Vu Meter driver

[Spencerleehorton]

I happy to build anything as long as it works!!!
I want to try and keep it simple, feel free to suggest something which is better

 

[moamps]

i wondered why it wouldnt work!!, what a con! so i need to get 12v to pin 3 and 5 right?

It should work as a (not perfect) half way rectifier (with single power supply). More info you can find here:

https://e2e.ti.com/support/amplifiers/precision_amplifiers/f/14/t/246940

 

[PRR]

> It should work as a

The kit opamp will not work with input(s) at V-. There IS a "one opamp" single-supply full-wave rectifier which does a right thing, but it needs a to-ground-input opamp, it throws asymmetric loading on the source, and will not peak-catch the output (which we want when using sluggish non-VU meter movements). I didn't even use it as a power-line averaging monitor.

If we bias-up the inputs, the meter output sits at +6V DC, burning the meter.

It is at best a mis-translation of a dual-supply meter driver.

I bet for another 9 clams you could just buy another low-price kit that works.

 

[Martin Griffith]

It needs some ECC83 cathode followers to make the VU meter needles look warmer

 

[ruffrecords]

That schematic has SO many problems, I think they were kidding you.

And so many that I don't want to start re-designing a cheap bit of junk kit which cost less than a piece of my brain.

Is a bi-polar +/- supply available?

It is a single supply. I think it is the standard jlm audio schematic.

Cheers

IAn

 

[Spencerleehorton]

well if someone could post a working VU meter driver which does it the right way please?

 

[Martin Griffith]

Hi Spencer, Merry wotsits, really I'd go for the simplest, such as anything by Doug  Self( Must buy his book one day) from Google books https://books.google.es/books?id=pVIdAAAAQBAJ&pg=PA484&lpg=PA484&dq=doug+self+VU+meter+circuit&source=bl&ots=9AMcR57QTc&sig=TZFh-JsNpdT28y7suhXg6nuRXUg&hl=en&sa=X&ved=0ahUKEwig0L-Wk4_RAhWBmBQKHetkCxkQ6AEILjAC#v=onepage&q=doug%20self%20VU%20meter%20circuit&f=false figure 18.3 I'd never use a VU, since I was brought up properly and used BBC type PPMs in the real analog days

 

[Spencerleehorton]

Ah ok, yes this does look simpler, will give it a go and see if I can print out some single sided dual meter ones.

 

[protosardo]

i use this

 

[Martin Griffith]

Protosardo, that's pretty miserable, 100uF coupling caps are very excessive, and a 100K gain set pot will be all crunched up at one end when setting it up, and it will only work with a VU meter that has its own internal rectifier

 

[Jano1954]

Here is a pretty extensive description for a VU-meter buffer.
I build it and it works ;
http://diy-tubes.com/image/data/manuals/vu-buffer-1.2-en.pdf

And here is the build thread of the JLM Vu-meter buffer

http://www.jlmaudio.com/forum/viewtopic.php?f=2&t=239

 

[Spencerleehorton]

Thank you jano that's perfect!

 

[PRR]

> It is a single supply. I think it is the standard jlm audio schematic.

Are we looking at the same thing?

Obviously it is single supply (and apparently does not work that way).

It is only superficially like the JLM meter *buffer* in the link posted by Jano1954. The JLM properly re-biases the DC in and out. The JLM does not peak-catch, so expects a pretty lively meter movement.

Plan from diy-tubes.com is same as the JLM, minor cap-value changes.

Plan posted by protosardo does peak-catch, but wants bi-polar supply, and adds a buffer which may not be essential. (I also think the 100K trimmer is large, also the 100uFd caps, but that is details.)

 

[PRR]

The as-sold "VU board", with variations.

 

[protosardo]

.......................................
Plan posted by protosardo does peak-catch, but wants bi-polar supply, and adds a buffer which may not be essential. (I also think the 100K trimmer is large, also the 100uFd caps, but that is details.)

The buffer is essential for me; do I get to this circuit the input signal and output that I want to keep as much as possible free from unnecessary loads.
the value of 100 mF for me is a standard for block dc in the op
trimmer 100-K really is a detail, anyway the circuit I posted it currently use.

 

[moamps]

The as-sold "VU board", with variations.

Variants 3 and 4 will not work satisfactory because of presence of VD4, IMO. 

Spence,
if your Vu meter is real one (with incorporated rectifier) you just need a AC buffer and a resistor  at output. If your Vu meter is just a 1mA ampermeter (without incorporated rectifier) you should use a AC  buffer and a rectifier (as  JLM did, for example). 
AC buffer  can be designed with single or dual power supply.

 

[Spencerleehorton]

i have various different types of non rectified meters, i do need a way of testing them to establish what uA they are, could be 50uA-500uA or 1uA or 10uA?

 

[PRR]

> not work satisfactory because of presence of VD4

I agree VD4 is ugly. But how does it not work?

VD4 is there because the precision half-wave rectifier has significant bleed on the peak-catch cap. VD4 would appear to block this, while adding a 0.5V dead-zone. The bleed is "only" 10K, and a 1mA meter with resistor will be <1K, so I don't see a real point in adding VD4.

There's still multiple problems. Fingering individual parts without full understanding is not helping Spencer. Since I know better VU boards exist under $10, I'm not inclined to put $13 of brain-pain into it.

 

[PRR]

> testing them to establish what uA

It is highly unlikely you have any <50uA movements.

So put 50uA of DC through and see what happens.

9V battery through 180K is 50uA. (Meter movement resistance is a few K and hardly matters.

If that barely budges, tap 9V through 10K through it. A 1mA meter will read 90% (of full scale; the VU % scale goes over 100%).

 

[Spencerleehorton]

Ah ok, so I could use a selection of resistors to test with a 9v battery, that's nice and simple.