Adjusting Analog VU Meter - diyAudio
Go Back   Home > Forums > Amplifiers > Solid State
Home Forums Rules Articles The diyAudio Store Gallery Blogs Donations FAQ Calendar Mark Forums Read

Solid State Talk all about solid state amplification.

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
 
 
Thread Tools
Old 27th April 2006, 06:13 PM  
Plundering the Planet From the Comfort of Home
diyAudio Member
 
DreadPirate's Avatar
 
Join Date: Jan 2006
Location: Northern Virginia, USA
Default Adjusting Analog VU Meter

I have a Kenwood KA-501 amp whose output meters are not indicating identically, one falls a bit short of the other. I have not verified yet, I intend to do this with an SPL meter, but I am assuming that the sound is of equal power from both channels and that the problem is in the meter. In a typical amp like this, what is the method of adjusting the needle sweep? My primary concern is to get them reading identically when an equal signal is applied to both channels and the balance knob is centered, regardless as to whether the reading really means anything.
 
Old 27th April 2006, 07:13 PM  
diyAudio Member
 
acenovelty's Avatar
 
Join Date: Aug 2004
Location: SF Bay Area
When you remove the face plate cover of the meter, there is a small set screw attached to the movement. Here you can change its relative setting to match the other side.
__________________
Two people can keep a secret if one of them is dead.
 
Old 28th April 2006, 02:44 AM  
anatech is offline anatech  Canada
diyAudio Moderator
 
anatech's Avatar
 
Join Date: Jun 2004
Location: Georgetown, On
Hi DreadPirate,
The set screw inside the meter is for setting zero.

There will be a PC board inside with some trim pots that will allow you to set the span.

You will need a 400~1KHz constant tone (I use a signal generator) and an accurate meter good at those frequencies. Your garden variety DVM is very little use past 120 Hz. A VTVM (calibrated) would be a suitable secondary instrument. Do not attempt to use a sound pressure meter. There are too many variables at work and you could easily get the same reading from each speaker and have the VU meter out by 3dB.

Get the service manual or schematic for this. There are other controls inside that can bring you grief if misadjusted. The smoky kind of grief.

-Chris
 
Old 29th April 2006, 03:39 PM  
Plundering the Planet From the Comfort of Home
diyAudio Member
 
DreadPirate's Avatar
 
Join Date: Jan 2006
Location: Northern Virginia, USA
I was suspecting there was some kind of onboard pot for this. I have posted the Kenwood KA-501 schematic here if anyone is interested in having it:

http://depositfiles.com/en/files/356...KA501.pdf.html
 
Old 29th April 2006, 03:41 PM  
Plundering the Planet From the Comfort of Home
diyAudio Member
 
DreadPirate's Avatar
 
Join Date: Jan 2006
Location: Northern Virginia, USA
VR3 and VR4, looks like.
 
Old 29th April 2006, 08:09 PM  
anatech is offline anatech  Canada
diyAudio Moderator
 
anatech's Avatar
 
Join Date: Jun 2004
Location: Georgetown, On
Hi DreadPirate,
Yes, those are the ones. Set them without a load (they just measure voltage output) to keep your amp cool while setting these. Set at "0" while running a signal in via a "Y" cord. Sine wave no higher than 1KHz or you may burn out the zobel network.

-Chris
 
Old 30th April 2006, 03:49 PM  
Plundering the Planet From the Comfort of Home
diyAudio Member
 
DreadPirate's Avatar
 
Join Date: Jan 2006
Location: Northern Virginia, USA
I'm not understanding the Y cord part, I think you are overestimating my digital prowess, I'm a rank beginner.

I do have a Dick Smith ESR meter that apparently has a usable 1KHz output, but I wouldn't begin to know how to utilize it.
 
Old 30th April 2006, 03:58 PM  
diyAudio Member
 
Join Date: Jul 2005
Location: North Derbyshire
As already suggested VR3 and VR4 adjust the two meters, they don't actually read in any particular units (and aren't really of much use anyway, just a visual gimmick).

No need to get carried away with audio generators and such (although it does make it easier and more accurate). Just play a mono signal through the amplifier and gently adjust ONE of the pots until the needles move the same.

The suggestion of the Y cord was just to give a mono input.

If you can't find a mono source?, how about radio?, or use a stereo source and adjust on that - but that will take a LOT longer until you're happy, as it's basically a question of making a slight adjustment and then playing a number of tracks to see what you think.
__________________
Nigel Goodwin
 
Old 30th April 2006, 04:07 PM  
anatech is offline anatech  Canada
diyAudio Moderator
 
anatech's Avatar
 
Join Date: Jun 2004
Location: Georgetown, On
Hi Nigel,
Thanks. I post how I would normally do things on the bench. Most people interpret the "0" as full power when in fact it's past clipping!

-Chris
 
Old 1st May 2006, 11:24 PM  
Plundering the Planet From the Comfort of Home
diyAudio Member
 
DreadPirate's Avatar
 
Join Date: Jan 2006
Location: Northern Virginia, USA
Done. I used a "white noise" file and set them even at about mid sweep. Oddly enough, they diverged a bit towards the home position, I'm guessing there is something wrong with the movement on one of them, but all in all worked fine. "Good enough for Government work," as they say.

Attached is a link to a nudie. There are two circuit boards, this one and one vertically attached to the jacks. I am guessing the one in the rear is the pre-amp? This board looks real easy to remove, would it be worth the trouble to re-cap the 15 or so 'lytic caps with polypropylenes? I've never done this before, but doesn't look too difficult...

http://depositfiles.com/en/files/386...Nudie.JPG.html

Thanks for the help!
 

 

Hide this!Advertise here!
Thread Tools

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
how to Analog Panel Meter's space2000 Solid State 9 20th May 2008 07:10 AM
FS: Radio Shack Analog Sound Level Meter Javachip Swap Meet 2 23rd October 2007 03:58 PM
how to make this esr meter work with 250uA Panel meter dytln_02 Everything Else 2 27th January 2007 11:13 PM
Circuit for analog VU meter G.L. Tirebiter Chip Amps 5 14th March 2005 07:42 PM


New To Site? Need Help?

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