Go Back   Home > Forums > >

Headphone Systems Everything to do with Headphones

directly coupled class A buffer for low-voltage headphones (work-in-progress)
directly coupled class A buffer for low-voltage headphones (work-in-progress)
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
Old 26th October 2020, 04:36 PM   #21
cellularmitosis is offline cellularmitosis  United States
diyAudio Member
 
Join Date: Jul 2013
I have a 1khz ultra-pure sine wave generator on order, and when it arrives these are the sorts of comparisons I’d like to start making (I suppose I could go ahead and build the circuit and give it a listen while waiting

One thing to consider is that an active ground means I don’t need an ideal voltage power supply. Some residual ripple is fine, because both the channels and the ground work together to eliminate it. If I did away with the active ground, I would need to be much more careful with my voltage supply.
  Reply With Quote
Old 26th October 2020, 05:08 PM   #22
laserscrape is offline laserscrape
diyAudio Member
 
Join Date: Dec 2017
No output coupling cap is especially useful for extra low Z IEMs also.

I seen this virtual ground techinique before with Szekeres VE and wondered if it's for simplicity sake or has benefits soundwise.
A bit similar to global feedback in that you are correcting things at the output error rather than starting off with well regulated supply, but at the same time it would allow a simpler/passive solution for the supply which is going to have its own influence on sound... or going beyond and feeding a well regulated supply to the virtual ground.
  Reply With Quote
Old 26th October 2020, 10:20 PM   #23
laserscrape is offline laserscrape
diyAudio Member
 
Join Date: Dec 2017
Just noticed this uses a negative supply only , not a split supply.
I don't get how it works when the input signal goes above 0 without input biasing?
  Reply With Quote
Old 26th October 2020, 10:34 PM   #24
cellularmitosis is offline cellularmitosis  United States
diyAudio Member
 
Join Date: Jul 2013
hehehehe, this circuit messes with your head a little

I can give you some hints if you like, but I donít want to spoil it for you
  Reply With Quote
Old 26th October 2020, 10:51 PM   #25
laserscrape is offline laserscrape
diyAudio Member
 
Join Date: Dec 2017
A hint would be nice, I'm 100% clueless.
  Reply With Quote
Old 26th October 2020, 11:05 PM   #26
cellularmitosis is offline cellularmitosis  United States
diyAudio Member
 
Join Date: Jul 2013
One way to think about this would be to imagine the circuit starts out with no current flowing. I imagine the fet source being all the way up at ground, so Vgs is zero, the fet is totally off.

The constant current source isnít happy with this, so it starts pulling the source down towards -V. As it pulls the source down, Vgs grows and the fet starts to turn on. When the right amount of current flows, the current source stops pulling and the circuit sits at equilibrium.

Now, as an AC signal appears on the gate, centered around ground, the negative going part is easy to think about. Vgs decreases, which causes the fet to try to turn off. The current source doesnít allow this and pulls the source even further down.

The positive going half of the AC signal works in the opposite way. Vgs starts to increase, so the fet turns on harder, allowing more current. The current source responds by pushing the source further up to limit the current again.

The part which is a bit tricky is to realize that the gate can go above the drain and the circuit still works. This is easier to think about in a more typical voltage situation. Imagine 5volts being on the drain, and source being at ground. If we put 5 bolts on the gate, the fet will start to conduct. Of course, if we put 10 volts on the gate, or 15, the fet just tries to turn on even harder. It doesnít matter that only 5 volts is on the drain.

  Reply With Quote
Old 26th October 2020, 11:12 PM   #27
cellularmitosis is offline cellularmitosis  United States
diyAudio Member
 
Join Date: Jul 2013
The only caveat here is that the fet can run out of headroom and start to clip if Vgth isn’t large enough to allow for an input signal of a certain size. In my case, my IEMs are sensitive enough that 0.2V rms is more than plenty. This is a small voltage relative to the gate threshold voltage of a 2N7000, so there is no problem.
  Reply With Quote
Old 26th October 2020, 11:18 PM   #28
cellularmitosis is offline cellularmitosis  United States
diyAudio Member
 
Join Date: Jul 2013
As an example, consider a fet with a threshold such that the current source needs to pull the fet source down to -0.5 volts in order to turn the fet on enough to get the 100mA bias current to flow. If a positive going 0.6V appears as input, this will obviously clip, because it is impossible for the current source to push the fet source to +0.1V, because it is impossible to push the source above the drain.
  Reply With Quote
Old 27th October 2020, 12:21 AM   #29
laserscrape is offline laserscrape
diyAudio Member
 
Join Date: Dec 2017
very cool, super sensitive IEMs sure have a lot of perks... I was actually thinking the other day how suited IEMs would be for passive I/V conversion in DACs, where very low voltages would still give usable levels.
  Reply With Quote
Old 27th October 2020, 02:32 AM   #30
cellularmitosis is offline cellularmitosis  United States
diyAudio Member
 
Join Date: Jul 2013
Iím actually right in the middle of working on my first DAC, and yes I could do exactly that
  Reply to this post

Reply


directly coupled class A buffer for low-voltage headphones (work-in-progress)Hide this!Advertise here!
Thread Tools

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
Directly-coupled buffer with only one supply rail? cellularmitosis Analog Line Level 8 8th October 2020 03:03 AM
TBJ's Class D - a discrete class D amp that anyone can build! (Work-In-Progress) tbj Class D 19 18th December 2019 12:45 PM
very simple class A buffer for headphones? laserscrape Tubes / Valves 39 12th December 2019 06:55 PM
bias voltage buffer series resistor on ac coupled opamp bnae38 Digital Line Level 42 11th March 2018 01:51 AM
DAC that will drive headphones directly jkeny Digital Line Level 7 27th January 2010 12:00 PM


New To Site? Need Help?

All times are GMT. The time now is 02:40 PM.


Search Engine Optimisation provided by DragonByte SEO (Pro) - vBulletin Mods & Addons Copyright © 2020 DragonByte Technologies Ltd.
Resources saved on this page: MySQL 14.29%
vBulletin Optimisation provided by vB Optimise (Pro) - vBulletin Mods & Addons Copyright © 2020 DragonByte Technologies Ltd.
Copyright ©1999-2020 diyAudio
Wiki