Rank: Member
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Joined: 2/3/2014(UTC) Posts: 3 
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Hi
I plan to build an 8ch DSP with integrated DAC and consider using BuffaloIII.
Since my gear and drivers constantly varies in the projects, I want to have analog gain control implemented on the analog output stage. The gain control should be individual for each channel or working in pairs and have step attenuation from 0 to -12/18dB. No need for remote control other than 9018 internal master volume.
Since gain can be adjusted by R1-R4 and R13-R16, can you recommend resistor values with that gain range in 0.5dB step?
Is it advisable to implement gain control this way or would you recommend other solutions... i.e. how will it affect THD and noise.
Yours sincerely
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Rank: Administration
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Joined: 10/24/2006(UTC)
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Generally speaking, you want your feedback loops as short as possible. Extending them can easily lead to oscillation/instability and noise injection.
Controlling it digitally would be the best approach.
One solution would be to control the volumes of the individual DACs as well as master volume. This woudl require some customer firmware and/or an external controller.
What are you using for DSP? Many DSP modules allow you to tailor the individual output channels, which you could do when you switch hardware setups, then just use the DAC's master volume.
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Rank: Member
Groups: Member
Joined: 2/3/2014(UTC) Posts: 3
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Thanks for you reply! The extension of the feedback loop is also my concern, hence the question. I was thinking about having the attenuator/resistor cluster mounted just above the PCB to keep the wiring as short as possible. An easier and better implementation would perhaps be having a balanced analog volume controllers on the IVY outputs? I'm looking at the MiniDSP MiniSharc. No problem with individual level control in this one, but I want to keep most of the controls in the analog domain. I would even prefer having the master volume implemented by means of analog attenuation. It has nothing to do with fidelity, but simply to avoid human or software error when fiddling with precious compression drivers worth 1000's of dollars. I've experience it more than once that full signal and full bandwidth have been fed to the mids and tweeters, last when using a "high end" multichannel ESS9018 DAC with an unstable digital volume controller. Therefore I want to make the DSP crossover as "idiot proof" as possible... to protect me against myself ;) Your recommendation for a proper implementation is therefore highly appreciated. Yours sincerely Edited by user Tuesday, February 4, 2014 8:56:01 AM(UTC)
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