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Old 30th May 2013, 07:40 PM   #51
diyAudio Member
Join Date: Jan 2008
Location: Toronto and Delray Beach, FL
I used a Sanders-type HV direct-drive amp for maybe 2-3 decades. With barely a hiccup. I believe that I and a "test panel" of friends are convinced it is audibly superior even to the 39 lb matching transformers in driving Dayton-Wrights and open-air D-W panels.

My amp really drive a large bunch of resistors with the panels barely counting in the load. Makes it easier to create a stable wide-band amp, rather than an amp to drive a largely capacitive load.

But with a 2400vdc B+ supply (and covering 140-3000 Hz range), I still wished for a bit more ooomph in a middle-sized living room (note, the D-W panels have quite wide spacing).

HiFi aspirations since 1957. Currently working on motional feedback again... the final frontier in audio

Last edited by bentoronto; 30th May 2013 at 07:43 PM.
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Old 30th May 2013, 10:57 PM   #52
diyAudio Member
Join Date: Feb 2008
Location: Jackson,michigan
Jcx, Yes ,I understand, I have much experience when working with HV cricuits.
I have repaired tube electronics (TV's) for many years as well as many tube RF linear amps, Neon Transformers and such.

But, Yes the risk is always there, Thanks !!!

The FET's do have a bit large of input capacitance, But their output capacitance is much smaller than the inputs and yes it is much larger than my current panels.

I have some High current opamps to drive the gate loads I figured about 40ma. but the ones I have are good for 150ma and I have some that will do 3 amps as well.
According to the data sheets they make nice square waves into a .01uf capacitance load......And stable!

I do like the IXYS stuff and would be my choice but I got these as samples just to get started.
I think IXYS requires me to have a Business domain type Email address so those will have to wait until I get one or just buy them outright as the ones I wanted were only $.87 each.
It was almost more for the shipping!!!

Ben, I have all of the Sanders and David P. Hermeyer schematics!!
I have been wanting to build them for many many many years, But I never got the tubes at a cheap enough price when I should have.

And, The power resistors were quite costly as well!!!
FET's will handle this quite nicely at a fraction of the cost!

I do know that at 5KV peak the panels get to about 106db and at 2.5KV peak the are in the +99db range.

I have measured this with an SPL meter while watching the input level going to a 1:256 step-up transformer on a scope and typically anything more than 5Vpeaks (1280Vpeak) was more than enough for average everyday listening.

A ClassA P-P amp running at 2.5kv to 3kv will easily produce my main goal and my 900V supply will be enough to make some decent sound.

I have a few MOT's lying around that I could use but I do plan on using a much higher frequency supply in order to cut the cost and space of the filter section of the main supply.

This will also allow me to better regulate it as well as I have had great success with my Variable HV Bias Supply.

As far as DC output protection I have thought about making the capacitors out of either a stack of glass plates or plastic material, I am not sure which one will be the least noisy, I probably won't use them at all.

I am not sure if I will be allowed to post the circuits here or not.
But,there are many of such circuits in these threads.
I will let you know as I go along of my progress, But, I will definitely have them up on the ESLDIY site.

If I can just get one to work well on only a 1500v supply I think that I may decide that it is ample for my needs.

Even my little panel needs about 300 to 400 watts to fully drive them, But again that is about 106db to 110db at one meter so add another 6db for my nearfield listening distance!!!!



Last edited by geraldfryjr; 30th May 2013 at 11:01 PM.
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Old 31st May 2013, 02:05 AM   #53
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Join Date: Feb 2008
Location: Jackson,michigan
The STF6N95K5 950V 9A N-CH TO-220FP ones seem to be the best of the bunch I got right now.
Even though they are the TO-220FP fully encased version even stacking them will hardly exceed their 25 watt disapation factor in my application.
A standard TO-220 version is rated at 90watts.

It has a gate capacitance 450pf.
And the output capacitance is only 30pf !!!

The STW4N150 1500V 4A is not to bad either as I have seen worse.
Rated at 160watts with an input capacitance of 1200pf.
And an output capacitance 120pf.

It looks like stacking two 950V Fet's will yield a better overall performance for higher powers if the non Isolated version (TO-220) is used.

Using the Isolated version will be nice with low power small panels and headphones. They could be all mounted on the same heatsink as they are isolated!!

Stacking 3 for 2850V ( 6 required) is still only 50watts peak for my 50pf (160Kohm) load alone so it may be marginal and run warm but i think it will work.

If I do have any heat issues then I will either lap them down and insulate them or just get some of the plain TO-220 versions.

This will definitely be better than the wasted power that is used up in a step-up transformer at more than 600pf to 800pf per core to start with!!!


Last edited by geraldfryjr; 31st May 2013 at 02:17 AM.
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