Problem with Bob Cordell's LME49830 and LT1166 - diyAudio
Go Back   Home > Forums > Amplifiers > Chip Amps
Home Forums Rules Articles diyAudio Store Gallery Wiki Blogs Register Donations FAQ Calendar Search Today's Posts Mark Forums Read

Chip Amps Amplifiers based on integrated circuits

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 16th December 2012, 03:23 PM   #1
diyAudio Member
 
Join Date: Aug 2012
Location: Germany near Munich
Default Problem with Bob Cordell's LME49830 and LT1166

Hello!

I built the lme49830 with bias IC LT1166 but it doesn't work very well.

The quiescence current at about +/-30V is 10mA.

The first issue was a oscillation at the gates of the fets. I changed C6 from 100n to 180n and the oscillation was gone.

Sine wave looks fine at the oscilloscope, but if I connect a speaker and a music source the sound is very distorted. It sounds terrible, like if the bias voltage is not high enough.

So I measured the gate voltages, the irfp240 gate voltage is about +1.7V and the IRFP9240 gate voltage was -0.7V. Is it ok?? I think not… ?!

So the next step was chancing C4 and C5 from 10pF to 27pF but nothing happened. It still sounds distorted…

Maybe it's because the red marked current source? Do I have to connect PIN1 of the LT1166 to V+ rail? I think my LME49830 will fire up if I connect Bias + with V+. So what does I1 mean?

I hope you can help me Thanks in advance!

Bernhard
Attached Images
File Type: png Bildschirmfoto 2012-12-16 um 17.09.21.png (152.2 KB, 585 views)
  Reply With Quote
Old 16th December 2012, 04:10 PM   #2
diyAudio Member
 
Join Date: Aug 2012
Location: Völkermarkt
You have to use 10mA current source there, as drawn.
Cheers, Vic.
  Reply With Quote
Old 16th December 2012, 04:54 PM   #3
diyAudio Member
 
Join Date: Aug 2012
Location: Germany near Munich
Ah ok thanks for reply.

Can I simply use a transistor and three resistors like shown in the image?

Click the image to open in full size.

Re would be Pin 1 of the LT1166.

It's a bit dangerous I think, if the current source blows up the hole rail voltage (60V) is at the lme49830 and will kill it
  Reply With Quote
Old 16th December 2012, 05:30 PM   #4
AndrewT is offline AndrewT  Scotland
diyAudio Member
 
Join Date: Jul 2004
Location: Scottish Borders
You have the CCS labels back to front.
The resistor R1 is the constant current sink.
I is fed from a +ve supply via a limiting resistor.
Re is set to zero ohms.

Now you need to turn the whole thing upside down to create a current source and use a PNP for the inverted voltage.
__________________
regards Andrew T.
Sent from my desktop computer using a keyboard
  Reply With Quote
Old 16th December 2012, 09:13 PM   #5
diyAudio Member
 
Join Date: Aug 2012
Location: Germany near Munich
I simply added a current source with a lm317 and it worked... not perfect but much better than before.

I figured out that this circuit is very, very sensible to the current source. So if it isn't exacly 10mA it doesn't work. So now I know what the problem is and can fix it.

@Andrew: why do I have to build the current source upside down? I added a circuit for the current source, can I do it this way?

Thanks.
Attached Images
File Type: png Bildschirmfoto 2012-12-16 um 23.12.43.png (14.9 KB, 510 views)
  Reply With Quote
Old 13th August 2016, 12:05 AM   #6
diyAudio Member
 
Join Date: Aug 2016
Hi mantabernd

I1 is used because Vtop (and Vbottom) pin, need a supply current to work right according de data sheet. Max value 75mA, common values between 15mA to 50mA. Current capability of BIAS pin of the LME49830 pin is below 3mA (according to data sheet) so a current source is needed to supply this current in order to the LT1166 works fine.

Probably your amplifier doesn't sound at the best quality because there is a current difference between N-channel and P-channel MOSFETs, since they are not totally symmetrical. Increase a little bit the value of the source resistors of the P-channel MOSFETs until both currents are the same.

Now I'm designing, simulating and building this amplifier, I would like to know how your amplifier sounds and if you did any improvement, I really appreciate that.

Best regards!
  Reply With Quote
Old 13th August 2016, 01:21 AM   #7
diyAudio Member
 
jackinnj's Avatar
 
Join Date: Apr 2002
Location: Llanddewi Brefi, NJ
Linear provides an excellent data sheet and application note on their website -- with a schematic for the current source(s)

LT1166 - Power Output Stage Automatic Bias System - Linear Technology
__________________
Why, silly hare, are you fleeing from the fierce jaws of the lion now grown tame?
  Reply With Quote
Old 13th August 2016, 12:31 PM   #8
diyAudio Member
 
jackinnj's Avatar
 
Join Date: Apr 2002
Location: Llanddewi Brefi, NJ
Article discussing other auto-bias designs:

Auto Bias

Auto Bias part II
__________________
Why, silly hare, are you fleeing from the fierce jaws of the lion now grown tame?
  Reply With Quote
Old 19th August 2016, 02:09 AM   #9
diyAudio Member
 
Join Date: Jun 2002
Location: Where work is
Default AutoNias

Quote:
Originally Posted by jackinnj View Post
Article discussing other auto-bias designs:

Auto Bias

Auto Bias part II
Links not working or is it just some problem at my end? The whole website seems to be down at the time of this writing.
  Reply With Quote
Old 19th August 2016, 03:01 AM   #10
BrianL is offline BrianL  United States
diyAudio Member
 
Join Date: Mar 2002
Location: USA
problem on your end, I think. Works for me today and previously
__________________
bel
  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
Bob Cordell's Power amplifier book ihan Solid State 7170 12th August 2016 01:16 AM
Another realization of Bob Cordell's THD Analyzer giulianodes Equipment & Tools 136 6th June 2016 08:06 AM
Bob Cordell's VinylTrak jan.didden Analog Line Level 61 26th March 2015 12:05 AM
LT1166+LME49830 design by Bob Cordell. Headbanger Chip Amps 6 6th October 2012 04:59 PM
LT1166 bias IC Sebastiaan Solid State 2 3rd September 2011 03:21 PM


New To Site? Need Help?

All times are GMT. The time now is 04:58 AM.


vBulletin Optimisation provided by vB Optimise (Pro) - vBulletin Mods & Addons Copyright © 2016 DragonByte Technologies Ltd.
Copyright ©1999-2016 diyAudio

Content Relevant URLs by vBSEO 3.3.2
Wiki