Megatron Electrostatic Headphone Amplifier

[Fitz]

Please keep us updated with the findings.

[kevin gilmore]

oh my god, where to start?  The 2 rectifier tubes are GZ34 correct? Full wave tube diodes run as half wave diodes. Why? +/-400v power supply appears to be completely unregulated. 2 x el84+12ax7 is regulated +300v power supply?

Original power supply caps rated at 450, definitely not enough. 550v just barely enough and that depends on whether the output tubes are actually warm before the rectifiers get warm.

input tube current sources replaced by single power supply and resistor?

cascode tube current sources replaced with resistor?

Not even sure how i would fix this. But the tube rectifier and unregulated power supply have to go. Probably enough room for a pair of GRHV power supplies (kerry style). 300v supply likely has to go too.

If its blowing fuses, could be that the high voltage transformer windings were not rated for >500v wrt ground.

Reminds me of mikhail.

Edited July 16, 2021 by kevin gilmore

[spritzer]

This is very much the return of Singlehour, same utter incompetence and utter disregard for safety and the customer

[rayofsi]

On 7/15/2021 at 9:14 PM, orientexpedite said:

Well, a couple of nice outcomes have arisen from the ire induced by the self-serving PM of thuytn , so far:

First, upon reporting the head-fi PM (word-for-word identical to the one he simultaneously sent here), Head-fi moderators immediately flagged his current account https://www.head-fi.org/members/tranhieu.83205/ "Caution: Incomplete Sales".  The account hasn't been wiped like the first account (with the T2 board and transistors), yet, since it doesn't seem he's actually sold anything via the current head-fi account.  But there's always fls.audio on Ebay with a couple of auctions about to close, now... and I suspect there is already more than one unfortunate victim like Paramesh out there.

Second, Thuan's "Megatron" is ready to go out the door to a member here who is more than capable of providing a comprehensive assessment.

With gratitude, my thanks!

I actually have bought something from Tran on head-fi. A CFA-3 build. It is working fine so far. I sent some pictures of the internals to Kerry when i first got it, and it didn't seem to raise any red flags. I also have one of his KGSSHV Carbon builds he sold on ebay. It does some crazy inrush that my lights in my room dim a second when it turns on, but works well otherwise.  I haven't used his carbon enough to know if it will fail, as i was lucky enough to get one of Kerry's T2s.

Also forgot to add, i have a SUSY Dynahi from Tran that is also working well. Haven't used in a little while though

If @Kerryis reading this, i'm waiting to get one of your CFA3's haha.

[orientexpedite]

I apologize in advance if this is news to absolutely no-one, but after reading the entire DIY T2 build thread in anticipation of receiving my build from George, I was surprised to find a name and handle that looked familiar: Tran, and Lil Knight.

A search showed that the schematics of the failed DIY T2 board/case buy were posted in 2013 by a fellow going by Lil Knight under blogspot account tee8tee84388…  to my eyes, that rather unique Blogspot/Reddit/Flickr handle looks very familiar:

Yes, this is the same Tran who later sold the DIY T2 parts kits on head-fi as kytuphicanh, which also happens to be the selfsame Tran that built my ‘Megatron’, stamped FLS Felitsa Audio.  That incomplete sale, along with Paramesh’s, outlined earlier, resulted in kytuphicanh being banned (and mostly scrubbed, likely due to dozens of historical classified sales) on head-fi, and a warning placed under his alter ego, tranhieu.

Tran is tee8tee4388 on reddit, tranhieu and kytuphicanh on head-fi, and fls.audio on sbaf and ebay…  and we now know that you can presently message him as thuytn right here on head-case, since he so generously reached out, asking me to shut up about my dead ‘Megatron’, because it would ‘heavily affect his future sales’.

