Discrete Opamp Open Design - Page 92 - 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 13th September 2012, 05:23 PM   #911
diyAudio Member
 
Join Date: Feb 2010
Location: Dallas Fort Worth area, Texas
Does anyone know what pins and mating sockets are specified for the pro modules?

Dave
  Reply With Quote
Old 13th September 2012, 05:45 PM   #912
RNMarsh is offline RNMarsh  United States
diyAudio Member
 
RNMarsh's Avatar
 
Join Date: May 2012
Location: 2457 Cascade Trail; Cool, CA. 95614
Default laying down some specs -

Quote:
Originally Posted by scott wurcer View Post
Dick, I'm afraid I have to stick with +24dBu output. There are no general purpose amplifiers specified at 1V out only. The JE990 and all available discrete op-amps I can find are specified at 20V p-p out. Professional mixing boards in general use 24V rails and the amplifiers are expected to drive 600 Ohms to near the rails.

There's nothing wrong with a headphone amp that's as loud as you would ever want at 1V, but it is fairly narrow in scope.

Before we build I have one more set of suggestions, that I will get to tonight.
Thats fine with me.... any level output as max but for apple to apple comparisons we can standardize on ref level of 1 volt into a load Z. And, at +24dbu also if you like as an option. I would not want to limit the discrete design to a level where IC's already can do the job. Like 600 Ohms. here, its more for the Highest-End consumer's applications.

Anyone else want to compete with their design? I put a circuit topology up that wasnt optimal for pro use but gives some good numbers as built and has good features to start things going. Remember your entry has to get built and tested and not a sim only. This is, after all, a DIY site not a tech journal. Thx - RNMarsh
  Reply With Quote
Old 13th September 2012, 06:57 PM   #913
diyAudio Member
 
Join Date: Feb 2010
Location: Dallas Fort Worth area, Texas
Quote:
Originally Posted by scott wurcer View Post
Lots of junction capacitance at the Vas output, wouldn't a buffer on the MOSFET gates help?
Scott,

There are a number of complimentary FETs from Fairchild in SO8 and Super SOT packages with Crss in the 65-100 pf range. Do you have an off the cuff figure of merit that might mitigate your concerns there?

Dave
  Reply With Quote
Old 13th September 2012, 07:16 PM   #914
diyAudio Member
 
Join Date: Feb 2010
Location: Dallas Fort Worth area, Texas
Quote:
Originally Posted by RNMarsh View Post
Thats fine with me.... any level output as max but for apple to apple comparisons we can standardize on ref level of 1 volt into a load Z. And, at +24dbu also if you like as an option. I would not want to limit the discrete design to a level where IC's already can do the job. Like 600 Ohms. here, its more for the Highest-End consumer's applications.

Anyone else want to compete with their design? I put a circuit topology up that wasnt optimal for pro use but gives some good numbers as built and has good features to start things going. Remember your entry has to get built and tested and not a sim only. This is, after all, a DIY site not a tech journal. Thx - RNMarsh
What about testing at a couple of selected load levels, 600R and something higher - say in the 10k to 47k range, publish distortion vs frequency, distortion vs voltage out. Testing at lower loads can certainly be optional if desired. We could potentially test noise, offset, PSRR, CMRR, IMD, open loop, other performance??..


I plan to build and test some SE and class A varieties. Not sure that they will compete on level with the monolithics Scott mentioned but they have been simulated and waiting for some impetus to build them for far to long. I'll come along for the ride.

Dave
  Reply With Quote
Old 13th September 2012, 08:18 PM   #915
RNMarsh is offline RNMarsh  United States
diyAudio Member
 
RNMarsh's Avatar
 
Join Date: May 2012
Location: 2457 Cascade Trail; Cool, CA. 95614
Quote:
Originally Posted by fitzfish View Post
What about testing at a couple of selected load levels, 600R and something higher - say in the 10k to 47k range, publish distortion vs frequency, distortion vs voltage out. Testing at lower loads can certainly be optional if desired.
Dave
The distortion is lower at high Z for any circuit and is not a taxing load that would challenge any designer. it must be able to also do lower Z at low thd than IC opamp/IC buffer combo. Or what's the point -- just use an IC. -RNM
  Reply With Quote
Old 13th September 2012, 09:02 PM   #916
diyAudio Member
 
Join Date: Feb 2010
Location: Dallas Fort Worth area, Texas
Quote:
Originally Posted by RNMarsh View Post
The distortion is lower at high Z for any circuit and is not a taxing load that would challenge any designer. it must be able to also do lower Z at low thd than IC opamp/IC buffer combo. Or what's the point -- just use an IC. -RNM
No misunderstanding there. The 600 ohm load is included in my list for testing, just as Scott advocated also. I am interested in what effect output loading has vs. other contributions to distortion so having the second, high impedance load data can be illuminating.

