Looking for HV fets for direct drive - diyAudio
Go Back   Home > Forums > Loudspeakers > Planars & Exotics

Planars & Exotics ESL's, planars, and alternative technologies

Please consider donating to help us continue to serve you.

Ads on/off / Custom Title / More PMs / More album space / Advanced printing & mass image saving
Reply
 
Thread Tools Search this Thread
Old 6th October 2012, 04:24 PM   #1
diyAudio Member
 
Join Date: Oct 2012
Default Looking for HV fets for direct drive

I'm looking to make some ELS units with direct drive and wondering if anyone has seen any reasonably priced transistors suitable for the job.
Tom
  Reply With Quote
Old 6th October 2012, 06:40 PM   #2
Bazukaz is offline Bazukaz  Lithuania
diyAudio Member
 
Bazukaz's Avatar
 
Join Date: Nov 2005
Location: Vilnius
Send a message via Skype™ to Bazukaz
Quote:
Originally Posted by madtom1999 View Post
I'm looking to make some ELS units with direct drive and wondering if anyone has seen any reasonably priced transistors suitable for the job.
Tom
I have used IRFBG30/IRFBG20 in the past. The amp was class A bridged; max. output voltage about 600V rms. Suitable for panels having high efficiency only or headphones.
There are many BJT transistors with higher voltage rating but their SOA is usually worse at the same supply voltage. What topology amp you are planning to build?

Last edited by Bazukaz; 6th October 2012 at 06:45 PM.
  Reply With Quote
Old 6th October 2012, 09:26 PM   #3
diyAudio Member
 
Join Date: Oct 2012
Default Whatever works!

When I find some more I'll just run a lot of spice sims and see what I can get to work best - I used to be a chip designer and got quite good with it many years ago and it should help get me into a nice stable area if there is one.
  Reply With Quote
Old 6th October 2012, 09:40 PM   #4
diyAudio Member
 
Join Date: Oct 2012
Default Had a thought

Just had a crazy thought - I thought I would ideally need more volts (than 600rms) to get it working well and then thought perhaps I could bridge two amps and then thought, mmmm, I could bridge the speakers!
Could work pretty well up to 2 or 3khz ....
Have you a circuit I could borrow?
  Reply With Quote
Old 7th October 2012, 12:01 AM   #5
Bazukaz is offline Bazukaz  Lithuania
diyAudio Member
 
Bazukaz's Avatar
 
Join Date: Nov 2005
Location: Vilnius
Send a message via Skype™ to Bazukaz
Quote:
Originally Posted by madtom1999 View Post
Just had a crazy thought - I thought I would ideally need more volts (than 600rms) to get it working well and then thought perhaps I could bridge two amps and then thought, mmmm, I could bridge the speakers!
Could work pretty well up to 2 or 3khz ....
Have you a circuit I could borrow?
Hi,
Looks like i have lost the complete schematic. Here is the screenshot of one half of the bridge. 600Vrms is already for a bridged amp. It has some severe shortcomings however:
1) low output voltage for most ESLs(except headphones & very sensitive units)
2) high power dissipation(constantly 40w for one bridged module) - active cooling needed
3) possibly lower safety because output voltage is not isolated from the ground.

So I have abandoned the idea some time after.
BTW why not use mains toroids ? Some of them give really excellent results and are readily available. I use 6x 230/8V units for a total stepup ratio of ~1:115.
Attached Images
File Type: png Direct drive amp.png (19.6 KB, 319 views)
  Reply With Quote
Old 7th October 2012, 12:28 AM   #6
jcx is offline jcx  United States
diyAudio Member
 
Join Date: Feb 2003
Location: ..
ESL loudspeakers can require middling kV

IXYS offers MOSFET up to 4 kV - still would need to cascade for some ESL

Class A is hugely power wasting for driving pure C load to 20 kHz when most music has <5 kHz power bandwidth

and even for ES headphones several of the "audiophile" direct drive amps do draw over 50 W continuous power

Last edited by jcx; 7th October 2012 at 12:32 AM.
  Reply With Quote
Old 7th October 2012, 12:49 AM   #7
diyAudio Member
 
Join Date: Nov 2009
Location: Los Angeles
Quote:
Originally Posted by madtom1999 View Post
I'm looking to make some ELS units with direct drive and wondering if anyone has seen any reasonably priced transistors suitable for the job.
Tom
You might want a look at this idea from EDN. Each amp can hit 1800 Vp-p and in push pull as needed for ESL, 3600 V p-p !! The question is can it deliver enough current to drive that big capacitor.

