Analog meter driver...

Where we discuss new analog design ideas for Pro Audio and modern spins on vintage ones.
Crusty
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Analog meter driver...

Post by Crusty »

I need an analog meter driver for a preamp project. Meter is a linear 1ma FS unit.

I was thinking of a simple peak meter driver using the 2252, something along the lines of That design note 101:

http://www.thatcorp.com/datashts/dn101.pdf

The threshold control would adjust the lower scale reading, and overall gain (R7) would be the overall scale reading. Adjusting the Ct value would control meter attack, and C2 would be the hold time (maybe not really the way to adjust attack time?).

If you want to be fancy, input buffer could be a 1250, and could even drive meter differentially with a 1606...

Thoughts?
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JR.
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Re: Analog meter driver...

Post by JR. »

dbx used to make a nice stand alone meter with a huge dynamic range. If you combine the rms detector with a VCA configured as a 2:1 compressor, you will square the meter range, or double in dBs. While reading -90dB with a mechanical meter is a little questionable. :roll:

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Crusty
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Re: Analog meter driver...

Post by Crusty »

Yikes, I think the 20db or so before clipping would be enough for my needs - with maybe a separate led "signal present/clip" circuit on the front end. Seems like too high-performance part for this task, but the price is right...
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mediatechnology
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Re: Analog meter driver...

Post by mediatechnology »

How much dynamic range do you need? You want liner dB scaling with that order sir?
Crusty
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Re: Analog meter driver...

Post by Crusty »

Oh I don't know what I want, as usual. :roll:

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
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mediatechnology
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Re: Analog meter driver...

Post by mediatechnology »

How 'bout this one:

Image
Crusty
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Re: Analog meter driver...

Post by Crusty »

Thanks, it might work nicely. I'll find the Neve ones to post too.

What's with dropping the V- rail? Is it only because of the 30v Vceo of the BC184?..
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mediatechnology
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Re: Analog meter driver...

Post by mediatechnology »

Crusty - I think it is to stabilize the "reference" at the bottom of RV3 and the resistor string above it.

You could probably make a simpler FW rectifier/peak detector.

I like this one:
Image

The inputs to the comparators are anti-phase.
Crusty
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Re: Analog meter driver...

Post by Crusty »

Thanks for the ideas, Wayne!

Oh, did I mention I have a single 60V rail to work with? :P
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mediatechnology
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Re: Analog meter driver...

Post by mediatechnology »

Not shown in my little block above is the polarity inversion at one of the LM339 inputs for FW peak detection. I think I have a better drawing somewhere.
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