current feedback electrostatic amp

[Kerry]

2 hours ago, spritzer said:

It will surely be done by 6pm on Monday!! 

I'll look into updating the board a bit.  Might change it all SMD and into stereo channels.

I'd like to mount this flat against the inside of the heat sinks (75mm less top & bottom plates), so I'd like to request the height of the boards be 2.6" or less if possible

[spritzer]

That's what I was thinking as well.  Might be slightly awkward though...

[kevin gilmore]

pbhv9560 and pbhv8560 are matched transistors for the front end, both 600v. better idea

2.6 inches, don't see how that can possibly happen unless I flip the outputs around and mount inside and under the board. would be impossible to work on if something blew up

2.7 x 3.7

 

Edited November 27, 2016 by kevin gilmore

[JimL]

7 hours ago, kevin gilmore said:

no this is the krell/Marantz style of doing unbalanced to balanced via the low impedance - cfa input.

Marantz still does this in products today.  differential gain way less than .1db, look at the graph. schiit has trademarked this as "schiit pivot point"

Ah, missed the resistor connection between the two halves.

[joehpj]

9 hours ago, JimL said:

So, if I understand this, it looks like this design really likes to be driven balanced.  If you have an unbalanced input (e.g. RCA) the negative input is grounded and the stator gets no signal, unlike the differential input designs which become a long-tailed phase splitter if you ground the negative input, thus providing a balanced output.  Correct?

Err... so do you mean the amps having differential input (eg. 2sk170 pair) output balanced signal no matter input signal was balanced or not?

And also if the above was true, what's the benefit of balanced input signal?

[congo5]

Yes these stat amps from kevin will make their own balanced signal output.

its the how that is not always clear to me.... Like Jim's question where a LTP will make balanced.

IF you have 2v out from your source then if balanced that would be 2v + 2v so stronger than a 2v single ended.... think Spritzer told me 6db.

I use a lot of computers so converting to balanced helps with the gain on some amps. (enough volume)

Question on the ksa1156/ksc2752:

on Mouser they have grade Y & O for the 1156 and only grade O for the 2752

also the Hfe grades are different between the two  O is 60-120 on the 1156 and  O is 30-60 on the 2752

so from what I see there is no way to get a hfe match from Mouser, perhaps CFB will fix?

Does It Matter?

[gepardcv]

Matching NPNs to PNPs is generally difficult. I'm guessing it will be sufficient to match NPNs and PNPs separately, i.e., get the 1156es close enough to each other and 2752s close enough. It should be possible to get to sets of 3% or better. 

Dumb question: what is PP on the silkscreen? And why two separate input blocks? If each board represents one polarity of a balanced channel, I'd expect just one input, just like there is just one output. 

[Craig Sawyers]

The +/- 400V looks a little close to the mounting holes, Kevin. As does the output connection.

[kevin gilmore]

a little cleanup, and .6 inch from center of output device to mounting pins. board file posted

[spritzer]

I'm working on an SMD version.   

[Sechtdamon]

For I have not enough info about technicalities and making an electrostatic amplifier, so I'm asking to you directly: Are you planning build some for selling Birgir?

Forgive me for my ignorance and straightforwardness.

Edited November 28, 2016 by Sechtdamon

[spritzer]

Maybe...  I'll certainly build one as this all started as a birthday present to me from Kevin.   

[Kerry]

Are the output transistors backwards?  If you mount underneath then I think they might be.

Looking forward to the SMD version.

[JoaMat]

Brainstorm - Output transistor on bottom side and the other components on the top.  There are some 300V and even 400V sot-23 devices.

[kevin gilmore]

58 minutes ago, spritzer said:

Maybe...  I'll certainly build one as this all started as a birthday present to me from Kevin.   

really, first I have heard of it 

on the second board, output transistors facing in, and under the board as well as the 2 surface mount.

might be possible to move the mounting hole another .1 inch

 

Edited November 28, 2016 by kevin gilmore

[sorenb]

are there any particular reason to building this amp? does it represent some kind of improvement in comparison to the other designs available?

[Sechtdamon]

39 minutes ago, sorenb said:

are there any particular reason to building this amp? does it represent some kind of improvement in comparison to the other designs available?

I guess Birgir partly answered it:

1 hour ago, spritzer said:

Maybe...  I'll certainly build one as this all started as a birthday present to me from Kevin.   

v    Made a correction.

Edited November 28, 2016 by Sechtdamon
correction

[sorenb]

1 minute ago, Sechtdamon said:

I guess Birgir answered it:

I guess not

[kevin gilmore]

build it, put it in a super fancy box, and sell it for $37k

betcha it sounds better than the high priced spread, at least no stupidly expensive and useless input transformers.

its a push pull amp, so it might actually sound a bit different.

besides which its winter what the fuck else are you going to do.

[JoaMat]

I'm going to feed ducks, sometime.

[Craig Sawyers]

You'd have to be quackers to do that 

[spritzer]

Is this better than the Carbon?  Nope, but that's also not why we do these things.   

[JoaMat]

I guess the 35uF electrolytic are on the board for some reason – why?

[kevin gilmore]

you need some power supply cap, and the wima's would make the board too big

[JoaMat]

I had 0.1uF wima in mind, but i'is to low?