best voltage follower, discrete opamp and whatnot - Page 3 - diyAudio
Go Back   Home > Forums > Amplifiers > Solid State

Solid State Talk all about solid state amplification.

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 4th May 2008, 05:10 PM   #21
Mooly is offline Mooly  United Kingdom
diyAudio Moderator
 
Mooly's Avatar
 
Join Date: Sep 2007
Quote:
Originally posted by gearheadgene

You know, Doug Self claims the 5534 is about as good as they come I guess he tried to build better circuits, unsuccessfully. Never mind what you may think of Doug Self, the 5534 sure looks good in simulation. If it has a fatiguing sound to it, then it sure would be nice to figure out why. Changing monolithic opamps on a circuit board is easy enough. But, the discrete stuff is going to build and trash, if it doesn't work out
I have a lot of time for Doug's work, his insight and theoretical knowledge in this field is second to non, but, and it's a big but, his designs while achieving remarkable technical proficiency fail to varying degrees at the final hurdle-how it sounds. The answer Doug will give is, "show me the evidence in some measurable form". I certainly can't. But my ears tell me ! The 5534 is not a bad OpAmp, far from it, but in a top flight system it is easy to demonstrate the "subtle" change swapping to a different type can produce. It's a matter of degree's, in absolute terms the difference is tiny, from a musical perspective it's enormous.
Only you can decide what works for you. If you can get hold of a squarewave generator do build a test circuit and 'scope the output. Try a 5534 and a TLO71 for starters.
Regards Karl
  Reply With Quote
Old 4th May 2008, 05:14 PM   #22
diyAudio Member
 
nelsonvandal's Avatar
 
Join Date: Nov 2006
Quote:
Originally posted by MikeB
When simulating a "high input impedance voltage follower", never forget to add a big resistor (~100k)...
Sorry, I'm a bit of a noob, but why 100k? I thought most modern CDPs or DAPs have a very low output impedance.

Quote:
Originally posted by jam
Nelsonvandal,

.................sorry to burst your bubble but it has. I have used variations of it with good results.

Regards,

Jam
It really wasn't meant to be a bubble, just a stupid question . Thank you for sharing your schematic. I'm going to try to use these JFETs in my little headphone "le classe A". The input stage is a typical diamond buffer.
  Reply With Quote
Old 4th May 2008, 05:23 PM   #23
AndrewT is offline AndrewT  Scotland
diyAudio Member
 
Join Date: Jul 2004
Location: Scottish Borders
Quote:
Originally posted by nelsonvandal
but why 100k? I thought most modern CDPs or DAPs have a very low output impedance.
I think what he is saying is that adopting a zero to low source impedance forces the simulator to report unrealistically low distortion predictions.
__________________
regards Andrew T.
  Reply With Quote
Old 4th May 2008, 05:26 PM   #24
MikeB is offline MikeB  Germany
diyAudio Member
 
MikeB's Avatar
 
Join Date: Apr 2004
Location: GŁtersloh
Quote:
Originally posted by nelsonvandal

Sorry, I'm a bit of a noob, but why 100k? I thought most modern CDPs or DAPs have a very low output impedance.
In this case the buffer would be unnecessary.

Well, try at least 10k, which is realistic if you have a 10k volume pot after the signal source.

The reason why this is important, is, the largest amount of distortion with buffer circuits is not produced in the buffer itself, it is created at the input. An unlinear behaving input attached to a not low impedance source creates vast amounts of distortions.

Diamond buffers do a very good job here.

As Andrew said, the distortions predicted with a 0ohm signal source are unrealistic low.
  Reply With Quote
Old 4th May 2008, 06:52 PM   #25
jam is offline jam  United States
diyAudio Member
 
jam's Avatar
 
Join Date: May 2001
Location: Auburn, CA, USA
Nelsonvandal,

JSorry! ust giving you a hard time.......

This is what you need................you could probably get away with leaving out the servo.

Regards,
Jam
Attached Images
File Type: png c2508.png (5.3 KB, 1069 views)
  Reply With Quote
Old 4th May 2008, 07:31 PM   #26
MikeB is offline MikeB  Germany
diyAudio Member
 
MikeB's Avatar
 
Join Date: Apr 2004
Location: GŁtersloh
Whoooaa! What a monster!

May i suggest something more simple and functional...
It has very high psrr, thd = 0.0002% (20khz,1v,1k) practically independent of source impedance, low dc-offset, simple, output impedance near zero.

It might need refinement in detail.
Attached Images
File Type: png jfet_buffer_1.png (3.3 KB, 1087 views)
  Reply With Quote
Old 4th May 2008, 08:12 PM   #27
MikeB is offline MikeB  Germany
diyAudio Member
 
MikeB's Avatar
 
Join Date: Apr 2004
Location: GŁtersloh
Or, may i introduce "Cadibu"?
Similar performance, but less good dc-offset... But, cheaper.

Mike
Attached Images
File Type: png bjt_buf_1.png (10.3 KB, 1041 views)
  Reply With Quote
Old 4th May 2008, 09:12 PM   #28
KSTR is offline KSTR  Germany
diyAudio Member
 
KSTR's Avatar
 
Join Date: Jul 2007
Location: Central Berlin, Germany
Michael,

Your feedback JFET buffer is a clever design!

When extremly controlled DC-offset is not a big issue, I suppose it would work well with selected and thermally coupled BF245C's, BF861C's or similar and then being a low cost design as well.

- Klaus
  Reply With Quote
Old 4th May 2008, 09:20 PM   #29
MikeB is offline MikeB  Germany
diyAudio Member
 
MikeB's Avatar
 
Join Date: Apr 2004
Location: GŁtersloh
It's not really a feedback design. It's a constant voltage, constant current design, sadly not mine. The principle is from steven.
The idea is, a device having no voltage/current fluctuations does not distort by principle.

Mike
  Reply With Quote
Old 4th May 2008, 10:06 PM   #30
KSTR is offline KSTR  Germany
diyAudio Member
 
KSTR's Avatar
 
Join Date: Jul 2007
Location: Central Berlin, Germany
As usual, it's a matter of viewpoint wether we call it feedback or not

Actually I made my way through the circuit regarding the PNP as the error amplifier which tries to establish a constant Vds accross the FET by controlling the NPN current sink. This controlled current sink also gives the low Zout of 0.1R, rising from ~20kHz with a 6dB/oct slope to ~10R at 10Mhz, as per sim (also getting your ballpark THD numbers). All this confirmes the feedback view, giving the gain values of a single simple common emitter stage. It is not direct signal feedback, of course, rather it is somewhat indirect via the constant Vds and constant Id.

Do you have a reference/link to the circuit (I don't know which Steven is meant)?

- Klaus
  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
Discrete OPAMP audio-gd Vendor's Bazaar 27 20th September 2012 04:02 PM
My discrete opamp udip Solid State 51 8th August 2006 07:33 AM
Single supply opamp - unequal rail voltage and opamp selection Hans L Parts 8 19th February 2006 02:15 PM


New To Site? Need Help?

All times are GMT. The time now is 08:37 PM.


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