Discrete Opamp Open Design - Page 57 - 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 30th August 2012, 08:56 PM   #561
diyAudio Member
 
Wavebourn's Avatar
 
Join Date: Sep 2006
Location: Pleasant Hill, CA
Send a message via Skype™ to Wavebourn
Quote:
Originally Posted by john curl View Post
For the record, I once added a chopper servo to my studio board design (shown earlier) and got very low offset, enough to drive an analog record head, directly, without a coupling cap. Try that, sometime, without a servo! '-)
Is a capacitor so scarce?

I was driving recording head by class D amp, long before "class D" name appeared. I don't remember if I used any coupling cap, most probably not.
__________________
The Devil is not so terrible as his math model is!
  Reply With Quote
Old 30th August 2012, 10:27 PM   #562
diyAudio Member
 
Join Date: Dec 2003
Location: Munich
Quote:
Originally Posted by RNMarsh View Post
Are we talking of SOTA audio or MKP cap coupled - anything will do?

Looking at the bigger picture of the whole recording/playback chain, multiple roll-off at the bass end has its accumulated consequences. DC-coupled all the way thru will make the sound a lot better than it is now. but, hay! Do what you like. Me? I dont listen to records at all any more. gave it all away to Kavi. That doesnt mean I always like the sound of CD better or LP any less. For me LP systems are just way, way too fussy to use and I'm not into that level of screwing around to get the best sound... and it Still didnt sound close to 'real' live music... and it wears out with use (!). They are like tires -- great when new. So try something else. On to the next great Hope. -RNM
...I also stopped using LP, for the same reasons.
So let's skip the 'no_offset-no_adjustment-DC_perfection' requirement from the spec. We simply don't have unsaint gain in the chain between line level and speaker.
The running discussion about offset is like optimizing the air drag coefficient of a combine harvester. Of course it can be done. It can even be done with great perfection and adorable know how, but it does not necessarily lead to a great harvester. It might even contradict. For an optimized air drag coefficient most likely one will end up with a very small ground clearance and narrow rotator....
If you have a solution with optimized air drag coefficient, but without impacting the relevant properties and without unsaint complexity - that's of course cool. Just put the schematic for discussion.
  Reply With Quote
Old 30th August 2012, 10:35 PM   #563
diyAudio Member
 
scott wurcer's Avatar
 
Join Date: Jan 2004
Location: cambridge ma
Quote:
Originally Posted by RNMarsh View Post
OK. Great. Done with this project. See you on the next one.
I still don't see Vgs matching between N and P channel tracking over temp, diff pairs make this a common mode error.
__________________
"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."
  Reply With Quote
Old 30th August 2012, 11:11 PM   #564
coluke is offline coluke  Italy
diyAudio Member
 
Join Date: Mar 2009
Quickly breadborded the design in #451, and did a few tests - did find only 10 2N5458s, so the selection was a little bit poor ; BC550/560 in the gain/driver stage, MJE243/253 running at ~70 mA in the output stage. At 10 dB gain BW is in the MHz range out of the box, and THD @ 1Vrms, 1 kHz into 30 ohm (~30 mW) is about 0.004% (only 2nd and 3rd harmonics), quite load insensitive (THD drops to 0.0038% into ~300 ohm). No compensation needed; DC drift good (for audio, at least) while not spectacular: output stage Iq rock stable, output offset in the +/- 5 mV range en plein air over a couple of hours. Well, it needs some more work, but seems promising - going to get plenty of J113s, do a better selection and see what happens

Ciao,

L.
  Reply With Quote
Old 30th August 2012, 11:14 PM   #565
bcarso is offline bcarso  United States
diyAudio Member
 
Join Date: May 2005
Location: Canoga Park, California
Quote:
Originally Posted by EUVL View Post
Brad,

I donít think I am discouraged as yet about the follower configuration.
I shall make some measurements with a 2SK246, which is essentially the same device in TO92.

Regards,
Patrick
Comparing the published datasheets, other than Idss bracketing and max voltage, it appears from the characteristic curves that the 2SK246 has a much smaller transconductance than each half of the 2SK2145.

