How to measure JLH Class A with a Scope - Page 8 - diyAudio
Go Back   Home > Forums > General Interest > Everything Else

Everything Else Anything related to audio / video / electronics etc) BUT remember- we have many new forums where your thread may now fit! .... Parts, Equipment & Tools, Construction Tips, Software Tools......

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 19th June 2008, 06:58 PM   #71
Mooly is online now Mooly  United Kingdom
diyAudio Moderator
 
Mooly's Avatar
 
Join Date: Sep 2007
Hello Chris,
What you are seeing is called overshoot, the reason why -- well thats another thing altogether. Have you used your own wiring layout for constructing it all ? I can't remember now without re reading it all. Is it on PCB's ?
In all honesty this is where it gets a bit difficult now. There are so many posible reasons why. It could be the way the returns to the zero volt line are made. Every piece of wire has to be treated as a potential "resistance" that could cause an unwanted voltage (signal) to appear across it. The returns for the C4/C2 & R2 are the most important in the amp. They should all go to the star earth not to just any "convenient" earth. I am not saying you have done this -- it's just something to bear in mind.
C2 the 330 pf -- thats fitted is it.
I don't really know what else to advise Chris, at the end of a keyboard there are so many posible pitfalls.
If you are really keen you could try rewiring one channel at a time to a star grounding scheme.
  Reply With Quote
Old 19th June 2008, 07:21 PM   #72
diyAudio Member
 
chris ma's Avatar
 
Join Date: Sep 2001
Location: Pickering, Canada
Ok,

then in grossly/ losely term when amp showing overshot behaviour what ill effect it would have to the sound quality of reproducing?

What do you mean C2 330pf ?
This amp is point to point hard wired, no pcb , the butcher style


Sorry C2 yes I have C2 intalled in amp
__________________
The Butcher
  Reply With Quote
Old 19th June 2008, 09:28 PM   #73
diyAudio Member
 
chris ma's Avatar
 
Join Date: Sep 2001
Location: Pickering, Canada
Hey Karl,

Problem identified. It was due to the wiring of the volume pot I just move the aligator clip and the wiring a bit and it changes the ringing to no overshot.

It was due to this mess of wires
Attached Images
File Type: jpg p6191290.jpg (67.8 KB, 103 views)
__________________
The Butcher
  Reply With Quote
Old 19th June 2008, 09:35 PM   #74
diyAudio Member
 
chris ma's Avatar
 
Join Date: Sep 2001
Location: Pickering, Canada
So I should have a better setup for the pot and wiring instead of loose wires soldered to the pot and to 4 aligator clips. And they are not shielded. Now the trace look exactly the same as the CD player connected direct to the scope except the vertical divisions is more with the amp output control by the pot.

This is the amp trace at 1kHz



PS. now I twisted the wires together and the overshot can be reduced now. It seems the amp is reproducing the squarewave without adding further extra freebies.
Attached Images
File Type: jpg p6191294.jpg (32.0 KB, 96 views)
__________________
The Butcher
  Reply With Quote
Old 20th June 2008, 06:37 AM   #75
Mooly is online now Mooly  United Kingdom
diyAudio Moderator
 
Mooly's Avatar
 
Join Date: Sep 2007
That looks great !!. It's all in the detail isn't it. Earlier on you asked about the quiescent current and I mentioned 1.6 Amp for the original. The updated JLH (not yours exactly -- the one I sent you) mentions I think 2 amps.
What you may find interesting to do is to connect your 'scope across the speaker when it's all playing and see just what voltage you actually put out when it's turned up loud. Try and calculate then what the peak and RMS power is into 8 ohm. You may be suprised how little power you need for normal listening. For ex 6 volts peak (not peak to peak) would be 4.5 watt's peak into 8 ohms. If it were a sine wave swinging 6 volts above and below ground that would then be 12 volts peak to peak or 12/2 which is 6 divided by root 2 ( 12/2=6. 6/1.414=4.24 watts RMS)
So whats next ???
  Reply With Quote
Old 20th June 2008, 11:26 AM   #76
diyAudio Member
 
chris ma's Avatar
 
Join Date: Sep 2001
Location: Pickering, Canada
Default Next Step?

I will check and re-bias the other 3 JLH amps before I build more.
I am using regulated PSU Mj15003 for mid, CLC PSU Mj21194 for high and Chipamp for subs doing active 3 ways per channel.

These JLH amps are so picky about the matching of output transistors may be I should build a matching tool with regulated power supply? Any suggestions?
__________________
The Butcher
  Reply With Quote
Old 20th June 2008, 11:28 AM   #77
diyAudio Member
 
chris ma's Avatar
 
Join Date: Sep 2001
Location: Pickering, Canada
Quote:
Originally posted by Mooly
What you may find interesting to do is to connect your 'scope across the speaker when it's all playing and see just what voltage you actually put out when it's turned up loud. Try and calculate then what the peak and RMS power is into 8 ohm. You may be suprised how little power you need for normal listening. For ex 6 volts peak (not peak to peak) would be 4.5 watt's peak into 8 ohms. If it were a sine wave swinging 6 volts above and below ground that would then be 12 volts peak to peak or 12/2 which is 6 divided by root 2 ( 12/2=6. 6/1.414=4.24 watts RMS)
So whats next ???
Do I set the scope at DC or AC ?
I guess it would have to be AC.
__________________
The Butcher
  Reply With Quote
Old 20th June 2008, 12:02 PM   #78
Mooly is online now Mooly  United Kingdom
diyAudio Moderator
 
Mooly's Avatar
 
Join Date: Sep 2007
Think about it The output is at zero volts DC. You only need set it to AC coupling if the signal you want to look at is sat on top of a DC voltage. Yours isn't so use DC coupling. You will find if you switch back and forth there is no difference.
  Reply With Quote
Old 25th June 2008, 03:23 PM   #79
diyAudio Member
 
Join Date: Nov 2005
Default Learning How ...

Chris,

You might want to read these freebies from TEK:

http://www.tek.com/Measurement/App_N...60W_6053_9.pdf

http://www.tek.com/Measurement/App_N...03W_8605_2.pdf

They outline how to make measurements with your scope ...

You could also find the User's Manual for your scope at the TEK site ...
  Reply With Quote
Old 30th June 2008, 04:12 PM   #80
diyAudio Member
 
chris ma's Avatar
 
Join Date: Sep 2001
Location: Pickering, Canada
Default Great Link

Thank you very much
__________________
The Butcher
  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
Can I use a scope to measure powerline noise? Saurav Parts 23 11th July 2012 06:37 PM
Measure the output of a bridged class D ocool_15 Class D 5 20th April 2008 07:12 PM
Great deal on Digital scope. Is this enough scope? hifimaker Pass Labs 1 1st May 2007 09:59 PM
Want to measure V on the scope: should I buy a new one or build a low noise preamp? Bricolo Parts 43 1st November 2005 08:41 AM
Can I look for (or even measure) distorsion on an amp with a dual scope? Bricolo Parts 17 17th September 2003 02:06 PM


New To Site? Need Help?

All times are GMT. The time now is 06:27 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