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

Group Buys Members group buys

xrk971 Pocket Class A Headamp GB
xrk971 Pocket Class A Headamp GB
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 14th June 2018, 09:55 PM   #1841
jebivetar is offline jebivetar
diyAudio Member
 
Join Date: Mar 2018
Quote:
Originally Posted by xrk971 View Post
I mistakenly thought the parts I had were thin film, when in fact they were thick film.
yup.



what are ideal electrolytic alternatives for the 100uF spot on the capmx?

there's a worldwide smd cap shortage and i don't think i even see any x7r 25V 47uF or higher MLCCs on digikey or lcsc.

i'm currently using a 100uf rubycon yxg, but not sure if there's something better suited.

Last edited by jebivetar; 14th June 2018 at 10:01 PM.
  Reply With Quote
Old 14th June 2018, 11:08 PM   #1842
xrk971 is offline xrk971  United States
Got Foam?
diyAudio Member
 
xrk971's Avatar
 
Join Date: Oct 2012
Location: Metro DC area
xrk971 Pocket Class A Headamp GB
Try looking for tantalum in SMD for larger values. Still available and fine for non low ESR requirements.
__________________
XRKaudio https://www.etsy.com/shop/XRKAudio
  Reply With Quote
Old 16th June 2018, 08:03 PM   #1843
jebivetar is offline jebivetar
diyAudio Member
 
Join Date: Mar 2018
Alright, some more questions about the resistors - the revised values specifically.

In the original low impedence BOM, R6 is 47R.

The first time you mention your revised low impedance resistor network it is 1R:

Quote:
R3 = 820R
R4 = 47R
R5 = 220R
R6 = 1R
Some posts later you describe it again in a reply to someone but mention only R3 through R5, and leave out R6.

Quote:
R3=820R, R4=33R, R5=220R
What's R6 in the revised network?
  Reply With Quote
Old 16th June 2018, 09:30 PM   #1844
xrk971 is offline xrk971  United States
Got Foam?
diyAudio Member
 
xrk971's Avatar
 
Join Date: Oct 2012
Location: Metro DC area
xrk971 Pocket Class A Headamp GB
R6 is the so-called gate stopper that is there to absorb any oscillations in the gate of the MOSFETs. It could be 0R, but I would leave it at 47R to be safe. I don't know what I was thinking if I ever suggested using 1R. Maybe 10R lowest. But my recommendation is leave at 47R.

R3 should be about 1k or 1k1 - adjust it to get the correct voltage at the source (pin 3) of the MOSFET. The best value is 1/2 of Vcc, but adjusting it too much also changes the bias through the JFET. If you are within 0.5v of 1/2Vcc, leave it alone.

R4 adjusts the relative H2 to H3 distortion (larger R4 will be greater H3 but lower overrall THD), but be careful as it also changes bias current - higher R4 is higher bias current. One of the most effective ways to decrease THD and keep a good H2/H3 profile is to use a voltage regulated DC step up for the power supply and adjust so that Vcc is about 18.2v. If you monitor the FFT in real time as you adjust, you will see the optimum place to be. Ideally R4 is somewhere between 33R to 52R, typically, even 39R could be a sweet spot.
__________________
XRKaudio https://www.etsy.com/shop/XRKAudio
  Reply With Quote

Reply


xrk971 Pocket Class A Headamp GBHide 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
BF862 based SE Class A Headamp without the HEAT xrk971 Headphone Systems 513 12th April 2018 08:44 AM
FS: F5X GB chassis and all GB parts Studley Swap Meet 6 21st May 2013 11:47 AM
Midgård, compact, low distortion, high quality, Class A Lateral FET headamp Neutrality Headphone Systems 23 12th March 2013 05:21 PM
Another Class A headamp idea Dxvideo Solid State 3 19th November 2007 08:08 AM
Pocket pre-amp & headamp digi01 Chip Amps 11 10th October 2004 12:49 AM


New To Site? Need Help?

All times are GMT. The time now is 02:53 PM.


Search Engine Optimisation provided by DragonByte SEO (Pro) - vBulletin Mods & Addons Copyright © 2018 DragonByte Technologies Ltd.
Resources saved on this page: MySQL 15.00%
vBulletin Optimisation provided by vB Optimise (Pro) - vBulletin Mods & Addons Copyright © 2018 DragonByte Technologies Ltd.
Copyright ©1999-2018 diyAudio
Wiki