Noisy 'clickless' analogue switches - 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 6th April 2012, 09:16 PM   #1
diyAudio Member
 
vielle568's Avatar
 
Join Date: Apr 2010
Location: Deux Sèvres
Default Noisy 'clickless' analogue switches

Hello,

I’ve a simple circuit for an instrument I’m building but I can’t seem to get it working correctly. Basically I’m sending an audio signal to a pre-amp; the signal is then pulsed by an analogue switch before being sent out to the power amplifier.

The problem I can’t overcome is the ‘clicks’ that come from the analogue switch. I’ve tried several different models; even special audio ‘clickless’ switches but it seems to make little difference. I have followed all the recommendations in the various datasheets but without success. Is the click due to the control signal or due to the switch turning on? The audio switches are supposed to turn on gradually to eliminate this noise but it comes out loud and clear on my system.

I have tried using a SPDT version to switch the amplifier input from signal to ground; the output was silent between pulses but the switch clicks were not eliminated.

I tried putting the analogue switch on the power amp speaker leads, but that only resulted in melting the IC. I would only suppose that if the chip was placed immediately after the pick-up that any click would be well amplified by the time it reached the speaker. Even without any audio signal through the circuit the switching clicks were still coming out loud and clear.


I’ve been using MAX4514 and SSM2412 switches recently (I have to use DIP packages, the others types are too small to handle).

So where am I going wrong? Is there such a thing as a ‘clickless’ analogue switch and if so how do I wire it up to keep the clicks at bay?

All suggestions welcome. Thanks.
  Reply With Quote
Old 7th April 2012, 06:53 AM   #2
Mooly is offline Mooly  United Kingdom
diyAudio Moderator
 
Mooly's Avatar
 
Join Date: Sep 2007
There are a number of reasons for this. If there is any DC differential between the switch elements then you are going to hear that as a noise/click/thump when the switch closes/opens. So with the switch open there should be identical DC conditions on the in/out pins... to within microvolts really. So a lot depends on the way the circuit is implemented. You mention that your is noisy with no signal so check this.

When you switch an audio signal, unless it is done at a zero crossing point (which is impractical and difficult) then again there is an abrubt step change in "DC" conditions and you hear a noise.

Breakthrough of the control signal can be an issue. A lot depends on the specific devices and the circuit impedances as to how much of a problem this is.
__________________
-------------------------------------------------------
A simulation free zone. Design it, build it, test it.
  Reply With Quote
Old 7th April 2012, 08:21 AM   #3
diyAudio Member
 
Join Date: Nov 2009
Location: Pune
Is it possible for you to share circuit diagram of the stages at the input of the switch and output of the switch?
__________________
There is always a first time....
  Reply With Quote
Old 7th April 2012, 10:37 AM   #4
AndrewT is online now AndrewT  Scotland
diyAudio Member
 
Join Date: Jul 2004
Location: Scottish Borders
A voltage controlled FET mute on each of the two channels to be swapped.
__________________
regards Andrew T.
  Reply With Quote
Old 7th April 2012, 02:01 PM   #5
diyAudio Member
 
vielle568's Avatar
 
Join Date: Apr 2010
Location: Deux Sèvres
If I tied both the input and output pins to ground with a capacitor would this be sufficient to eliminate the voltage differential that you mentioned? I suppose the only way to find out is to experiment.

As mentioned previously, the clicks are present even when there's no input signal connected to the analogue switch. I've tried reducing the voltage of the triggering signal and adding a decoupling cap which seems to have a slight effect but isn't the solution.

AndrewT, could you please explain a little more about your suggestion of the voltage controlled FET mute? Thanks.

I've attached a schematic of the section of the circuit involving the analogue switch; there could be a major error in the design that I haven't noticed (I'm an ME not an EE). Basically the signal from the preamp is split in two through a unity gain signal buffer/splitter; one signal passes directly to the main amp and the other is pulsed by the analogue switch. There's a panpot in the line out to control the two signals.

