[NoPants]

I guess the Megatron hasn't been discussed here because it's exclusively a DIY affair at this point. I thought I'd take the opportunity to create some space to talk about it, for both before and after it leaves my hands.I'd rather start a thread here than have some discussion going on somewhere inappropriate, or offline. To be honest I dislike reviews and impressions, but I do understand the need when there are new designs afoot. There are probably less than 10 of these out there at the moment so there is that as well, ironically enough none of whom talk here. We also seem to be on the cusp of a new wave of Stax amplifiers so I think it makes sense to start documenting them, to help people get a better understanding of what their (or their builder's) options are.
 
Some info: 

1. Kevin Gilmore, Spritzer Design. If you are reading this then you are probably familiar with these people already. All credit goes to them, they designed it and I along with a handful of other people decided to kludge things together.
2. It's an electrostatic, hd800s need not apply. You can try though, not covered by warranty
3. I think the units out there are running on dual-rail 400 or 450V at the output
4. all-tube, 2x 12au7 2x 12ax7, 2xEL34. I've been getting asked a lot about the tube complement and options. All of these tubes are pretty famous so I don't think I need to cover things except for some stuff specific to the Megatron:
   1. 12au7s have a "super" variant known as the e80cc, which requires double the filament current
   2. 12ax7s have some similar variants such as the 5751, etc. which should not be used because it decreases the system gain. To paraphrase the internet, the 12au7 and 12ax7 section is providing most of the voltage gain,
   3. EL34 = 6CA7. There are substitutes which have been discussed but I won't bother listing them here. If you know what you are doing you probably also know enough to make an output tube substitution yourself and not kill yourself in the process
   4. Popular variants:
      1. 12au7: RCA, sylvania, telefunken
      2. 12ax7,:JJ, telefunken
      3. EL34: SED, RFT, Mullard, Matsu****a, Amperex
   5. it might be worth pointing out at this point that the tubes cost is significant, I think the cheapest standard price for 8 EL34's is already 300 USD. You shouldn't need to swap out the output tubes all that often unless you think you have the ears of god, but I'll leave that to the listener. There is certainly some merit in swapping the 12au7s and 12ax7s, I'd recommend doing this first.
5. To put this in the perspective of existing Stax amplifiers out there, this is might best be viewed as a relative of the rebuilt ES-X designs. I'm only saying this because of the interstage coupling betwen gain stages, as well as the presence of a direct-coupled output stage.
6. It's a self-balancing output stage, which means there's no balance/offset adjustment like the KGSSHV/KGST/BHSE/etc. designs
7. It's hot
8. It's pretty hot
9. It's really hot, 200W- of which 85W goes to the filaments.
10. not pet-friendly

 
I wanted to include the pictures I've taken but I've an opportunity to get some nice shots done (i.e. not by me). I'll insert those when I get a chance. One of the nice things about the amplifier board is that it basically has to look impressive once you put everything together. In the meantime I can post some of other people's builds. To put it in perspective, I started thinking about building this at the beginning of 2014, and have only just finished it into something that anyone can use. It's a pretty simple build as far as the boards go, but managing the casework is something else entirely.If people have  problem with me posting their work just talk trash in the thread and I will remove them.
 

 

 

 

 

 
 
I'm going to go ahead and omit the names of the builders, they know who they are and I haven't asked them for explicit permission. It shouldn't be to hard to backtrack these photos for those who are seriously interested. I apologize for using some unfinished photos here and there, just wanted to show that the typical architecture involves separate power and amplifier cases, due to the size and power requirements.
 
If anyone has any questions please feel free to ask. I'm probably going to take another post to do (ugh) listening impressions.
 
For those who aren't interested in that- it sounds like an amplifier An amplifier that happens to be good.

