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

The Lounge A place to talk about almost anything but politics and religion.

SET sound question
SET sound question
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 22nd April 2018, 04:22 PM   #161
chip_mk is offline chip_mk  Macedonia
diyAudio Member
 
Join Date: Jul 2005
Location: Skopje, Macedonia
Quote:
Originally Posted by Bigun View Post
But the 2SK1815 isn't a bipolar transistor
Sorry, my bad. I had 2SC1815 on mind, in fact this particular chart.
Attached Images
File Type: png 2SC1815 Hfe vs Ic.PNG (20.5 KB, 75 views)
  Reply With Quote
Old 22nd April 2018, 04:35 PM   #162
chip_mk is offline chip_mk  Macedonia
diyAudio Member
 
Join Date: Jul 2005
Location: Skopje, Macedonia
Quote:
Originally Posted by Bigun View Post

The gm is Ic / Vt.
Sure, in ideal world where Rb = 0
Attached Images
File Type: png Equi gm.PNG (9.6 KB, 72 views)
  Reply With Quote
Old 22nd April 2018, 04:45 PM   #163
DF96 is offline DF96  England
diyAudio Member
 
Join Date: May 2007
Quote:
Originally Posted by traderbam
But there is a really big difference between using a gain-consuming NFB loop and simple degeneration in terms of the impact on the signal.
Degeneration does not consume gain?

Quote:
we all know what "no NFB" means if we suppress our pedantry.
It is not pedantry to ask whether "no NFB" actually means 'some NFB, albeit no GNFB''.

Quote:
I find this thread interesting because some responses highlight the pervasive problem that if all you can "see" is THD then naturally you think every sonic characteristic root cause is discoverable if only you stare at the THD graph long enough.
I am not going to search through this thread to see who first mentioned THD, but it could be you. My experience is that it is most often mentioned by those who wish to ignore it, while implying that others (who have not mentioned it) are bound by it.

Quote:
Originally Posted by Bigun
It's not quite so simple, people are all too focussed on talking about voltage gain and of course there is no active element that creates voltage gain - they are all transconductance devices.
A device is what you consider it to be. Use the model which best fits the application. A triode operated into a very high impedance is best seen as a voltage gain device, while a BJT operated from a high impedance source into a low impedance load is best seen as a current amplifier. Either can also be regarded as a transconductance device, given different conditions.

Quote:
Originally Posted by traderbam
Whether you decide to control the charge by voltage or current is up to what suits your circuit.
Yes.
  Reply With Quote
Old 22nd April 2018, 04:53 PM   #164
DF96 is offline DF96  England
diyAudio Member
 
Join Date: May 2007
Quote:
Originally Posted by hellokitty123
As far as I understand BJTs are different from mosfets in that the low impedance input was purposeful to create electron holes in between the doped areas which allow electrons to jump the gap.
No, the low input impedance of BJTs is a nuisance. It can be regarded as non-ideal behaviour, which is why the current gain is rather random from sample to sample and varies all over the place with collector current.

Quote:
Intrinsically BJTs need to be current driven but I think from an effective standpoint they are just low input impedance, low vbe turn-on mosfets.
No, different effect so different behavour.

Quote:
If there was a true ultra low input impedance current driven transconduction device it would revolutionize the industry, but unfortunately as far as I know voltage is required to practically make an electronic switch.
Common-base BJT driving a resistive load?

Quote:
Originally Posted by traderbam
We must be living in different universes. So “gm is non-linear but at least it is consistent”; good luck with that.
But this is exactly how precision circuits are designed: gm is predictable. 'BJT is a current amplifier' is what we teach newbies who don't understand the exponential function.
  Reply With Quote
Old 22nd April 2018, 07:09 PM   #165
Bigun is offline Bigun  Canada
diyAudio Member
 
Bigun's Avatar
 
Join Date: Jan 2009
Location: Waterloo, ON or Herefordshire UK
SET sound question
Quote:
Originally Posted by DF96 View Post
A triode operated into a very high impedance is best seen as a voltage gain device, while a BJT operated from a high impedance source into a low impedance load is best seen as a current amplifier. Either can also be regarded as a transconductance device, given different conditions.
Exactly my point, a device by itself is not a voltage amplifier - it needs a load, an impedance is needed to convert the devices intrinsic output current signal to a voltage.
__________________
"The test of the machine is the satisfaction it gives you. There isn't any other test. If the machine produces tranquility it's right. If it disturbs you it's wrong until either the machine or your mind is changed." Robert M Pirsig.
  Reply With Quote
Old 22nd April 2018, 07:33 PM   #166
hellokitty123 is offline hellokitty123  United States
diyAudio Member
 
Join Date: Dec 2017
Location: Connecticut
Quote:
Originally Posted by DF96 View Post
Common-base BJT driving a resistive load?
Only useful in limited circumstances. I meant an electronic switch that functions entirely in the current realm.
  Reply With Quote
Old 22nd April 2018, 07:57 PM   #167
Bigun is offline Bigun  Canada
diyAudio Member
 
Bigun's Avatar
 
Join Date: Jan 2009
Location: Waterloo, ON or Herefordshire UK
SET sound question
Not at all, the common base is actually quite common and useful. It is used as the top device in a cascode and folded cascode; it can be used as a VAS device too TGM4 amplifier
__________________
"The test of the machine is the satisfaction it gives you. There isn't any other test. If the machine produces tranquility it's right. If it disturbs you it's wrong until either the machine or your mind is changed." Robert M Pirsig.
  Reply With Quote
Old 22nd April 2018, 09:16 PM   #168
hellokitty123 is offline hellokitty123  United States
diyAudio Member
 
Join Date: Dec 2017
Location: Connecticut
Yes, those are by definition, limited circumstances.
My point was if a true current input transconduction device existed with an ultra low impedance on both the gate and the source then circuits could function almost entirely in the current realm. Parasitics would no longer matter. It would be the ideal electronic switch. Except trying to troubleshoot such a circuit would be tricky. I'm no transistor scientist but I'd guess a true current amplifier can't be made.

Last edited by hellokitty123; 22nd April 2018 at 09:26 PM.
  Reply With Quote

Reply


SET sound questionHide 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
Sound quality question Dxvideo Chip Amps 61 27th April 2008 05:51 PM
basic question about sound. Theli Everything Else 12 2nd December 2006 08:22 PM
question about sound in Zen4 Buhl Pass Labs 16 14th April 2004 04:44 PM
The Burr Brown sound and a pot question trespasser_guy Parts 0 22nd April 2003 08:09 PM


New To Site? Need Help?

All times are GMT. The time now is 08:51 AM.


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