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static voltage for attenuverter offset
MUFF WIGGLER Forum Index -> Music Tech DIY  
Author static voltage for attenuverter offset
ovian
Hello

I would like to build a module that is just a static 5v so I can run it into my attenuverter that does not have an offset. I know there are a few schematics floating around on here about how to divide down the +12v or use a 78l05. My question: is there any problem with just pulling the 5v directly from my power supply to a jack on my front panel? Just want to make sure there is no harm that could be caused by doing such a thing.

thanks
J3RK
It mainly depends on how accurate you would like it to be.

You can use a regulator, a resistor divider, a Zener diode, or a precision reference. I would include an op amp buffer (just unity gain).
EATyourGUITAR
It also depends on your power supply, your bus board, what modules you have in the case connected to 5v. If you have a bus board with a 7805L and there are no 16 pin modules in the case right now then you have the only your front panel jack connected to your 7805L in theory. The problems start when you patch that to something and the tip shorts to the ring during insertion. You could smoke the bus board the patch cable etc... Adding a precision buffer with an output resistor maybe 1K would help. 100R would be more accurate but it would get hot if you short it.
ovian
Thanks for the info.
Sounds like it would be best to do something with a bit more robust of a design.
SphericalSound
For experimental purposes, attaching a 1k resistor to the 5volts line should work nicely

Anyway filtering the + power with the tipical 10R/10uF combo plus a 7805 regulator, plus a 1k resistor at the end is a pretty simple thing to do and robust. Maybe not dead precise 5volts but as lon as you are going to attenuate or invert in later it doesn´t need to be that precise. You just need a random (5v) reference to later mangle it.
CLee
One reason not to just bring the power supply to a jack is that if you short it you’ll be shorting out the supply. If it’s a Euro or 5U system, every time you plug or unplug a patch cord you short the module output for an instant when the jack tip touches the sleeve of the input
abelovesfun
CLee wrote:
One reason not to just bring the power supply to a jack is that if you short it you’ll be shorting out the supply. If it’s a Euro or 5U system, every time you plug or unplug a patch cord you short the module output for an instant when the jack tip touches the sleeve of the input


This is exactly correct. At minimum, I would have a power inlet with some caps for smoothing and resistors or ferrites for protection, and then have a regulator with some diodes for protection.
EATyourGUITAR
If you use a pull-up to an LM4040 it doesn't matter if your tip shorts to ground during insertion. You also don't need to add a protection resistor anywhere since you already have one. This has the lowest parts count, most robust, lowest price, highest accuracy of anything suggested so far in this thread.
CLee
Not as low parts count as EyG’s solution, but buffered, short circuit protected, and will stay at 5v as you patch it around

EATyourGUITAR
I'm not against other solutions. I'm not against healthy debate. I like CLee and all that he has contributed to this forum. It definitely is a much larger body of work than anything I have done.

However, I just wanted to point out that my solution already has short circuit protection. The 100pf is only needed for the first 1ms of accuracy. I don't mind waiting to charge the capacitance of the cable. The voltage drop across 330R is more than the 2R solution of raw lm4040. We are introducing input offsets of an opamp by adding an opamp. I have a $7 opamp I use to buffer precision references. This is part of a design I never released. But I used it after a switched resistor network that had impedance constantly changing depending on the position of the switch. The opamp buffer had a purpose of creating low impedance output at a constant impedance regardless of loading. Here I don't see it as adding anything beneficial to the design. But anyway, thanks to CLee for taking the time to draw a schematic. It shows his circuit and also the other smaller circuit. I really do like the 10R output as an option. I like how it connects to the input of the opamp where it is less likely to cause damage. It's pretty cool but I would only use it to buffer this switched reference I'm working on.
CLee
No worries, throwing ideas out there...

I copied the S&H output buffers from my Quantizer. The resistors on the op amp are to keep the output constant as the load changes. Yes there’s offsets from the op amp. I guess the question is what are you after, a voltage that’s exactly some level or one that’s always the same but may not be an exact reference voltage.
EATyourGUITAR
this is perfect for Sample & Hold!
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