Tran, aka Lil Knight, aka tee8tee4388 on blogspot, takes credit for posting his failed DIY T2 board buy schematics here (Posted by Lil Knight, 12:21am, Wednesday, July 31, 2013):

http://tee8tee4388.blogspot.com/2013/07/t2-diy.html

Tran aka tee8tee4388 takes credit for my rather ‘unique’ (and dead) Megatron on reddit:

Fls.audio aka tee8tee4388 aka Lil Knight aka Tran takes credit for my Megatron build here on SBAF: https://www.superbestaudiofriends.org/index.php?threads/845-dht-set-electrostatic-headphone-amp.8740/

And Thuan Tran aka Lil Knight here shows off his Stax circa 2009, shipping labels and invoices on Flickr under the same tee8tee4388 user name, as he himself references in the below Reddit post:

https://www.reddit.com/r/headphones/comments/a2dsoo/was_randomly_skimming_through_an_old_flickr/

https://www.flickr.com/photos/8128018@N06/page2

https://www.flickr.com/photos/8128018@N06/page4

This particular Tran quote on Reddit, as above, caught my eye (regarding Singlepower): “They stole lots of people’s money by not delivering amps. That sucks because their amps sounded very good, much better than the stuffs by Woo now.”

Indeed, that ‘sucks’.  How long was Singlepower around for?  Who has filled the void?

Tran’s ‘Megatron’ as sold to me omits all CCS loads, contains no inrush current limiting of any kind, has severely underrated power supply capacitors, a failed transformer/winding, and can hardly be called a ‘Megatron’ in the first place.

Fls Audio ‘creations’ still sell today on Ebay.  Buyer beware.  You now know who you’re buying from.

[kevin gilmore]

i just noticed this. amplifier says its push pull amplifier.

the megatron is NOT a push pull amplifier. Its dual single ended current source.

[orientexpedite]

5 hours ago, kevin gilmore said:

i just noticed this. amplifier says its push pull amplifier.

the megatron is NOT a push pull amplifier. Its dual single ended current source.

Tran’s exact Head-fi listing under user kytuphicanh was:

FS/FT - Reference OTL PP Stax tube amp (Megatron)

Cute.  Wonder what else is missing in the build?  We’ll know soon.

[kevin gilmore]

working on this megatron disaster from the pictures. Awaiting delivery of the item to confirm i have not made any mistakes in diagnosing the mikhail class fuckups.

1) The filament windings for the output tubes are all tied together. The 4 current sources are limited to +/-100v before the tubes arc. The gain output tubes are all referenced to ground and that violates the maximum cathode to filament voltage by 300v. This is the same as the singlepower esx disaster and every one of those also blew up. The filament transformer MUST be replaced and all the tubes rewired. which requires removal of the amp board. You need 6 filament windings for the output tubes plus a winding for the input tubes plus a winding for the -15v.

left transformer left filament winding (blue wires) (notice tied to ground) for the current stage tubes and right filament winding also tied to ground for gain stage tubes.

Since the amp board is missing the first stage current source which was replaced by a resistor to -45v and the second stage current source is missing, its easier to do a new board.

2) The high voltage transformer is also fucked. each 400v power supply is running on half wave rectification which results in amperes of ripple current at 30hz. 2 center tapped windings at 630v required plus pair of filament windings necessary to convert the tube rectifiers to dual full wave rectification. Guess what, new transformer required. even with a solid state rectifier a new transformer is required as the high voltage winding has no center tap. major stupid here.

pretty sure i have identified a source for replacement transformers, just need to know the hole sizing and spacing.

3) have not even figured out the +300v supply yet, so many fuckups.

So pretty much this is a complete and total rebuild. With the covid economy, could be months to get the repair parts.

Edited September 11, 2021 by kevin gilmore

[spritzer]

I agree, a complete rebuild is in order.  Nothing really aside from input wiring, attenuator etc. could be reused. 

I would ditch that stupid tube PSU and just fit a new PSU board there.  We could whip up something nice and simple but yeah, part shortages now are a total nightmare.  Want a 10M90S... that will be 50weeks... 

[orientexpedite]

Adding to my embarrassment and frustration, these things were priced and even named similarly to Mikhail's Singlepower ES-1 and ES-2 stuff.

This "Reference Megatron" (turns out not a Megatron at all) is stamped the "ESHA-2", and shares a chassis with the FLS Audio "ESHA-1", Tran's "845 DHT SET" amp, paraded around in his "custom would transformer" workshop on SBAF : 845 DHT SET electrostatic headphone amp | Super Best Audio Friends

The first local head-case member to look at the amp (it was just returned yesterday) measured the "custom transformers"... they indeed are shot and need to be replaced, and it was two years before the amp blew up. 

