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The Joshua BOM lists 90.9R/6k81 (R4A/R6A) and 200R/3k74 (R7A/R9A) for the second and third stage (relay) dividers, but these calculate to -0.115dB and -0.452dB attenuation instead of -1dB and -2dB steps I'd expect.
Maybe the resistor values are mixed up or am I wrongly assuming -0.5dB/-1dB/-2dB/-4dB etc. steps?
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The JT has 128 .5dB steps (-64dB max). The thing to remember is that it's a binary progression through the divider pairs, not one pair per step.
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Is there any support for Joshua Tree Attenuators with a different output impedance?
I see people asking for this but you offer the (750ohm) so I was trying to do some math so I could change the resistors.
In checking the math, a few of the JT relay steps appear wrong:
I calculate-0.5dB/-0.12dB/-3.72dB/-1.73dB/-5.62dB/-14.7dB/-31.8dB
Binary steps would be: -0.5dB/-1dB/-2dB/-4dB/-8dB/-16dB/-32dB
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I think you are misunderstanding me. The steps are like this:
00000000
00000001
00000010
00000011
00000100
.
.
.
Each bit representing a relay and it's associated resistors.
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Hi Brian I'm controlling the Joshua Tree with arduino I2C bus (Hifiduino), and wish to confirm the following: Maximum volume = 255 Maximum attenuation = 128 Mute = Any number below 128 I guess the steps are correlated, ie 255-254-253-252-............-128 Thanks Edited by user Saturday, August 25, 2012 6:19:23 PM(UTC)
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You have the right idea. :) Any time the 7th bit is not set the JT is muted.
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