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TINA spice simulation gives floating warnings
TINA spice simulation gives floating warnings
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Old 29th October 2019, 12:56 AM   #1
inkl is offline inkl  Russian Federation
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Cool TINA spice simulation gives floating warnings

Hey guys!


I'm trying to simulate a simple mic preamp with TINA. Here's the circuit I'm using.


So I created a simulation, here it is.


When I run ERC Analysis it's all green. But when I run DC Analysis -> Table of DC Results, I get 2 warnings:

- Pin 1 of Voltage Pin Vout is floating

- Pin 2 of capacitor C3 is floating.


I tried to change that part multiple times but no luck.

Please help me out here.

Thanks!
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Old 29th October 2019, 01:00 AM   #2
rayma is offline rayma  United States
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You need a resistor (say 100k) to ground on the output. The output DC voltage is not defined
unless there is a DC path to ground, or some other node.
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Old 29th October 2019, 01:07 AM   #3
inkl is offline inkl  Russian Federation
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Sorry, since I do this the first time - should I add something to the simulation or change the circuit?
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Old 29th October 2019, 01:09 AM   #4
rayma is offline rayma  United States
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Change the circuit.
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Old 29th October 2019, 01:34 AM   #5
inkl is offline inkl  Russian Federation
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I changed the simulation accordingly - added the R5 100k.


Here's what I get in terms of gain:


Click the image to open in full size.

Would this be enough to hear a single water drop? I'm not sure.
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Old 29th October 2019, 01:43 AM   #6
rayma is offline rayma  United States
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You'll have to try it, but that's certainly not a loud sound. The mic should be close.
There's something wrong with the gain scale in the graph.
Maybe cutting off the bass (say around 400Hz) will help to reduce noise.
The midband gain of your circuit is around +27dB.

Last edited by rayma; 29th October 2019 at 02:07 AM.
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Old 29th October 2019, 01:43 AM   #7
PRR is offline PRR  United States
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Quote:
Originally Posted by inkl View Post
...Here's the circuit I'm using.
- Pin 1 of Voltage Pin Vout is floating
- Pin 2 of capacitor C3 is floating.
That's not the plan in your simulator. And I don't have TINA here to read your TINA file.

But I bet it objects to having one end of a capacitor "floating". SPICE *insists* on figuring the DC voltage on every node before it does any other analysis. But the "floating" end of a cap can float to ANY voltage.

Anyway in real life you would have a LOAD.

Put a reasonable load on that output after the capacitor. Now SPICE's tiny mind will figure the DC voltage here is 0.0000V and be happy.
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Old 29th October 2019, 02:01 AM   #8
PRR is offline PRR  United States
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> Would this be enough to hear a single water drop? I'm not sure.

Insufficient information. How much sound power in the drop? How far away? In a room or in the open? What are you going INto? High-gain line input, headphones, mike input?

That's why mike amps have gain controls. In this one, make R4 about 1k. This gives gain of 1 to 100. Most jelly-bean opamps will be clean-enough at gain of 100(*). Set up your system, drip your water, and trim VR1 for happy results.

(*) the slower opamps working at gain of 100 may not have the extended treble to cleanly reproduce, say, Ginger Baker's cymbals. However even the antique '741 opamp at gain of 100 would be flat to 10kHz, which really is all you need in most situations, especially when working very-soft where system and ambient noise intrude.
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Old 29th October 2019, 02:17 AM   #9
inkl is offline inkl  Russian Federation
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Let's take SPL 25 dB at the 10 meters distance (32 ').
The idea is to get the input level out of this to connect to a standard line-in.


I tried changing R4 to 1k and then setting VR1 to different levels - it's doesn't change much, still sround -35 dB.


ok, I'll read more about this op amp and see if I can make it better.


Thanks for the hints. I'm still do not understand how this works and I hate this. I'm still reading but I thought I'd make something real.
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Old 29th October 2019, 02:21 AM   #10
rayma is offline rayma  United States
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Quote:
Originally Posted by inkl View Post
Let's take SPL 25 dB at the 10 meters distance (32 ').
There's no way this could ever work if you position the mic 32' from the water drop sound
that you want to pick up. The mic would have to be very close.
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