Input Attenuation to feed meters (switch?) - diyAudio
Go Back   Home > Forums > Design & Build > Construction Tips

Construction Tips Construction techniques and tips

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 24th July 2012, 06:13 PM   #1
diyAudio Member
 
Join Date: Jul 2012
Default Input Attenuation to feed meters (switch?)

I've done a bit of searching and everything I've found relates to attenuating a signal that will be further processed after the drop, but all I need to do is reduce input before the signal hits the meters, from an independent output dedicated to them (accessory output from my DAC) so quality after attenuation isn't crucial for me.

I've built a passive switcher in the past, couldn't I just figure out how much resistance I would need, and then add the resistors in series at each corresponding position before the meters?

If so, would all the positions be joined at the meters' +/- end, so the attenuated values used would be determined by the switch?
  Reply With Quote
Old 24th July 2012, 06:20 PM   #2
Mooly is online now Mooly  United Kingdom
diyAudio Moderator
 
Mooly's Avatar
 
Join Date: Sep 2007
Are these mechanical "VU" style meters ?

If so then you need a rectifier (and a bit more beside) to enable the meters to respond. AC won't cause them to deflect.

I not very clear from your description what you are trying to do.
__________________
-------------------------------------------------------
Installing and using LTspice. From beginner to advanced.
  Reply With Quote
Old 24th July 2012, 06:27 PM   #3
diyAudio Member
 
Join Date: Jul 2012
Thanks for your reply, and sorry for not being clear. Yes, they're mechanical VU's and they've got built in rectifiers and cards (not sure what the cards are called but they've got the necessary resistors to work with signal). I've tested them and have been able to get "0VU" from a 1kHz signal from my system.

What I'd love to do is create an attenuation circuit for the meters to display different (attenuated) values, like "0" (for full signal) and then "-6" (figure out how much resistance I need for this) and so on.

I was hoping to be able to accomplish this by having the input signal go into a rotary switch with maybe 3-4 positions, and adding the necessary resistors at each position, then feed the meters with the signals and determine what signal moves them via the switch, hope that makes sense!
  Reply With Quote
Old 24th July 2012, 06:35 PM   #4
Mooly is online now Mooly  United Kingdom
diyAudio Moderator
 
Mooly's Avatar
 
Join Date: Sep 2007
Where there are a lot of unknowns then it might be simplest to just use a potentiometer (or preset) to determine the values needed. Then measure the value and fit a fixed resistor/s

There are a lot of unknowns... such as what voltage do the meters need to show 0DB. What is input impedance of the meter, and so on.

With a rotary switch you could use 4 preset pots and set them exactly how you want.
__________________
-------------------------------------------------------
Installing and using LTspice. From beginner to advanced.
  Reply With Quote
Old 24th July 2012, 06:39 PM   #5
Mooly is online now Mooly  United Kingdom
diyAudio Moderator
 
Mooly's Avatar
 
Join Date: Sep 2007
Just to add... the presets can be wired in series (possibly... it depends on the meter. If the meters have on board powered electronics then series connected may not be the best solution) or better still wired as a true divider with the output taken from the wiper and the ends of the pot grounded.

Can you see how that would be wired to the switch. Four presets in parallel with the wipers going to the four poles of the switch and the meter to the switch "output".
__________________
-------------------------------------------------------
Installing and using LTspice. From beginner to advanced.
  Reply With Quote
Old 24th July 2012, 08:32 PM   #6
diyAudio Member
 
Join Date: Jul 2012
Thanks Mooly, great info! I think I understand what you're saying. If I understand this right, I would split the input signal (from my interface, it's 0.775v = 0dBu) into four, each one having a preset pot attenuated accordingly, going into a position on the switch (one wouldn't have one as it would be the "0" position) and then use the poles on the switch as an output to the meters. Hopefully I've understood this correctly, thanks again!
  Reply With Quote
Old 25th July 2012, 07:22 AM   #7
Mooly is online now Mooly  United Kingdom
diyAudio Moderator
 
Mooly's Avatar
 
Join Date: Sep 2007
Yes, that's it. The value of the pots depends on the meter sensitivity (its resistance)

If you use the lower example remember that the pots are all in parallel and so a load on the DAC output.

Another scheme is to construct a single divider chain with 4 resistors whose tappings then go off to the switch. That's the hardest one to do but the most elegant
Attached Images
File Type: jpg img007.jpg (220.4 KB, 25 views)
__________________
-------------------------------------------------------
Installing and using LTspice. From beginner to advanced.
  Reply With Quote
Old 25th July 2012, 03:55 PM   #8
diyAudio Member
 
Join Date: Jul 2012
Much appreciated! I think this will definitely do it; thanks again for all your help and for taking the time to draw these schemes!
  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
Do domestic Kwh meters (ordinary electric meters) record reactive power. Mooly Power Supplies 17 30th October 2011 10:18 PM
Input voltage attenuation jeffdavison Tubes / Valves 14 13th September 2008 03:21 AM
BOZ input attenuation value?? rtate Pass Labs 6 24th August 2008 04:42 AM
Input attenuation on Leak amp patrickamory Tubes / Valves 15 16th July 2007 05:52 PM
Elegant way to feed parallel data-input DAC chips ? Bernhard Digital Source 27 18th April 2005 09:28 PM


New To Site? Need Help?

All times are GMT. The time now is 01:24 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