POP with stepped attenuator
« on: January 29, 2019, 06:14:18 AM »
Hi everyone,

I'm building a summing mixer and I put some stepped attenuator and at each step I have
some POP, CLOC.
It is break before make contact...

Do you have any technique to avoid this ?
Or is it a bad component maybe ?

Thank's


ruffrecords

Re: POP with stepped attenuator
« Reply #1 on: January 29, 2019, 08:46:17 AM »
Pops and clicks are usually cause by dc voltages. Can you post a schematic showing the stepped attenuator and what it is connected to?

Cheers

Ian
www.customtubeconsoles.com
https://mark3vtm.blogspot.co.uk/
www.eztubemixer.blogspot.co.uk


'The only people not making mistakes are the people doing nothing'

Re: POP with stepped attenuator
« Reply #2 on: January 29, 2019, 08:58:17 AM »
Hi Ian,

The attenuator is this one ; https://tinyurl.com/y8yevyfr

And I think you know that : I'm using it for the gain in the V475-2C board, instead of Rg.
I don't know where to plug the ground from the attenuator.
Myabe that it...

Here is the schematic of V475-2C : https://groupdiy.com/index.php?topic=44805.msg561354#msg561354

JohnRoberts

Re: POP with stepped attenuator
« Reply #3 on: January 29, 2019, 10:06:54 AM »
I didn't chase down the specific active circuit but if the stepped attenuator goes momentarily open circuit between switch positions that can cause a large step in the closed loop gain. This is not unlike wiper bounce in conventional pots and why they work to eliminate wiper bounce (where the wiper is momentarily open circuit).

Depending upon the topology you may be able to mitigate with a capacitor.  Perhaps a make before break switch would eliminate that, but I do not have any experience with that.

JR
John Roberts
http://circularscience.com
Tune it, or don't play it...

Re: POP with stepped attenuator
« Reply #4 on: January 29, 2019, 01:44:51 PM »
Thank you John !

Re: POP with stepped attenuator
« Reply #5 on: January 31, 2019, 12:45:11 PM »
Hi Ian,

Here is the simple schema of how I plugged the gain rotary switches.

dmp

Re: POP with stepped attenuator
« Reply #6 on: January 31, 2019, 03:09:48 PM »
See this other thread all about the v475:
https://groupdiy.com/index.php?topic=13857.msg748754;topicseen#msg748754

I searched for 'gain' and found a post saying Rg from 0 ohms to infinite adjusts the gain from -12dB to +6dB

You mean using the mentioned switched pot for RG (Feedback-Rs)?
Could work technically but I'm not sure about the pot travel behaviour (it seems to be a log pot).
With the pot completely closed (= whiper shorted) you will get -12dB,totally in circuit (100k) I guess you might get some +5dB or so,e.g. I have Volkers recommended 48k7 to get +4dB for the RGs.
To get +6dB you need an open condition for RGs (=infinity).

When you use a break before make, your resistance is momentarily infinite and your gain is momentarily +6 dB
Wrong kind of switch. Get a make before break. Or just use a pot.

Re: POP with stepped attenuator
« Reply #7 on: January 31, 2019, 05:32:46 PM »
I mistake, the gain pot is a "make before break".
So the seller told me that normally it doesn't make POP sound.
So I think I'm wrong somewhere...
But my knowledge is limited with that...

The seller also told me : "Some people will make their own amplifier in Direct Coupling (i.e. there is no input/output capacitor), this step potentiometer will have POP sound."

Does anyone know something about this coupling capacitor technic ?
« Last Edit: January 31, 2019, 06:49:44 PM by lars on »

dmp

Re: POP with stepped attenuator
« Reply #8 on: February 01, 2019, 03:57:25 PM »
I would test the switch. Just attach an LED and small power source so the light will change intensity as you flip the switch. If the LED goes out between switch positions, then the switch is opening between positions, and the 'pop' is explained by a momentary surge in gain. 

Re: POP with stepped attenuator
« Reply #9 on: February 01, 2019, 06:57:36 PM »
Good idea !
I'll do that tomorrow.
Thank's !


JohnRoberts

Re: POP with stepped attenuator
« Reply #10 on: February 01, 2019, 07:26:08 PM »
Easier than that perhaps, if you have a VOM with continuity function. Probe between wiper and two adjacent switch positions while slowly rotating the switch shaft... listen for the tone to drop out if break b4 make.

JR 
John Roberts
http://circularscience.com
Tune it, or don't play it...

Re: POP with stepped attenuator
« Reply #11 on: February 02, 2019, 10:03:32 AM »
I tested the switch with the contuity test and there is something strange.
This is a 21 steps switch, the first 6 steps are continue but the others Not !??




David Kulka

Re: POP with stepped attenuator
« Reply #12 on: February 05, 2019, 10:35:35 PM »
DC makes things worse but even without DC any kind of stepped level control will make clicks when it is turned with audio present. The same can happen with software based level changes. A transient is being created (either positive or negative, it's random) which presents an audible click.
« Last Edit: February 05, 2019, 10:52:14 PM by David Kulka »

[silent:arts]

Re: POP with stepped attenuator
« Reply #13 on: February 06, 2019, 02:42:17 AM »
A stepped attenuator is the wrong part for switching gain in a V475 summing amp.

dmp describes the problem very well:

When you use a break before make, your resistance is momentarily infinite and your gain is momentarily +6 dB
Wrong kind of switch. Get a make before break. Or just use a pot.

but don't use a pot either! since you need a very tight tolerance between the two RGs in each channel.


 

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