Small and easy ESL amp - diyAudio
Go Back   Home > Forums > Amplifiers > Tubes / Valves

Tubes / Valves All about our sweet vacuum tubes :) Threads about Musical Instrument Amps of all kinds should be in the Instruments & Amps forum

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 2nd March 2006, 02:26 PM   #1
knubie is offline knubie  Norway
diyAudio Member
 
knubie's Avatar
 
Join Date: Jun 2005
Location: Bergen
Post Small and easy ESL amp

Respect to all you tube dudes from a newbie...

Too keep us busy up here in cold artic Scandinavia (except for chopping ice and chasing away icebears from the garbage bins) we have bought us an ESL kit from ER-Audio.
To make it a real challenge, did so without output transformers!!
The Viking spirit goes on....

It is now time to get a tiny little output from them. I've read a lot of designs and Morgan Jones x3 so many times that it's falling apart.... so I'm ready to come out of the closet! Regarding safety I'm scared stiff, I've been electrocuted by 220V in the shower, 10 years ago...

I was planning on doing a Tubecad/John Broskie design as attached. A 6C45PE or 5842 driver and a EL34 for output for a cheap and easy start with a +/- 300V bipolar PS.
So I have a couple of questions I can't seem to find the answer from.
-An ordinary output transformer with secondary unconnected, can act as an anode load for the output stage. How do I choose this, do I just care about the primary resistance fitting with the output tubes? Frequency response and all this will have no impact...and so on... Anything else? (I bought second version of MJ's book to find an answer but no luck!)
-How hot can we put the operating point for EL34's?
With a choke load the peak possible voltage swing is almost twice the HT, how should this affect my choice for operating point? I have 600V over the tube, so do I put operating point at 400V, 450 or 500V or something?
- Will this bipolar PS mess up the possibility for twice the HT voltage swing? There is still 600V over the tubes, but 300 of these are negative!!! It's mentally distressing!!!

Comments will be much appreciated...


I will then by parts and get back to you guys...
Attached Images
File Type: jpg tubecad-esl.jpg (35.2 KB, 889 views)
  Reply With Quote
Old 2nd March 2006, 06:02 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
I think this schematic is for headphones, not for larger ESLs...
  Reply With Quote
Old 3rd March 2006, 11:11 AM   #3
knubie is offline knubie  Norway
diyAudio Member
 
knubie's Avatar
 
Join Date: Jun 2005
Location: Bergen
Default Schematic

Yes schematic was used for headphones, but I'm going to use more powerful tubes... I don't aim for very high Sound Pressure Levels's so to say. A electrostatic headphone is still just a smaller capacitor...
  Reply With Quote
Old 3rd March 2006, 12:31 PM   #4
EC8010 is offline EC8010  United Kingdom
diyAudio Moderator Emeritus
 
EC8010's Avatar
 
Join Date: Jan 2003
Location: Near London. UK
You need a lot of voltage swing to drive ESLs. Really a lot. A good starting point would be to use a conventional EL34 power amplifier (with output transformer) and take the output directly from the anodes. Don't worry about not loading the secondary of the output transformer. Unless you're in the habit of grossly overdriving the amplifier (like a guitarist), you won't damage the output transformer.

Resistive loading of the output stage is feasible for headphone amplifiers but not for loudspeakers. To get the same voltage swing using resistive loading as choke/transformer loading, you need twice the HT. Assume 400V across each valve, and 70mA through it, that would be 28W dissipated in each anode load resistor and require an 800V HT. You will find that the cost of an amplifier rises very quickly with rising HT voltage.

Once you've gained a bit of confidence with EL34 at 400V, you might want to try KT88 at 500V or PL519 at even more. After that, you're looking at the smaller transmitter valves.
__________________
The loudspeaker: The only commercial Hi-Fi item where a disproportionate part of the budget isn't spent on the box. And the one where it would make a difference...
  Reply With Quote
Old 3rd March 2006, 05:31 PM   #5
316a is offline 316a  England
diyAudio Member
 
