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My DIY electrostatic headphones - Page 52

post #766 of 2596

I also sent a message to Koss regarding this matter.

Now I want to build a tube amp for my stats (the eXStata does its job, but you see, it doesn't glow softly red in the dark frown.gif ). I have the egmont clone in mind (the schematic can be seen on the 7th post of this thread) for which the 6S4A are on their way. I have a small question regarding the power supply. The transformers I am ordering are custom and it really doesn't cost more to go with 25VA, 35VA or even 40VA rather than 16VA. I thought it could be something like this :

2*250VAC for a current of :
                      - 5mA per 6AS4  at idle
                      - 1mA per 12AX7 at idle

1) 16 VA  (using 7mA for each  6AS4 and 2mA for each 12AX7 )



2) 25 VA ( using 10mA for each 6AS4 and 5mA par 12AX7)

(I also have to mind the size of the transformer though)


Also regarding the power supply, I understood I needed to separate the heater supply of the 12AX7 from the 6S4A. Are two windings enough ? I mean, feeding the four 6S4As with the same heater winding isn't a problem ?

Edited by bidoux - 4/5/13 at 11:22am
post #767 of 2596

I always over spec by at least 1.5 and for something like this I'd go double. 


I would also not use the 6S4A in that circuit as it is, they need different plate resistors.  The circuit could also use some extra gain and adding feedback is a good idea.  Not much you can do about the gain and adding feedback kills some of it. 


You need two windings, one for the front end and another one for the ouput tubes.  Since the amp is run off a bipolar PSU the tubes are way over their cathode-filament limit. 


Personally I'd not build this as an Egmont but rather build a scaled down version of the ESX.  You need another pair of tubes but not a whole lot of extra parts.  You also need a simple 40V DC supply which is left floating on top of the -350V supply to properly bias the amp. 

post #768 of 2596

Hello spritzer


Thank you very much for your input. I am definitly following your recommendations for the transformer


I followed the link in your signature. The schematic is not much more complicated, but the power supply gets bigger. Casing will also be a pain. I think I will be satisfied by building a small but working amp (and I have no high end phones that require more). The bigger things might come later ...


Do you think i should try to use a pair of 7n7 (they are cheaper than the 6AS4 biggrin.gif ) instead of the 6AS4 ? I think you have both versions, that is why i'm asking. As for the feedback, two 60k resistors from plate to cathode as done on tubecad is correct ?

post #769 of 2596

I've had signatures turned off for so long I forgot about the link...  tongue.gif  The PSU only gets a bit bigger, one extra tap to feed a small PSU attached to the - side of the HV supply.  It's a far better amp though... 


The 7N7 can't handle as much voltage and power as the 6S4A but it is a nice tube.  Same goes for the 5968 Tubecad used in his amp.  I had a PCB made for that version of the amp back in the day. 


I used 200K and a 1uf/630V cap for the feedback line, plate of the 6S4 to cathode of ECC83. 

post #770 of 2596

You are tempting me and that is no good biggrin.gif I am not sure I will have the time, money or skills to build something like a ES1/2 ... I am a bit puzzled by this ...


I see you used the old bh supply. Are there equivalents to for the 2SA1968 ? It seems that these are long gone ...

post #771 of 2596

You can use any PNP in that spot as long as it has sufficient breakdown, and enough gain.


Breakdown doesn't actually need to be the full input voltage, just Vin - Vout (although it should have quite a bit of headroom in this position). I use a 375V PNP in my BH supply and have never had problems with it.


The gain needs to be high enough so that the base current is low enough as to not starve the LED of bias current through the 200K resistor. 

Edited by dude_500 - 4/6/13 at 7:18am
post #772 of 2596

We've modified the PSU to use 10M90's a while back.  It just acts as a CCS for the pass fet and the 10M90 is ideal for this role. 


The A1968's aren't gone, it's just that KG and I have half the world supply... tongue.gif


You can use what ever PSU you want though.  I just used the BH supply since it was the only one that fit the odd Single Hour box. I have a mini ESX that I will be casing up sometime soon and it will probably use some very simple PSU. 

post #773 of 2596

It was the stax mafia all along depleting the transistors ... Knew it biggrin.gif

Thank you both. If I carry on one project or the other I will certainly have more questions, but I will make sure to post in the right topic  ...


To catch up with the original subject, I am trying another small cell experiment. The first one didn't have big enough holes seeing how tchick the pcb actually is. I also reduced the spacer thickness to 0,4mm. Still need to drill the second stator though.

post #774 of 2596

Somebody has too keep these transistors...  redface.gif


If you haven't got your heart set on tubes then we have made a new version of the KGSSHV with transistors in current production.  As it stands now you can buy everything for the amp from Mouser minus transformer and PCB.  smily_headphones1.gif

post #775 of 2596

spritzer: what's your opinion on STAX SRM-006t (the old one - now discontinued)? I had it borrowed for few months and I compared to my amp (JFET-MOSFET: see signature) and I was quite dissapointed how bad the SRM-006 sounded.

post #776 of 2596

It's the same as the SRM-T1 and all the other Stax tube amps.  Good circuit hampered by the costs of building amps such as these and the parts available.  The tubes are the worst culprit as they are asked to operate at 700V which is far above their comfort zone.  Then we have the PSU and how the tubes are used.  Take the same circuit with some 6S4A's with CCS and a good PSU and it is a very nice amp indeed. 

post #777 of 2596
Thread Starter 

I would highly recommend KGSSHV.  It's easy to build and sounding very nice.  o2smile.gif


Wachara C.

post #778 of 2596

Has anyone ever actually tried to make an SR009 style diaphragm? I'm finishing up the design work on my next pair of headphones and got the idea that maybe this could be done, at least to limited extent, in a DIY manner.


Something like the following:




The two characteristic thicknesses would have to be dependent on material. I'm thinking for FR4, might be able to use 1.6mm stock and mill the openings down to maybe 0.4 or even a bit thinner. Stainless could of course go a lot thinner, but manufacturing would be harder. 

post #779 of 2596

What should be the effect of this "reinforced" stator? Lower distortion?

post #780 of 2596
Originally Posted by AmarokCZ View Post

What should be the effect of this "reinforced" stator? Lower distortion?


The goal is to have the majority of it be very thin. To be honest, I don't know all the technical acoustic reasons, but I've read all over the place and in this thread that the SR009 gets a lot of its benefit over the SR007 by having the stators be extremely thin.

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