If you power it from a large DC supply then the relays may drop out after the amp starts to make any odd noises (as many do) as the rails collapse. Ideally you want the speakers to drop out pretty quickly once you turn it off.
If the transformer in the amp is an 18-0-18 and producing normal -/+ 24 volt DC rails then you simply use one of the 18 volt windings (either) to power the board.
If the transformer in the amp is an 18-0-18 and producing normal -/+ 24 volt DC rails then you simply use one of the 18 volt windings (either) to power the board.
It does make a bit of a difference to how it works depending how the transformers are wired.
If the windings are connected in series and you use a single bridge rectifier it works as expected.
If you keep the windings separate and use two bridges and form the amplifier ground connection by connecting the negative of one supply to the positive of the other then I think it will still all work OK but technically the voltage the board sees is 'less pure' due to the four diode bridge affecting the input to the board as seen from ground... its complicated
but I don't think it will make any difference at all because the board itself has no effect on sound quality and does care over how pure the supply is in absolute terms. I think it will be fine.
If the windings are connected in series and you use a single bridge rectifier it works as expected.
If you keep the windings separate and use two bridges and form the amplifier ground connection by connecting the negative of one supply to the positive of the other then I think it will still all work OK but technically the voltage the board sees is 'less pure' due to the four diode bridge affecting the input to the board as seen from ground... its complicated
but I don't think it will make any difference at all because the board itself has no effect on sound quality and does care over how pure the supply is in absolute terms. I think it will be fine.
its complicated
Ha. I'm getting that sense
It's there a thread or a book or a video or something that you know of that covers transformer wiring for amps in general? The grounding bit in general escapes me at this stage.
Seems there are a lot of variables resulting in quite a few different wiring options/requirements.
- mains voltage
- one transformer or dual mono
- primary voltage
- one or two primaries
- secondary voltage
- number of secondaries
- centre tap or dual and how it is wound
It'd be good if I could find a solid resource in dummy terms (i.e. no differential calculus) that explains how to wire up each of these permutations and why.
I don't know of any book or single resource...
Choose your primary voltage to suit your own mains supply. They have to be the same.
Two independent secondaries allow you to make two independent supplies (not linked electrically in any way) but you can if you wish then go on to link the DC supplies produced to make a dual rail supply.
How its wound is more involved and not something you really need be concerned over. Your choice will normally be between physical types such as toroidal or small EI construction types (the square ones) and so on.
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I don't know if this helps but for some of the topics you can think of the two secondaries (or single) as a battery.
If you have two 9 volt batteries and wire them in series you get 18 volts. Take a wire from the centre point and you have a -9-0 +9 supply (a split or dual rail). This supply is all linked. You can not connect plus 9 to minus 9 without causing a short.
Wire in parallel and you get the same 9v but now with twice the current ability.
Choose your primary voltage to suit your own mains supply. They have to be the same.
Doesn't matter to you as such... multiple primaries are to allow use in different parts of the world with different mains voltage. There can be two, three or even more 'primaries' of different voltage and you wire them in series to equal your mains voltage. For example 230 volt mains might use either a single 230 volt primary or a dual 115 and 115 primary. You would wire those in series. A user on 115 volt mains would wire them in parallel.
Has to suit your application, what you are building. You can not easily work around an unsuitable choice.
A bit like the primary issue. If your application calls for a single rail supply you can use a single primary. If its a dual rail supply (a minus and plus rails) you usually need a dual secondary where they are wired in series or two separate windings where you wire them in series. The first has three wires where one is a common connection and the other has four wires. You join them in series to make it like the three wire.
Two independent secondaries allow you to make two independent supplies (not linked electrically in any way) but you can if you wish then go on to link the DC supplies produced to make a dual rail supply.
How its wound is more involved and not something you really need be concerned over. Your choice will normally be between physical types such as toroidal or small EI construction types (the square ones) and so on.
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I don't know if this helps but for some of the topics you can think of the two secondaries (or single) as a battery.
If you have two 9 volt batteries and wire them in series you get 18 volts. Take a wire from the centre point and you have a -9-0 +9 supply (a split or dual rail). This supply is all linked. You can not connect plus 9 to minus 9 without causing a short.
Wire in parallel and you get the same 9v but now with twice the current ability.
That's an exceedingly generous and very informative response, @Mooly. Thanks again. I'd hoped to spare you the trouble, hence the book/resource question. Didn't mean to take up so much of your time.
I'll going to wait on my other amp bits and then come to a decision on the board power supply situation. 🙂
I'll going to wait on my other amp bits and then come to a decision on the board power supply situation. 🙂
After messing around in MS Paint to get it all straight in my head, I think I get what you're saying.
It doesn't seem like there's a compelling reason to do the dual bridge rectifier thing, and I should just wire the dual primaries in series and treat is exactly like a centre tap. The F5M Bipolar Supply board seems to do this for me, as it has two through holes labelled CT. I imagine I can just power the DC protect board by using this centre tap (DC Protect 'G' wire soldered into the supply board in the same hole as one of the two CT secondaries) and either of the other secondary wires for V+ as long as it's taken before the supply board (could even do a piggyback faston off the bridge AC in?). Shouldn't matter which wire because either one is 18VAC away from the CT. Am I close? I feel like I am?
It doesn't seem like there's a compelling reason to do the dual bridge rectifier thing, and I should just wire the dual primaries in series and treat is exactly like a centre tap. The F5M Bipolar Supply board seems to do this for me, as it has two through holes labelled CT. I imagine I can just power the DC protect board by using this centre tap (DC Protect 'G' wire soldered into the supply board in the same hole as one of the two CT secondaries) and either of the other secondary wires for V+ as long as it's taken before the supply board (could even do a piggyback faston off the bridge AC in?). Shouldn't matter which wire because either one is 18VAC away from the CT. Am I close? I feel like I am?
That looks fine
Thanks mate.
Drawing that, I think grasped a few things that had eluded me for a while. I have to remember to do that more often!