6EM7 Headphone Spud - Please comment - 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 7th December 2010, 03:56 PM   #1
6L6 is offline 6L6  United States
diyAudio Member
 
6L6's Avatar
 
Join Date: Oct 2010
Location: Denver, Colorado
Default 6EM7 Headphone Spud - Please comment

Hello all!

I recently came across a pair of Hammond 125CSE for such a deal that I could not pass it up. (Free...)

Anyway, I have decided to make a 6EM7 SE 'Spud' amp for headphones. Total overkill in the output department, but what the heck, right? That's what volume controls are for.

Primary impedance will be as high as can be made, 8-10k, to help with coupling, linearity and to keep output a little lower. The 30ohm resistor across the secondary is to help keep the transformer loaded properly and attenuate the output a bit as well.

PSU voltages are not written in stone, I need to go to my project box and see exactly what I have to use. It will be tube-rectified with a normal CLCRC filter.

Schematic is based from a project of Tom McNally.

Click the image to open in full size.

Any comments are welcome from anybody who has experience with this sort if thing! I have never made a Headphone amp and am very open to pointers and suggestions.
  Reply With Quote
Old 7th December 2010, 06:29 PM   #2
diyAudio Member
 
artosalo's Avatar
 
Join Date: Feb 2010
How much gain do you need ?
What is typical output voltge and the impedance of the headphones ?

At first the output section seems to be biased very hot !?
What is your target plate dissipation ?

Hammond 125CSE has quite low inductance which in typical SE-output stage causes the loss of bass response, but the ra of 6EM7 (2nd section) is very low (750 ohms).
Therefore I believe the op-transformer will work fine even at bass frequencies (< 100 Hz).
  Reply With Quote
Old 7th December 2010, 06:30 PM   #3
diyAudio Member
 
dsavitsk's Avatar
 
Join Date: Jan 2005
Location: Hartford
It's a pretty straight forward design that should work OK. What headphones is this for? For low Z, gain will be very high. You might leave out the cathode bypass cap on the first stage to keep this under control a little. Also, loading with something smaller than 30R might also be useful for soaking up some power.

The biggest challenge will be noise, and you may find that AC heaters won't work, or that a B+ regulator is in order -- even just a few zeners and a pass transistor of some sort can work wonders.
  Reply With Quote
Old 7th December 2010, 06:31 PM   #4
Gluca is offline Gluca  Italy
diyAudio Member
 
Gluca's Avatar
 
Join Date: Nov 2004
Location: Back to Italy
go for a direct couple design (check the gain you need!). that's my H/P amp

Click the image to open in full size.
  Reply With Quote
Old 7th December 2010, 07:43 PM   #5
6L6 is offline 6L6  United States
diyAudio Member
 
6L6's Avatar
 
Join Date: Oct 2010
Location: Denver, Colorado
Thanks for the feedback so far!

Gain - I will be using a CD player with 2v output.

I am planning on using 32-64ohm headphones. Grados some day... I have a set of 64ohm Sennheiser that will get replaced - I don't find them to be very comfortable. I thought that 30ohm on the secondary would be appropriate with that kind of headphone - please correct me if I am wrong.

Voltages as drawn are too high - I'm thinking that 250 on the power stage and 200 for the voltage gain stage...

Could bias on the first stage be done with a diode?

PSU - I have an 8H 150ma choke that I am wanting to use. Tube rectified with 5Y3, then CLCRCRC I have a number of 47uf 450v caps to use up. DC heaters seem to be mandatory as well.

Last edited by 6L6; 7th December 2010 at 07:51 PM.
  Reply With Quote
Old 7th December 2010, 08:40 PM   #6
diyAudio Member
 
artosalo's Avatar
 
Join Date: Feb 2010
Quote:
Gain - I will be using a CD player with 2v output.
Then you need no gain, I think.
What would be sufficient power input to headphones ?
Would 30 mW be enough ? One volt across 30 ohms headphones is 33 mW.

Quote:
Could bias on the first stage be done with a diode?
It can be done, but I do not see any reason why to use diode instead of resistor. Please, somebody tell me.

I would try a topology something like this:

Click the image to open in full size.
  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
Next project 6EM7 mashaffer Tubes / Valves 31 28th September 2008 05:13 AM
6EM7 Amp jaymanaa Tubes / Valves 12 24th July 2008 04:01 AM
Output transformer for a 6EM7 headphone amp firestorm Headphone Systems 6 4th January 2008 09:58 PM
yet another 6em7 amp rman Tubes / Valves 6 17th October 2007 02:26 PM


New To Site? Need Help?

All times are GMT. The time now is 06:40 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