Since my "Reference Megatron" fls.audio amp listed for 5.5K USD (and came out closer to 6K USD with the shipping nightmare from Vietnam), how long before all the other non-reference amplifiers sold under fls.audio on ebay blow up?  Paramesh's amp lasted 15 minutes....

 

 

[kevin gilmore]

The output stage at least is definitely megatron. DC coupled with tube current source driving a gain tube.

The rest of it has significant changes, why i don't know.

[spritzer]

Same reason as always, zero clue what the fuck they are doing... 

[kevin gilmore]

a quick game than anyone other than birgir or orientexpedite can play.

look at the amp board above.  now look at some of the other pictures of the real amp board.

anyone know the 4 required major components that are missing? First one gets 10 booby points.

hint:

https://www.head-case.org/forums/topic/10783-megatron-electrostatic-headphone-amplifier/?do=findComment&comment=551186

 

Edited September 15, 2021 by kevin gilmore

[kevin gilmore]

its here

filament transformer for sure smoked. as in hole in the potting likely where the flames were shooting out.

has that wonderful singlepower extreme smell.

If anyone knows where to get transformers like this made, let me know. specs are as follows.

 

Filament transformer, mounting holes 85mm square threaded with 4.5mm bolts

4 x 6.3 volt at 2 amp

2 x 6.3 volt at 4 amp

1 x 12.6 volt at 1 amp

18 volts @ 1 amp

Primary 2 x 115vac

High voltage transformer, mounting holes 100mm square threaded with 4.5mm bolts

Primary 2 x 115vac

2 x 5 volt at 2 amp

2 x 630volt center tapped at 200ma

510 volt center tapped at 130ma

6.3 volt at 1 amp

 

So many bad solder joints. grounding shields on the small tube sockets essentially force removed with a side cutter. Yikes.

Notice the required missing corner out of the new board. Fucking idiot made the case first then found a way to cram everything inside.

Edited September 18, 2021 by kevin gilmore

[G600]

Sweet piece, for sure...

[spritzer]

That thing is so utterly fucked.  Pure limitless incompetence all around there. 

I think we need a list of badly made crap, RSA, McAlister etc.  Viva Audio is the newest one I'm laughing at, holy crap they are badly made and the part choices there make no sense at all.  They use PSU caps notorious for shorting (Rifa) as coupling caps... in 20k$ amps.  Very Singlepower...

[kevin gilmore]

So i figured that i would test the 300v supply to see if its worth saving.   But no, BOTH transformers are < 1 ohm on the primary.  But no way was i expecting this. And the bias resistor for the headphones really is 100k.  Very bad for the headphones.  A voltage multiplier *7 from 90v. unregulated, no zeners, no protection, no anything. But wait there is more, hand made circuit boards with a dremel tool. This all has to go. But wait, the first picture is a regulated power suppy whose sole job is to drive the power led in the switch.

 

[spritzer]

100K!!??  Yeah any headphones connected to that amp won't live much longer and the distortion must have been pretty intense....  Gotta love it when people go for complete incompetence... 

In the age of super cheap PCB's, none of that makes any sense. 

[kevin gilmore]

back of circuit board.  look at that filament wiring. and the corners notched out of the board.

bias board. its even worse, after the 100k resistor 2 x .022uf caps to ground tied directly to the headphones.

Edited September 18, 2021 by kevin gilmore

[spritzer]

Who needs to twist wires and caps after the ballast is a big fucking no-no

[kevin gilmore]

bias circuit

DO NOT DO THIS!!!

megatronschem2.PDF

[spritzer]

So basically this with an extra stage and a healthy dose of fuckup

 

[kevin gilmore]

the input wiring is monster cable magnetically shielded cable. Says so right on the cable.

And it was a quad balanced pot wired as unbalanced.

[luvdunhill]

7 hours ago, kevin gilmore said:

And it was a quad balanced pot wired as unbalanced.

Maybe they chose the best two sections out of four!

[G600]

Pretty nice Dremel skills, by the way 😂