Pultec clone - grounding problems

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Winston OBoogie

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Something like this then. Thanks.

Yes that second one down is it. Connect your last filter cap to the negative rail, ground it there, and then on to the tube heaters
Depending on your transformer specs and losses, you may need a cap right after the bridge too.

Of course, if you have about 1V spare after the balanced filter, then one step up from that scheme above would be to use a cap multiplier in lieu of the last series R and shunt C.

You'll loose about .7V on the base to emitter drop, and a little across the feed resistor due to the transistor's base current, but it will afford you the ability to use a bigger time constant and it'll really go a long way to getting rid of ripple.

However, even if you divide up what is usually shown as a single RC filter in heater supplies into two filters with half the resistance and twice the capacitance per, it'll work better than one single filter.

Cool beans 👍
 

Nbtone

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Yes that second one down is it. Connect your last filter cap to the negative rail, ground it there, and then on to the tube heaters
Depending on your transformer specs and losses, you may need a cap right after the bridge too.

Of course, if you have about 1V spare after the balanced filter, then one step up from that scheme above would be to use a cap multiplier in lieu of the last series R and shunt C.

You'll loose about .7V on the base to emitter drop, and a little across the feed resistor due to the transistor's base current, but it will afford you the ability to use a bigger time constant and it'll really go a long way to getting rid of ripple.

However, even if you divide up what is usually shown as a single RC filter in heater supplies into two filters with half the resistance and twice the capacitance per, it'll work better than one single filter.

Cool beans 👍
I guess I need the special software to figure what parts I need for my particular heater circuits. At least that’s the conclusion I’ve drawn from researching capacitance multipliers. I really never thought of measuring ripple in the heater circuit. I always measure it at the anode, where the ac signal is riding the dc supply voltage. How does ripple in the heater circuit affect the sound of the amplifier?
 

Nbtone

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I’ve read that dc heater supplies make the audio sound “bleached”. The ac heater supply I have hisses a little, and I have no idea how to get it out.
 

Winston OBoogie

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I’ve read that dc heater supplies make the audio sound “bleached”.

Bad DC can cause more issues with noise than AC so, caveat emptor.
But I don't really know what you mean by "bleached".
If you have good DC, and a good layout, I suppose the 'bleaching' in this case = eradication of hum



The ac heater supply I have hisses a little, and I have no idea how to get it out.

I don't know what a hissy ac heater is either tbh.

Do you mean it's causing high frequency noises?
I thought you found that AC grounding the heaters with a capacitor from the winding's centre tap worked.

Regardless, it's hard to diagnose when we don't know the circuit, the layout etc.
 

Nbtone

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Bogen mx60a schematic is what I base my preamps on.
The line level one at the bottom is interesting to use with my sound board. I run an aux out to the input and run the output to a channel strip. I haven’t been able to get all the hum out of it yet.
The mic input preamps work good going from an instrument to an amplifier. I’ve got all the hum out of these, but there’s some very low level hissing when plugged into an amp.
As far as layout goes I’ve tried all kinds of stuff, and I’m making progress. Sometimes I find that leaving things alone for a while is the best way to get something done.
 

morls

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Update:
I’ve got the components, and am designing the PCB layout. I’m now wondering about the wiring. The rectifier PCB will be beside the main board, with AC in and DC out at either end:

This is the wiring I’m thinking of, the AC path is:
mains in back corner, up the same side to switch:
power transformer next to mains in;
6.3VAC out of PT
*rectifier*
6.3VDC in to main board, next to PT.

I’m wondering if I should run the 6.3VAC from the PT up towards the front, beside the power switch wiring, so that the DC is output at the rear, next to the IEC socket and PT?

The alternative is to connect AC to rectifier at rear and then run 6.3VDC from the front of rectifier board to the rear, and then into the main PCB. This means a run of DC heater power alongside, or very close to, the mains switch wiring.

I think the first option is the way to go, but any advice would be welcome.
Thanks
Stephen3FAB48A8-2F81-4741-926C-23CD3DBFB6D7.jpeg
 

morls

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..the "mF" rating in sim - isn't that mili-farad? In which case, real biggies.....

They are!

I'm using 2 x 15000uf per filter stage, so 6 per unit. I was surprised at how heavy 12 of these were.

I hope I'm not making a dangerous mistake...
 

Winston OBoogie

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I didn't take note of the capacitor values to be honest, but I'm not sure I see an issue unless the physical size is prohibitive. Jakob?

On the layout, what's on the new heater pcb - rectifiers, reservoir cap, and filters? ie. everything for the DC heaters?

The one loop you should keep small is the heater AC wiring, diodes, and first reservoir cap so, your option two sounds like it'll do that.
Still twist the wires from the DC output end of your new pcb and route them back to the heater input of your main pcb.
 

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