Discrete Opamp Open Design - Page 167 - 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 14th October 2012, 01:32 PM   #1661
qusp is offline qusp  Australia
diyAudio Member
 
qusp's Avatar
 
Join Date: Oct 2009
Location: Brisbane, Australia
thanks for the insight....

I know its a long thread to read, but these themes of complexity have been well chewed over.

Last edited by qusp; 14th October 2012 at 01:39 PM.
  Reply With Quote
Old 14th October 2012, 02:17 PM   #1662
RNMarsh is offline RNMarsh  United States
diyAudio Member
 
RNMarsh's Avatar
 
Join Date: May 2012
Location: 2457 Cascade Trail; Cool, CA. 95614
Default choices --

backing up a bit as I have been distracted from this forum --- The foil resistors by Vishey and others have been used in high end audio for a long time -- JCurl talked to me about them about a thousand (or more) years ago... Use them if you want them...and can get them and pay for them but the Dales are soooo cheap I thought they would appeal to many cash strapped DIY as a better part than typical mfr parts. They have lower thd than adc/dac [BTW -I have a QuanTec resistor analyzer.]

the 2n556__ are pretty good in matching out of the box - I used them in a design (TAA) back in the day. I see the one i used is no longer made (:-()... but the others - higher volt et al are still around and so ordered a dozen just to have on hand -in case they stop making those, also. Also used the dip motorola MPQ-6 ____ for their ease and werent a bad match for compliments.... if package dissipation limites are not a problem. They are still around in some models and now with second sources. Might find a place to simplify the circuit build that has a lot of individual parts/transistors.

Maybe just do the layout for smd as many here want to use it.... and someone can do another pcb for the thru hole guys. Or they'll do it in Taiwan sooner than later and offer it on eBAY in both ways. Like they do for DAC's.
BUT -
Just make it with your suggested parts which are SW blessed - that includes transistors.... or just use what he spec'ed and Get Er Done. Or you'll have to peel those gold stars you just got from SW off your foreheads.

IMO a buffer needs to be excellent as a stand-alone design... very low thd and dc offset on its own. That way it can be used with the SW-OPA and other projects that only need current boosting/low Z driver. Same 24v rails. Though it seems the existing design can just be scaled up in the output stage so an additional buffer isnt needed for it.

I must have missed something, Its late here. Tomorrow a fourth-world family is coming to stay with me for a week in DisneyLand - (Bangkok) then to the beaches of Phuket for another week.... spoil them with love. My hope is that the girls will never want to settle for rice farming once they have seen a better life and what they can do with thier education. OOOooop. wrong forum 10-4 and out.

Last edited by RNMarsh; 14th October 2012 at 02:31 PM.
  Reply With Quote
Old 14th October 2012, 04:04 PM   #1663
rsavas is offline rsavas  Canada
diyAudio Member
 
Join Date: Aug 2012
Location: Ontario
Default My Layout version done, ready for review!!

Hello folks,
Okay, this was a fun exercise, I got the comps in a tight as I could. I usually stick with a 25mil place grid but a couple I had to move with a 10mil grid. I thought that it was going to be a nightmare but actually it was not that bad after I did an initial placement and started to connect the guides. Managed to route all but a few at 12mil, just a couple nets, I had to wick down to 8mil to get through those SOT-143B
I put VCC & VEE planes on the bottom. There is no room on top for an effect ground plane. Vias (37) @ 30 pad/16mil FHS. I'll attach some drawings, original schematic, I posted had an error.
Size is 1.225x1.0 inch. I see that the John Hardy 990 measures, 1.125 x 1.125 x 0.600
Have some questions however!!
1) What to do about a ground plane? 3-4 layers = expensive
2) Supply decoupling?
3) Mounting footprint?
4) Need to verify the schematic I drew up?
So there you have it

Cheers Rick
  Reply With Quote
Old 14th October 2012, 04:09 PM   #1664
rsavas is offline rsavas  Canada
diyAudio Member
 
Join Date: Aug 2012
Location: Ontario
Default Docs

See attachments, let me know what you think?
Problem with cramming this tight, is each ref position is hard to identify, no effect Silk screen text!!
Attached Files
File Type: pdf BOT_COPPER.pdf (33.3 KB, 78 views)
File Type: pdf TOP_COPPER.pdf (29.0 KB, 61 views)
File Type: pdf TOP_PLACE_OUTLINE.pdf (20.0 KB, 68 views)
File Type: pdf SCHEMATIC1 _ PAGE1.pdf (16.0 KB, 132 views)

Last edited by rsavas; 14th October 2012 at 04:31 PM.
  Reply With Quote
Old 14th October 2012, 04:19 PM   #1665
qusp is offline qusp  Australia
diyAudio Member
 
qusp's Avatar
 
Join Date: Oct 2009
Location: Brisbane, Australia
need ground plane. if we want to keep it neat and small, 4 layer is more expensive yes, but if we are all happy to throw in for a GB then I doubt it will be a big deal overall. As a plus it will deter at least some of the inevitable pirates from just lifting the layout

