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.
The transformer will be dual 18v secondaries, rather than centre tapped. Not sure if that makes any difference to the wiring?
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.
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?
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!
The LED across the power supply (LED 2) should be lit all the time power is present.
LED 1 also lights constantly providing there is no DC offset present. If an offset is present LED 1 flashes and the relay drops out. You can test this by connecting a 9 volt battery to either offset sensing input. It should flash whichever way around you connect the battery.
LED 1 also lights constantly providing there is no DC offset present. If an offset is present LED 1 flashes and the relay drops out. You can test this by connecting a 9 volt battery to either offset sensing input. It should flash whichever way around you connect the battery.
Folks:
I have an opportunity to add a small speaker protection board to a finished project. The Store's version is too large but Prasi's version (which is the same circuit as the Store's other than his use of VOM1271T-1 instead of mechanical relays; see post #708) will just fit. My question: will the board work reliably when the input voltage is 20 VAC? It doesn't seem to be a problem for the rest of the circuit, but I can't figure out the VOM1271T-1 data sheet to see if that part would be an issue.
I should note the amp will soon be returned to my daughter living in Brooklyn, NY, where one might expect interesting variances in the AC voltage. My reading of 20 VAC was taken when the line voltage was 120 VAC; at what point will dips in the line voltage affect the speaker protection board?
Thank you,
Scott
I have an opportunity to add a small speaker protection board to a finished project. The Store's version is too large but Prasi's version (which is the same circuit as the Store's other than his use of VOM1271T-1 instead of mechanical relays; see post #708) will just fit. My question: will the board work reliably when the input voltage is 20 VAC? It doesn't seem to be a problem for the rest of the circuit, but I can't figure out the VOM1271T-1 data sheet to see if that part would be an issue.
I should note the amp will soon be returned to my daughter living in Brooklyn, NY, where one might expect interesting variances in the AC voltage. My reading of 20 VAC was taken when the line voltage was 120 VAC; at what point will dips in the line voltage affect the speaker protection board?
Thank you,
Scott
My thoughts 🙂
470 ohm is OK even if your supply goes up a bit to say 22 volts but you are running the photo diodes in the couplers at the very upper end of their range (50ma max) I would say something like a 560 or 680 ohm would just bring that down a bit with no ill effects.
The data sheet shows little gain from currents over 15ma. 680 ohm would give (20-2.8)/680 which is still 25ma. The 2.8 volt is the combined drop of the two series photo diodes. Even your supply fell to say 18 volts you still have 22ma flowing which is still more than enough. I would imagine the total supply voltage could go down as low as 12 volts or less before any issue with the photo relay part was an issue even with 680 ohm. The rest of the circuit might not work as expected at that value but the relay part would.
470 ohm is OK even if your supply goes up a bit to say 22 volts but you are running the photo diodes in the couplers at the very upper end of their range (50ma max) I would say something like a 560 or 680 ohm would just bring that down a bit with no ill effects.
The data sheet shows little gain from currents over 15ma. 680 ohm would give (20-2.8)/680 which is still 25ma. The 2.8 volt is the combined drop of the two series photo diodes. Even your supply fell to say 18 volts you still have 22ma flowing which is still more than enough. I would imagine the total supply voltage could go down as low as 12 volts or less before any issue with the photo relay part was an issue even with 680 ohm. The rest of the circuit might not work as expected at that value but the relay part would.
I am at a loss here and wonder if someone may see something glaring in my build. I have used an 18vac tap from amplifier toroid, I have also used a stand alone 24vac transformer hooked to the speaker delay and dc protection board. The first time powered up w 18vac it smoked Q4. I compared the MPSA06 transistor to my mouser order and confirmed it is EBC. I replaced it, checked for bridges, and brought it up on a variac and smoked it again. I replaced it with 2n3904 with same result. Led 2 comes on with even 1/4 power on variac, led 1 starts to oscillate and then the relay start buzzing before Q4 dies. Thank you in advance. Ps Despite the odd sizes all resistors are 1/2 w or greater.
You probably have a short from the collector of Q4 to the positive rail and that could only be caused by the two diodes fitted back to front or some issue with the relay connections. Can they be fitted incorrectly.
There is no high current path into Q4 other than those routes. Any issue with 'just' a faulty Q4 or incorrect fitting etc etc would not damage anything. All that would happen is the relays would either operate all the time or never operate. Nothing would burn.
Can someone who has built this confirm which of these is correct. V2 and V3 diagrams have different transistor location numbers. T4 in V2 becomes Q5 in V3. All other references seem the same apart from switching from T to Q designators.
I puzzled over this for a moment as in the post above as T4 would have no obvious means of burning but Q4 in V3 does.
I puzzled over this for a moment as in the post above as T4 would have no obvious means of burning but Q4 in V3 does.
Mooly, thank you for looking at this. My work (the one that pays the bills) has kept me from diving in to this more. I will also admit I am good at following schematics and understanding the function of discrete components but can get lost easily enough taking the schematic and applying it to the PCB and seeing a fault at PCB level. I will see if I can find a reason for Q4 to let the magic out with the schematics you posted, last I checked the schematic was behind a broken link so thank you again.
Hello has anyone built the SSR protect based on diya I posted a while back. I haven't been following this , so just wanted to know if there any updates.
Thanks
Prasi
Thanks
Prasi