So it's only really a matter of using another Bridge Rectifier, and a slight modification to the wiring, I could probably squeeze that in, Learn something new everyday 🙂
Just curious as to where your psu fuses will be located and why? Eg: between transformer and rectifiers OR between rectifiers and caps OR after caps?
Thanks, Interesting read, although I don't really get the Third Rectifier (CRFI) and as I'm using a Toroid Transformer I don't have a "Belly Band", The Case is connected to mains Ground, so also interesting to see the 1nf De - Coupling Caps from Chassis ground to the input ground, The RCA connectors I have used are isolated from chassis.
That's something I still need to work out, they would need to be a high amperage if they go between the Transformer and rectifier, or Rectifier and Caps due to the High surge current at power up, probably so big they might be ineffective should a fault occur, the only place really is between the PSU caps and the amp modules, unless I do away with them completely, as they make it very difficult to keep any wiring tightly bound or twisted 😕
Magnum IA125 amp, for which I posted schematic, had no fuses of any kind anywhere, not even mains fuse. With lateral MOSFETs one can get away without fuses. Failures due to maniacal usage are possible but for home applications usually no fuses are needed.
You could use secondary protection fuses of the correct rating .. but would consider a simple soft start circuit to limit the in rush current. I have them before the bridge rectifier with no issues ..
This rectifier is to block low voltage hum, but in case that the amplifier ground (not the case!) accidentally would go up to a rail voltage (damaged PCB, cabling, or whatnot) it would trigger a fuse (which has to be there obviously...). It is a very efficient measure to avoid mains hum, yet allowing protection.
Pass used this tecnique too, now I think he is using a Thermistor instead.
A little dangerous for my liking.
For novices, note the mains fuse should be the first thing the mains cord live conductor meets; it should come before the on-off switch. And the metal chassis should always be earthed.
I think fuses are a good idea as your amp has no other over-current or SOA protection. Has it ever blown a fuse in the past?
I would also be inclined to put the fuses after the caps. Your mains fuse will protect the power supply. These fuses protect speaker and transistors and you want them to blow fast.
The wiring doesn't have to be twisted tight. That makes the wires longer. Run closely bunched and cable-tied is fine. A deviation for an in-line fuse is ok. You could get away with thinner wire if that helps.
Some people use MOSFET switches and other electronic protections. Some use triacs which short the psu downstream of the fuse to make sure the fuse is taken out before the power transistors. It gets all a little complicated for what you are trying to do. You've run these amps for years, I understand, without any problems so you don't need to go over the top.
Keep zero volt line between caps as short as possible then that becomes star ground.
Have B+ and B- come into the caps from one side only and then out on the other side only and you shouldn't have any problems.
No, The amps have never blown fuses in the past.
As it stands, the mains comes in through a mains IEC (Kettle Style Connector) which itself has its own fuse, so before the switch and the transformer primary, I've kept it at 3.15A Anti Surge, If I remember correctly, anything lower blows periodically due to the inrush current.
The Earth from this connector is connected to the Chassis.
The wiring, PSU to boards, etc, are as you suggested, except for a small section where they run past the fuses, I was going to try this method and see how it goes, if there is any stray hum or whatever then I may rethink and look for inline fuses. As it stands, I have managed to keep all ground wires tied (Bound) together.
The DC fuses (after the caps) are 2A anti surge as that's what I had handy at the time, I might swap these for quick blow types at a later point.
That is really how things are at the moment since I re dressed the wiring to keep the looms tied together.
Thinking back to the first build, which was probably a bit of a mess in a wiring respct, gave me no issues, hum or noise wise, This build is much tidier, with more thought and suggestions put into practice.
That had crossed my mind, but with such a compact case, I'm now limited to what else I can fit in there.
See bottom right hand side with caps and star ground.
This circuit is very quiet.
An externally hosted image should be here but it was not working when we last tested it.
@Nigel. Is that a valve or a big IC? I like valves.
Where does the transformer centre-tap connect...to GND? If so there will be charging currents through the star ground. Using a transformer without centre-tap is ok.
Where does the transformer centre-tap connect...to GND? If so there will be charging currents through the star ground. Using a transformer without centre-tap is ok.
The centre tap goes to the GND pin on the pcb.
The circuit works it is dead quiet with no hum.