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Re: Analog meter driver...
Posted: Fri Jun 27, 2008 3:27 am
by Crusty
Hey Wayne,
Could you check the Rbias formula on page two on this data sheet?:
http://www.thatcorp.com/datashts/dn123.pdf
Looks like the parsing's not right...or should I still be bugging Frank Thomas with this stuff? LOL
Re: Analog meter driver...
Posted: Fri Jun 27, 2008 12:39 pm
by mediatechnology
Shoudn't it be Ibias= (2x1mA)+650 uA?
I think the eq below it should have two parenthesis in the numerator as well.
Re: Analog meter driver...
Posted: Fri Jun 27, 2008 1:16 pm
by JR.
Crusty wrote:Oh I don't know what I want, as usual.
In gerneral, I was thinking a ppm would be more useful for a preamp output than a vu; especially driving DAWs. I have a couple circuits borrowed from Neve for ideas. These will give, more or less, the standard BBC scale/ballisitics. (I wonder if they are really still valid for digital recording?...)
Circuit needs to drive an analog meter 1mA FS. I thought maybe a 2252 That chip could make an interesting and accurate driver for a linear scale.
Maybe I should just do vu-scale, as people are used to it. (I myself would be happy with no meter or clip light at all on a pre output, since it's sort of redundant to the recorder's metering.) Market research says otherwise...LOL
I agree Peak info is useful in the context of digital recording.
The PPM standard , something like a 4 mSec attack is useful to ignore very narrow impulses or transients.
I am also a fan of ave or rms to reflect apparent loudness.. while a mechanical meter is somewhat limiting with LEDs you can display both.
Back when I made consoles with mechanical meters I included peak LEDs in addition.
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I am currently working on a microprocessor that does the whole shebang inside, but this may be a bit much for the casual DIYer.
JR
Re: Analog meter driver...
Posted: Fri Jun 27, 2008 3:57 pm
by Crusty
Thanks John.
Should I
really be ignoring fast transients with digital recording in mind?
I'm sort of back to thinking about the linear-scaled idea with the detector/vca again. Or even maybe (don't cringe), driving it from a dedicated pic micro...
mediatechnology wrote:Shoudn't it be Ibias= (2x1mA)+650 uA?
I think the eq below it should have two parenthesis in the numerator as well.
I think if you follow the solve from left to right rule, it's o.k. to write that way. At least the answer's right on that one! LOL
Re: Analog meter driver...
Posted: Fri Jun 27, 2008 6:10 pm
by mediatechnology
I would have solved it that way but it could possibly be ambiguous. A few parenthesis doesn't hurt tho.
I'm an RPN guy. I bought an algebraic calc the other day as a spare and it's confusing (to an RPN guy) as hell.