I'm about to measure the sample I'm testing for that parameter. I also have a lot of 246s I could measure.
  Reply With Quote
Old 31st August 2012, 12:05 AM   #566
bcarso is offline bcarso  United States
diyAudio Member
 
Join Date: May 2005
Location: Canoga Park, California
Default 2145 gm

Quote:
Originally Posted by bcarso View Post
Comparing the published datasheets, other than Idss bracketing and max voltage, it appears from the characteristic curves that the 2SK246 has a much smaller transconductance than each half of the 2SK2145.

I'm about to measure the sample I'm testing for that parameter. I also have a lot of 246s I could measure.
Well I just snapped the source lead off of 2145 sample #1, but it served its purposes admirably

Sample two has Idss of 2.80mA, and the follower circuit an offset of -5mV. The transconductance is 13.3mA/V, based on the 6dB attenuation of a low-level 2kHz signal. This corresponds reasonably well with the datasheet curves, which are for a 10V Vds.

This indicates that midband noise should be, for the follower, about 1.29nV/sqrtHz (the current source Idss load entails a 3dB increase in equivalent input noise). Not too shabby, but I will attempt a noise measurement at some point as well. The 3dB additional noise could be eliminated, with a good deal of additional work, if the devices were in fact isolated, but so it goes --- in most applications that noise will be negligible.
  Reply With Quote
Old 31st August 2012, 12:24 AM   #567
diyAudio Member
 
Wavebourn's Avatar
 
Join Date: Sep 2006
Location: Pleasant Hill, CA
Send a message via Skype™ to Wavebourn
Quote:
Originally Posted by coluke View Post
Quickly breadborded the design in #451, and did a few tests - did find only 10 2N5458s, so the selection was a little bit poor ; BC550/560 in the gain/driver stage, MJE243/253 running at ~70 mA in the output stage. At 10 dB gain BW is in the MHz range out of the box, and THD @ 1Vrms, 1 kHz into 30 ohm (~30 mW) is about 0.004% (only 2nd and 3rd harmonics), quite load insensitive (THD drops to 0.0038% into ~300 ohm). No compensation needed; DC drift good (for audio, at least) while not spectacular: output stage Iq rock stable, output offset in the +/- 5 mV range en plein air over a couple of hours. Well, it needs some more work, but seems promising - going to get plenty of J113s, do a better selection and see what happens
.
Great amp, Coluke! One more in ths thread!
__________________
The Devil is not so terrible as his math model is!
  Reply With Quote
Old 31st August 2012, 12:39 AM   #568
diyAudio Member
 
john curl's Avatar
 
Join Date: Jul 2003
Location: berkeley ca
Wavebourn, the previous analog record amp design used 30uF polycarbonate caps. I just could not justify them in this design.
  Reply With Quote
Old 31st August 2012, 12:50 AM   #569
bcarso is offline bcarso  United States
diyAudio Member
 
Join Date: May 2005
Location: Canoga Park, California
Default 2145 seems to be a two-chip dual

Sample #1 having served its country well, I ground down through the encapsulant to uncover the innards. I finally got to a square positioned over a gate lead about 400um on a side. It's plausible that this is one of the chips --- that's about the size of a 4416 chip, which transistor, although lower capacitance than the 2145, does not take up all of the die size.

And I still have fingerprints, although as I rubbed away I switched fingers from time to time. I guess this is what safecrackers were supposed to do, to increase their sensitivity.
  Reply With Quote
Old 31st August 2012, 01:51 AM   #570
dimitri is offline dimitri  United States
diyAudio Member
 
dimitri's Avatar
 
Join Date: Oct 2002
Location: retired
Send a message via ICQ to dimitri
Quote:
I shall make some measurements with a 2SK246, which is essentially the same device in TO92.
This is not correct: 2x2SK117=2x2SK209=2SK2145=2SK3320

Brad, 2SK2145 IS 1nV/sqrtHz device. 2SK246 has 10 dB higher noise voltage

Last edited by dimitri; 31st August 2012 at 02:02 AM.
  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 10:41 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