Moskido - Hybrid Aikido/MOSFET amplifier

[Hylle]

Beau, does this kinf of diode bridge need to be on a heat sink?

[dvh99]

Originally Posted by beau2317

OK OK I updated the PSU schematic.

great beau.
this will be very helpful for future builders.
gonna put those resistors in in a bit and test.

[dvh99]

or could be reasonably more.
my ps costed about (xformers * 3 plus little for softstart) 300 euro = 420usd.
8 mosets =70 euro = near 100usd.

tubes from ebay 60 euro plus little things (screws wire switches inlet speaker terminal rca inputs).

or you can go the 10usd a piece way .

whatever you do buy LARGE heatsinks cause mine runs very hot at 1amp per fet (4 per channel).
i cannot touch the heatsink without burning myself so my bias will go down slightly probably.

[Dagwood]

Thanks for the reply's re the costs

Things always seem to cost more in New Zealand ( Thanks Adidas ) I guess mainy with postage. I have a few transformers being made and in both the US and UK at the moment, it is only possible because family are beinging them across on holiday.

It looks like a great project and will definitely be on my to do list.

Cheers

P.S have noted heat sinking!!!!!

[dvh99]

still have that annoying hum.
running out of ideas here.

i even have lifted the xformers with no change.

the sound is amazing but this hum is driving me nuts!

[dvh99]

without the tubes in zero hum, i have to get my ears very close to the speaker to hear anything.

gonna try a few 100ohm resistors parallel to the 100nf that go to chassis ground but am afraid that won`t work either.

my speaker cable is 12 meters long, could this have anything to do with the hum?

[beau2317]

So the resistor divider/cap that references the heaters made no difference? Be sure to measure the voltage on the heaters with respect to ground. Are they sitting at the correct voltage? Should be 1/4 of B+

I don't think the 12 meter speaker cables are the problem. Not for hum at least. But it's really too long for the best sound..

OK so it's down to the aikido as the problem. Are you wishing now that you'd bought the Broskie PCBs? It's hard to debug the aikido when it's wired up point to point. But the idea is that you want to have the Aikido built separately from the mosfet stage, with it's own star earth point. Then connect that earth point to the mosfet side earth with one (thick) wire. The output from the aikido is just two wires from the two coupling caps. No earth wires here.

If you still have problems, try just putting in the second tubes (6SN7s). Does that hum?

OK now the chassis - is that earthed from the mains supply? Do you have the back-to-back diodes and 10R that lift the PSU 0V from chassis earth?

Also try disconnecting the common mode filter on the heater supply. That's nothing to do with hum so remove it and see if that helps.

Perhaps you can take some hi res pics of the test setup and email them to me (or PM)

[beau2317]

Diode bridge : for the moskido supply the bridge rectifiers most definitely needs a heatsink. Mine are on the main chassis. For the tubes it's not needed as they only pass say 50mA

[dvh99]

1/4 of b+ check (88v - 348v)
6.45v heater supply.

diodes with 10r are installed.

will separate the grounds next.

if nothing helps i will send some hi res pictures.

thanks in advance.

[dvh99]

with just 6sn7 the hum is less pronounced.