How to quiet stepped atenuator?

guest1632 · « **on:** 23 Jun 2004, 05:59 am »

I'm going to be buying soon a preamp with a stepped atenuator. One of the drawbacks is when you either turn up or down the "volume control" it will sometimes make a crackling noise. Is this due to an offset voltage somewhere? Is there a way to quiet them down without the sound being modified for the worst? Thanks.

ooheadsoo · « **Reply #1 on:** 23 Jun 2004, 07:26 am »

That stepped attenuator doesn't "make before break" its connections so there is a little pop when you turn the knob, right? Or at least not a clean one. I think the cheapest thing to do is actually buy a better SA and install it. However, they're quite pricy. I got a cheap one and it does that, but it's not too bad in my opinion.

guest1632 · « **Reply #2 on:** 23 Jun 2004, 02:56 pm »

Quote from: ooheadsoo

That stepped attenuator doesn't "make before break" its connections so there is a little pop when you turn the knob, right? Or at least not a clean one. I think the cheapest thing to do is actually buy a better SA and install it. However, they're quite pricy. I got a cheap one and it does that, but it's not too bad in my opinion.

Hi, Well, this one is in the Purist. The WAF could be affected, especially with no remote. I actually ment to post this in the lab circle. Well if anybody has any ideas, let me know.

Malcolm Fear · « **Reply #3 on:** 23 Jun 2004, 07:57 pm »

Hi Ray
What brand of pre amp / stepped attenuator are you talking about?
I went down this road with a DACT line stage, DACT selector and a DACT stepped attenuator.
It "cracked" badly. Couldn't fix it. Sounded awful anyway.
Used the DACT attenuator in a passive and then in an AKSA GK-1 preamp (see Aspen amplifiers here).
The problem disappeared.

Occam · « **Reply #4 on:** 23 Jun 2004, 08:31 pm »

As ooheadso said, you've probably got a break-before-make switch in this attenuator. Not ideal, as the following amplification stage sees a rather large disturbace of its 'ground reference', as between stops, the output (wiper) is floating, hence a pop.

Assuming you 'wants to dance with the one that brung ya", I'd suggest the following-

For each channel (pole/wafer) on the switch, wire a resistor of 2 to 3X the 'impedance' of the attenuator between the wiiper (output) and its signal ground. Assuming this is a switched series attenuator, you can measure this attenuator impedance by hooking up an ohmmeter between the attenuators input and ground connection. If you've a '50k' attenuatior, simply wire a 100k-150k resistor between the wiper (output) and ground. This paralell resistance will change the 'taper' of the attenuator as you've introduced a parralell resistance (that effect is minimized by using a substatially larger value that that of the attenuator), but will substantially reduce that 'popping' problem as it will minimize that ground reference disjuction.

Certainly not as ideal as replacing that break-before-make with a proper make-before-break, bespoke switched attenuator, but at a cost of 2 resistors, it should greatly minimize the annoyance.

Then again, it might simply be dirty switch contacts on a proper make-before-break switch. Prior to 'resistorizing' your switch (in the absence of specific information) I'd spay the sucker [EDIT: OUCH!!, although I actually get quite hostile to some equipment, it might be better just to spray] with your choice of aerosol electrical switch cleaner, and see if that fixes the problem

Yet another EDIT - I searched the Circle and realized you're referring to the IRD Purist Preamp, and visited the IRD site.
This is not a passive switched attenuator, but rather an active pre consisting of an voltage amplification stage, stereo switched ladder attenuator, and output buffer(s). Even if the switched attenuator uses break-before-make switch, as the following active circuitry is known, the buffers, I'd be surprised that Mr. Wishman did not adress the issue within the implementation. I'd suggest you contact Mr. Wishman via PM or email.

eico1 · « **Reply #5 on:** 24 Jun 2004, 12:47 am »

I agree with you, there must be a large offset at the input of the device. If other users of this pre do not experience this issue, you might as well get yours fixed!

steve

Curt · « **Reply #6 on:** 24 Jun 2004, 08:19 pm »

All switches (in audio) are MBB (make before break), including the Purist's ladder attenuator Swiss rotory switch. Else you could blow your speakers.

