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diyAudio Member
Join Date: Mar 2002
Location: San Francisco, USA
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Jordan, I took a look at ftorres' cascaded ladder attenuator design. I agree that his has superior usable range, but it also uses twice as many relays! After reading his article, I don't buy his logic about not doing the make-before-break when the LSB does 000->111 or 111->000. Unless my calculations are wrong (again), I think you can engage, for example, -70dB and -60dB dividers simultaneously to produce a -66.7dB divider of 25.0KΩ and 11.5Ω. You can also engage the 0dB and 8.75dB dividers to produce 0dB (duh). So, if you are going from -70dB to -68.75dB you stop by -66.7dB on the way there. Not too bad of a jump, I don't think.
Similarly going from -20dB to -18.75dB takes a stop at -25dB. Not too bad of a bobble. Certainly it isn't as bad as if you just let the relays flop, in which case you would go to mute between each setting.
The actual problem comes in when you are going from -10dB to -8.75dB. In this case you make a stop by -0dB on the way! This could be avoided by using separate latches for each bank of relays, and controlling their timing separately.
Finally I noticed that the -10dB divider seems wrong. It should be 34KΩ and 16KΩ, not 60.4KΩ as marked in ftorres' drawing.
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