Current conveyor as a voltage amplifier - Page 5 - diyAudio
Go Back   Home > Forums > Source & Line > Analog Line Level

Analog Line Level Preamplifiers , Passive Pre-amps, Crossovers, etc.

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 24th November 2012, 09:36 PM   #41
RNMarsh is offline RNMarsh  United States
diyAudio Member
 
RNMarsh's Avatar
 
Join Date: May 2012
Location: 2457 Cascade Trail; Cool, CA. 95614
Very nice topology with great results. What happens when the 47K's go to the output instead of the jFET source? -RNM

Last edited by RNMarsh; 24th November 2012 at 09:39 PM.
  Reply With Quote
Old 24th November 2012, 09:51 PM   #42
bcarso is offline bcarso  United States
diyAudio Member
 
Join Date: May 2005
Location: Canoga Park, California
Quote:
Originally Posted by dadod View Post
As I don't have the models nor real fets with a higher pinchoff voltage I did it in this way. Distortion is down but not so much as I expected.
You will get slightly better results probably with a higher-pinchoff device, but you can also use floating voltage sources in sim. And as well, you can use DMOS and floating voltage sources. My results for the input buffer alone, a 10k source resistance, 20kHz 1V peak, were -113.7dBr at the input and -113.4dBr at the output for 2N4391/2N5114 as cascode devices; with a 2N7000 and a ZVP3306 and a 7V floating gate bias, these results got to -119.0dBr input, -118.1 dBr output. Note that the greater spread in the input and output numbers suggest we're started to see a larger contribution from the basic stage, barely.

The 7V floating voltage is not as bad to implement as it may sound, as photovoltaic optocouplers have around this amount of open-circuit voltage. Alternatively, since they last the shelf life, batteries will work.

But the 246/103 are nice, as they have high breakdown voltage. Unfortunately they are scarce.
  Reply With Quote
Old 24th November 2012, 10:17 PM   #43
diyAudio Member
 
keantoken's Avatar
 
Join Date: Aug 2006
Location: Texas
Blog Entries: 2
I know Curl suggested the 2N4416 to use in place of SK170 for lower capacitances, but I don't think there is a P channel equivalent.

Why worry about distortion so much? It is vanishingly low and the profile is good, no high order harmonics. I think it is time to address noise performance and other things, in case the low distortion may be for naught.
  Reply With Quote
Old 24th November 2012, 11:29 PM   #44
bcarso is offline bcarso  United States
diyAudio Member
 
Join Date: May 2005
Location: Canoga Park, California
Quote:
Originally Posted by keantoken View Post
I know Curl suggested the 2N4416 to use in place of SK170 for lower capacitances, but I don't think there is a P channel equivalent.

Why worry about distortion so much? It is vanishingly low and the profile is good, no high order harmonics. I think it is time to address noise performance and other things, in case the low distortion may be for naught.
If low distortion is easy to do, it should be done IMO. And it's worthwhile to understand the mechanisms. I find the "distortion at the input" behavior is often neglected, and I was pleased to see an explicit discussion in Self's recent Small Signal Audio Design.

But certainly noise is another critical parameter, in fact I tend to worry about it more than distortion per se. A quick glance at the current amp portion suggests that things will be dominated by thermal noise of key resistors, with the input and output buffers and other semiconductors a relatively small contribution.

And yes, there are no P channel equivalents to the process 50 (2N4416, 2N5486, etc.). Motorola used to make some not-too-far-off parts (MFE4012 for example) but they have been gone for ages. And it's hard to deal with the low mobility of holes in Si, the reason why the SJ74s have to be so big and high capacitance to have comparable transconductance and noise.
  Reply With Quote
Old 24th November 2012, 11:58 PM   #45
diyAudio Member
 
keantoken's Avatar
 
Join Date: Aug 2006
Location: Texas
Blog Entries: 2
Yeah, input distortion is not talked of much. You can increase OLG to the moon but eventually it does not gain you anything because it only decreases load-dependent distortions. For instance Early affect on the input transistor is input-dependent, not load dependent, and NFB cannot fix this, only cascoding. Miller compensation is another good example. Regardless of whether the amp is under load or not, the miller cap always loads the circuit and creates a distortion lower limit.

