TA7318P Vu meter driver, peak hold?

jtvrdy · Sep 17, 2013

Hi,
the vu meters from my Tascam M700 console are based on the TA7318P, I do not know if it would be possible to modify the circuit or change the op for show peak and hold it for a moment.

thanks,

PRR · Sep 19, 2013

> possible to modify the circuit or change the op for show peak and hold it for a moment.

No easy way. You have to replace everything around the TA7318P with something else, twice, and add a multiplexer to display both readings.

jtvrdy · Sep 21, 2013

then it would be easier to add a new circuit to display the peaks on separate leds, any schema examples?

bruce0 · Sep 21, 2013

jtvrdy said:
then it would be easier to add a new circuit to display the peaks on separate leds, any schema examples?

schematic in this post has peak hold.

VU/PPM/other meter - true full wave precision rectifier, separate adjustable rise and fall dynamics (VU/PPM/other), Peak hold or slower peak dynamics, or none.

The peak hold circuit section is highlighted at the top (third stage). Very common circuit concept (most of that section is duplicated but the top version is slightly different with all the bells and whistles and prevents the timing cap from leaking in peak hold mode). I think the source of the peak hold circuit is referenced somewhere in the schematic.

(Warning there is a bug in the LED chain in this circuit. but peak hold is fine.)

http://www.groupdiy.com/index.php?topic=47820.msg672944#msg672944

jtvrdy · Sep 24, 2013

thanks bruce0,

to have a faster release I suppose I need only change the C005 2.2uF to smaller value..
or need to change something else?

bruce0 · Sep 25, 2013

I didn't look at your schemo, but in the schemo I referenced "rise time" is controlled by R6 (the rise time on the clip hold section has no control and is as fast as possible), fall time is r7 and r8 for the main meter and clip hold section respectively. Changing the cap effects both rise and fall times.