Go Back   Home > Forums > >
Home Forums Rules Articles diyAudio Store Blogs Gallery Wiki Register Donations FAQ Calendar Search Today's Posts Mark Forums Read

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

6DJ8 hybrid headphone amp
6DJ8 hybrid headphone amp
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 18th January 2017, 06:53 PM   #1
easphyx is offline easphyx  Bulgaria
diyAudio Member
 
easphyx's Avatar
 
Join Date: Jul 2016
Location: Varna, Bulgaria
Default 6DJ8 hybrid headphone amp

After a long delay I have finished my hybrid. Some notes about it's architecture:
  • Common cathode amplifier with active load.
  • Non inverting topology. Bipolar inverter works as a level shifter as well.
  • Class A CFP push-pull output biased to 100mA
  • Recom R-78HB6.5-0.5 SMPS module for filament (with 0.51 Ohm resistor in series to obtain 6.3 V)

Schematics:
kS8uYXq.png

lCmgDRS.png

Assembled board:
YvOLMrf.jpg


Full project in GitHub: https://github.com/e-asphyx/Single-6DJ8-Hybrid
Attached Files
File Type: pdf hybrid.pdf (67.2 KB, 54 views)
__________________
GitHub profile

Last edited by jazbo8; 19th January 2017 at 07:32 AM. Reason: Image size
  Reply With Quote
Old 18th January 2017, 09:46 PM   #2
BinaryMike is offline BinaryMike  United States
diyAudio Member
 
BinaryMike's Avatar
 
Join Date: Apr 2010
Location: Oregon
6DJ8 hybrid headphone amp
That 47uF electrolytic cap in the feedback loop is going to trouble a lot of folks. Can you post performance measurements?
  Reply With Quote
Old 18th January 2017, 10:09 PM   #3
easphyx is offline easphyx  Bulgaria
diyAudio Member
 
easphyx's Avatar
 
Join Date: Jul 2016
Location: Varna, Bulgaria
Quote:
Originally Posted by BinaryMike View Post
That 47uF electrolytic cap in the feedback loop is going to trouble a lot of folks. Can you post performance measurements?
I can post SPICE files and modelled frequency response.

Click the image to open in full size.

I pick up feedback signal from the output, after DC decoupling caps. So feedback circuit cutoff frequency must be as low as possible to avoid clipping at low frequency.
Attached Files
File Type: asc Hybrid 2.asc (4.7 KB, 10 views)
File Type: txt ECC88.txt (889 Bytes, 8 views)
__________________
GitHub profile
  Reply With Quote
Old 18th January 2017, 10:14 PM   #4
easphyx is offline easphyx  Bulgaria
diyAudio Member
 
easphyx's Avatar
 
Join Date: Jul 2016
Location: Varna, Bulgaria
The same plot starting from 1 Hz

Click the image to open in full size.

So I've found 47u a good compromise

Edit: and finally, 0.47u input cap protects from clipping caused by DC offset. So it's all because of my decision to pick up a feedback from the very end.
__________________
GitHub profile

Last edited by easphyx; 18th January 2017 at 10:19 PM.
  Reply With Quote
Old 19th January 2017, 02:12 PM   #5
kylej1050 is offline kylej1050  United States
diyAudio Member
 
Join Date: Nov 2013
47uF there has a cutoff frequency of ~0.6Hz so I'd say that's pretty low!

The only problem with that is if it does clip it stays ugly longer.
  Reply With Quote
Old 19th January 2017, 09:51 PM   #6
BinaryMike is offline BinaryMike  United States
diyAudio Member
 
BinaryMike's Avatar
 
Join Date: Apr 2010
Location: Oregon
6DJ8 hybrid headphone amp
My concern is that nonlinear components in the feedback divider get their nonlinearities supersized. I believe Douglas Self has said that electrolytic capacitor distortion becomes insignificant if signal voltage across the cap stays below 80mV at the lowest frequency and highest amplitude of interest. Just shooting from the hip, it looks as if this circuit may not satisfy that criterion.
  Reply With Quote
Old 19th January 2017, 10:02 PM   #7
easphyx is offline easphyx  Bulgaria
diyAudio Member
 
easphyx's Avatar
 
Join Date: Jul 2016
Location: Varna, Bulgaria
Quote:
Originally Posted by BinaryMike View Post
My concern is that nonlinear components in the feedback divider get their nonlinearities supersized. I believe Douglas Self has said that electrolytic capacitor distortion becomes insignificant if signal voltage across the cap stays below 80mV at the lowest frequency and highest amplitude of interest. Just shooting from the hip, it looks as if this circuit may not satisfy that criterion.
Can you give me a reference? He wrote many great books.
And thank you. I didn't think about this aspect.
__________________
GitHub profile
  Reply With Quote
Old 20th January 2017, 01:23 AM   #8
BinaryMike is offline BinaryMike  United States
diyAudio Member
 
BinaryMike's Avatar
 
Join Date: Apr 2010
Location: Oregon
6DJ8 hybrid headphone amp
In Small Signal Audio Design, published 2010, near the end of chapter two on page 60: "From this data, it appears that the AC voltage across an electrolytic capacitor should be limited to below 80 mVrms if you want to avoid distortion."
  Reply With Quote
Old 20th January 2017, 06:53 PM   #9
easphyx is offline easphyx  Bulgaria
diyAudio Member
 
easphyx's Avatar
 
Join Date: Jul 2016
Location: Varna, Bulgaria
Quote:
Originally Posted by BinaryMike View Post
In Small Signal Audio Design, published 2010, near the end of chapter two on page 60: "From this data, it appears that the AC voltage across an electrolytic capacitor should be limited to below 80 mVrms if you want to avoid distortion."
Thank you! I've found this book in PDF, will read on weekend. Expected voltage across fb cap at 20Hz is about 95mV peak to peak. At least it sounds really good, I'm satisfied.
__________________
GitHub profile
  Reply With Quote

Reply


6DJ8 hybrid headphone ampHide 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

Forum Jump

Similar Threads
Thread Thread Starter Forum Replies Last Post
6DJ8 headphone amp vixr Headphone Systems 18 28th December 2013 04:42 AM
Hybrid headphone amp..... stenak Tubes / Valves 7 13th March 2013 04:08 AM
Can someone help me with DIY hybrid preamp? 2sk170 - 6dj8 - cascode mwmitchell Tubes / Valves 2 5th May 2012 02:17 PM
6DJ8 or 12xx7 for hybrid amp (Monarchy) Interious Tubes / Valves 56 6th December 2008 06:46 AM
6922/6DJ8 headphone amp impressions.... Morse Headphone Systems 9 6th March 2003 02:18 AM


New To Site? Need Help?

All times are GMT. The time now is 08:14 PM.


Search Engine Optimisation provided by DragonByte SEO (Pro) - vBulletin Mods & Addons Copyright © 2018 DragonByte Technologies Ltd.
Resources saved on this page: MySQL 14.29%
vBulletin Optimisation provided by vB Optimise (Pro) - vBulletin Mods & Addons Copyright © 2018 DragonByte Technologies Ltd.
Copyright ©1999-2018 diyAudio
Wiki