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current feedback electrostatic amp


kevin gilmore
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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 :)

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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

cfae2.jpg

 

Edited by kevin gilmore
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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.:palm:

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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?

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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?

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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. 

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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  :D

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 by kevin gilmore
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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 by Sechtdamon
correction
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