Tube amp to drive 4 ohm headphones? - 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 12th July 2013, 06:36 PM   #1
Speakerholic
diyAudio Member
 
Join Date: Aug 2011
Location: Near Eminence KY
Default Tube amp to drive 4 ohm headphones?

Thanks for clicking in!

I am new to the tube amp world, but would like to learn enough to one day build my own. I have to start somewhere however, and I need to drive an experimental set of headphones I am building based on the Neo3 PDRW tweeters over in this thread. To my displeasure I have discovered all of the various amps I can find on the internet aren't "rated" anywhere near down to the 4 ohm impedance of the neo3s. I don't want to introduce distortion or melt the amp. The good news is however, as they are isodynamic planer drivers, the impedance not only never drops below 4 ohms, but is actually entirely flat across the board. Virtually zero dips or peeks whatsoever. From what I do know about amps in general, this makes them easier to drive than a conventional cone, but their extremely-low-for-headphones impedance is making me nervous. Also, they are very sensitive and I need something with a very low noise floor to test them properly. I'm not looking for anything amazing at the moment, just something to tweak them and finish them out. I'd like to not spend hundreds of dollars right now if possible, although I'd certainly be willing to in the future!

I appreciate any advice!
  Reply With Quote
Old 12th July 2013, 07:28 PM   #2
diyAudio Member
 
Join Date: Mar 2013
Default amp for 4 ohm headphones

You won't find a "headphone amp" that has 4 ohm capability because by definition a headphone amp is designed to handle the much higher impedance of headphones, anywhere from 40 to 600 ohms.

I suggest that you look at low powered tube amp with a 4 ohm speaker tap and then wire a female stereo phone plug jack to the amp outputs. Jolida and Mini Watt come to mind. (no affiliation)

Just make sure that the amp is common ground on the outputs (most are)as that is what a headphone jack requires.

Good luck with your experiments.
  Reply With Quote
Old 12th July 2013, 07:34 PM   #3
diyAudio Member
 
pmillett's Avatar
 
Join Date: May 2005
Location: Dallas (but I am not a Texan!)
To drive 4 ohms, you'll need a design more like a very low power speaker amp, rather than a headphone amp.

To be honest, if I were you, I'd start off with a small solid-state amp using a power opamp or a chip amp.

Do you know how much voltage you need into 4 ohms?

Another thing you may want to experiment with is varying the damping factor - the output impedance of the amp. This can be as simple as inserting a resistor or even a pot in series with the output. But you'd want to start out with something with a very low Zo, which again suggests a solid-state amp... or a tube amp with a lot of feedback.

Once you understand what the ideal amp is (output, gain, Zo) then it's pretty easy to optimize a tube amp circuit for it.

Pete
  Reply With Quote
Old 12th July 2013, 09:25 PM   #4
diyAudio Member
 
ruffrecords's Avatar
 
Join Date: Jun 2007
Location: Holt, Norfolk
Pete Millet designed an excellent headphones amp using the ECC99 tube and an output transformer. I improved this idea by altering the topology to include unconditionaly stable negative feedback. I also tesed it with low cost Edcor transformers rather than the very good but very expensive Sowter ones that Pete used. The results were excellent. So my suggestion to you would be to build either Pete's or my headphones amp but change the output transformer to something like and Edcor XSE10-4-8K

EDCOR - XSE10-4-8K

Cheers

Ian
  Reply With Quote
Old 15th July 2013, 08:20 PM   #5
Speakerholic
diyAudio Member
 
Join Date: Aug 2011
Location: Near Eminence KY
It looks like I won't be able to find a 4ohm headphone amp at all, so my options are modifying a low power speaker amp or building one myself, tube or otherwise solid-state.

I love the idea of building one myself, I wanted to do that eventually anyway. I'd like to go the route you suggested Ian, I'm interested in your improvement with unconditionally stable negative feedback. Could you point me towards the path of getting started? I'm a quick learner but I've never built an amp before. (Edit: Well, from scratch, anyway.)

Thanks for all of your input guys!

