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Old 23rd February 2004, 01:46 PM   #1
Rookie is offline Rookie  Serbia
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Default Attenuation levels for stepped attenuator

Hi!

I'm planing to build a Gainclone with a 12-stepped attenuator for volume control. Which are the optimal values for attenuation? Are 6dB steps good choice?

Thanks
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Old 23rd February 2004, 02:00 PM   #2
HDTVman is offline HDTVman  United States
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Hi Rookie.

It's just my opinion but I think 6dB steps are to course. The attenuators that I've build I used 2dB steps for the first few and then went to 3dB for a while and then 4dB for the last few.

The 12 step switch is the problem. I would recommend trying to find a 24 position switch and giving yourself finer steps.

Like I said, it's just my opinion.

Later BZ
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Old 23rd February 2004, 02:45 PM   #3
Pedja is offline Pedja  Serbia
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Rookie,

Twelve steps are not a lot, so I think you cannot get the universal answer for your question. The answer will depend on the things like the source output level, amplifierís gain and speakerís sensitivity. But it can be tuned well enough.

Pedja
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Old 23rd February 2004, 04:22 PM   #4
Nuuk is offline Nuuk  United Kingdom
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This also depends on which Gaiclone you build. If building the inverted design, I strongly recommend the attenutor specified on my Gainclone FAQ page.
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Old 23rd February 2004, 05:30 PM   #5
BStrum is offline BStrum  United States
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Default On volume controls

I recently built an amp using LM3886s. It sounds great!!

I built a preamp using AD 825s which was very easy and really opened up the sound stage. Back to this at the end.

I went through the volume control selection process, the criteria where cheap and good. (both scientific terms) I first tried an ALPs 50K 34 step attenuator which I bought on e-bay (lots availble) for 15.00.

It really sucked - snap crackel and pop - blew up a test speaker (my fault). I could have gotten a lemon.

I then purhcaed 2 Noble Black Beautys, 31 step steroe vlume controls. These work GREAT - smooth and quite with 31 steps.

I paid 19.95 each on e-bay.

Now backe to the pre-amp...

I built a prototype on a jumber board.

I set the input resistors so that a 50K control gave a maimum gain of ~ 2.5 (22K which I had on hand) and tested using a regulated +/- 15 volt supply. Sounded good.

I then switched to two 9 volt batteries.....unbelievabel improvement!!!!!!!!!!!!!!!

Bill
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Old 24th February 2004, 02:19 PM   #6
GregGC is offline GregGC  Canada
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I do use 12 step MBB (very important) switch. I find 12 steps very good for me. The only thing is (as mentioned in the previous posts) that after you build it you'll have to find for yourself the optimum steps for the beginning of the attenuator. I havenít corrected it yet (it's still quite acceptable) but I need larger steps at the beginning of the range. I use a $3 cheapo MBB rotary switch and it works great. I wouldn't go to 24 steps especially if you have separate switches for the two channels. At the end it's a personal choice.

Have fun.
Those are the values that I use, but I need to decrees them for the first 3 steps. Still very good overall.
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Old 24th February 2004, 03:57 PM   #7
BStrum is offline BStrum  United States
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Default Gregs $3.00 MBB Switch

Greg,

Can you tell us the source for cheap 12 position (ideally 2 pole) MBB swithces you are using.

Thanks
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Old 24th February 2004, 04:34 PM   #8
Variac is offline Variac  United States
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Here's a nice calculator:

http://quadesl.com/attenuator.html

Anyone have an opinion about what a good value for total attenuation is in dB ?
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Old 24th February 2004, 04:42 PM   #9
Nuuk is offline Nuuk  United Kingdom
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Quote:
Anyone have an opinion about what a good value for total attenuation is in dB ?
How long is a piece of string?

It depends on what you are attenuating. Standard IGC, standard NIGC, buffered version, if so does the buffer have gain, gain of the amp etc etc.
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