Simple and inexpensive Passive Balanced Attenuator possible? - diyAudio
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Old 6th April 2010, 05:45 PM   #1
cersepn is offline cersepn  United States
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Default Simple and inexpensive Passive Balanced Attenuator possible?

Okay, i think i've pretty much read every thread there is to do with passive balanced attenuators here already, and i still have some more questions.

The cheap stepped attenuators that goes on ebay such as these -> 100 kOhm Stepped Attenuators, Qty:6 - eBay (item 160419314868 end time Apr-07-10 17:41:24 PDT)
seem to, accordingly to the guys here, have the clicking sound, that's out for me. I've read some posts here that detail how a balanced setup could be done with these attenuators but it doesn't get rid of the clicking noise.

The Goldpt 4 deck stepped attenuators are just a little more than i can afford, likewise with the DACT/TKD attenuators.

I've read the threads on the lightspeed attenuator as well, but it seems like he's out of stock for a balanced config. Same deal with the joshuatree.

What other options do i have? All i need is a true balanced volume control for use with one pair of monitor speakers that will give me almost perfect channel balance at all volume levels and not exhibit any funny popping/clicking sounds when i'm changing the volume. Would that be impossible to get for say, less than USD150?
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Old 6th April 2010, 07:27 PM   #2
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30 years ago I was a tech at Toshiba. They had stepped stereo volume controls. No clicking or zipper noise. These were switches with the reistive elements printed onto the boards and looked just like a stereo pot. From what I recall a 1.5-2dB step. I"ll try and get a part# for you.
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Old 6th April 2010, 08:01 PM   #3
Xoc1 is offline Xoc1  United Kingdom
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My stepped attenuators do not make any clicking noise.
If the switch contacts are make before break, then there should not be any noise when adjusting the volume.
It amost suggests that the previous user was using them in a DC coupled circuit with a small offset voltage. This would produce a switch click.
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Old 7th April 2010, 05:56 AM   #4
Calvin is offline Calvin  Germany
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Hi,

most switched attenuators suck, because of their highish and non -constant output impedance or because of low resolution, i.e. step-number count.
A clever solution to this is a low out-impedance switched resistor network that works in bit-wise stepping. You just need 6 switches (relais) for 63 equal steps, 7 switches for 127 steps.
A complete DIY solution can be found at Eijndhoven Family Home
You may calculate the resistor values for lower output impedance or take the values of Jos. The kit already features IR-commandability, so even comfort is high

jauu
Calvin
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Old 7th April 2010, 12:15 PM   #5
cersepn is offline cersepn  United States
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Thanks for all the suggestions. I found these
Balance XLR 23 Step Attenuator Potentiometer 100K Log - eBay (item 290419007537 end time Apr-27-10 05:53:28 PDT)

But i'm not sure how the wiring is done for a balanced config. Any ideas?
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Old 9th April 2010, 10:05 AM   #6
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The wiring diagram should be supplied by the vendor,it's very simple.

With that type of switch your input and output impedance will change with the position. A ladder atten. would take 8 sections instead of 4.

Google 'series', 'shunt', and 'ladder attenuator' for a better understanding.

Best, Bill
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Old 9th April 2010, 05:23 PM   #7
cersepn is offline cersepn  United States
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Quote:
Originally Posted by Bill Fuss View Post
The wiring diagram should be supplied by the vendor,it's very simple.

With that type of switch your input and output impedance will change with the position. A ladder atten. would take 8 sections instead of 4.

Google 'series', 'shunt', and 'ladder attenuator' for a better understanding.

Best, Bill
Thanks Bill. I did some more reading up and am still confused about the input and output impedance varying with position. What does that ultimately mean?

I came across another post here
http://www.vt4c.com/bb/viewtopic.php...7fa0faa2344a94
with "As most experts here will know, an attenuator for a 'passive preamp' is a completely different problem than for inside a preamp.

In a passive setup, you have the problem of balancing (compromising) between adequate load for your source & also minimising source impedance for your power amp. 10~15kohm pot is typically what passive guys end up trying." being particularly intriguing.

So if i'm reading this right, in my case where i'm using this attenuator in between my DAC and my active monitors, i should be looking to get a 10-15K instead?

Last edited by cersepn; 9th April 2010 at 05:36 PM.
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Old 10th April 2010, 12:32 PM   #8
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Yes, a 10k would be the best compromise as long as your dac output impedance is not too high. You could have trouble if it has a tube output stage, but even then, most would work fine. I misspoke in my earlier post, a series att has constant input impedance and would work fine except the signal has to pass through many series resistors, especially at lower volume positions.

The ladder is the best because there are only two resistors in the circuit at any setting, but it requires two switch sections for each signal line, so an 8 pole switch is necessary for stereo balanced.

The shunt has many good qualities but it's input impedance does change, and some output circuits don't respond well. You also lose some output from the dac even turned all the way up, so that would depend on the voltage your amps need and how loud you listen. Even with these limitations, it's worth trying because it is the simpleist and most cost effective way to make a balanced att. Erno Borbely has written a bit about their use, check out his website. For stereo, all you need is 4 resistors and a dual log pot or series att switch.

Best, Bill

Last edited by Bill Fuss; 10th April 2010 at 12:37 PM.
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Old 10th April 2010, 01:02 PM   #9
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At the Borbely site, go to 'kit upgrades' and click on 'components'
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Old 13th April 2010, 04:23 PM   #10
tvicol is offline tvicol  Romania
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We have opened a group-buy, but the interest is not so big as expected. :-(
Our passive r2r / shunt volume controller will support balanced mode as well.

GB for R2R audio volume / input selection pcb

Regards,
Tibi
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