Vielle568
Attached Images
File Type: jpg cct2.jpg (96.7 KB, 242 views)
  Reply With Quote
Old 7th April 2012, 02:25 PM   #6
AndrewT is online now AndrewT  Scotland
diyAudio Member
 
Join Date: Jul 2004
Location: Scottish Borders
caps leak current when a bias exists between the plates.

If you use a DC blocking capacitor and leave the connection end unterminated you will find that the unterminated connection develops a voltage that approaches the voltage on the biased side of the capacitor.

Your switch could be behaving exactly like an unterminated connection. Over a short period of time the switch contact voltage changes from 0V ref signal ground.

Clicking the switch to the terminated connection allows that voltage to dissipate. That is your click.

Do not leave any connections unterminated.
__________________
regards Andrew T.
  Reply With Quote
Old 7th April 2012, 03:04 PM   #7
diyAudio Member
 
vielle568's Avatar
 
Join Date: Apr 2010
Location: Deux Sèvres
I have found a solution; I don't know if it's a good solution but it works well enough for my needs.

I added two 104 caps going between ground and the analogue switch input and output pins. I can only assume that these act as decoupling caps and bring the DC voltage levels on these two pins at more or less the same level (0V) and as a result the 'click' from switching has now become almost inaudible.

Thanks everyone for your help and suggestions. They were greatly appreciated.

Vielle568
  Reply With Quote
Old 7th April 2012, 05:42 PM   #8
Mooly is offline Mooly  United Kingdom
diyAudio Moderator
 
Mooly's Avatar
 
Join Date: Sep 2007
104 caps are 0.1uf (100,000pf)

If I understand you correctly then you have these across the audio output to ground !

If that's what you mean then that's not good tbh.
__________________
-------------------------------------------------------
A simulation free zone. Design it, build it, test it.
  Reply With Quote
Old 7th April 2012, 10:53 PM   #9
diyAudio Member
 
vielle568's Avatar
 
Join Date: Apr 2010
Location: Deux Sèvres
That's how I have connected it up; with a cap to ground on the audio signal line either side of the analogue switch. Initially I tried 1uF caps but there was an obvious attenuation in the signal getting through to the amplifier. The caps were then reduced to 100nF (0.0000001F) and the signal recovered its strength and the clicks from the analogue switch remained almost inaudible.

Am I effectively shorting out the audio signal by adding these caps? I'd like to know what I have done incorrectly. It seems to be working OK at the moment.

Vielle568

Last edited by vielle568; 7th April 2012 at 10:57 PM.
  Reply With Quote
Old 8th April 2012, 06:32 AM   #10
Mooly is offline Mooly  United Kingdom
diyAudio Moderator
 
Mooly's Avatar
 
Join Date: Sep 2007
Yes, you are shorting the audio with these caps. At 10Khz the 0.1uF cap has a reactance (or "resistance") of only 160Ω or so. Add another on the other side of the switch and it's not good.

You need to find the reason why it clicks.
With no signal you should have 0.000 volts DC on top of that 470K resistor. With the switch open you should also read 0.000 volts DC on the output of the switch even though it is "open". If those conditions are not met then there will be a click when the switch operates.

If you have the patience to read through all this then it might help... similar problem on a Rotel amp.
Help with DC on volume pot
__________________
-------------------------------------------------------
A simulation free zone. Design it, build it, test it.
  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
Top quality main switches for audio-hifi comp (Rotary and Pushbutton Power Switches) tiefbassuebertr Parts 12 10th March 2010 04:14 PM
noisy noisy noisy noisy noisy tube dsavitsk Tubes / Valves 50 20th February 2006 04:07 PM
ad1853 clickless volume control tubesarehot Digital Source 0 7th July 2004 11:23 PM
Analogue switches Jan Dupont Parts 3 17th July 2003 08:19 PM
Noisy pots and switches! walker Everything Else 14 23rd November 2001 08:51 AM


New To Site? Need Help?

All times are GMT. The time now is 04:43 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