 

[NoPants]

I'm probably going to write stuff using the following equipment, mixed and matched based on how I feel:
 
Headphones:
-007mk1
-009
-Sigma
-HE60
-maybe Lambda Signature, no one seems to care/like this headphone
 
Amplifiers:
-Megatron
-BHSE (DIY)
-KGST
-KGSSHV
-if I somehow keep at this in a timely manner, KGSSHV Carbon + Original BH
 
Source:
-Schiit Yggdrasil
-AR-T Segue D/A Converter (AD1862, released 1995? I think)
 
Other Stuff:
-ifi iusb
-gemini cable
-ar-t legato II
-audiophileo ii
 
Music:
-Whatever I've been listening to lately
 
If you guys have any specific preferences as far as genre goes, please let me know here and I will do my best to queue up Darude -Sandstorm instead

 

[Earspeakers]

I'm nearing the end of building one. Nearly all the parts are placed and soldered, I have the transformers, just need a case. Compared to other Stax amps this is a monster - 8 EL34s! I actually have matched quads of NOS Mullard xf2 if it turns out I like it. It's also unusual in that it uses tube drivers (12AU7/AX7) and isn't DC coupled (it has coupling caps). I opted for teflon Relcaps (or some other, that French brand) as with coupling caps I really only like teflon. Despite the proliferation of tubes the amp circuit is pretty simple, not a lot of components up on the amp board. 
 
I've heard it's one of the warmest of the Stax amps, no wonder with all those tubes and coupling caps in there. I suspect that the sound is less a 'wire with gain' and is driven by the sound of your caps (2 ea in the signal path), with some contribution to all those tubes and their associated circuit. So I'm guessing it'll be the least favorite of my amps, I like wire with gain and aren't in the camp of Stax owners looking for warmth.

 

[NoPants]

it is blanket statements about sound like that that should be avoided regardless of whether they are accurate or not. it is also part of why I felt compelled to write despite never having done so before

 

[Rossliew]

Good stuff. Please keep it up!

 

[Rossliew]

Btw when you mentioned it's really hot, are you saying like fireplace hot?

 

[Earspeakers]

it is blanket statements about sound like that that should be avoided regardless of whether they are accurate or not. it is also part of why I felt compelled to write despite never having done so before

 
Sorry, what statement, that I've heard it's a warm sounding amp? It's not a blanket statement, just repeating what I've heard others say.. Likewise for all my statements about how amps sound, I get tired of writing "to my ears" and such before every sentence, but I hope it's clear. I don't mind saying things about how I think things sound, I hope it's clear that it's all FWIW (e.g. not much) and just a personal perspective.

 

[gepardcv]

The self-balancing output is my favorite feature of the Megatron. Minimal fiddling with boards running 350-500V rails always welcome. Don't think I'll build one, though. Too much casework hassle, and I don't have room for a two-box rig.

 

[NoPants]

 
009, Megatron vs BHSE:
 
I was asked to compare these amplifier. It makes sense given the tube complement and parts cost, not to mention both run hot enough that "sauna capabilities" should be included in the feature list
 
This comparison was using the Yggdrasil.
Tubes were
amperex DD-getters for the BHSE
telefunken e80cc, JJ 12ax7, RFT EL34, SED EL34 CCS
 
demo tracks included Darude - Sandstorm and others whose names I can't quite recognize:
Nier- Gestalt and Replicant OST
Hozier - Hozier
Cesaria Evora - Radio Minelo
holst - the planets
 
Bass: BHSE certainly seems like it extends deeper, but the Megatron seems to have a bit more texture when it first starts kicking in. Initial impact is a bit softer on the Megatron
 
Mids: Female vocals are shifted a bit closer to center stage on the Megatron. There's a bit of shout to male vocals on the BHSE. Performance seems similar, choral arrangements are more pleasing to listen to on the Megatron.
 
Treble: Initial impact on the BHSE is much stronger than the Megatron, but the Megatron seems to have a more natural decay. Fairly noticeable if you focus on cymbal splashes and violin bowing. Both amplifiers have great extension.
 
The trend in the microdynamics here seems to be that the BHSE is a more aggressive option for the Stax because the inital attack seems to be accentuated. Between this and the Megatron, the Megatron might be a better 009 pairing for longer listening sessions. I have yet to try this because of energy/heat concerns, and I can't listen to the 009 for very long anyway. I think both are really competent choices, and it's probably just a matter of preference at the end of the day. In 2015 it seems like people are expressing preferences for more treble energy for that "sparkle" and "air". 
 
From a holistic standpoint I think the Megatron has a more neutral presentation- no particular band is emphasized. This might come at the expense of some soundstage and excitement(?) that makes the BHSE as appealing as it has been since its introduction. Also worthing noting- Megatron is slightly better at projecting images forward, based on what limited classical listening I did.
 
