Michael Fearnley's vu meter driver circuit

Status
This old topic is closed. If you want to reopen this topic, contact a moderator using the "Report Post" button.
Michael Fearnley's vu meter driver circuit - How does it work?

Hi,

Recently I have read Michael Fearnley's article about vu meter driver circuit at the Objective Sounds website, and found it very interesting. I then simulated it with single rail power supply, and assembled the circuit. However, the actual circuit is not working as expected. There is not signal at the meter terminal. Can somebody help to point out where could I go wrong? Thanks a lot.
JC1969UVmeterDriver_DCIN_Simulation.png

JC1969UVmeterDriver_DCIN_SimulationWaveform.png

VUMeter_MichaelFearnley.png


Jazzclassics
 
You need to bias the opamp's input at 2.5V with a divider.

Note that 5V supply is not sufficient for a TL0XX. You should use a TLC271 for example.
Thank you very much Elvee. I am actually using LM358 in place of the TL082. Is that a 20K/20K divider at the opamp's positive input ok for bias it?

attached is the LM358 datasheet. View attachment LM358-D.PDF

Jazzclassics
 
hi Sajti, thank you for your suggestion. Could you be more specific where to put that cap? Or maybe post an example circuit. I am lost here why i need a cap to block the DC in the feedback path, because I have not come cross such a circuit. Please enlightening me further.

Hi,

I see on Your picture: C3 is the mentioned capacitor. Sorry, I just checked the original schematic. It will be OK with the divider, and C3.

Sajti
 

PRR

Member
Joined 2003
Paid Member
....Michael Fearnley's article about vu meter driver circuit at the Objective Sounds website....

It would have been kinder for all to link to the article you were reading, so we would know what you were talking about, and spot possible confusions.

Driving VU and other AC Meters - Simple High Performance Circuits

His "VU meter" circuits *omit* input and power connections. They do not work as shown.

His Fig 8, "Universal Volt-meter with selectable...." *does* have the input and power and bias connections completely detailed. Use that power/bias scheme to power-up the VU meter plan. The input needs a resistor to the C3 C2 node.
 

Hi Mchambin,

thank you for your suggestion. that looks a simple circuit. Have you built it? How did it work?

I wonder that using one opamp is the simplist and cheapst way to drive two vu meters in a stereo setup. Do you think any of Michale Fearnley's circuit good to build? And I see many commercial circuits on ebay. Do you think any of them good to use?

I see you are using LTspice. Here I attach the simulation file for you to play with and if possible, feedback your valuable comments. Thank you.

JC1969UVmeterDriver_DCIN_SimulationWaveform.png

JC1969UVmeterDriver_DCIN_Simulation2.png

View attachment VUmeterDriver_SingleRail.zip
Jazzclassics
 
It would have been kinder for all to link to the article you were reading, so we would know what you were talking about, and spot possible confusions.

Driving VU and other AC Meters - Simple High Performance Circuits

His "VU meter" circuits *omit* input and power connections. They do not work as shown.

His Fig 8, "Universal Volt-meter with selectable...." *does* have the input and power and bias connections completely detailed. Use that power/bias scheme to power-up the VU meter plan. The input needs a resistor to the C3 C2 node.

Hi

thanks for your post. Please could you point out how to make the circuit work? The simulation file is at the below link.

https://www.diyaudio.com/forums/sol...ys-vu-meter-driver-circuit-2.html#post5680877

Jazzclassics
 
Hi Mchambin,

thank you for your suggestion. that looks a simple circuit. Have you built it? How did it work?

I wonder that using one opamp is the simplist and cheapst way to drive two vu meters in a stereo setup. Do you think any of Michale Fearnley's circuit good to build? And I see many commercial circuits on ebay. Do you think any of them good to use?

I see you are using LTspice. Here I attach the simulation file for you to play with and if possible, feedback your valuable comments. Thank you.

Jazzclassics
This was built for 4 microphones preamplifier. This worked perfectly good right away.
The 4 Vu meters monitor the preamplifiers on the 4 XLR output connectors. We used cheapo chinese Vu meters ( 650 ohm ) for their vintage look.
Later I figured, 4 diodes is overkill, a single diode would do the job as well.
 

PRR

Member
Joined 2003
Paid Member
It MUST be rectified. Yes, it should have NO capacitor.

Correct.

The original old time Vu meter .... with a germanium diode.

The true VU meter used Copper Oxide rectifier.

For lack of any other great need, copper oxide rects have vanished from the market. Ge diodes are a poor replacement. Your higher-Z driver in the other thread is a good simple hack. It does not give proper damping for true VU meters, but you won't get that from low-cost meter movements anyway.
 
Hi Everyone,


I thought I'd contribute rather late, but contribute nonetheless and say that the circuits shown are mainly conceptual and are shown in their simplest form (i.e. without AC input coupling/DC decoupling) and assume that they will be connected to a low impedance (at DC and AC) source.


I will shortly modify the article to show this as I have been receiving a fair few e-mails from people who have built the circuits as shown as standalone units and in some cases haven't even referenced the input to ground.


I didn't think at the time of writing that people would be building them verbatim and without the peripheral components necessary for them to be operated as standalone units.


Cheers :D !
 
Status
This old topic is closed. If you want to reopen this topic, contact a moderator using the "Report Post" button.