Split-supply to single-supply conversion? - diyAudio
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Old 3rd May 2011, 11:18 PM   #1
Khron is offline Khron  Romania
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Default Split-supply to single-supply conversion?

Greetings (again),

Just a quick one: is there any simple way of converting a normal, split-supply amp, to work with a single-supply?

From my fiddlings in LTspice, it seems to be only a matter of providing an adequate mid-supply voltage to the input reference, but there might be implications i'm not entirely aware of... Hence my request for input from brighter minds

Yes, i AM aware of the inevitable output capacitor, but that's beside the / my point.
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Old 3rd May 2011, 11:23 PM   #2
AKSA is offline AKSA  Australia
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Yes, Khron, that works fine and is quite practical.

There are advantages to this topology - one of them guaranteed speaker protection - but you should note that lag compensation needs to be increased about 50% over a split supply.

Hugh
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Old 3rd May 2011, 11:40 PM   #3
Khron is offline Khron  Romania
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Ok, so far so good Nice to know...

Now, the amplifier in question is a slightly modded "Load-invariant" as per Dr. Self. Due to the low DC input impedance, i had to "offset" the resistive divider that gives the input bias voltage (6.8k from V+ to "mid", and 10k from "mid" to ground.

Might there be some slightly less... "barbaric" rules-of-thumb i could try to follow?
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Old 4th May 2011, 12:15 AM   #4
AKSA is offline AKSA  Australia
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No, that's all you need..... but the fb AND input cap will now be heavily polarised (no bad thing!) so should be upgraded to approx 2/3 of the single rail voltage.

Insert a trimmer on the offset adjust so that you can adjust for perfectly symmetrical clip, that's a handy feature to maximise rail efficiency.

Hugh
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Old 4th May 2011, 12:44 AM   #5
Tajzmaj is offline Tajzmaj  Slovenia
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Check Quad's psu...
http://quad405.com/606schematic.pdf
I've experimented with such psu on other amps and that's true that it is necessary to adjust it to get simetrical clip.....look at 606 schematic(9K1 and 10K resistors). But I suggest to bias this voltage splitter little higher. If I'm not wrong I've used 470E for R38 and R39 and transistors were MJE 15030/31.....with small heat sinks.
Best regards
Taj
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Old 4th May 2011, 01:11 AM   #6
Bigun is offline Bigun  Canada
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Quote:
Originally Posted by AKSA View Post
cap will now be heavily polarised (no bad thing!)
It has been shown through careful measurements (Electronics World Jan 2003 - C. Bateman) that a polarizing voltage can increase the distortion from the capacitor. However, it might be a pleasant distortion
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Old 4th May 2011, 08:25 AM   #7
Tajzmaj is offline Tajzmaj  Slovenia
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And I also must agree with Bigun......
But this method is good if you want to use some transformer which you ,,find,, somewhere........that is the only reason when I use such psu. It is money saver.....
Regards
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Old 4th May 2011, 08:45 AM   #8
Khron is offline Khron  Romania
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It's more of a "complexity-saver" I'm planning to put together some sort of small-scale live PA setup, and i've already got a nice class-D single-supply full-bridge for the subs / mid-bass drivers, and a nice Self amp for the compression drivers. I was trying to make sure if and how i could hook up these tweeter amps across the same power supply

Thanks everyone for the input
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Old 4th May 2011, 08:49 AM   #9
AKSA is offline AKSA  Australia
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Bigun,

Distortion gets a bad rap. It's almost a neurosis.

If we talk of a musical instrument, it's harmonic profile, or timbre......

And I can assure you the 'distortion' of a polarised input cap sounds pretty good.

Hugh
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Old 4th May 2011, 09:00 AM   #10
Khron is offline Khron  Romania
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Well, on one hand, like i just mentioned, this is for a PA application, and on the other hand, LTspice says this should (?) be capable of 0.003% THD @ 10k, near full power (which it shouldn't reach anyway ), so... I think i might "have room" for some cap distortion, so to speak Plus, it'll only see use somewhere above 1KHz...

Mr Hugh, since i have your attention, might i be so bold as to ask you to take a peek into my other thread in this forum?
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