Reusing analog VU meters from an old tape deck

[andante]

Has anyone tried to use analog VU meters from an 80's tape deck? These can be bought for pennies nowdays in working condition. I was thinking for putting them in a headphone amp, just for looks, not that it would serve any useful function. LED VU meter kits are plentiful, but there is nothing as cool as a set of analog ones.

It is my understanding that analog meters require a lot more circuitry then chip-driven LED ones, so I was wondering if a typical tape deck is designed in a way that would make it easy to rip out meters and use in your own amp.

 

[skyskraper]

doing my research on these meter a few weeks ago i came across this circuit http://www.mitedu.freeserve.co.uk/Ci...Audio/palm.htm

i was thinking about putting them on my m3, with a cmoy style preamp and a diode on the output of it

 

[rickcr42]

It is not the meter that is the limiting factor but end use.

Unless for purely decorative reasons you will need to consider meter ballistics and what it is being used to monitor or why then set the intial adjustments for the purpose.

"0 VU" means different things to different gear so the satndard you set is all about end use.

BTW-using an analog meter for average level monitoring and a couple of peak leds for the instantaneous monitoring will give you a very good idea exactly wqhat is going on with the signal but the requirements are way different for analog and digital so design accordingly.

 

[skyskraper]

here is a little bit of vu circuitry that i found in a book im reading atm:

can't really tell you much more about it apart from whats in the image. the +v is 9.4v at the v input of this circuit, im thinking that the vu meter it would have been used with originally would be a ballistically corrected bbc style number, i couldn't tell you though sorry! the 2n508 seems to be less widely available from some places, so you might want to look at the datasheet to maybe find a substitute thats easier to come across. the pot is to adjust the vu calibration, and the circuit it comes from gives the vu part an amplified signal, so maybe a simple op amp to give some gain to a non amplified signal would be the go?

rod elliot's page on vu and ppm meter's http://sound.westhost.com/project55.htm also has plenty of cool info.

 

[amb]

skyskraper, the circuit you posted is just a simple one-transistor amplifier (in common-emitter configuration). It can be used to drive a VU meter, but only if the meter has a built-in rectifier. Otherwise the needle is going to want to buzz up and down around the "rest point" (even hitting the left stop). Most stereo tape deck meters are not going to have built-in rectifiers, so the previous circuit you posted would be a more appropriate one.

 

[skyskraper]

could you not simply stick in a diode and have the same effect?

 

[amb]

Quote:

Originally Posted by skyskraper could you not simply stick in a diode and have the same effect?

Yeah, you could add a diode to the output, but it won't be within the feedback loop like the other circuit. Also, the output impedance of the one-transistor amp is a lot higher than the opamp circuit, so it won't have the fast attack/slow decay characteristics if you add the smoothing capacitor too. No big deal, though., for visual amusement the one-transistor circuit plus diode will work ok.

 

[skyskraper]

cool good to know the info

 

[cyteen]

More simple than the Rod Elliot version but with a pcb in the second link.

http://www.jlmaudio.com/AT51%20DIY%20VU.pdf

http://www.techniguitare.com/projets.../VU_PDF_TG.pdf