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kevin gilmore

current feedback electrostatic amp

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5 hours ago, sbelyo said:

I measured the pin spacing on the boards as well as the BH Ultramini PSU.  They're all 5.08mm  The MKDSN series are all 7.62mm

It doesn't look like they'll fit and I don't see anything in that size higher than 300V 

Thats weird. Are you sure?

I'm consulting the Phoenix dates on Mouser website and I see this:

Paso:

5.08 mm
Método de conexión:
Screw
Valor de corriente:
13.5 A
Voltaje máximo:
400 V
Serie:
 

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I've used a bunch of MKDSN 5.08 spaced from Mouser, they exist (for example 651-1729131). 

Also, note that the 400V is its CAT III rating (see data sheet).

The CAT II rating, which is more relevant for an amplifier for home use, (think broadly home appliances connected to a wall outlet) is 630V.

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Those do work...  I was focused on the 400V rating and didn't realize the different CAT rating thanks.  What transformer did you use?

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Trafo depends somewhat on the psu also: if you’re using GRHV you only have 20-30V or so in dropout voltage (or even less if I remember correctly). 

360V secondaries puts you at about 510V DC unregulated, so that leaves quite a bit to be turned into heat by the psu pass transistors if you’re aiming for 400V output.

Edited by MLA

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1 hour ago, MLA said:

Trafo depends somewhat on the psu also: if you’re using GRHV you only have 20-30V or so in dropout voltage (or even less if I remember correctly). 

360V secondaries puts you at about 510V DC unregulated, so that leaves quite a bit to be turned into heat by the psu pass transistors if you’re aiming for 400V output.

Sorry. You are right but a clarification:  I am using my universal PSU (GRHV) and I put the transformer data.

For this amplifier I´m thinking about use a specific PSU. Maybe I ´ll use a Mini BH and a trafo with [email protected] X2 

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18 hours ago, jose said:

Is not it better to ask all the questions at once? 😉

You only need HV: [email protected] x2

 

 

I'll try, I was just posting as they came to mind

Congo5 used a 300V @ 340mA and wound up with 399Vdc using a BH Ultamini psu

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Yea, good enough for me

on USA ~122vac with an Antek  AS=1T300

   and my "as built" BH supply

pick a transformer, measure its output.

build your power supply and test what it needs to regulate

then adjust accordingly, might not have exact output you want, doesn't matter if within 10% or so

if I send my transformer and PS to Jose it might not work good enough on his line voltage

you have to test and set it up or run a bit more regulation and heat to have some headroom

 

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28 minutes ago, sbelyo said:

I'll try, I was just posting as they came to mind

Congo5 used a 300V @ 340mA and wound up with 399Vdc using a BH Ultamini psu 

Do not worry, don´t take it the wrong way. I told you to have all information in a single post and we can consult it quickly. 

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No worries, lol

My mains run at the same voltage so I'll start with that transformer

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Amplifier built on Gary’s (congo5) boards. I really like this one . Cheap and easy to build - and it sounds really good.

IMG_0239.thumb.JPG.136f6a174ceba4f3a53dd9b03500ec53.JPG

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On 1/30/2019 at 5:10 PM, JoaMat said:

Amplifier built on Gary’s (congo5) boards. I really like this one . Cheap and easy to build - and it sounds really good.

IMG_0239.thumb.JPG.136f6a174ceba4f3a53dd9b03500ec53.JPG

What case is that?

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Modushop heat sink 300 mm X 80 mm and Modushop Galaxy Maggiorato front and back panels. I buy them as spare parts. Brackets and aluminium plates for top and bottom I get from a local shop.

I've drilled and tapped M4 holes at both ends of heat sinks to fasten the panels.

Below is a board attached to 200 mm X 80 mm heat sink - temperature stabilazed at about 50 degrees Celsius. With 300 mm heat sink temperature stabilized at 42 degees. Current stabilized at 20 mA with resistors as silk screen.

IMG_0238.thumb.JPG.fa3a7f145729fb57fb886f59574b5c45.JPG

Edited by JoaMat
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Thanks folks. No matching. I use our kitchen table as workbench and to avoid some nasty conflicts with wife….

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I feel the ginatricot bag is part of minimizing nasty conflicts...  ;)

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  • Haha 3

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Reduced the 2k resistors at base of input transistors by 100 ohms steps. 1.7k give approximately 7.5 mA and I have decided to keep it there until further…

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OK, now I’ve reached further. Replaced all eight 2K resistors with 2K trimmers. Makes it easier to change the current. Set at 1.6K current start at 2.5 mA and climbs to 4.5 mA. IMO it’s still an interesting amplifier and I believe it’s possible to build an all SMD version.

IMG_0065.thumb.JPG.002a52d78b3385b9bc7848693d6597cb.JPG

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Increasing trimmers resistance always increase corresponding side’s current and vice versa. If upper trimmer (ksa1156) increases corresponding side’s output voltage increases and the other decreases. If lower trimmer (ksc2752) increases corresponding side’s output voltage decreases and other side increases. So far I’ve preadjusted all eight trimmers to the same resistance. Resulting in roughly the same current of all for channels and in an output voltage of some positive volts - all good and not needing any further action. To me it has been a bit tricky to turn all trimmers to achieve better balance and offset than when the preadjusted.

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A very early layout attempt. Have to figure out how to spread the parts. Board size 2.65in x 0.87in.

146876482_SMDtop.thumb.JPG.3de99e65adec1ba91c140f1ead555397.JPG1856531596_SMDbottom.thumb.JPG.c171a8b22d7b19835985729beae4c37d.JPG

Edited by JoaMat
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With congo5's blessing, Jose and I had PCB fabricated for our use.

These are proven boards - a few working amps have been built. The boards are 2mm thick, 2oz copper (see pic.).  

There are a few remaining sets available, PM me if interested.

 

ES CFA PCB.JPG

Edited by mwl168

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I'm not sure why but I'm always involved in all wars. :D

7.2x2.5 or 183x63.5mm

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