David
  Reply With Quote
Old 15th July 2013, 09:47 PM   #6
diyAudio Member
 
ruffrecords's Avatar
 
Join Date: Jun 2007
Location: Holt, Norfolk
Here's a link to the orignial thread about the improved tube headphones amp:

Improved Tube Headphones Amp

The schematic of one channel is in the first post. If you look at the very last post in the thread by techbiker you will see he is very much a beginner and did successfully build one

And here is a link to Pete Millet's orignal design that inpsired it:

ECC99 SRPP Headphone Amp

Before we go any further we need to check the sensitivity of your headphones. You are using an unusual driver so we cannot assume the sensitivity is going to be anywhere similar to that of regular headphones. From what I can gather they seen in general to be of lower sensitivity than regular headphoes. Do you know what sound level in dB SPL is produced for an input power of 1mW?

Cheers

Ian
  Reply With Quote
Old 15th July 2013, 10:00 PM   #7
Speakerholic
diyAudio Member
 
Join Date: Aug 2011
Location: Near Eminence KY
Thank you!

As far as sensitivity, you are very correct about them being less sensitive than normal headphones. I wouldn't hesitate to say they are extremely less sensitive. I don't yet have an effective way to measure sensitivity, but I have been considering the purchase of the "Dayton Audio OmniMic V2 Precision Measurement System"

Would this be effective to measure sensitivity @ 1mW? (Edit: I'm not sure how it handles headphone measurement.) Right now the best I know is the manufacturer's specification @ 90.5 dB 2.83V/1m.

David

Last edited by Thetwinmeister; 15th July 2013 at 10:04 PM.
  Reply With Quote
Old 15th July 2013, 10:19 PM   #8
diyAudio Member
 
ruffrecords's Avatar
 
Join Date: Jun 2007
Location: Holt, Norfolk
Quote:
Originally Posted by Thetwinmeister View Post
Thank you!

As far as sensitivity, you are very correct about them being less sensitive than normal headphones. I wouldn't hesitate to say they are extremely less sensitive. I don't yet have an effective way to measure sensitivity, but I have been considering the purchase of the "Dayton Audio OmniMic V2 Precision Measurement System"

Would this be effective to measure sensitivity @ 1mW? (Edit: I'm not sure how it handles headphone measurement.) Right now the best I know is the manufacturer's specification @ 90.5 dB 2.83V/1m.

David
OK, 2.83 volts rms into 4 ohms is 2 watts!!! but that is for 90dB SPL at 1 metre. You will probably be operating at about 1cm which would be 40dB louder of 130dB SPL. You clearly don't want it that loud but 20dB less at 110dB SPL would be pretty loud and that would need only 20mW of power. So it looks like the available 200mW from the heaphone amp is going to be enough even allowing for some acoustic losses in the headphone itself.

I have zero experience/expertise in measuring headphones so I cannot advise you on what would be suitable but perhaps it won't be necessary.


Cheers

Ian
  Reply With Quote
Old 15th July 2013, 10:35 PM   #9
Speakerholic
diyAudio Member
 
Join Date: Aug 2011
Location: Near Eminence KY
Okay good, I like the sound of measuring not being necessary. I have done some reading into measuring the frequency response of headphones. It was originally suggested for the purpose of EQ'ing the neo3s, but it turns out to be quite a bear to tackle. I imagine measuring sensitivity would be much more simple, but where there is math and manufacturer specifications I am satisfied.

By the way, I got them sounding great without EQ through physical alteration.

I'll start educating myself on amplifier design asap!

David
  Reply With Quote
Old 16th July 2013, 12:19 PM   #10
diyAudio Member
 
Join Date: Jan 2002
Location: Tyrone Ga. U.S.A.
With a power requirement that low you probably will not need any voltage amplification so could just use a current buffer. Doing this with a mosfet is
real easy. If I just had to have a 1/2 watt tube amp I would think about
modifying this circuite. I would replace the 2 voltage dain stages with just
one triode stage and just use one or 2 output tubes.
Attached Images
File Type: jpg otlse.jpg (39.0 KB, 150 views)
  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
Bridging two 300W in 8 ohm amplifier to drive 1200W in 8 ohm rhythmsandy Solid State 3 2nd December 2012 05:47 AM
Amp for 16 ohm headphones (MDR-EX71SL)? AudioLapDance Solid State 3 7th December 2011 03:20 PM
single tube to drive 300ohm headphones sunrise Tubes / Valves 26 10th March 2009 12:09 PM
Can the Golden Tube Audio SE-40 SE drive 16 ohm woofers? nelsondog Everything Else 1 11th November 2007 05:00 PM
Converting a yarland amp to drive headphones arvin Tubes / Valves 0 27th February 2007 01:29 PM


New To Site? Need Help?

All times are GMT. The time now is 01:10 PM.


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