316a's Avatar
 
Join Date: Dec 2002
Location: West London
Hi ,
I had some degree of success driving DIY mid and top panels directly . I built a simple dedicated amp using a 7236 double triode , , driven by a 6EM7 input stage/concertina , coupling caps to the output valve formed a high pass filter for the panels . A standard PP output transformer was used and was connected as an autoformer , in other words the 7236 anodes were connected to the UL taps and the anode taps were connected to the stators . Diaphragm was biased negative , stators sat at 250V After a few arcs and sparks and a few more self-inflicted problems with the panels , (my fault I got a bit too 'heat gun happy' !!!) , I got it to sound ok but it was just too lethal to bring indoors ! I also did not have enough decent iron to buildup a bass amp . Eventually I cap-coupled to the stators with teflon caps , changed the 7236 coupling caps to 0.22uF and ran the bass drivers (Jordan JX150) from the transformer secondary . I never got the panels to integrate well this way though .

cheers

316a
  Reply With Quote
Old 3rd March 2006, 07:09 PM   #6
Bazukaz is offline Bazukaz  Lithuania
diyAudio Member
 
Bazukaz's Avatar
 
Join Date: Nov 2005
Location: Vilnius
Send a message via Skype™ to Bazukaz
It is interesting for me how output power for ESLs is dependant on drive voltage.For as i understand, twicing drive voltage (assuming bias voltage is not changed) , twices output power(3db).But , the required driving power quadruples(P=(U^2)/2 . That would mean that , for each 3db output SPL rise wee need 4 times more drive power ? Is it correct ?

Lukas
  Reply With Quote
Old 3rd March 2006, 07:12 PM   #7
Bazukaz is offline Bazukaz  Lithuania
diyAudio Member
 
Bazukaz's Avatar
 
Join Date: Nov 2005
Location: Vilnius
Send a message via Skype™ to Bazukaz
Sorry in typing , P = (U^2)/R
  Reply With Quote
Old 4th March 2006, 07:51 AM   #8
knubie is offline knubie  Norway
diyAudio Member
 
knubie's Avatar
 
Join Date: Jun 2005
Location: Bergen
Default Voltage drive

Voltage swing is needed and the more the better, but the smaller the capacitance the less voltage swing is needed. Martin Logans need f.ex. a lot less than Quad's ESL. People have reported with Martin Logans that produce 300-400V p-p swing produce an almost decent listening level.
The reasons for my questions is simply to unravel how to produce the highest possible voltage swing. ER-Audio's ESL are very low capacitance so less current is demanded for the high's. So I'll try EL34 at 400V.
EC8010: I was planning on using choke loaded output stage, except for the primary resistance I don't know which parameteres to look for in a choke (books say nothing). Also with a choke one can swing to almost twice the HT voltage as in Morgan Jones "The Beast" esl amp. So choke is going in....
316a: Interesting...
Bazukaz: Formula, as I can recall it is correct, and power requirements quadruples for each doubeling of SPL...

Attached is Thorsetn's setup (as posted her) for an ESL amp....
Attached Images
File Type: gif untitled.gif (25.5 KB, 619 views)
  Reply With Quote
Old 4th March 2006, 07:58 AM   #9
knubie is offline knubie  Norway
diyAudio Member
 
knubie's Avatar
 
Join Date: Jun 2005
Location: Bergen
Default Correction...

Correction, drawn by Thorsten, design by Morgan Jones and build by Jon Finlayson... Nice to be correct...
  Reply With Quote
Old 4th March 2006, 12:55 PM   #10
EC8010 is offline EC8010  United Kingdom
diyAudio Moderator Emeritus
 
EC8010's Avatar
 
Join Date: Jan 2003
Location: Near London. UK
Actually, design by Thorsten, drawing by Morgan, build by Jon.

The choke: Ideally, one would like a low-capacitance choke, but as you're going to hang 1nF or so in parallel, even that isn't crucial. The other aspect that's important is the inductance; you need it to be sufficiently high that it doesn't shunt the load at the lowest frequency of interest.
__________________
The loudspeaker: The only commercial Hi-Fi item where a disproportionate part of the budget isn't spent on the box. And the one where it would make a difference...
  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
small-signal (small-power) fast switching complementary transistors Lola Luna Solid State 3 8th April 2010 07:51 PM
Small-signal (or small power) pentode that can handle 400V (or more)? GordonW Tubes / Valves 12 13th June 2008 02:07 AM
PC-speakers + small amp (key words: small, cheap) rho Multi-Way 8 18th May 2006 01:19 PM
Cheap, small, and easy to build (pcb) amp for studio? massappeal129 Solid State 2 1st March 2003 12:23 PM


New To Site? Need Help?

All times are GMT. The time now is 02:04 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