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Old 30th April 2013, 10:32 AM   #21
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Quote:
Originally Posted by greenKnight View Post
Also optimising magnet size to angle increment so one relay closes as the next one opens will be difficult.
Couldn't agree more. I suspect using some steel yoke type arrangements to steer the magnetic flux where you want it may be required.
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Old 30th April 2013, 10:34 AM   #22
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And what total dynamic range do you seek?
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Old 30th April 2013, 11:45 AM   #23
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Quote:
Originally Posted by greenKnight View Post
Also optimising magnet size to angle increment so one relay closes as the next one opens will be difficult.
Not much of a choice, the Reed type determines whether to use H31, H32, H33 or H34.
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Old 30th April 2013, 01:19 PM   #24
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Sorry Jacco, I'm playing catch-up here. Your reference to the H31,H32 etc eludes me. Can you add more detail.
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Old 30th April 2013, 01:24 PM   #25
AndrewT is offline AndrewT  Scotland
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I use coarse attenuation jumps in a switched attenuator.
For fine adjustment, I find a continuous track vol pot much more convenient.

If very quiet, quiet, normal, loud, very loud, party level meets the listeners required range of SPL then a 6 step attenuator (-30dB to -0dB, or a bit wider maybe 10dB per step) would be good enough for me.
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Old 30th April 2013, 01:56 PM   #26
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Quote:
Originally Posted by greenKnight View Post
catch-up
Standard rectangular magnets for Reed switches.

Width x Length ;

H31 : 0.06'' x 0.50''
H33 : 0.12'' x 0.75''
H32 : 0.19'' x 1.00''
H34 : 0.24'' x 1.00''

Reed switch diameter sets the magnet type, e.g. an H31 is used for a 0.07'' body diameter reed switch.
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Old 30th April 2013, 09:20 PM   #27
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Thanks Jacco I understands now.
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Old 30th April 2013, 11:05 PM   #28
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Okidoki.

For an example, the Reed switches in the Weiss attenuator are Hamlin's smallest, Miti-3(V).
Glass body of 1.78-1.80 mm diameter x 7mm length (0.07/0.71'' x 0.276'')

So the magnets used by Weiss are H31 (specified at 5mm/0.2'' distance from the Reed switch).
0.06'' height of an H31 magnet leaves so little to grab hold of, so to prevent them from dropping off, Weiss wrapped a transparent sleeve around the bar that holds the magnets.

The magnets are also 7/32'' longer than the glass body of the Reed switches, so Weiss had to position them higher, magnet top is almost flush with the solder tabs of the switches.
See piccy =>
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Old 5th May 2013, 07:33 AM   #29
dheming is offline dheming  United States
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Thanks for all the feedback guys. Mercury wetted would be ideal, but as you mention they are way too expensive for the amounts required in this project. I've been looking at the various reed switch offerings and Hamlin seems like the way to go. Next step will be to choose a specific model and order enough to do a simple series attenuator first. Seems like the biggest challenge will be getting the mechanical aspects such as switch spacing and magnet choice just right to get a make-before-break action.

For the ladder attenuator version I'm thinking that stacking two SPST reed switches directly on top of each other for each step might work. I wonder how the magnet setup will have to be modified for that. This is where testing will be the only way to know what will and will not work. As was mentioned maybe some kind of steel yoke or surrounding each stacked reed pair with a small steel oval-tube sleeve would make them behave like a single DPST reed switch.

I'd like to have at least 60dB of total attenuation with 1dB per step. While doing professional audio work I tend to vary the monitor levels by quite a bit depending on what I'm doing. This is especially true when doing restoration and noise reduction work. When isolating noise sometimes I turn it way up then turn it back down to hear the result. So I'm all over the place which is why I'd like 1dB steps throughout the range. This is also why I want a tunable spring pressure on the detent. I would like a light amount of tension so that it can be turned up and down quickly.
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Old 12th May 2013, 04:00 AM   #30
dheming is offline dheming  United States
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Decided to go with the Hamlin FLEX-14 series for the first prototype. This is the specific one: FLEX-14 15-20 Hamlin Inc | HE556-ND | DigiKey

They should be here sometime this coming week. These ones have long leads so they will be much easier to work with than the first ones I got. Looking forward to playing around.
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