The reason ladder attenuators can make a clicking sound (they are very different from series step attenuators) is that they only put two resistors in the signal path at any time (this is why they sound the best). The two reistors form the voltage divider that reduces the volume level. When you change levels in a ladder circuit the MBB switch connects two sets of these resistor dividers together for an instant before it releases the first set. When both sets are connected the resistors have a reduced value (ohms Law) sometimes half of what a single set would have and the output signal level can jump a bit during these make-n-break transisitions. That's when you can sometimes here a clicking sound.

The great sound quality advantage of a ladder circuit (IMO) is worth learning how to handle the ladder attenuators. They are easy to master so don't be afraid of them.

I have never found a pot or transformer that sounds better than a good ladder attenuator. The simpler, just two resistors, the beter in audio.

guest1632 · « **Reply #7 on:** 25 Jun 2004, 04:37 am »

Quote from: Curt

All switches (in audio) are MBB (make before break), Hi Curt, That answers my question. A couple of the tour reviews mentioned the crackling sound when changing the settings. Just wondered if that could be an offset voltage somewhere. Ok, won't worry about it. thanks.including the Purist's ladder attenuator Swiss rotory switch. Else you could blow your speakers.

The reason ladder attenuators can make a clicking sound (they are very different from series step attenuators) is that they only put two resistors in the signal path at any time (this is why they sound the best). The two reistors form the voltage divider that reduces the volume level. When you change levels in a ladder circuit the MBB switch connects two se ...

Dan Banquer · « **Reply #8 on:** 25 Jun 2004, 05:34 pm »

I find that with the Elma Rotary Switches, which I believe are used on the DACT attenuators. that taking them apart and soaking them in isopropyl alcohol does a good job. I just did that to one of the Elma rotary switches I use for a stepped attenuator and it now works just fine. BTW: 91% pure isopropyl alcohol is readily available at your local drugstore for low money. Just don't drink it or you're going to wind up sounding like Nathan!

d.b.

Curt · « **Reply #9 on:** 25 Jun 2004, 05:51 pm »

Quote from: Dan Banquer

I find that with the Elma Rotary Switches, which I believe are used on the DACT attenuators. that taking them apart and soaking them in isopropyl alcohol does a good job. I just did that to one of the Elma rotary switches I use for a stepped attenuator and it now works just fine. BTW: 91% pure isopropyl alcohol is readily available at your local drugstore for low money. Just don't drink it or you're going to wind up sounding like Nathan!
d.b.

This won't fix a step "ladder" attenuator, stop it from clicking 100%. You can't change the circuit design by cleaning it

Cleaning a noisy "series" step attenuator switch may help. This type of attenuator should not make any noise during switching. They sometimes do if the switch is dirty.

BTW IRDs switch is custom made by Elma to our SPECs. They do make a pretty good switch.

JoshK · « **Reply #10 on:** 25 Jun 2004, 06:01 pm »

I have never been bothered by the Ladder attenuator in my Purist. Only if I switch inputs with the volume way up (sometimes I forget when switching from AV system), does it ever make a loud click. It is usually quite soft.

Dan Banquer · « **Reply #11 on:** 25 Jun 2004, 06:05 pm »

"This won't fix a step "ladder" attenuator, stop it from clicking 100%. You can't change the circuit design by cleaning it "
Don't get me started Curt, I was just trying to be helpful. It's Friday afternoon, and I have better things to do than cut your latest marketing to shreds.
d.b.

Curt · « **Reply #12 on:** 25 Jun 2004, 07:13 pm »

Quote from: Dan Banquer

"This won't fix a step "ladder" attenuator, stop it from clicking 100%. You can't change the circuit design by cleaning it "
Don't get me started Curt, I was just trying to be helpful. It's Friday afternoon, and I have better things to do than cut your latest marketing to shreds.
d.b.

Put your knife away Dan, don't cut me to threads

I ment no harm.

I'm not marketing, just browsing AC, and what I said is true.

I thought you, and some others, missed that Ray (who started the thread) was talking about a ladder circuit which is quite different (as you know) from a series circuit. With a ladder there is always some noise.

Enjoy your weekend.

Curt · « **Reply #13 on:** 25 Jun 2004, 07:27 pm »

My bad. Ray didn't mention a ladder in this post

Sorry about that.

I do believe know the preamp Ray is talking about (from our emails) and it does have a ladder circuit step attenuator.

Just want to point out all step attenuators are not the same.