Megatron Electrostatic Headphone Amplifier

[Aspirant Audiophile]

I received a Megatron built by Søren Brix two days ago. Simply based on who had a Carbon available in stock at the time, I also bought Søren's Carbon.

I understand that head-case isn't really the place for 'listening impressions'. And, my grasp of audio engineering leaves much to be, uh, grasped. So I'll only note this:

I really, really like the Carbon, to the point that I'm now looking for a 007mki specifically to pair with the Carbon.  Before receiving the Megatron, I was pretty down on my x9000s, and I was buying into the negative reviews. The Carbon does not fit the x9000s, in my opinion.

I am no longer down about the x9000s, not one bit, because Megatron.

I don't dispute any of the negative opinions of x9000s--I don't have enough experience to agree or disagree--but I do believe I found the right amp to pair with x9000.

Perhaps most relevant for head-case is my 'listening impressions' of Soren. Soren has been, in a word, delightful. I'm not an easy person to deal with--Soren was patient, thoughtful, fair, and he gave low-bias recommendations (when begged). 

Soren prefers to use stock, non-boutique components. I have no idea whether that professional stance does or doesn't make a difference. I do know that Soren has a clear philosophy of work, and I grew to admire his reasons.

Thank you Kevin Gilmore for your design, and thank you Soren for bringing it into fruition.

 

 

Edited November 13, 2022 by Aspirant Audiophile
typo

[kevin gilmore]

so i posted this elsewhere because people really want to spend large amounts of money on an electrostatic amplifier that uses a pile of 300b.

this is the first of two.

Megatron xl  with 4 x 300b

Megatron xxl with 8 x 300b

Power supply #1   goldenreferencehv all solid state

Power supply #2   tube rectified lc filtered no regulation solid state regulated bias.

Power supply #3   tube rectified lc filtered 4 x 6l6gc fully regulated voltages. 300 volt tube rectified and 6bq5 regulated power supply. solid state regulated bias

high voltage rectifier tubes are gz34 (5ar4)  300v rectifier tube is ez81

 

I figure a megatronxxl with power supply #3 should come in at a retail built price of $40k

evidently one or more companies are making dc supplies that slam 7 amps into cold 300b resulting in tubes that don't last very long. so this will have a slow start quad 5v power supply board. the xxl will have 2 of these boards.

amp chassis will be about 14 x 14 x 4 inches. power supply box should be the same size.

 

the spice simulations indicate that minimum distortion is set at about 33ma, so this is likely to eat about 300 watts total power consumption.  distortion will end up about .01% at full voltage swing.

 

Edited March 24, 2023 by kevin gilmore

[spritzer]

300B's have been ordered so time to show Woo Audio and Hifiman how this should done. 

[nopants]

Is this similar to what you had in mind for the original Megatron with EML tubes? (If it wasn't already made that is)

[jamesmking]

14 hours ago, kevin gilmore said:

so i posted this elsewhere because people really want to spend large amounts of money on an electrostatic amplifier that uses a pile of 300b.

this is the first of two.

Megatron xl  with 4 x 300b

Megatron xxl with 8 x 300b

Will the stn9360 still be ok as a substitute for the 2sa1968?... it would be nice for the megatron 300B to use in production parts...

[spritzer]

Maybe better to go with the 2SA1627A in TO126 form.  These pretty much the only 600V pnp's though. 

[kevin gilmore]

that section runs on 300 volts.  ksa1156 is in stock at mouser now. would work fine. i think the pinout is backwards from 2sa1968 so just rotate it around.

the emission labs tube with the octal base and the center tap filament would make things much easier but would limit the amp to those tubes. so its the standard 4 pin socket.

Edited March 25, 2023 by kevin gilmore

[mwl168]

6 hours ago, kevin gilmore said:

that section runs on 300 volts.  ksa1156 is in stock at mouser now. would work fine. i think the pinout is backwards from 2sa1968 so just rotate it around.

 

This what I did exactly with my Megatron.

[kevin gilmore]

had to make the board bigger because of the diameter of the 300B

pictures not same size (major squares are 1 inch)

 

Edited March 27, 2023 by kevin gilmore

[nopants]

might be worth making the cap spaces bigger if you can, I'm sure people are going to try and shove boutiques there (I know I did for the EL34 version)

[JoaMat]

TTP15 pin 3 seems to be a trim pin. Can that pin be used for -Vout?

[kevin gilmore]

yep, a trim pin.  not really necessary unless someone comes up with a reason.

all parts on order.

[JoaMat]

but you have connected negative traces to trim pin on layout above... or am I just confused? 

[kevin gilmore]

fixed. glad someone is paying attention.

Edited March 28, 2023 by kevin gilmore

[justin]

no RK50 option?

On 3/25/2023 at 5:44 AM, kevin gilmore said:

that section runs on 300 volts.  ksa1156 is in stock at mouser now. would work fine. i think the pinout is backwards from 2sa1968 so just rotate it around.

the emission labs tube with the octal base and the center tap filament would make things much easier but would limit the amp to those tubes. so its the standard 4 pin socket.

that is for the EML-only version 🥰

[kevin gilmore]

was saving that for the xxl version

ok, fine

 

 

Edited March 28, 2023 by kevin gilmore

[mwl168]

[JoaMat]

Maybe one can feed heater direct from the Traco? A small test showed that current starts at 4.2A, decreases below 3A in 2 – 3 seconds and below 1.5A after another 3 - 4 seconds.

Tested both a EML 20B-V4 and a 300B.

From Traco datasheet:             Output Current Limitation         120 - 200% of Iout max.
                                                                                                                              145% typ. of Iout max.

 

Edited April 4, 2023 by JoaMat

[kevin gilmore]

the idea is to make the environment for the stupidly expensive tubes as friendly as possible. there are rumors of 300b in one or more amplifier companies with an average tube life of 8 months. For something that should be 10,000 hour tubes.

my circuit limits the start current to 1.5 amps for 30 seconds.

[sorenb]

Have been tinkering a bit with the XL'ish.
Build one based on EMS 20Bs and another based on EMS 300b (picture)

A major improvement to the Megatron for sure.
Really enjoyable to listen to, toe tapping.
Whether 20B or 300b I found those pretty similar sounding in this configuration.

[mwl168]

So EL34 for the CCS tubes and EMS 20B for the output tubes? 

Any other modifications needed other than accounting for the 20B filament supplies?
 

[MLA]

Really nice!

From picture, it looks like Ecc99s or similar replacing the ksa1156s?

[sorenb]

4 hours ago, mwl168 said:

So EL34 for the CCS tubes and EMS 20B for the output tubes?

Yep, EL34 for the CCS tubes and (EMS 20B or 300b) for the output tubes
Here's the 20B version before power switch/volume knob etc.

 

Quote

Any other modifications needed other than accounting for the 20B filament supplies?

Kevin already posted what is necessary. Using 20Bs is pretty straight forward, 300b is another story and requires a bit of tail resistor tweaking.

Quote

From picture, it looks like Ecc99s or similar replacing the ksa1156s?

Not using either, but you probably figured that out looking at the above pic 🐵

[MLA]

11 hours ago, sorenb said:

Not using either, but you probably figured that out looking at the above pic 🐵

Indeed. Damn, I actually thought I had figured something out  

[JoaMat]

On 5/17/2024 at 10:16 PM, sorenb said:

...
Build one based on EMS 20Bs and another based on EMS 300b...

Emission Labs 20B and 300B, is that the 4 pins socket or the octal socket with center tap filament?