Quote:
Originally Posted by Edwood  Great to see an update to the DA10.
But why still no proper volume knob? Even with a rotary encoder, it would still be much better than a toggle switch.
That toggle switch stands in the way of the DA11 being a perfect standalone product.
-Ed
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Here is why:
The matching between channels is far better (!) then a dual analog pot,
And it holds its accuracy over the whole range. Say you want 60dB range. That means 1000 to 1 resistance range. Now take 2 pots and mount them on a single shaft (dual pot). The mechanical tolerance plus the resistor matching needs to be at least 10000 to 1 to get 10% matching over the range... The results are way off the mark. I could add fuel on the fire by mentioning that the pot resistance is semi logarithmic curve...
Now, with my scheme, you get .1dB absolute accuracy over the whole range, and the matching between channels is even better then that.
Also, unlike analog potentiometers, when you set the gain with a digital display, you get reliable and predictable level (such as 56 mean 24dBu, 55 means 23dBu...). When you move an analog pot, you lose the calibration. Some people want such accuracy (mastering engineers, hearing tests labs and others)
Digital attenuation also provides accuracy but digital attenuation causes loss of bits (around 1 bit loss for each 6dB attenuation). When attenuating by analog means, you do not truncate digital bits.
Also, the digital controlled analog attenuation does not have the wear and tear of a mechanical pot:
With analog pot, the signal itself passes through the pot contact (friction between a conductor and the resistive material).
With a switch, the contact resistance can deteriorate to 100 Ohms (don't worry it will not happen), and everything still operates like new. The switch does not pass analog, it is just an "up one" or "down one" command.
Rotary encoder is also a friction based device, and while not as bad as a pot, it does pass the signal and it does wear out over time. Doing a rotary for 56 positions at 1dB steps may not be practical. Some analog attenuators use 2 rotaries, such as for 1dB step and the other for 10dB steps. Say your setting is at 20dB and you want to change it to 19dB. You first need to attenuate to 10, then you need to do 9 steps to 19dB... This is not user friendly way... The switch is better - note that the switch controlled volume speeds up when you hold the switch up or down.
The digitally controlled analog attenuation is much costlier then a dual analog pot. I chose that method for the above reasons.
I will be out for a few days, going to give a lecture at AES (Audio Engineering Society) in Mexico City.
Regards
Dan Lavry
