HELP with DIY ladder attenuator !!!!!
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 2nd July 2011, 02:07 PM #1 mcgreg66   diyAudio Member   Join Date: Nov 2010 Location: Berlin HELP with DIY ladder attenuator !!!!! Hi, I want to built a 24step 100k stereo ladder attenuator with this switch - 4 pole 24-step Attenuator / Potentiometer *GOLD Plated* bei eBay.de: Video Cables Connectors (endet 09.07.11 03:15:16 MESZ) for a KT88 SE tube amp For calculating the resistor values I used this website Stepped Attenuator Resistor String Calculator - Neville Roberts Question 1....... I wonder about the strange resistor value steps between step 6 and 8..are they correct...?! Step 6 and 8 are nearly the same and I need to use the same resistors as I surely don't find the exact values!!!! Step 1, Attenuation = Infinity dB, Rx = 100000 ohms, Ry = 0 ohms, Resistor = 0 ohms. Step 2, Attenuation = 66 dB, Rx = 99950 ohms, Ry = 50 ohms, Resistor = 50 ohms. Step 3, Attenuation = 58 dB, Rx = 99874 ohms, Ry = 126 ohms, Resistor = 76 ohms. Step 4, Attenuation = 51 dB, Rx = 99718 ohms, Ry = 282 ohms, Resistor = 156 ohms. Step 5, Attenuation = 45 dB, Rx = 99438 ohms, Ry = 562 ohms, Resistor = 280 ohms. Step 6, Attenuation = 41 dB, Rx = 99109 ohms, Ry = 891 ohms, Resistor = 329 ohms. Step 7, Attenuation = 38 dB, Rx = 98741 ohms, Ry = 1259 ohms, Resistor = 368 ohms. Step 8, Attenuation = 36 dB, Rx = 98415 ohms, Ry = 1585 ohms, Resistor = 326 ohms. Step 9, Attenuation = 34 dB, Rx = 98005 ohms, Ry = 1995 ohms, Resistor = 410 ohms. Step 10, Attenuation = 32 dB, Rx = 97488 ohms, Ry = 2512 ohms, Resistor = 517 ohms. Step 11, Attenuation = 30 dB, Rx = 96838 ohms, Ry = 3162 ohms, Resistor = 650 ohms. Step 12, Attenuation = 28 dB, Rx = 96019 ohms, Ry = 3981 ohms, Resistor = 819 ohms. Step 13, Attenuation = 26 dB, Rx = 94988 ohms, Ry = 5012 ohms, Resistor = 1031 ohms. Step 14, Attenuation = 24 dB, Rx = 93690 ohms, Ry = 6310 ohms, Resistor = 1298 ohms. Step 15, Attenuation = 22 dB, Rx = 92057 ohms, Ry = 7943 ohms, Resistor = 1633 ohms. Step 16, Attenuation = 20 dB, Rx = 90000 ohms, Ry = 10000 ohms, Resistor = 2057 ohms. Step 17, Attenuation = 18 dB, Rx = 87411 ohms, Ry = 12589 ohms, Resistor = 2589 ohms. Step 18, Attenuation = 16 dB, Rx = 84151 ohms, Ry = 15849 ohms, Resistor = 3260 ohms. Step 19, Attenuation = 14 dB, Rx = 80047 ohms, Ry = 19953 ohms, Resistor = 4104 ohms. Step 20, Attenuation = 12 dB, Rx = 74881 ohms, Ry = 25119 ohms, Resistor = 5166 ohms. Step 21, Attenuation = 9 dB, Rx = 64519 ohms, Ry = 35481 ohms, Resistor = 10362 ohms. Step 22, Attenuation = 6 dB, Rx = 49881 ohms, Ry = 50119 ohms, Resistor = 14638 ohms. Step 23, Attenuation = 3 dB, Rx = 29205 ohms, Ry = 70795 ohms, Resistor = 20676 ohms. Step 24, Attenuation = 0 dB, Rx = 0 ohms, Ry = 100000 ohms, Resistor = 29205 ohms. Question 2 Some DIY tell that they order many more pieces of one resistor value to measure and select them for exact channel balance... Is this really necessary if I'm using high-quality resistors like Kiwame or Shinkoh?! And... Question 3 How to calculate the max attenuation needed?! Sometimes it starts with -65dB sometimes with -75dB?!? Depends on power of amp?! Triode mode: 5+ watt output per channel Ultralinear mode: 10+ watt output per channel And efficiency of the speakers (89dB)?! Thanks for HELP!! Gregor
 4th July 2011, 11:45 AM #2 sregor   diyAudio Member   Join Date: Jan 2006 Location: massachusetts Q1 - the steps are not all the same - starts out at 8 db, then gets smaller until step 8, where it is 2 db. Q3 - the simplest way is trail and error. Other factors would be listening volumes and habits, back ground noise, personal choice. You are looking at the volume at the lowest step - my own experience is that I never listen to music on the lowest position, so it is kind of not a factor. YMMV. __________________ Steve

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