High-voltage amplifier uses simplified circuit | EDN

G
  Reply With Quote
Old 7th October 2012, 01:03 AM   #8
kevinkr is offline kevinkr  United States
diyAudio Moderator
 
kevinkr's Avatar
 
Join Date: Sep 2004
Location: Boston, Massachusetts
Blog Entries: 6
Was looking at that design and my impression is that there are a lot of errors in the schematic, fix the obvious errors and it appears to me given the typical gate capacitance of power mosfets the power bandwidth is quite limited, perhaps even under 1kHz.
__________________
"Extraordinary claims require extraordinary evidence." - Carl Sagan
  Reply With Quote
Old 7th October 2012, 02:11 AM   #9
diyAudio Member
 
Join Date: Feb 2008
Location: Jackson,michigan
I have many models that I have done in Circuitmaker using the IRFBG30's and similar FET's.
All class A as well, Bridged of course.

I have found that you need about 5Kv to 10Kv peak voltage to make an ESL really sing depending on the size of the panel.
As the bigger the panel (more surface area) the less voltage will be required to reach a certain amount of SPL's.

At the time I started on such designs the IRFBGxx series was the highest voltage that could be found cheaply.
So, in order to get a higher voltage swing I had experimented with stacking (cascoding) the FET's.
This worked very good only I never finished one for such a high range of voltages yet.

I proved my circuit for 200v using 3 or 4 IRF510's about 4 years ago.
Some of my design are similar to Bazukaz circuit only minus the gate driver transistor and they can be found here,

All Discrete Class-A Headphone Amp

This was also before I learned about how to use a current source in place of the resistor in the top half.
This is something that I now understand and hopefully will be continuing such a project soon and I would be very interesting in seeing your results as well.

All I need is some more FET's.

There are many more higher voltage FET's to choose from now, But you want one that has the lowest gate capacitance you can get and these types will generally cost much more although I have found a few that aren't to bad cost wise.

The lower the gate capacitance the less power that will be required to drive them as by the time you get up to 20Khz and higher to faithfully reproduce a square wave the gate current gets quite high in order to have an acceptable slewrate.

Also to fully drive a 1' x 4' panel at these levels it will require on the order of about 900 of power.
Being that an ESL panel has a 6db per octave rise in response after equalization this won't be much of a problem, Just something to consider wile designing such an amplifier.

I have found that considering the current requirements and Pd of some FET's, against cost, That stacking the lower voltage ones may be a viable alternative.
Last year I found some nice 500v to 650v Fet's with a fairly high Pd for like .25$ to .89$ a piece.
I was going to buy up all of the ones for .25$
They were some discontinued parts and I never jump on it, But they may still be available.

Doing it this way will also be a larger construction technique, But having it being spread out will also make it easier to work on and help keep the HV isolated from possible flash over issues between the stages causing a catastrophic failure of the whole thing as each FET stage will need to be adjusted in order to have an equal voltage across each stage.

Then there is the cooling issue and I have thought about putting the whole thing in an oil bath as well.
I have put a lot of thought into these and I still like the idea of a large solid state direct drive amplifier.

I have a design somewhere in my archives that I was going to try using some IRFBG30's stacked up powered from a MOT that I have been saving for some time.
It should produce about 6KV p-p on a 3100v supply.
Even some thing like this may be ample for a larger panel.
But at least twice this will be required for the little panels that I have been experimenting with to get over 105db.

Then there is the issue of the filtering the supply!
A switching supply may be more suitable and cheaper as they are available and used in today's modern microwave ovens.
I found a very nice one on the web that a HAM had done up as it was quite impressive!
But is was only at 1200 volts output.

I had finished my Variable HV supply about a year ago and it is precision regulated and has enough current to pull a constant arc at 5KV.
I have been bitten by this supply as it does a peak voltage of 13.8kv and it is no joke!!

Just a few things to consider.

Cheers !!!

jer
  Reply With Quote
Old 7th October 2012, 02:14 AM   #10
diyAudio Member
 
Join Date: Feb 2008
Location: Jackson,michigan
That schematic from EDN has lots of error's and there was never a follow up or any corrections for it.

jer
  Reply With Quote

Reply


Hide this!Advertise here!
Thread Tools Search this Thread
Search this Thread:

Advanced Search

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off


Similar Threads
Thread Thread Starter Forum Replies Last Post
WTB : Direct Drive Standalone TT Drive Razorblade Swap Meet 0 2nd January 2011 05:22 PM
HV Direct Drive tube amp. sasha Tubes / Valves 26 18th November 2007 07:19 PM
I need a HV insulator for TO247AC FETs... batee Power Supplies 17 2nd February 2007 10:02 PM
chipamp to drive heavy fets? h3 Chip Amps 0 14th December 2005 03:24 AM
How many parallel fets could BOSOZ drive? Michael Rothacher Pass Labs 7 18th February 2004 12:44 AM


New To Site? Need Help?

All times are GMT. The time now is 06:27 AM.


vBulletin Optimisation provided by vB Optimise (Pro) - vBulletin Mods & Addons Copyright © 2014 DragonByte Technologies Ltd.
Copyright 1999-2014 diyAudio

Content Relevant URLs by vBSEO 3.3.2