When one starts to think in terms of rejecting and isolating distortion, rather than attenuating it, the need for tons of feedback and high-gain stages diminishes. The Baxandall mirrors are a critical part of this circuit.
  Reply With Quote
Old 25th November 2012, 07:52 AM   #46
dadod is online now dadod  Croatia
diyAudio Member
 
dadod's Avatar
 
Join Date: Apr 2006
Location: Zagreb
Quote:
Originally Posted by RNMarsh View Post
Very nice topology with great results. What happens when the 47K's go to the output instead of the jFET source? -RNM
Thanks RNM,
when I did it with the input buffer distortion increased slightly, and with the output buffer no change.
Damir
  Reply With Quote
Old 25th November 2012, 06:59 PM   #47
bcarso is offline bcarso  United States
diyAudio Member
 
Join Date: May 2005
Location: Canoga Park, California
Quote:
Originally Posted by bcarso View Post
A quick glance at the current amp portion suggests that things will be dominated by thermal noise of key resistors, with the input and output buffers and other semiconductors a relatively small contribution.
Ooops must have forgotten to hit Submit.

A rough-out on noise revealed the base current shot noise of Q5 and Q7 to be significant. As well those transistors have somewhat high rbb', according to Gerhard about 130 ohms for the BC550 for example. So we could help things out with lower rbb' parts, and fixing some of the base current noise effects. Note that the substantial base current for the output devices is recycled by the auxiliary parts and makes only a small contribution.

I also had to raise the bias current for Q10, the lower auxiliary PNP, to prevent it "running dry" at about 10V rms out. I went to 50k for both bias resistors.
  Reply With Quote
Old 25th November 2012, 07:51 PM   #48
diyAudio Member
 
keantoken's Avatar
 
Join Date: Aug 2006
Location: Texas
Blog Entries: 2
BC327/337 are better in the low-Rbb department, so I've been told, and they have great quasi-saturation characteristics just like the BC5x0.

I'm a bit confused about noise, the BC5x0 series is supposed to be low-noise, but is supposed to be noisier than the BC3x7 series which doesn't have noise in its datasheet.
  Reply With Quote
Old 25th November 2012, 08:16 PM   #49
bcarso is offline bcarso  United States
diyAudio Member
 
Join Date: May 2005
Location: Canoga Park, California
Quote:
Originally Posted by keantoken View Post
BC327/337 are better in the low-Rbb department, so I've been told, and they have great quasi-saturation characteristics just like the BC5x0.

I'm a bit confused about noise, the BC5x0 series is supposed to be low-noise, but is supposed to be noisier than the BC3x7 series which doesn't have noise in its datasheet.
Many times manufacturers have produced a part for a specific application and touted it as such (e.g., "saturated switch") and in the process wound up with a low base spreading resistance, which others then discover to have low noise at sufficient collector current and low source impedances. A classic example was the Motorola 2N4403, which in its day gave very good results for low source Z compared to so-called "low noise" devices.

Historically, the transistor moniker "low noise" has been extensively misapplied irrespective of impedance. Often the achievement of high beta, hence potentially low current noise, has been at the expense of thermal noise from rbb'. But it is possible to get both low resistance and high beta. The now-sadly-discontinued 2SA1316 and 2SC3329 have 2 ohm rbb' and high beta as well. Note that to have parity between thermal noise and referred collector current shot noise the devices need to be operated at about 7mA. Then with beta of 500 and thus Ib of 14uA, the shot noise in that current (the minimum of current noise) is about 2.1pA/sqrtHz, which will contribute according to the source impedance another equivalent input voltage noise term.
  Reply With Quote
Old 25th November 2012, 09:01 PM   #50
dadod is online now dadod  Croatia
diyAudio Member
 
dadod's Avatar
 
Join Date: Apr 2006
Location: Zagreb
Noise
Attached Images
File Type: jpg noise.jpg (219.5 KB, 203 views)
  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
The InSense Current Conveyor bcarso Digital Source 17 20th August 2012 09:11 AM
An inverting current conveyor approach bcarso Digital Source 0 30th July 2012 06:12 PM
High voltage, low current output stage for class D amplifier ionomolo Class D 45 15th February 2011 06:03 PM
voltage vs current Raj1 Solid State 1 12th June 2004 05:35 AM


New To Site? Need Help?

All times are GMT. The time now is 11:56 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