Discrete Opamp Open Design - Page 322 - 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 Today, 07:30 AM   #3211
diyAudio Member
 
keantoken's Avatar
 
Join Date: Aug 2006
Location: Texas
Blog Entries: 2
Quote:
Originally Posted by john curl View Post
We usually use ballast resistors, like 10 ohms in series with each emitter. 5 ohms would probably work OK.
Depending on Ic and Pd, you might not need any at all. BC3x7 are linear down to very low voltages so if you make Vce small you may not even need the resistors.

I made a thermal simulation to get an idea. Based on this you only get thermal instability beyond 20% if you violate Ic*Pd<860u for the TO92 package where the transistors are thermally coupled.

But I see no need to operate the BC3x7 at more than 1Vce so I don't think we actually need any ballast resistors at all.

Top traces are junction temperature, bottom traces are Ic for transistors 5 and 6.
Attached Images
File Type: png BC337-40_parallel_currenthogging.png (67.8 KB, 14 views)
  Reply With Quote
Old Today, 08:01 AM   #3212
diyAudio Member
 
Join Date: Sep 2007
Send a message via Yahoo to linuxguru
Quote:
Originally Posted by keantoken View Post
2: Almost nonexistant quasi-saturation - no better known transistor for low-Vce low-power applications such as C-multipliers, giving PSRR up to over 70db (the BC5xx follows closely at 60db, I wonder if newer BISS transistors from NXP could be better?). This also makes them ideal for current mirrors where gain is lost through quasisaturation (BIG mistake to use high-voltage japanese transistors here).
I guess this applies to both the NPN and PNP, as well as the SMD versions that use the same die - BC807/BC817. I'll give them a try in a current mirror shortly - I've used BC847C/857C in current mirrors earlier and they seem to work OK, but maybe the 807/817 are good substitutes with lower noise.
  Reply With Quote
Old Today, 08:14 AM   #3213
diyAudio Member
 
Join Date: Nov 2011
Location: Cooktown, Oz
Quote:
Originally Posted by stormsonic View Post
Your work have inspired me to start measuring transistors in my parts bin. Found another decent performers, Zetex ZTX651/751.
How did you measure the noise performance and what numbers did you get?

1mA & 3mA would be good
  Reply With Quote
Old Today, 08:18 AM   #3214
diyAudio Member
 
keantoken's Avatar
 
Join Date: Aug 2006
Location: Texas
Blog Entries: 2
Oops, I discovered the last simulation went into runaway after 10 minutes. The actual number is Ic*Pd<460u, and you'll probably want to stay well under this. 10mV (1R at 10mA) degeneration moved it back up to 860u.
  Reply With Quote
Old Today, 08:51 AM   #3215
diyAudio Member
 
Join Date: Nov 2011
Location: Cooktown, Oz
Quote:
Originally Posted by gerhard View Post
Do you mean me? "Joachim Gerhard" and "Gerhard" are different entities :-)
My apologies Dr. Hoffmann

Iono is indeed impressive.

If I still had a working turntable I would be tempted to ask to borrow it for some listening tests. I still have a couple of MC cartridges.
  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
discrete opamp help blackpowderaudio Parts 0 16th December 2009 03:46 PM
THAT transistor headphone amp (250ma discrete opamp) design sanity check. Russ White Headphone Systems 19 13th December 2007 12:52 PM


New To Site? Need Help?

All times are GMT. The time now is 09:16 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