Megatron Electrostatic Headphone Amplifier

[DonAudio]

I purchased a megatron board and power supply board from Joachim. I believe I have a complete list of the parts necessary to build except for the following. I was wondering if anyone would be able to guide me to an appropriate source for these items. Any help would be appreciated:

Qty	Value	Ea			Schematic X-Ref
12	2sc4686a	1.4	16.8		Q1-4, Q9-10
4	2sa1968	0.7	2.8		either this
4	ixtp01n100d	1.29	5.16		or this
4	2sa1486	1.86	7.44		Q15-16
4	2sc2705	0.46	1.84		Q11-12
4	2sc2240	0.38	1.52		Q13-14
4	2sa970	0.38	1.52		Q17-18
2	LSK389	10	20		Q19,Q22
2	2SC1815	0.19	0.38		Q20
2	OP27GPZ	1.93	3.86		U2, 6
2	2sc3675	1.22	2.44		Q5, 15

[congo5]

Megatron?

this looks like an older KGSSHV BOM

if so http://www.bdent.com/

[mwl168]

No sure what's the currency used for the parts price. If it's USD, many of thm look way low to me.

[joehpj]

No this is wrong for megatron. At least no lsk389 is needed

[bravi]

The 1000pf and 3900pf 1000v capacitors for the psu board are listed as obsolete with mouser and digikey. Has anyone tried alternatives such as metalised polypropylene caps of the same value? Can it be used? The one I have tentatively shortlisted are shown as useful for high dv/dt apps. Appreciate some guidance on this. 

By the way, I have installed stn9360 using small conversion pcbs instead of 2SA1486, as the 2SA1486 lot I had purchased all topped out at around 310v on the transistor tester.

[Leve]

Bravi.. the 3900pf capacitors listed in the BOM here: https://docs.google.com/spreadsheets/d/1tQvwqsARXGge6Tw6edqicCDti6Mite2F24T5YddyEEc/edit#gid=0 are available from Mouser, and are a film type.

RS have several options listed for the 1000pf if you can't find them at Mouser.. the problem you have to watch going to a different type is that there's not a lot of room where these go on the board, so check the size and lead spacing.

Glad to see another Megatron going together "down under".. mine is just about ready for it's initial start up (fingers all crossed here).  

[palchiu]

On 2016/5/5 at 9:47 AM, DonAudio said:

I purchased a megatron board and power supply board from Joachim. I believe I have a complete list of the parts necessary to build except for the following. I was wondering if anyone would be able to guide me to an appropriate source for these items. Any help would be appreciated:

Qty	Value	Ea			Schematic X-Ref
12	2sc4686a	1.4	16.8		Q1-4, Q9-10
4	2sa1968	0.7	2.8		either this
4	ixtp01n100d	1.29	5.16		or this
4	2sa1486	1.86	7.44		Q15-16
4	2sc2705	0.46	1.84		Q11-12
4	2sc2240	0.38	1.52		Q13-14
4	2sa970	0.38	1.52		Q17-18
2	LSK389	10	20		Q19,Q22
2	2SC1815	0.19	0.38		Q20
2	OP27GPZ	1.93	3.86		U2, 6
2	2sc3675	1.22	2.44		Q5, 15

This should be KGSSHV's BOM

[bravi]

Hi Leve,

 

Thanks for the reply. Located the 3900pf piece. Using the reference provided the 1000pf cap comes up as a ceramic disc cap made by Murata and indicating obsolete.  Yes, I can that disc space is limited, but may have to think of a different way to locate if it does not fit.

 

Cheers!

[Leve]

These are showing as out-of-stock at RS, but I have some here I can send you if you want to drop me a pm with your details:

http://au.rs-online.com/web/p/ceramic-single-layer-capacitors/7214975/

Update.. they have several options in stock, but still happy to send you some if you prefer:

http://au.rs-online.com/web/p/ceramic-single-layer-capacitors/7214966/

http://au.rs-online.com/web/p/ceramic-single-layer-capacitors/8313036/

[Leve]

Finally - another Megatron is alive.. all the voltages came in within a couple of volts, and it really is a great sounding amp. I still have a bit of mounting and case work to do before it's finished, but listening is a constant distraction.

The only issue I have is that I find I'm mostly up into the last 10% of the pot, and I'm wondering if I have something wrong, or is it just because the Mk 1 007 headphones are that hungry ? Any advice would be appreciated.

[chinsettawong]

Your amp looks really nice.  Please show us the underside as well.

About the volume, it might have something to do with your source putting out too soft sound too.  Please check.

[Leve]

28 minutes ago, chinsettawong said:

 

28 minutes ago, chinsettawong said:

Your amp looks really nice.  Please show us the underside as well.

About the volume, it might have something to do with your source putting out too soft sound too.  Please check.

Thank you chinsettawong.

The source is a Yamaha SACD player (CD-S2100) so it's a balanced 2v output.

Here's the underside with board not yet fully mounted and transformers not yet hooked up:

[johnwmclean]

Beautiful work!

[eggil]

Congratulations on a very nice build!

[bravi]

Very nice build Leve. The VCaps will really let the sound bloom after some time.

I hope to start the case preparation for my build this week end. The boards need just one or two more bits  I begin testing.

[astrostar59]

Leve does your pot have a 100K resistor load on it? I replaced my pot resistor on my Passive pre-amplifier for a 10K load, which redialed the gain to the pot. 

Edited October 7, 2016 by astrostar59

[Leve]

3 hours ago, astrostar59 said:

Leve does your pot have a 100K resistor load on it? I replaced my pot resistor on my Passive pre-amplifier for a 10K load, which redialed the gain to the pot. 

No. The input goes directly to the pot and from the pot directly to the board. At full volume I measure about 0.5 ohms between input and output. The pot is Khozmo's new relay based design.

[spritzer]

I finally finished this one today after about... 4 years or so...  Let's just say that I hate anything with umbilical cables...   

Besides the madness of using 4 mains transformers and the super short filament winding's for the CCS tubes this was easy enough.  Running at +/-400V off a BHSE power supply with the dropper resistor and zeners to feed the front end.  Only main difference is the 12VDC supply used to heat the front end tubes so the board was cut up pretty bad.  Next one will use the Megatron V2 pcb's in about 3 years or so... 

[nopants]

how do you like it against the other amplifiers in your stable?

[spritzer]

It's excellent, nothing short of that for an all tube design.  Gives the BHSE a run for its money...

[JimL]

Great job, spritzer and congratulations!  Perfect for those cold Icelandic summers.  

[wink]

Can you do one in solid state....?     

[johnwmclean]

Really beautiful!

[spritzer]

I might do a version of this circuit with SS CCS just to make it a lot less complicated. 

[mwl168]

According to the Gerber viewer I used, the Megatron board dimension is 228.6mm x 228.6mm. Can someone confirm? 

Thanks!