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Old 7th January 2006, 12:36 AM   #1
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Default stepped attenuator

Hi all,
I've got an Eico HF-81 integrated amp. It's got a selector for input source and also a second 2 gang selector for amp1 amp2 stereo, reverse. etc. I would like to convert this second selector into a stepped attenuator for the aux input . I'm sure I can easily determine the contact workings of the switch but I'm not sure of the resistance values that would work best. My cd player puts out about 2v and of course some cds higher output than others. I really don't hear any actual clipping but sometimes it just sounds overdriven. Suggestions would be appreciated.
My plan is to run the aux output from the first selector to the proper spot of the second and then add resistors to the contacs on the switch itself. I could do a schematic if needed .


Steve
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Old 7th January 2006, 01:26 AM   #2
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Attenuators are made from shorting (make before break) switches, while selectors are made from non-shorting (break before make) switches. So, a reasonable idea falls apart.

An alternative to an auxilliary attenuator is to place padding resistors on the AUX I/P jacks. Pick a pair of resistors that total 10 KOhms. 5 K + 5 K would give you 6 dB. of extra attenuation. 3 K + 7 K would give you approx. 10.5 dB. of extra attenuation.
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Old 7th January 2006, 02:22 PM   #3
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I see what you mean. Could I put one or more different resistors on this switch in series using the lugs? If there was infact a momentary break in the input signal would there be potential damage??
Thanks
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Old 7th January 2006, 03:24 PM   #4
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I'm afraid the popping noises would cause damage. JMO, better safe than sorry.

Pick a fixed attenuation value that restores good functionality to the existing volume control circuitry. You are not alone in dealing with the "hair trigger" issue.

Do you have enough room to replace the non-shorting switch with a shorting part? Mouser catalog # 10WW026 is an Alpha 1 deck, 2 pole, 6 position device that costs $1.57. Catalog # 10WR027 is an Alpha 2 deck, 2 pole, 7 position device that costs $3.17.
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Old 7th January 2006, 03:49 PM   #5
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Thanks Eli
I have room so that makes alot of sense. I think I'll try several values like you suggest since I have a sub box and If I find more than one that I like, then I'll get a shorting switch and put it in. If one works good all around then I'll just stick it in the circuit at the jack.
Thanks alot

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