How many steps in custom ladder attenuator - diyAudio
 How many steps in custom ladder attenuator
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 20th February 2003, 08:05 PM #1 diyAudio Member     Join Date: Mar 2002 Location: San Francisco, USA How many steps in custom ladder attenuator Greetings prophets. I am building a ladder attenuator for my preamp, using a rotary encoder, some logic, and relays. I wonder how many steps I should include. I have always used 24-position switched, which has never been enough, but I don't know how many might be "enough". The attenuator is two channels, and adding a step costs a few marginal dollars. Groups of eight are convenient, because of the 8-bit shift registers I am using, so I am considering 32, 40, or 48 steps. Schematics, artwork, and source code will of course be added here when I am done. P.S. Hifi, someday I will finish those drawings and send them to you. Have patience!
 20th February 2003, 08:14 PM #2 The one and only     Join Date: Mar 2001 In my experience, 32 is plenty, but you want it to go down to about -60 dB at the next to bottom versus the max. This results in 2 dB per step. We do this, but we have to use a nonlinear set of values and a look up table to keep the resolution per step.
 20th February 2003, 08:17 PM #3 diyAudio Member   Join Date: May 2001 Location: London UK Re: How many steps in custom ladder attenuator The attenuator is two channels, and adding a step costs a few marginal dollars. Groups of eight are convenient, because of the 8-bit shift registers I am using, so I am considering 32, 40, or 48 steps. --------------------------------- Go for the 48 steps; even with 31 steps, I am always fiddling with the volume control. I often wonder how people can use 24.
 20th February 2003, 08:26 PM #4 diyAudio Member   Join Date: Nov 2002 Location: Florida My preamp has, I think, 24 steps which, for me, is fine. What helps is that the preamp also as an attenuation switch. By flicking that switch, the volume drops down - one can use this to answer the telephone and when done talking, flip the switch again and not have to redial in the volume setting you once had. What also works is that you can flip the attenuation switch on, and increase the volume setting, and get a finer resolution in volume settings. This only works for the lower volume levels, but I doubt this would be a problem, as this is where you would want greater resolution anyway. In effect, this technique gives a 24 step volume control extra steps.
 21st February 2003, 06:56 AM #5 diyAudio Member   Join Date: May 2001 Location: London UK What also works is that you can flip the attenuation switch on, and increase the volume setting, and get a finer resolution in volume settings. This only works for the lower volume levels, but I doubt this would be a problem, as this is where you would want greater resolution anyway. In effect, this technique gives a 24 step volume control extra steps. [/B][/QUOTE] ------------------------------- A shunt attnauator should be fine, but anything else in the signal path is not desirable ie. switch contacts.
 21st February 2003, 09:19 AM #6 diyAudio Member     Join Date: Aug 2001 Location: Ingolstadt Germany I once used a 24 step with per step 1dB + a 3 position switch with 3 x 24dB attenuation. For me the 1 dB steps were really too small and after a while I always used three or more "clicks". Now I´ve got a 24 step ladder with 3 dB steps wich get a bit coarser below -60dB and am very satisfied. For me smaller steps are not neccessary. william __________________ een ooievaar is geen konijn want zijn oren zijn te klein!
 21st February 2003, 12:15 PM #7 diyAudio Member     Join Date: Jul 2002 Location: Toronto, Canada I'm also using 24 steps and it's enough for me. __________________ www.audiosector.com “Do something really well. See how much time it takes. It might be a product, a work of art, who knows? Then give it away cheaply, just because you feel that it should not cost so much, even if it took a lot of time and expensive materials to make it.” - JC
 21st February 2003, 06:08 PM #8 diyAudio Member   Join Date: Mar 2002 Location: USA One could build the attenuator that looks more like a "relay DAC" that has far more steps than the number of relays because certain attenuations are the result of closing more than one relay simultaneously. I think that this is what Nelson was trying to say. In fact, I designed a shunt attenuator using 16 relays that would do 0.125dB steps over a range of 0->60 db. This could be done with readily available Vishay resistors. Even 0.1% relays could be used if you had a way to calibrate the attenuator and build the ROM lookup table. Maximum error at any setting can be less than 0.05 dB Siegfried Linkwitz maintains that the better the accuracy of your audio system, the more you need to set volume to the "correct" level. And he's one smart cookie! This would argue for better resolution than the standard 24-position attenuator. __________________ bel
 21st February 2003, 07:03 PM #9 diyAudio Member   Join Date: May 2001 Location: London UK In fact, I designed a shunt attenuator using 16 relays that would do 0.125dB steps over a range of 0->60 db. This could be done with readily available Vishay resistors. Even 0.1% relays could be used if you had a way to calibrate the attenuator and build the ROM lookup table. Maximum error at any setting can be less than 0.05 dB Siegfried Linkwitz maintains that the better the accuracy of your audio system, the more you need to set volume to the "correct" level. And he's one smart cookie! This would argue for better resolution than the standard 24-position attenuator. [/B][/QUOTE] ----------------------------------------------- I agree; is your design published anywhere? With my system, I like to set to at least 1dB and would prefer 0.5. This gets the soundstage just right .
 22nd February 2003, 12:13 AM #10 diyAudio Member   Join Date: Mar 2002 Location: USA Nope, not built nor published. To be able to do w/o VERY expensive resistors (0.005% Vishays at unique values) would require laboratory standard AC calibrator. Lost access to that before I was able to assemble and test the project. Someday... __________________ bel

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