Generic Power supply for first watt (or class A?) amps

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Hi All,

I realised that having one set of earball's and multiple (first watt and other) amp's (mostly incomplete or with some issues) that building one common power supply made a great deal of sense. I can only listen to one at once!

My question to all is 'what is the ideal generic, adjustible supply for class A amps?'

My thinking has got as far as...

+/- 23V rails with the ground point selectable (ie 0/46 or +/- 23) - that said, where to switch?

Regulated or not? I have a 'spare' chassis featuring a pair or 75mm*300mm conrad sinks so I could dump a fair bit of heat for regulated supplies... But this also defines the chassis size

I've an abundance of nice 2x30VAC and 2x15VAC torroids about as well as a pair of 2x18V chinese cheapies... What to use? Regulating dual 30VAC down to +/- 23VDC seems excessive... But i can afford the heat budget perhaps?

Consider this an exploratory for now. I'll get thinking about cap bank's and cap values and how two best utilize what I have for now.

List of parts on hand to come!
 
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Parts to work with

One (part) chassis measuring about 345mm x 75 mm x 300 mm internal... Thinking if I add spacers then it's 87mm height internal and I get a bit of ventilation as well.

lots x bridge regulators and a few pcbs for discrete options with snubbers)
8 x 100000uF 30V very large caps (never used as they dont really fit in anything... Call it 77mm diameter though, and 143mm high)
12 x 22000uF 25V caps
12 x 22000uF 50V caps (80 mm high, but 35mm diameter, height not including solder legs)
8 x 15000uf 35V caps (screw in, 75mm total height, 35mm diameter)

Various mosfets etc for various regulator options...
 
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...and the parts

what I've got to work with...
 

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Official Court Jester
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say that with 2x24Vac xformers and adequate (read-plenty) cap bank(s) , one could cover most , if not all , FW jobies

no regulation , one secondary/one bridge approach , proper umbilicals

no mentioned switching of ground or anything (except mains) , proper wiring executed in amp's case

that would be how I would do it
 
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I'm doing a class A amplifier power supply, and for what it's worth, I've decided to add a few things "while I've got the hood up" that aren't always included:


  • inrush current limiter using Ametherm SL22-40005 NTC device

  • bypass relay which shorts out the inrush current limiter xxx milliseconds after power-on ("RLB" in attached image)

  • output muting relay which keeps the speakers disconnected from the amplifier for the first yyy msec after power-on
In my opinion, these circuits are relatively simple and relatively easy to get working correctly. And they provide huge psychological benefits (extra margin of safety) for relatively small cost, so why NOT put them in? After considering the ideas, you might decide you feel the same way.

edit- sorry, "hood" is US car slang for "bonnet"; it gives access to the engine compartment

_
 

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Thanks for the responses :)

Dennis - I've multiple 625VA, 2 x 30VAC transfo's and a few 300VA 2 x 15VAC units too, as well as a few other 300VA options (less nice generic items). I've a few single ~ 35VAC 500VA transfo's too (~double 18VAC... hmm :scratch:)

ZM - The challenge is in using what I have, not the ideal! :h_ache:. I originally planned to design it to match a potential F3 build, as well as the dual rail Pass builds, but perhaps I should build the exception by itself given I have the parts...

Does the 24VAC xformers not leave me with a compromise of ~ 30VDC rails and all the requisite additional heatsinking required on each of the amps chassis? After thinking about it a bit I wondered if 4 x ~20VDC floating supplies might do the trick for most builds - easy enough from the 15VAC secondaries I have available
 
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space?

@Mark - noted! I can't help but consider the enormous amount of space in each amp chassis that wont be filled by caps and xformers... and think about the different ways I can awkwardly fill the space instead...

Pictured is the F6 build I filled to the brim... :facepalm: And I didn't get the speaker protect in in the end.

Edit - no need for hood/bonnet explaining - US tv has indeed conquered the worlds english. :)
 

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ZM - I was tempted by the idea I could take a 30Vac secondary and split it (after rectification) with a virtual ground for dual rail purposes or leave it as is for the single supply options.

Then I wondered if I could use a 35Vac secondary and regulate it as well.

Then I started drawing diagrams for an all things in one class A supply, and then though I should lie down and consider what I actually could use :/

Still not sure if thats a silly idea or not actually!
 
I don't know whether it is sacrilege to suggest this here, but have you considered a 24VDC switching supply? Regulated, quiet (at audio frequencies, not so much at 100s of kHz). Light weight, small size, no problem with continuous duty. Cost almost nothing, example --
FreeShipping 24VDC 5A 120W Switching Power Supply Driver for Monitor camera/LED Strip AC 100~240V Input to DC 24V-in Switching Power Supply from Electrical Equipment & Supplies on Aliexpress.com | Alibaba Group

I recently made a 55W class A amp using some 36VDC Chinese switching supplies, worked perfectly.
 
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Hmm, done some more thinking and I'm tossing up between 4 x 20VDC floating linear supplies (which would allow 2 x 40VDC supplies for single supply amps, albeit with less effective capacitance) and 2 x ~46VDC regulated supplies and then putting an active ground circuit either in the amp or the power supply should split rails be required.

I'm realising though that I don't know enough to judge which is 'better', whatever that may mean... The prompting for this thought process is an F5 build which refuses to stop hummmmmmmmmmming whatever I do and an F6 build which is more power supply than amp! Some where I have a spice sim of an amp playing an actual sound file and the sag on the rails as a result. I may have to model various options and see the end result.

Simple is always better in the long run though...

@JR_W The pcb's are great. I've used them and they're perfectly suitable for a linear supply. I just started wondering about a common supply for lots of amps and realised that it made a great deal of sense for one set of ears and lots of amps and started trying to cram every good idea about power supply's into one box...

@bwaslo - I've used these and have two on hand for an f4 build sometime. I've used one in a fetzilla build and I'm quite happy with them! That said, there's a tiny bit of hum that is un-ignorable once you hear it... The ACA is excellent in terms of hum and that's running of SMPS as well, so perhaps it's luck of the draw...
 
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Probably depends on the particular model of SMPS, I guess. The ones I used (MS-250-36) gave me zero hum, though with a circuit that has very good PSRR, so that might be a factor too.

In a Class A amplifier single ended (CCS or choke fed), the supply shouldn't sag when playing sound, highest dissipation is with no sound. With constant current source fed, it shouldn't budge at all, with choke only at low frequency. With push-pull operation, though, each supply will wobble some with signal. That's where regulation is handy.
 
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So, a question then. Assuming I go for 4 x 20VDC floating supplies, how would you organize the umbilicals?

My thinking at the moment is 2 umbilicals with 2x +ve rails, 2x negative rails, 1 x GND, and 1x speaker return to the PSU ground (per umbilical).

Any thoughts?
 
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What about the Universal PSU in the DIY Store? Anybody use those?

The name "Universal Power Supply" bugs me when referring to the power supply board in the store. It has no facility for even a simple regulated power supply. Peter Daniel's power supply board does both.

Anybody use those?

I just finished building one and it's a fine PS board for a power amp.
Makes life much simpler and faster.
 
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