Last edited by qusp; 14th October 2012 at 04:22 PM.
  Reply With Quote
Old 14th October 2012, 04:59 PM   #1666
diyAudio Member
 
grhughes's Avatar
 
Join Date: Mar 2005
Location: Cubicle Sweet Cubicle, Springfield, Missouri, USA
Pirates are out there! The whole idea about this is a shared design but they have another agenda. A shared design is vulnerable. The Chinese will have this built and avaliable for sale shortly I bet. Ray
__________________
" "The fool doth think he is wise, but the wise man knows himself to be nothing but a fool." Will Shakespeare
  Reply With Quote
Old 14th October 2012, 05:06 PM   #1667
diyAudio Member
 
grhughes's Avatar
 
Join Date: Mar 2005
Location: Cubicle Sweet Cubicle, Springfield, Missouri, USA
In a book LOW NOISE CIRCUIT DESIGN by Motchenbacher and Fitzen they compared noise among jfets. They stated that the 2n3821 had the lowest noise of any jfet they tested. Second was the 2n4416A. Motorola made a plastic version called the MPF3821 and there is existing stock of this device. Does anyone know anything about this or is the newer Hitachi/Toshiba devices even lower noise? Thanks, Ray
__________________
" "The fool doth think he is wise, but the wise man knows himself to be nothing but a fool." Will Shakespeare
  Reply With Quote
Old 14th October 2012, 05:35 PM   #1668
rsavas is offline rsavas  Canada
diyAudio Member
 
Join Date: Aug 2012
Location: Ontario
Default top assembly

Top assembly drawing.
Took me equivalent of < one working day to get this far, so it ain't hard to duplicate. Suggest to put some copyright's notices on the material, if we want to protect the information? I have not seen any copyright notices on material on this site!
Seems that all the jfet mfg's can agree on a standard pin out, in SOT23, so can substitute parts quiet easilly.
Lifting the layout, all the connections are done on the outside foil layers. The ground plane will only have connection to the low side of C4 and de-coupling. I have no de-coupling caps in this design yet!!
Attached Files
File Type: pdf TOP_ASSY.pdf (32.1 KB, 71 views)

Last edited by rsavas; 14th October 2012 at 05:53 PM.
  Reply With Quote
Old 14th October 2012, 05:41 PM   #1669
diyAudio Member
 
Lazyworm's Avatar
 
Join Date: Nov 2003
Location: Stockholm in Sweden
Send a message via ICQ to Lazyworm
I have a small Swedish company togheter with a friend within manufatoring of high end products.
I have good contact with a company in South Korea that manufactor and assemble our PCB for the amplifiers.
I can check prices with them bth with and without component mounting if that is interessting.

//Jonas
  Reply With Quote
Old 14th October 2012, 05:46 PM   #1670
bcarso is offline bcarso  United States
diyAudio Member
 
Join Date: May 2005
Location: Canoga Park, California
Quote:
Originally Posted by grhughes View Post
In a book LOW NOISE CIRCUIT DESIGN by Motchenbacher and Fitzen they compared noise among jfets. They stated that the 2n3821 had the lowest noise of any jfet they tested. Second was the 2n4416A. Motorola made a plastic version called the MPF3821 and there is existing stock of this device. Does anyone know anything about this or is the newer Hitachi/Toshiba devices even lower noise? Thanks, Ray
Motchenbacher and Fitchen, and the later M. and Connelly are well behind the times on specific devices, albeit excellent books for basic theory. The series and parallel noise data, aka voltage and current noise data, presented graphically in the first three appendices of the 1973 book, although still relevant are very old now.

Not sure where you found the statement about the 2N3821, although M&F comment about its low gate current noise at one point. It is a small geometry device and therefore higher series noise than many.

JFET noise goes down with channel width given the same channel length. Effectively you are paralleling more devices. But parallel noise goes up, so there is a limit to the improvement. For most audio apps, but emphatically NOT condenser microphone preamps, the impedances in the circuit are relatively small, frequencies fairly low, and thus parallel noise from the FET is not a significant contribution. But capacitance goes up too. The likely best JFET for many applications available today, having low capacitance along with low voltage noise is the NXP part BF862. Low C means we can parallel more of them before the total C gets bothersome. Voltage breakdown is low so it is often best to use in a cascode to limit the drain voltage.

Toshiba makes great parts but has discontinued most of them. Linear Integrated Systems makes almost-direct replacements of some, and is working on others. There are other specialty houses like Interfet who support the nuclear science people and make good stuff as well.
  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 10:38 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