EM83 VU Meter

[Heffa]

I want to use a EM83 as a VU meter on my next amp, an OTL headphone amp.
Today I threw together a test, using this schematics I found somewhere:



It kind of works, but the sensitivity is waaaay to low, so it only displays a small flickering when I play music to the inputs.
Has anyone here used a tube like the EM83 for a VU meter before? How can I increase the sensitivity? Should I try to use some kind of op-amp to increase the voltage swing of the signal?
All feedback is appreciated

 

[Lavane]

Ive seen what looks like op amps used in a few of the kits I've seen for sale. Some even put up a schematic along with pictures of the kits. Maybe look up some of the kits and see what's on the board? The kits using that type of tube tend to be more expensive than the the ones that use the tubes with the straight bars that light up.

 

[Tubologic]

The EM83 is not sensitive enough for your application and there's no way to increase the sensitivity without adding an extra voltage gain circuit. It can be done with opamps but then you'll need an extra low voltage power supply to feed the chip. Or you can use small signal high voltage FET's which can be powered by the EM83 B+ supply. Or (why not) a tube... The design below use both (no schematic included) but looks quite complex for what it does:

https://www.simonlaw.com.au/electronics/em83-vu-meter/

 

[Heffa]

The EM83 is not sensitive enough for your application and there's no way to increase the sensitivity without adding an extra voltage gain circuit. It can be done with opamps but then you'll need an extra low voltage power supply to feed the chip. Or you can use small signal high voltage FET's which can be powered by the EM83 B+ supply. Or (why not) a tube... The design below use both (no schematic included) but looks quite complex for what it does:

https://www.simonlaw.com.au/electronics/em83-vu-meter/

Thanks, I have seen this design before but as you said it seems unnecessary complicated.
I think I will start with some op-amp circuit first, might even pick up a small board from eBay or such and try that first. I'll use a simple voltage doubler from 6.3V to 12-14V or so to power it.

 

[gadget73]

Sounds like the perfect use of a twin triode tube to me. No need to fuss with low voltage supplies that way.

 

[Heffa]

Sounds like the perfect use of a twin triode tube to me. No need to fuss with low voltage supplies that way.

I will look more into this as well - problem is I don't think I know enough of tube topology yet to design this myself, bu there is plenty of schematics out there.
If I understand the few datasheets available on EM83 they would like 0-8V swing on the grid, so that's why my music signal was too low.
A gain of 8-10 or so is probably enough to drive the EM83 correctly.

or, I might very very well have misunderstood it entirely. Anyway, I will have to test it more

 

[gadget73]

If you only need that much, a 12au7 or any other low-mu twin triode thats handy will do. There are some charts for common resistance coupled amps that will tell you what plate and cathode resistors to give whatever amount of gain is needed. Mostly it depends on what supply voltage you have available.

 

[Heffa]

If you only need that much, a 12au7 or any other low-mu twin triode thats handy will do. There are some charts for common resistance coupled amps that will tell you what plate and cathode resistors to give whatever amount of gain is needed. Mostly it depends on what supply voltage you have available.

Thanks, I will try to find some of these chart and look into it more.

 

[Heffa]

After some testing with a couple of different tubes, I finally got it to work today - i amplify the music signal with an ECC81 preamp stage, and now my EM83 works as I intended, as a VU meter

My prototype is a horror to look at though, good thing I am completely alone in my mancave - wouldn't want to risk anyone touching anything here...

 

[trainbuftony]

Nice work.
When I prototype out the same basic thing I also determined than an additional gain stage was needed and i used a 12AX7. I ended up giving that unit to a friend who wanted to try a low power single ended amp. It was just a simple 2 stage single ended amplifier but instead of conventional power tubes, I paralleled the sections of a 6sn7 and used that to drive a standard console pull output transformer. Truly a junk box build.
Oh geez I've gone and woken up a zombie thread.
You should be careful they'll suck your brains out, I'm probably safe, but you should be careful.