DC Meter for audio

Hello all,

A little sideline topic related to my preamp project. A few weeks ago I managed to get hold of an old Sifam Peak Signal Level meter with the intention of eventually replacing a broken VU meter with it. The one I've got looks a lot like the type that were used on old Ferrograph series 2 machines - as some may know, these meters are 'backwards'. It's 1mA FSD (tested it and it's pretty linear) but the needle rests on the '10' and moves towards the '0' as input gets closer to 1mA.

I assume there's circuitry involved to drive it (ECC82 comes to mind from a Ferrograph schematic) but I was wondering if it would be possible to utilise it so that it rests at 0 and responds to an audio signal to give an indication of the signal. I don't need this to be accurate to any degree, I just need to see a visual representation of the sound that I can calibrate to give me an idea of where the signal might clip. I have a Ferrograph recorder that uses a very similar meter, which sits at 0 (adjustable) when powered up but returns to 10 when powered off.

If it's going to be a difficult job I might be better looking for something else!

Cheers

I examined the manual from my series 6 ferrograph and in that machine, the meter appears to be driven by half of an ecc83, and there's also a '1S130' rectifier involved. I think there's also a pot (1k comes to mind) to set the zero.

Also found this but not sure if it's relevant here http://www.giangrandi.ch/electronics/vu-meter/vu-meter.shtml

The "reads max when dead" meters really suggest they go in the plate circuit of a variable gain tube with AVC around it. At idle the tube works high gain thus high current, say 10mA. Signal causes the AVC to bias the tube more off, toward 1mA and "0"mA. The point is that common radio IF tubes have a near log response this way.

This is meant for an original BBC PPM type circuit using valves.  IIRC, Great Guru Baxandall published a circuit using valves in Jurassic times.  Search old Wireless World articles for GGB's preamp stuff.

If you want to use 'modern'  circuitry, just turn it upside down so it looks right.

This is meant for an original BBC PPM type circuit using valves.

Search for MNA/3 in the Beebs R+D site (lost the address)

> Search for MNA/3

http://www.bbceng.info/ti/eqpt/C_9.pdf

That's for the input folks. Might be a bit beyond my ability for the moment but I'll have a read through