Schematic queries

Thread Starter

J Tel

Joined Feb 14, 2021
3
Hi,

I'm an amateur enthusiast on electronics.
I'm trying to build the following schematic
It is a "log amp" converting voltages from Hz/V to V/oct for analog synthesizers.

korg ms02 schematic queries.png


I have some basic queries regarding building this on a breadboard.

1) All the points circled in red are + and - points.
Are that supposed to be connected on my power supply (+12V / -12V)
Am I right?

2) Circle in purple, is an arrow that is "connected" to the positive of the input jack.
How should I connect this point exactly ?

3) On the green arrow, seems that the middle leg of the potentiometer goes back to the one of the other legs.
Should I just bridge the middle and the third leg?

To be honest I ve tried to built this on a breadboard with an external adjustable laboratory power supply.
Sadly, the results are not as should be.

When I connect a 5V input, the output was around 3.6V.
When I connect a 8V input the output was around 5.6V.
Also unfortunately, any of the potentiometers didn't change anything at all on the output...

You can take a look below what voltages should be right : Screen Shot 2021-03-12 at 11.58.00 PM.png


I hope that my queries are clear.

Any suggestions, advice or comments are welcome.

Jim
 

Attachments

MaxHeadRoom

Joined Jul 18, 2013
22,671
That appears to be a +ve, 0, -ve supply.
The green arrow it seems is just indicating a pre-set pot symbol..
VR5 is a set as a var resistance not a potentiometer.
i.e. slider is connected to one side.
 

Yaakov

Joined Jan 27, 2019
2,442
Hi,

I'm an amateur enthusiast on electronics.
I'm trying to build the following schematic

I have some basic queries regarding building this on a breadboard.
1) All the points circled in red are + and - points.
Are that supposed to be connected on my power supply (+12V / -12V)
Am I right?


Yes,

2) Circle in purple, is an arrow that is "connected" to the positive of the input jack.
How should I connect this point exactly ?


That is a normal, the jack has a contact that is closed when the plug is not inserted and is lifted when it is.

3) On the green arrow, seems that the middle leg of the potentiometer goes back to the one of the other legs.
Should I just bridge the middle and the third leg?


Yes, the outside part of the potentiometer is wired like a fixed resistor in series and the wiper is shorting a varying portion of it.*

*I am not certain about this anymore, the schematic's symbology is a little different than I am used to. I think it's right but I'd wait for someone more certain.
 

Thread Starter

J Tel

Joined Feb 14, 2021
3
Hi,

Thank you very much for your help!
I really appreciate it.

To be honest, I can't understand the term "variable resistor". I thought it was just a potentiometer.

One more thing.
When I plug a 5V input to the jack, I got 3.6V at the output either if I power my circuit or not.
Power has nothing to do with the output... (?)
So, I assume that I do something wrong on the power supply.

I use this power supply with the 3 pins (+ - and ground)
Screen Shot 2021-03-13 at 3.20.34 PM.png

Is it that strange?

Any suggestions, advice or comments are welcome.
Jim
 

Alec_t

Joined Sep 17, 2013
11,984
Your pic shows a shorting link between -ve and ground. Try removing the link.
On the maker's web-site, that supply is described as 'single channel' and appears to be a single polarity one with the option to ground the -ve. Your schematic calls for a dual-polrity supply.
 

MisterBill2

Joined Jan 23, 2018
8,231
Hi,

Thank you very much for your help!
I really appreciate it.

To be honest, I can't understand the term "variable resistor". I thought it was just a potentiometer.

One more thing.
When I plug a 5V input to the jack, I got 3.6V at the output either if I power my circuit or not.
Power has nothing to do with the output... (?)
So, I assume that I do something wrong on the power supply.

I use this power supply with the 3 pins (+ - and ground)
View attachment 232618

Is it that strange?

Any suggestions, advice or comments are welcome.
Jim
This is not the supply you need. The requirement is for a dual supply providing both negative and positive relative to the common. That jumper bar in the picture will not help at all. Disconnecting it will bring no benefit in this application.
 

Thread Starter

J Tel

Joined Feb 14, 2021
3
Hi,

Thank you for your replies and your help.
I will try to remove the link to the above laboratory power supply to check if it will work.

But generally, I'm planning to use this circuit to my eurorack modular synth.
Modular synth provides this power supply for the other modules (see picture)
You can see that each slot can provide +5 / +12 / -12 / ground.

Do you believe that kind of supply would work?Screen Shot 2021-03-15 at 1.38.40 PM.png

Thank you in advance
Jim
 

MisterBill2

Joined Jan 23, 2018
8,231
If you have a supply of both +12 V and -12 V and the common between them that should work very well with the circuit you showed. AND it became clear that those resistors with the oval around them and the "MF" designation were specified as Metal Film types, which are lower noise devices. That is reasonable because noise on a pitch control line would certainly be very objectionable.
 
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