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Old 29th January 2004, 03:05 PM   #1
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Default Cheap source/step'd-attenuator switches:

If you can handle 12 steps (or 11+"mute"), AllElectronics has surplus 1 pole/12-position rotary switches for $1.75 right now.

They also have 4-pole/3-position rotary switches for source selection at just $1.35.

Cheap way to experiment with a passive, stepped attenuated setup.

Scroll to bottom of the page here:

http://www.allelectronics.com/cgi-bi...425&type=store

These guys are surplus, so it may not last. Fixed $6.00 shipping (for small order/slow boat-style) so it may also pay to look thru some of the other small stuff there. Always fun to explore at All Electronics, anyway.

GnD
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Old 29th January 2004, 06:15 PM   #2
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Default I ordered one

a few months ago, after asking over the phone whether it was make-before-break... nobody could help me at that time so I ordered one anyway just to see, I usually order for about $50.

The one I got was break-before-make.... so not useable for a stepped attenuator. You could use it for a selector in- or out-put.

At least that's what I think, if anyone has another way of putting in use as a attenuator, let me know!!!!

And by the way, don't you need a 2 pole version for each channel?
I may be asking stupid question but my ineptitude is massive!


Jean-Pierre
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Old 29th January 2004, 06:17 PM   #3
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If you'll be doing your switching fast enough, it still might work in attenuator
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Old 29th January 2004, 06:21 PM   #4
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Default oh Peter.....

you are terrible,

you should see me handling my soldering iron.... shaking like a 120 year drunken sailor! and then you expect me to handle an attenuator swiftly?

hahahhahahahhahahahh




Jean-Pierre
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Old 29th January 2004, 06:30 PM   #5
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Default Serializing attenuators

Assume you want to have a master volume and a
separate adjustment for every channel (For example 0 to -10dB).

What would be the best way to add this to an amplifier?

Harry
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Old 29th January 2004, 09:23 PM   #6
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I can see break-before-make not working in the shunt configuration. It would briefly go to max volume between every setting. But why couldn't I use the stepped attenuator in series (with the series input resistor), heading into the input?

Starting with the high values (say 33k) and working down (with an open circuit in the very first position for a mute), would this work?
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Old 29th January 2004, 11:26 PM   #7
Alex S is offline Alex S  Singapore
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Quote:
Originally posted by GrahamnDodder
But why couldn't I use the stepped attenuator in series (with the series input resistor), heading into the input?
Yes, you could. i.e. switch the in-line resistor value and keep the shunt fixed. In fact I prefer this scheme to the more common shunt arrangement where the shunt value is switched.

By the way, re your original post, I have used these inexpensive rotary switches in the past (there are listed as "Midget rotary switch" in RS Component) and they worked pretty well.

One thing to note is: do not over-tighten the mounting nut. The plastic housing can flex and affect the smoothness of the turning mechanism.
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Old 30th January 2004, 03:45 AM   #8
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Default if that is correct

then I will go ahead and try it out...
i have the excel sheet to calculate the R value and also have one that Peter dropped us....


I will elt you know what happens!

J-P
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Old 30th January 2004, 04:36 AM   #9
Alex S is offline Alex S  Singapore
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Default Re: if that is correct

Quote:
Originally posted by uvodee
i have the excel sheet to calculate the R value and also have one that Peter dropped us....
J-P
I don't know what spreadsheet you're using... the end formulas are different for different attenuation schemes; BUT the basic principle is just a simple voltage divider - I hope you know what that is.

Also, for inverting configuration (IGC), the pin Vin- is at virtual ground, the input impedance is Ri (the feedback resisitor). Therefore the effective shunt value is the shunt resistor // Ri. If you don't understand what I'm saying, don't proceed.
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Old 30th January 2004, 04:44 AM   #10
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You get what you pay for. I've got a very nice looking, sealed Electroswitch unit. I've seen a photo of it on this forum, so someone else here uses the same model. I paid $25 each for four of them thinking I'd save money over the $$$ Elma units.

The one I kept (I traded away the others) has lots of contact bounce and some of the contacts do not always "make before break" as they should, resulting in static and intermittent function.

I'm ditching it for a $$$ Elma when I make my next order from Michael Percy.
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