Again, these differences are minor and you probably woul not be able to find any faults in either amplifier if you used them alone. I should note that I listen at a higher level than normal (no number to quote), as I think electrostatics need some volume to really sound great. That probably comes off at a parrot statement at this point, and I certainly can't explain why that seems to be the case. Levels were more or less matched during the A/B.
 
Both amplifiers are fairly revealing, and it's difficult to say which is more accurate. It has been documented previously but it's really easy to turn up the Megatron to very high levels, everything is very listenable (addictvely so) for a very wide range of the volume turning. It's enough of an issue that it should come off as a legitimate warning. The BHSE's aggression on the initial attack makes it more difficult to do the same.
 
Hopefully this helps some of the inquiries I've been getting via PM. I was originally going to start with the KGSSHV but I'm pretty flexible, which also describes the butt out of which I am talking

 

[Jones Bob]

Thanks Nopants. Well written and an enjoyable read.

 

[Ali-Pacha]

Great thread !

 
Ali

 

[FrankCooter]

Really appreciate you starting this thread.
 
There's a huge amount of work in a project like this and it's a great thing to share the results with us all.
 
Hope to see your Megatron at the upcoming NorCal meet.
 
I'll be there with my 845 electrostatic amp.
 
Should make for some interesting comparisons.

 

[NoPants]

Unfortunately the outlook for that meet isn't looking too rosy at the moment, some things with work. I have been chasing your DHT amplifier for a while though, as well as Kevin's. To be honest I don't know how you can tear your amplifiers down (so I read) after building them up like this, I think I'd be in tears.
 
The Megatron resolved a lot of bias I held against AC-coupled amplifiers, since most of Kevin's portfolio is DC-coupled. It has made me more tolerant of other toplogies, which is why I've started looking into the hotrodded SR-X as my first P2P effort. Was also a good opportunity to try out boutique coupling caps though it didn't seem to amount to much. For the record, I originally built the Megatron with wima mkp10s and mundorf mkp's which eventually became auricap XO's and mundorf supremes. 
 
Currently waiting on a timed relay so I can delay the startup of the PSU, then I can continue with the comparisons. Probably KGSSHV next, since that seems to be the most common high-end amplifier out there and the benchmark for the past few years.

 

[NoPants]

Forgot to mention that there is a reputable builder out there who's looking to build 4 Megatrons, should be easy enough to deduce who it is

 

[FrankCooter]

   
 
The Megatron resolved a lot of bias I held against AC-coupled amplifiers, since most of Kevin's portfolio is DC-coupled. It has made me more tolerant of other toplogies, which is why I've started looking into the hotrodded SR-X as my first P2P effort. Was also a good opportunity to try out boutique coupling caps though it didn't seem to amount to much. For the record, I originally built the Megatron with wima mkp10s and mundorf mkp's which eventually became auricap XO's and mundorf supremes. 
 
 

 
In general, I too prefer DC coupled amplifiers, but great amps can be built with all coupling topologies. No matter what you're listening to, no matter how extreme the equipment is,  there are always going to be  capacitors somewhere in the chain. Same goes with transformers, which are a personal interest of mine.
 
Being a balanced design with at least some global feedback, I'm not surprised that the Megatron  seems relatively immune to cap rolling. In general, I think "cap rolling" is overated to begin with, but it's much more likely to make a difference in a single-ended zero-feedback design than something like the Megatron. Like most other "tweaks", the biggest improvement is the first step off the bottom. I've tried pretty much everything out there. I like oil caps. I've owned a few expensive ones, but nowadays I use the cheap surplus Russian K-40's on everything.
 
To some extent, I would assume the same immunity to be true of "tube rolling" in the Megatron. The first stage 12AU7's would probably make the most difference ( I like vintage Mullards). The second stage 12AX7's would be next, ( Telefunkens if money is no object), and finally the EL-34's.  I would think that the lower EL-34's that actually pass signal would make more difference than the upper EL-34's, which if I understand correctly, merely serve as active plate loads for the signal tubes.
 
Since I've never actually heard a Megatron, everything I've said is pure speculation. So feel free to correct me if you have contrary experience.
 
Thanks to Kevin Gilmore for contributing this design and others to the community. Even though it's unlikely I'll ever build one, I learn a lot from studying  the designs and greatly enjoy the  discussions.