A slightly different kind of voltage amplifier - diyAudio
Go Back   Home > Forums > Blogs > RJM Audio Blog
Home Forums Rules Articles diyAudio Store Gallery Wiki Blogs Register Donations FAQ Calendar Search Today's Posts Mark Forums Read

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
If I put my notes here, I might be able to find them again later!
Rate this Entry

A slightly different kind of voltage amplifier

Posted 12th December 2016 at 10:44 AM by rjm
Updated 21st December 2016 at 04:50 AM by rjm

(which is a current feedback amplifier)

Lately I have been looking again for a discrete transistor voltage gain amplifier for line level duty that isn't just another op amp.

I keep coming back to variations on this circuit. It's a diamond buffer input with current mirrors in the mid-section strapped around a voltage divider / feedback loop that provides the gain. This backs out into either another diamond buffer or, in the revised version below, a standard Sziklai output stage which can be more easily scaled up as needed for a headphone amp for example.

An offset bias adjust circuit could be added to trim the output offset voltage. Or use a coupling cap. It's a few hundred mV otherwise.

Circuit gain is R4/R6, approximately. The total value of R4+R6 should be kept about 20 kohms. C1 is a compensation capacitor. Circuit gain as shown is 14 dB, -3 dB at 250 kHz.

As with all CFA, the choice of the feedback resistance R4, R6 is critical. The gain can be varied from about 3 dB (R4 = 10k, R6 = 10k) to the 14 dB shown. Setting the gain higher, either by reducing R6 or increasing R4 runs into problems with stability and bandwidth, respectively.

The simulated distortion figure is -95 dB for 0 dB output into 600 ohms. The PSRR is about 35 dB over the audio bandwidth (at output, for A=14 dB).
Attached Thumbnails
Click image for larger version

Name:	pre07.png
Views:	141
Size:	141.9 KB
ID:	2159   Click image for larger version

Name:	pre07-freq.png
Views:	83
Size:	129.4 KB
ID:	2160  
Attached Files
File Type: asc pre07.asc (5.9 KB, 86 views)
Total Comments 0

Comments

 
Hide this!Advertise here!

New To Site? Need Help?

All times are GMT. The time now is 10:12 PM.


vBulletin Optimisation provided by vB Optimise (Pro) - vBulletin Mods & Addons Copyright © 2017 DragonByte Technologies Ltd.
Copyright 1999-2017 diyAudio

Content Relevant URLs by vBSEO 3.3.2
Wiki