with same rating with a Single PS?

Greg Erskine 28th July 2003 02:04 AM

Hybrid fourdoor,

Nuuk site answers the technical side of your questions very nicely, but can I add:

1. I don't think you need the Velleman PS kit. The PS for a GC can be as simple as a transformer and a bridge rectifier or 4 (or 8) diodes. (and fuses ARE required on the primary at least)

2. 25V could be reaching the max recommended voltage. I am currently running my GC from a single 12-0-12 300VA toroid and I was absolutely shocked at the volume generated by these little buggers considering my speakers are very inefficient. (85dB I think)

3. You will find a lot of conflicting opinions, so sometimes it is just better to try it for yourself.

TechnoGeek 1st August 2003 03:40 AM

I purchased a 25-0-25 toroid in my gainclone project. I decided to go near the top of the documented supply voltage range so I could get the most power out of it...but it was suggested to me that the chips will generate a fair bit of heat when being supplied that high.

I'm going to try it with the modest heatsinks I have. If it runs too hot, I may try dropping the voltage using diodes in series with the power supply. Each one in series with the power supply drops the voltage by about 0.7 volts. Two diodes in series with each rail should bring it down to about the voltage you would get using a 24-0-24 unit. I would locate these diodes in the power supply enclosure, away from the chips.

I'm not sure if adding diodes in series with the power supply rails will cause any sonic degradation. Perhaps someone could comment on that? :scratch:

If it does end up sounding bad then I will probably build another amp with this transformer and get a lower voltage one for my LM3875 gainclone. I've read about good results with an 18-0-18 tranny.

Good luck!

AudioFreak 1st August 2003 04:01 AM

Quote:

Originally posted by S.C
What is the effect on sound when we using One PS or Two PSs to power two channels?:scratch: Will it sound better and louder if we use two separate one with same rating with a Single PS?

Expect the following advantages by giving each channel it's own power supply...

1) You'll get far less crosstalk / intermodulation between the 2 channels (PSRR with these chips it quite high so that's probably not a major point but it never hurts)

2) Assuming that you dont skimp on power supply rating, you'll get less voltage sag under load by using individual power supplies and so you'll get closer to rated power output for a given rail voltage.

Quote:

Originally posted by grege
The PS for a GC can be as simple as a transformer and a bridge rectifier or 4 (or 8) diodes. (and fuses ARE required on the primary at least)
And of course, dont forget about the filter capacitors.

JOE DIRT® 1st August 2003 04:37 AM

you can also do the math after rectification and capacitance you will get quite a larger voltage
My opinion is to never run a device so close to its S.O.A> in that respect you will benefit to the sonic benefits of its purpose

Greg Erskine 1st August 2003 06:03 AM

Quote:

Originally posted by AudioFreak
And of course, dont forget about the filter capacitors.
The thing with these gainclones is the filter caps are actually on the opamp (usually 1000uF) and not necessarily near the PSU. Although some poeple use additional filter caps at the PSU many don't.


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