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LM3914 Loading down the reference voltage

Fluffyboii

Member
Hi, So I want to make some kind of VU meter + adjusting tool for my modular synth modules. I decided to use TL431 as a reference voltage source so I can set 10V or 5V with a flick of an switch. When I connect this reference voltage of 10 volts to the 6th pin of the LM3914 and following this circuit for the rest I got absolutely nothing outputted on the LEDs when I tested it with a 9V battery for input.
1660410272439.png

I removed the zener diode and the 1K resistor thats connected to it and connected it to the reference before all of this. I saw that when 6th pin is connected to the TL431 the reference voltage dropped down to 3.5V and recovered when I disconnected the TL431. So I assume the LM3914 is drawing some current from the 6th pin which was something I did not except. Should I buffer the reference or am I missing something.
 

Nigel Goodwin

Super Moderator
Most Helpful Member
Post the circuit you used with the TL431 - you are aware that the minimum voltage from a TL431 is about 2.5V, and above that is set by two resistors.

Also, if I recall correctly?, you want the LM3915 for a VU meter, the 3914 is linear, and useless for VU.
 

Fluffyboii

Member
Post the circuit you used with the TL431 - you are aware that the minimum voltage from a TL431 is about 2.5V, and above that is set by two resistors.

Also, if I recall correctly?, you want the LM3915 for a VU meter, the 3914 is linear, and useless for VU.
TL431 circuit is the one you said, 1K resistor to cathode and two 10K resistors to get 5V but instead I add 2 more 10K resistors series with the R1 so I could have 10V and have 5V with a switch that shorts those 2 10K resistors when needed. But for testing it was essentially 30K for R1 and 10K for R2.
1660418321902.png

I know you need a logarithmic response for a VU meter but I already have a real analog VU meter I will make a circuit for so this one is more for adjusting the pots on the synths and having some random moving led when not doing so. It is like resting 8 years in my toolbox so I wanted to use it for something while waiting for new parts to ship.
 
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Nigel Goodwin

Super Moderator
Most Helpful Member
I've not seen it's datasheet for a few decades, but what are the current requirments for R1 and R2, are 10K and 30K low enough to pass enough current.

As for the 3914 you will be VERY disappointed with it, as it's completely useless as a VU meter.
 

eTech

Well-Known Member
Hi, So I want to make some kind of VU meter + adjusting tool for my modular synth modules. I decided to use TL431 as a reference voltage source so I can set 10V or 5V with a flick of an switch. When I connect this reference voltage of 10 volts to the 6th pin of the LM3914 and following this circuit for the rest I got absolutely nothing outputted on the LEDs when I tested it with a 9V battery for input.
View attachment 138222
I removed the zener diode and the 1K resistor thats connected to it and connected it to the reference before all of this. I saw that when 6th pin is connected to the TL431 the reference voltage dropped down to 3.5V and recovered when I disconnected the TL431. So I assume the LM3914 is drawing some current from the 6th pin which was something I did not except. Should I buffer the reference or am I missing something.

Your circuit looks good. It should work as you've shown.
Recheck parts, wiring, voltages and currents.
 

audioguru

Well-Known Member
Most Helpful Member
The LM3915 audio meter IC ain't made no more no more. Because I was probably the only person buying them.
The LM3914 linear meter IC is still made in a surface-mount package.
A VU audio meter needs logarithmic, not linear steps.

Both ICs already have an excellent adjustable reference voltage (pins 7 and 8) so why add an external reference voltage??
 

Fluffyboii

Member
The LM3915 audio meter IC ain't made no more no more. Because I was probably the only person buying them.
The LM3914 linear meter IC is still made in a surface-mount package.
A VU audio meter needs logarithmic, not linear steps.

Both ICs already have an excellent adjustable reference voltage (pins 7 and 8) so why add an external reference voltage??
So can you adjust its reference voltage and it doesn't move when power supply voltage changes. Then you are right tl431 is not needed. I shall search this more.
 

Fluffyboii

Member
Plenty of LM3915 (not production plenty, one off plenty) :



Regards, Dana.
They still sell them here but it is unreasonably high priced. I can get 25 NE555's at that price. Aliexpress has some cheap ones but shipping and tax here makes it bad. Maybe If I bulk buy I can make a nice spectrum analyzer with them. I assume in that case I would also need unreasonable amount of op amps too for filters.

Edit: I got five LM3915 from China, idk if they will work but I also wanted to get AD633 and few op amps for cheap. Will right about it when they arrive.
 
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Fluffyboii

Member
5 pieces for $ 8

5 pieces for $ 5

Not counting shipping.

Does not sound overpriced to me.


Regards, Dana.
I live in a country where buying stuff from Ebay is not logical because there are insane shipping costs and taxs. The ones on Aliexpress was suspiciously cheap so I am not expecting much but we will see.
 

Fluffyboii

Member
Are the LM3915 ICs from China "real" or "fakes"?
You never know. Probably fakes or reject products. There is also no way the AD633 I bought for 2 dolars is real since it is a 10 dolar chip. I don't expect anything but I should be able to get a refund if all is for naught. I got some China NE5532s that do work. Wouldn't use them for serious stuff for sure tho.
 

Fluffyboii

Member
The chips arrived. I bought some LM13700, LM3915, TL072, TL074, AD633. AD633 is not working and overheating when power is connected. I tested with some small voltages at input pins to see if it would actually multiply, it did throw some random negative value before I pulled it out cus it was overheating. TL072 and TL074 at least did work when I replaced the op amps in my VCO with them. Did not test the LM13700 and LM3915. If they work as well I may buy some more because AD633 was destined to be fake because of its super cheap price but other ones were more reasonable priced yet they are usually 1/5 of what I pay to get them locally.
 

alec_t

Well-Known Member
Most Helpful Member
Last edited:

ChrisP58

Well-Known Member
Most Helpful Member
The chips arrived. I bought some LM13700, LM3915, TL072, TL074, AD633. AD633 is not working and overheating when power is connected. I tested with some small voltages at input pins to see if it would actually multiply, it did throw some random negative value before I pulled it out cus it was overheating. TL072 and TL074 at least did work when I replaced the op amps in my VCO with them. Did not test the LM13700 and LM3915. If they work as well I may buy some more because AD633 was destined to be fake because of its super cheap price but other ones were more reasonable priced yet they are usually 1/5 of what I pay to get them locally.
Please post the entire circuit you're using for the test of the AD633.
 

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