The point for me is an interesting challenge as part of a hobby that I enjoy. The genisis of this thread was after all a discrete, low parts count op amp that approximates the performance of ICs, correct? (paraphrased, not quoted)

I have no objections to testing of other loads interesting to you if a design/designer can do so. I will have to add some bias and have some other thermal considerations with the parts I am using.

If your desire is to compare the circuits here into headphone loads let's specify a standard set of loads to test as optional additionas to the op amp centric loads. 15, 30, 60 150, 300, and 600 ohm cover pretty much everything but electrostatics, correct? Want to add a reactive component to the load to verify low-z stability further?


Dave
  Reply With Quote
Old 13th September 2012, 09:06 PM   #917
diyAudio Member
 
Join Date: Feb 2010
Location: Dallas Fort Worth area, Texas
If comparison of the various circuits presented here is the desire we should define gain setting for reporting as well at each load impedance. How about 1, -1, 10, and 100 for op amp versions?

1 and 4 for headphones?

Testing and reporting becomes quite burdensome quickly!


Dave
  Reply With Quote
Old 13th September 2012, 09:12 PM   #918
diyAudio Member
 
scott wurcer's Avatar
 
Join Date: Jan 2004
Location: cambridge ma
Quote:
Originally Posted by RNMarsh View Post
The distortion is lower at high Z for any circuit and is not a taxing load that would challenge any designer. it must be able to also do lower Z at low thd than IC opamp/IC buffer combo. Or what's the point -- just use an IC. -RNM

There are any number of IC ADSL drivers that drive headphones just fine. Our own jcx has published designs and there is at least one commercial product. The data sheet specs are not audio based but much more brutal, Rload = 10 Ohms, Vo = 6V, f = 100kHz and still -90dBc there are several that easily drop to -100dB or better into 30 Ohms.
__________________
"The question of who is right and who is wrong has seemed to me always too small to be worth a moment's thought, while the question of what is right and what is wrong has seemed all-important."

Last edited by scott wurcer; 13th September 2012 at 09:19 PM.
  Reply With Quote
Old 13th September 2012, 09:15 PM   #919
diyAudio Member
 
john curl's Avatar
 
Join Date: Jul 2003
Location: berkeley ca
Kindhornman, the schematic I put up was designed for Parasound 18 years ago. We made prototypes then, but Parasound decided NOT to build this product, so this schematic has lain fallow for the last 18 years. I found it accidently this week in a manilla folder that I seldom look through.
However, just today I DID get a copy of Linear Audio Vol. 4. (Thanks Jan) and to my amazement, I saw virtually the SAME input and second stage (with small changes). I guess that Bob Cordell is on track! '-)
Perhaps when the time is right I can put the FIRST stage in, as well, as it is slightly different, and 3dB quieter, or so.
Anybody want to buy a slightly dated phono stage, that sounds pretty good, I have a prototype or two sitting around the lab. '-)
  Reply With Quote
Old 13th September 2012, 09:35 PM   #920
RNMarsh is offline RNMarsh  United States
diyAudio Member
 
RNMarsh's Avatar
 
Join Date: May 2012
Location: 2457 Cascade Trail; Cool, CA. 95614
Quote:
Originally Posted by scott wurcer View Post
There are any number of IC ADSL drivers that drive headphones just fine. Our own jcx has published designs and there is at least one commercial product. The data sheet specs are not audio based but much more brutal, Rload = 10 Ohms, Vo = 6V, f = 100kHz and still -90dBc there are several that easily drop to -100dB or better into 30 Ohms.
The non-IC discrete here should do that and more, if possible -- Key to design for: be very simple -- use the fewest transistors. Low cost, easy to find parts. Drive low Z. No dc servo. wide OL bandwidth. THD and noise < -100db ref 1v. Gain at a range of 4-10X etal. Others can decide what more can be done by their design. -Thx RNM
  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 05:02 PM
discrete opamp help blackpowderaudio Parts 0 16th December 2009 04:46 PM
THAT transistor headphone amp (250ma discrete opamp) design sanity check. Russ White Headphone Systems 19 13th December 2007 01:52 PM


New To Site? Need Help?

All times are GMT. The time now is 02:06 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