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Re: DAC I/V conversion

68.100.112.131

Posted by Pooge on June 26, 2004 at 12:14:40

In Reply to: Re: DAC I/V conversion posted by Dave Davenport on June 26, 2004 at 10:02:00:

Dave,

I realize the last thing you need in this stage of product development is my kibitzing, but if, for example, the OPA660 I/V suggested by Thorsten works well, it could be a low cost, on-board implementation to get started with, without throwing away too much money to bypass it later to a different output stage. For minimal addition, you might be able to get a lot more boards sold initially that would be fully complete and working. Then, people could choose to spend money to upgrade later. I think more people would feel more comfortable with a smaller initial investment. The more people that buy the initial board, the bigger the market for the upgrades. Of course, if these cheaper alternatives are terrible, that would not help your image, so I could understand if that is not something you would want to do. But if they still give you a great sound as good as anything else, it's not bad for a start. But you have already invested a lot of time and thought, so I also understand your desire to get off the pot.

I haven't even studied the OPA660 to know how it works. It is a transconductance device, not an opamp or transimpedance. The data sheet shows a common base application, but I haven't yet even studied how Thorsten connected it up, or even what kind of load it creates. It is a very high frequency (100Mhz) device though, and includes an output buffer for basically a one chip solution. Also, I haven't seen a voltage tolerance spec for the PCM1794. It could be that a small I/V resistor would be entirely within the spec. If so, maybe it could be filtered with a parallel cap before a decent opamp as another alternative.

In my situation, your passive output has a too high output impedance for my TVC. The tube unit would not be something that I would spend that much for as an initial investment. That leaves me looking for an alternative right up front--which takes time--which would delay my purchase of the DAC, etc.... But then, most people don't have TVCs, so the passive stage might be fine for them.

Although the DAC current output at the edge of the boards allows many alternatives for the best options, I believe that a board with onboard, disableable I/V conversion, rather than a required add on, could be a better seller, and create a larger market base for your upgrades. But you've probably already mulled this over and made your decision, and want to get out what you have. It sounds like you are at the stage of board development where you don't want to do this, so I understand.

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