kevin gilmore

Megatron Electrostatic Headphone Amplifier

741 posts in this topic

>>MEGATRON<<

The rollers are gonna have a field day.

Twelve tubes, count em. Yay Team Overkill!!

Edited by livewire

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Kevin,

what happened of the original design to resort to the usual EL34? I personally prefer real triodes to pentodes, even when triode strapped, and parallel 5687 as power stage did sound an interesting idea (also one of my fav triodes). What's the reason? Filament supply? Not enough gain? Simply more parts?

Thanks.

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There must be 20+ original designs. I'm going to give away all the board files, and nothing

prevents people from building whatever they want. But a compact monster amp can't

be a bad thing.

The thing with the 5687's is that they behave very badly if you push them over +/-300.

And given the Rp of the tube, the most you can get is 1150 vppss. Since there are no

1kv triodes unless you use really expensive dht's you have to use el34's strapped as triodes.

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Minor issues..

Missing (or deleted?) the protective diode between the TL783 In and Out.

Making "AC2" and "-" for the bridge rectifies (KBU4x) were reversed (patterns are OK).

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The pattern for the bridge rectifier, i'm aware of, but since the printing never shows up...

but i will fix it anyway. How i missed the diode on the tl783 i'm not sure, i know

where it cut and pasted it from, and the original has the diode ??

Thanks Inu.

Edited by kevin gilmore

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Oops, Making > Marking. facepalm.png

How about adding protection resistors (5.1K 1W) to the outputs?

Edited by Inu

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If possible,

For the 0.22uF/1000V

Add extra mounting hole for the PCM 22.5mm capacitors (EPCOS)

For the 0.1uF/450V(400V)

Add extra mounting hole for the PCM 15mm capacitors (EPCOS and MKP10)

Edited by Inu

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On the power supply, I'm a little nervous about how close the 7912 output trace to the terminal block is to the heatsink mounting hole. Also, did you intend to ground the FET heatsinks?

On the amp, all of the ground solder pads aren't split up to slow down the heat dissipation, so they'll suck to solder to on that size of a board.

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Moved the 7912 a bit. All of the heatsinks are grounded. It may not show up well.

I made the thermal's thicker so that they can be seen now.

I've never had any trouble with a regular soldering iron soldering solid ground pads.

It makes a significant difference in the performance of the amplifier, those little crosses

add a fair amount of resistance and increase noise. So i like to keep everything

in the signal path with the lowest resistance to ground.

Edited by kevin gilmore

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Indeed solid thermals shouldn't be a problem for a good soldering iron. A good Weller or Oki isn't that expensive and makes soldering so much easier.

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Thanks for the info. I've got a 100W XYtronic which I've never had problems with. I was more wondering about how newbie-friendly this was supposed to be, though it makes sense that the Stax Mafia would put a good iron in every newbie's hands.

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I tell every noob to just buy an OKI PS-900 and skip over the cheap stuff. I'm all for using cheap stuff where you can get away with it but cheap soldering irons are just that, cheap. Only exception would be the military surplus stuff Kevin brought to CanJam. :)

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Am I correct to guess that the costs estimate for this build excluding chasis, volume pot, input jacks and tubes should be no more than US500 to US600? I believe the PSU should costs more?

Costs of tubes is where the numbers will fluctuate greatly correct? Any default tube type or manufacturer recommended?

Edited by Victor Chew

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Kevin,

Not flipped NFB line. azn.gif

Each 6CA7 sinks or sources about 27mA (11W) is correct?

450V Line (included 300V line) = total 61mA/ch

-450V Line = total 54mA/ch

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27 ma per tube is exactly correct.

The teflon octal sockets on ebay are about $10 each

the teflon 9 pin sockets seem to be about $12 each

likely way cheaper overseas. Not sure how much

the capacitors are.

maybe about $600 in parts total including the power supply, not including

the transformer or the tubes.

Edited by kevin gilmore

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Are PCB's planned for the Megatron? :)

Edited by eggil

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Biirgir is going to do the prototype run very soon

Edited by kevin gilmore

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I can feel the sense of excitement.

Will the DACT or other attenuators be incorpotated as an option in the boards?

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not unless people let me make the board bigger.

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Given that none of us can agree on attenuators I do think it is best to keep them offboard. I certainly wouldn't be caught dead with an RK27 in this amp... :)

When I have a bit of time I'll order boards from me and KG so we can test the beast.

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How about remove RK27 then use space for add 2SA1968 0.5mA (150mW) CCS option for the 2nd stage?

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I still like the idea of being able to board mount the attenuator. I'd be perfectly fine if the board grew a bit to incorporate a DACT attenuator.

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