Megatron Electrostatic Headphone Amplifier

[nopants]

any particular need for the interstage over normal ac coupling? 

[Milosz]

I haven't been following this thread but recently became interested....And now  I have tried to read through the whole thread diligently.... I may have missed it, but is there going to be a group buy of amp and power supply PC boards for the Megatron?  Again, excuse me if missed that but I just haven't seen any mention, except I read that  Birgir has had a board (or boards?) made....

[kevin gilmore]

there was a group buy of boards. all gone now.

 

lil-knight seems mia at the moment, if that continues, someone

else will have to do the next board run.

Edited December 18, 2013 by kevin gilmore

[Milosz]

Thanks for the info.

[FrankCooter]

I have a couple of extra KGSS power supply boards if you're interested.

 

The amp section looks like a good candidate for point-to-point construction.

[spritzer]

Aside from the CCS stuff then it would be easy to simply wire up.  I also have a less insane version of the Megatron on the back burner with SS CSS and a simplified input stage.  Pretty much a ESX maxed out...

[Peleus]

Hi~ 

I'm newbie here. I'm interesting in the megatron amp and planning to build one for the Stax 007.

 

The power supply of the amp seem is major issue for me, cause I couldn't not found schematic of universal power supply designed by KG.

 

And I've read this thread, searching and googleing in the internet, couldn't found any thing but this: http://gilmore.chem....versalpower.jpg

 

Any information will be very welcome. Thanks!

[chinsettawong]

You'll want to look at the schematic of power supply for KGSSHV.  It's the same thing.

[spritzer]

It's the same thing as the KGSSHV but with two things added, a C- supply for amps such as the BATE and ESX and it has a delay circuit as well.  That PCB is huge though... 

[Peleus]

Thanks! I'll try to figure out how to make this power supply.

[spritzer]

No problem supplying you with the Gerber files but this has never been tested. 

[Peleus]

Thanks, Spritzer. Please sent it to me by my e-mail: [email protected]

[spritzer]

Now that I've looked over the files I'd recommend highly against using this.  Works just fine but it has all the problems of the first run of KGSSHV psu's so the odds of it going arcy sparcy are huge. I'm not going to spend one second fixing them either.  

 

I'd just use the current HV psu and add a separate delay line. 

[justin]

what were those problems since i probably have one of those PCBs here

[spritzer]

The minus rail really likes to meet ground in a violent way.  Lift up the caps (I use m3 nylon spacers) and all resistors and you'll be fine.  Also... flux on the boards is a big no no. 

[nopants]

Thanks! I'll try to figure out how to make this power supply.

 

It's been discussed earlier in the thread but you can use a dropping resistor to derive 300V for the front-end from the HV rail of the KGSSHV power supply. You should remove the 3904's for megatron duty.

Edited January 2, 2014 by nopants

[Peleus]

Hi~ guys

 

Is it work to mod the bias supply in KGSSHV PSU board to 300V for Megatron 300V PSU? And, how to mod?

 

I think changing the Zener diodes to 300V, is that correct?

[nopants]

fucking canada mail my 200ma xformer faster

[RiStaR]

Hi~ guys

 

Is it work to mod the bias supply in KGSSHV PSU board to 300V for Megatron 300V PSU? And, how to mod?

 

I think changing the Zener diodes to 300V, is that correct?

 

Hi Peleus,

 

What would you be doing for bias voltage for your amp? Just something to think about... If you're sharing it with that 300v line, you may want to be careful with using the right heatsink for the 10m90s. From memory, all my input tubes draw about 20+W. The max for the 10m90s is about 40W i think.

 

Since you haven't started, if you're living in a place that has a high ambient temperature (in the tropics it's normal to be about 30+C), you may also want to consider off-boarding the fqpf8n80c instead of the onboard heatsinks... I was eating through the LT1021s on the + line (they would no longer keep the voltage consistent but drop them an extra +-30v after some random intervals) from the heat when the PSU was closed up with just vent holes at the top.

 

I've since used a larger offboard sink for the fqpf8n80cs and added vents (those used in aircraft cabins for the aircon) to the side of the PS casing to bring the temps way down. 

[Peleus]

Thanks! RiStaR. I will keep in mind the issue of heatsinks. 

 

The 300V is power supply to 12AU7 & 12AX7, so I wonder the bias psu on the KGSSHV PSU board mod to 300V psu.

 

Is it work? 

[spritzer]

The front end draws almost no power so a stock KGSSHV psu setup should be fine.  To get a 300V output you need a transformer with far lower voltage, you need to adjust the voltage divider and set the zeners to 350V. 

[nopants]

Transformer arrived, took about an hour just to hook up all the filaments and power properly. My 12A* rail is sitting at 272, so just under 10ma draw for the frontend using 20k to drop from 450 to "300". The transformer seems to do fine after a few hours, the output filament transformer (76VA) runs a fair amount hotter.

 

It's been a while since I've had an amplifier other than the 323s to use. I forgot how easy it is to crank the volume super high because there's no treble-induced fatigue.

[kevin gilmore]

 I forgot how easy it is to crank the volume super high because there's no treble-induced fatigue.

 

A problem owners of diy T2's seem to have

[RiStaR]

Peleus. do follow nopants' figures. Obviously my memory must be shot and added another 0 to the actual figures. 

[nopants]

A problem owners of diy T2's seem to have

I'm not going to fall for your tricks, I'm too poor to build a T2!

 

I have to save towards that BHSE (on which I already dropped the downpayment) on order to bridge the gap between all-sand and all-tube. 

Edited January 30, 2014 by nopants