analog attenuation

[natbit]

Hi, I wanted to keep a voltage at ~-12V then switch it to a voltage with some linear respose associted with another unimportant parameter, this last sectiom is easy, I just need a reliable circuit to switch from this -12V up to the value between 0 and 4 V, any circuit sugeations?

 

[Dean Huster]

A 4066 or a CMOS analog multiplexer.

Dean

 

[Nigel Goodwin]

I would suggest you give more details, and a circuit diagram, I don't really understand what you are trying to do?. A CMOS switch 'may' be a possibility, but without more details it's not possible to be sure.

 

[natbit]

guys it's good to get a response...may I redirect u to the duplicate I posted in electronic design forum on MIDI to CV EZ, thanks and apologies

 

[natbit]

making a CV control unit for my old synth

 

[natbit]

"Hi everyone, I was looking at making a simple MIDI to CV convertor for with my old synth [KAWAI 100F] using a 16F84a and DAC0800 and was looking for some neat sugestions other than going for more bits...the synth itself requires a simple linear -0.11 V/note response from 3.6 V -> 0, easy enough, when inactive though it is -12 V -read from synth...my question is 1) how can i breadboard a circuit that will switch from ~-12V to the required note when active? AND 2) Is -12 V really necessary? *I have synth circuit - CV input goes to PC741C opamp/comparator * and so how can a pot be placed there somewhere to vary that 'inactive' CV whilst/during breadboarding? thanks."

 

[natbit]

Nigel, hopefully u will understand why I provided no schematic, since none yet exists, secondly it is amazing to see u guys trawl thru the posts and only hit up those in "general electronics chat" when an equivalent post existed in much more detail in "electronics design" anyhow back to the topic...and please explain to me Nigel what is so difficult about understanding the need to hold a signal @ ~-12V and switch it to the desired "note-on" signal somwhere between 0 and 3.6 V! I would have thought this explanation was A) concise enough and b) detailed enough, the problem I wish to resolve is 1) DAC 8 bits not enough to get resolution of 0.11 V / note between -12 V and 3.6! 2) -12V is the inactive state, shurely it would be easiest to switch between it and the "note-on" voltage in hardware, rather than getting a DAC with more bits...I have looked at the CMOS 4016 and 4066 and decided that yes, this may suit my purpose, with -7.5 V and 0 V as inputs, so the analog output siganl becomes the sumation of voltages from the DAC and 4066. Is this a correct interpretation?

 

[Nigel Goodwin]

secondly it is amazing to see u guys trawl thru the posts and only hit up those in "general electronics chat" when an equivalent post existed in much more detail in "electronics design"

It's quite obvious, there was no apparent relation between the two threads, one asked about modifying a synth, and this one didn't - so most of the replies here have been asking for clarification of the question.

anyhow back to the topic...and please explain to me Nigel what is so difficult about understanding the need to hold a signal @ ~-12V and switch it to the desired "note-on" signal somwhere between 0 and 3.6 V! I would have thought this explanation was A) concise enough and b) detailed enough

Not at all, because there was no context to the question, so it didn't make much sense - once you explained what it was for things became much clearer.

the problem I wish to resolve is 1) DAC 8 bits not enough to get resolution of 0.11 V / note between -12 V and 3.6! 2) -12V is the inactive state, shurely it would be easiest to switch between it and the "note-on" voltage in hardware, rather than getting a DAC with more bits...I have looked at the CMOS 4016 and 4066 and decided that yes, this may suit my purpose, with -7.5 V and 0 V as inputs, so the analog output siganl becomes the sumation of voltages from the DAC and 4066. Is this a correct interpretation?

Yes, if you use an opamp you can sum voltages together - an 8 bit DAC should be fine, it can give you 255 different notes.

There are numerous projects on the net for doing this, for various synths, I was given a faulty Korg Polysix a while back (still not mended it yet though) - when I searched for diagrams I found a number of sites with designs for Midi to CV converters. These may well give you some clues?.

 

[natbit]

The KORG polysix has some real awesome tones, I have the poly 800 and it is shite compared to the '6'. thanks for the clarification Nigel, i appreciate it. I have seen most of the designs u speak of and they generally either make an R-2R or use a DAC, I'll be using the National DAC0800, it's a little different to others on the net, not much. keep u posted

 

[Nigel Goodwin]

The KORG polysix has some real awesome tones, I have the poly 800 and it is shite compared to the '6'.

I was given it as faulty, I think originally it just needed the keyboard contacts cleaning, but it's been stored for a number of years and the battery has corroded the board. I managed to find a good site with circuits and details of how to repair the board, I've cleaned the board off, but not got round to repairing the damaged tracks yet.

One day!.

 

[natbit]

yeah, that's always a ***** Pb/Cd/Hg/SO4/H+ etc... the *ususal suspects* that stuff really annoys me but the Six has got to be worth it from memory I think it's a dual (analog) oscillator with limited 6 note polyphony?? The '800' is digital and grainny and it would'nt be so bad if it didn't effect the filter sweep type fx 'drastically' :x , but 6 is totally different...thick, rich...forgivingly analog.