eXStata DIY Electrostatic Amp for Intermediate DIYers

[wiatrob]

Quote:

Originally Posted by pabbi1 /img/forum/go_quote.gif Let's just say I know what 800Vpp sounds like...

Oh, I think there might be a way around that (he says cryptically)

 

[Sherwood]

Got it up in the computer rig right now fed balanced by a DACmagic and an E-MU 0404 -- holy hell. This thing is a tone monster. Great instrument placement, great dynamics, great soundstage, great everything. I'm in to build one, without a doubt. This sounds significantly better than my Normals out of a transformer through the Moth EC2a3, which is a great amp.

FUN!

 

[ericj]

Currently burning in:

 

[smeggy]

Excelent work, eagerly waiting on more tubey impressions when ready

 

[manaox2]

Quote:

Originally Posted by smeggy /img/forum/go_quote.gif Excelent work, eagerly waiting on more tubey impressions when ready

X2!

 

[pabbi1]

Well, since I am actively working on other amps while listening, I really can't add much, save that we are tweaking as we hear certain things.

For 98% of what I am aware of, the voltage swing will be more than sufficient. Where we are identifying it is not, work is still being done to add headroom.

I am going to also defer to others next weekend to offer brutally honest impressions without me guiding any opinions or impressions. Gonna turn them all on, and let others have at it.

It is journey.

 

[ericj]

With only about 8 hours of burn-in, this amp sounds great to me. For one thing, even with the crazy rats nest of wiring on the workbench, it's dead quiet.

I've got it hooked up single-ended to my EMU 0404 pci card, through the entirely passive tape loop output on the Rotel RA-820bx you see in the picture above. The tape loop and input selection work the same when the rotel is turned off, so it's probably just a resistor divider.

I know the 0404 is actually a balanced source, but i don't have the right cables to hook it up that way. I could make those cables, but the 0404 is my only balanced source. I don't foresee ever putting a set of XLRs on the backs of these enclosures, at least not for my own use. Performance with single-ended input is most important for me.

By the way, although you see three transformers in the picture above, only the black Hammond is hooked up right now. The two triads are for the sand amp. At present I'm using the PS board i built for the sand amp so that i could get the tube board up and running faster. I've since completed the 2nd PS board and will bring it online tomorrow night.

The triads together are about $10 cheaper than the hammond. They have twice the HV current of the hammond we're using for prototyping, but lack the heater winding.

 

[smeggy]

Thanks Eric.
I was wondering whether the Hammond 380(?) might be a better transfo for this, it's not much more expensive but supposedly a significantly better transformer. I doubt it's necessary but you never know. Well, I don't anyway

 

[ericj]

bigger iron is being considered for the hybrid amp. The triads offer far more current than the SS amp needs - if people prefer to use a hammond for the SS amp, though, it does work - iirc sachu had one up for a while that way. You waste the heater winding, but that's no big deal.

There are probably some good toroids and R-cores that work too - these are just what we're prototyping with. The triads are super-economical, though.

 

[smeggy]

I guess being somewhat of a fashion victim I'd ideally want a transfo that's both powerful and reasonably good looking for top mounting. I'm only getting the tube version and it'll have bottom mounted sinks so the tubes can go out the top as well. I'd like it to look stylin' and those triads, cheap and powerful as they might be, are ugly as all hell.

 

[sachu]

Finished everything except the heatsink mounted transistors. Can't seem to locate the heatsink compound. Will get to it tomorrow.

Transformers should arrive in a couple of days so I get get the two additional PSUs fired up.

Edit:

Smeggy, I have two Hammond 269JX transformers for our builds.

They have marginally higher voltage secondaries and current than the standard 270AX Hammond. BUt Still very doable. They were about as cheap as the Triads on ebay and were difficult to pass up for the price..

 

[smeggy]

excellent news sachu. On another front, I've figured out a nice way to do the removable baffle. It's part way there and It's a hassle but should work well

 

[wiatrob]

Quote:

Originally Posted by smeggy /img/forum/go_quote.gif I guess being somewhat of a fashion victim I'd ideally want a transfo that's both powerful and reasonably good looking for top mounting. I'm only getting the tube version and it'll have bottom mounted sinks so the tubes can go out the top as well. I'd like it to look stylin' and those triads, cheap and powerful as they might be, are ugly as all hell.

You won't have to worry about it if you go tubed (you get a ugly hammond!) - but the Triads do present an opportunity for cool trafo covers :^)

 

[ericj]

Quote:

Originally Posted by wiatrob /img/forum/go_quote.gif You won't have to worry about it if you go tubed (you get a ugly hammond!) - but the Triads do present an opportunity for cool trafo covers :^)

haha.

I'm surprised those triads come with case mounting tabs. I've seen that style of transformer in gear before - usually all those tabs sticking out the side are neatly embedded in a circuit board.

 

[luvdunhill]

looking nice guys!

The best I can tell, there is somewhere around 20 different 6S4A construction variants. Does anyone have any tube preferences yet?

I'm looking around for one odd ball to complete a construction matched octet, perhaps someone might be willing to see what they have on hand?