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kevin gilmore

Megatron Electrostatic Headphone Amplifier

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spritzer    1,444

How about remove RK27 then use space for add 2SA1968 0.5mA (150mW) CCS option for the 2nd stage?

I'm always a fan of using up some of these 2SA1968's... :)

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Victor Chew    13

Why not lets have it all (ie. CCS and the DACT)? Makes the boards bigger but .... after all its a "Megatron"rolleyes.gif .

Edited by Victor Chew

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kevin gilmore    990

Inu must be playing with spice biggrin.png

yes it would have to be a 2sa1968, because nothing else is stable at 500 microamps.

or a 2sa1486. The 10m90s won't work. Actually the real number is 450 microamps.

Neither of these are in current production. Could probably get away with ksa1156.

dn2540 also won't work because leakage at likely temperatures is more than 500 microamps.

and with the 12ax7 in the first stage, the gain is a bit high at 65db. so i'm playing

with a 12au7 at the moment. brings the gain down to 52db.

removing the pot probably does not help with the space needed for the current sources.

We will see...

Edited by kevin gilmore

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spritzer    1,444

I'm going to order some boards soon, one for me and one for Kevin.

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Remolon    17

The voltage gain of the 6SN7 varies from 13 to 16. If the source provides 2V (a CD player), the second stage grid, U3 (U4), could receive 26V. With R8 of 300K, and R7 of 1K, 400V for B+ will provide an adequate bias of U3?

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spritzer    1,444

Ain't that the truth. We rush from project to project as we keep coming up with something we like. We often loose track which is why we draw up PCB's now as we go along.

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I've got some T2 boards on stand by, but am not sure if I should proceed in light of these new projects coming out. Would it be wise to wait for the SS T2 or is that a ways off into the future? just itching to start buying BOM parts:)

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eggil    67

Any news on the Megatron? BTW, never had a chance to test the 1968's I got from EBay but the 2 I tested before my trip were around 1060V

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spritzer    1,444

It's me who's holding up the Megatron as I'm waiting on more PCB designs before making a bulk order. Lack of time to make those but I'm getting close. :)

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eggil    67

Which BC560 is the correct one for the Megatron? I don't think there is a BOM or a schematic yet. is there?

http://www.mouser.co...key512-BC560CTA

or this one?

http://www.mouser.co...lkey863-BC560CG

Also, I assume these ones are correct:

http://www.mouser.com/Search/ProductDetail.aspx?R=KA7812ETUvirtualkey51210000virtualkey512-KA7812ETU

and

http://www.mouser.com/Search/ProductDetail.aspx?R=KA7912TUvirtualkey51210000virtualkey512-KA7912TU

Edited by eggil

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spritzer    1,444

I do have one RK27 sitting here so I might use it but I just got these lovely PCB's for the Alpha pots that I'm dying to use...  :)

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n_maher    5,472

Birgir,

Are you guys at all worried about having at least one of the filaments connect so close to the pot/input? Seems like a place for noise to get in early on unless one is very careful. The power supply must be a bit of a beast as well.

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spritzer    1,444

That filament was always supposed to be DC powered but 12VDC operation would have been a better idea in hindsight or even running them at 25V.

 

My plan for this one is to run it off a BH power supply with it and the power transformer in a separate chassis.  The amp chassis will also have to have mains running to it as the filament windings for the CCS tubes need to be as close as possible to the tubes.  So that will be 4 transformers for this one and all in the largest Galaxy cases.  Half the size of the ESX for a far more complicated amp... should be fun.... :D

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