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i'm on a roll... the kgsshv

kevin gilmore

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I've never seen a ceramic knife break, these are harder than steel, not just a regular ceramic used in planes and bowls.

Do you have any Ceramic knives?

The insert that comes with them tells all the things you can do to break them. They break easily.

Knife steel breaks easily as well if it is too hard. The "harder" a knife is, the easier it is to break. I have a knife by Fallkniven made to address these characteristics. It is a laminate blade with a very hard edge laminated over a softer back bone.

Here's the link for anyone who may be interested.


So, the reason why my original question. Ceramic screws would seem easy to break from the shearing forces and even the stretch from Torquing. I'm fascinated by them though. Except for the cost, that part is not fascinating, it's shocking!

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I have chips in my kyocera ceramic knives just from the knife hitting

pieces of beef or chicken bones. They do break.

The macor i use (machinable glass ceramic) works great in compression

mode, but absolutely horrible in the other direction.

Thanx for that info(Macor) They make some neat looking things out of that stuff.

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So, basically any shoulder washer that has enough length would be just fine? I still a bunch left from my Beta22 build. Wondering if I could use them...

Also, would this aluminum oxide insulator work for lower voltage MOSFETs like the ones in the Beta? If it's better, in term of heat transmitting, than the thermasil I'm using, I'll just buy a bunch and replace the thermasil.

No idea what shoulder washers for the Beta22 are like, so can offer no opinion.

But if you check the thermal resistance of the 4171G you will find it is the same as for thermasil. Alumina has actually got way more thermal conductivity than thermasil, but the 4171G 2mm thick so the numbers balance out. The main thing is that if you draw things out on a piece of paper, you'll quickly see that the breakdown distance is the thickness of the washer, irrespective of the shoulder washer bush length. So although thermasil might have a breakdown potential of 1kV or more, the *actual* breakdown around the hole in the insulator is only a couple of hundred volts. The only way to make use of the native breakdown potenial is to use insulators without a hole, and use a spring clip to hold the transistor at the right pressure.

The 4171G has 2mm, which is good for a couple of kV. Don't forget to use heatsink grease.

The only screw technology that I know of that will take the torque needed for optimum heat transfer (1.1Nm for TO220 and 0.4Nm for TO126) is steel.

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Here's a pic of the finished psu after trimming the output.

I will check and re-trim once it is hooked to the amplifier pcbs.

The pro bias output is at 586VDC, about 1% above nominal.

Two things I noted, one - this sucker is HEAVY!

I will need to mount some type of center support block under the pcb.

Secondly, upon startup the inrush current is substantial. I have not measured it

but the transformer makes a loud pulsing hum, like and arc welder would.

About a half second later when the caps are charged, the noise stops.

I am considering adding a MOV to the hot side supply line.

(click or mouse-over to enlarge)



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MOV would be a good idea or you can just add a CL60 thermistor to the transformer which is what Pass does on his amps.

The alternative, used on old Krell power amps (and many high power pro amps) is to have a power resistor in series with the transformer which is shorted out by a relay after a second or two. Various delay circuits are used, either discrete component or 555 based.

It has the advantage, as compared with a thermistor, that the impedance in series with the transformer winding is kept to a minimum.

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If you can get a relay with the right voltage coil, it will latch automatically, and drop out when the power is turned off.

Or you could put another resistor in series with the coil so that it latches when the voltage rises to about 90% of the rail voltage.

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Excuse my ignorance, I've never attempted to build a stat amp before.

I have a question for the gurus. What is the best way to ground this thing?

I want to avoid ground loops and due to the high voltage on the supply rails,

I've got the heebee jeebees about connecting the amp / psu grounds directly to chassis ground.

Much of my doubt is due to I've noted that unlike other lower voltage circuit board designs,

these boards have isolated mounting pads (isolated from the adjacent pcb ground plane).

Therefore I've been wondering if the high voltage circuit ground should be isolated from the mains / chassis ground.

Lastly, with the balanced XLR input connectors, does the ground (pin3) connect to the chassis (as seen in other designs)

or do I connect it to the amp ground on the pcb, or just float it with no ground while running balanced source inputs?

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