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Mixing and 555's..

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sickform

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I have tried searching around, and cant seem to find a solution.

I am sending two IC555's to a summing mix output.

At the moment I am outputting the signal in the graph attached (4.2v).
But I do not get a return to 0v. It only returns to 1v and then back to 4.2v.

Is it necessary to achieve a 0v-4.2v output?

If so, how would I achieve this?

I am planning to connect via a unbalanced phono/line input (such as a DJ mixer MIC input/Phono input) or any other means for recording/performing.


Any help on this would be appreciated. Thanks in advance!





PS. I am getting a problem with mixing the two signals together. They seem to blank each other out at the OP amp stage and onwards when I have the mix set to certain settings. (I am using a simulator.)

I can upload voltages/currents or diagrams etc of anything that may help.
I have tried inverted and non-inverted with the same result.
 

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Can you post the circuit? The op-amp, is it a rail to rail op-amp? Not using a rail to rail op-amp would explain the offset in the posted image.

Ron
 
Can you post the circuit? The op-amp, is it a rail to rail op-amp? Not using a rail to rail op-amp would explain the offset in the posted image.

Ron


Would this be a rail-to-rail?
(Im using TL072's)

I can also send you a Circuit Wizard file if it is easier to see than this?

Please ignore some of the labels as they were just copied and paste from various places on the circuit to save time..

I hope this is clear enough. (Please excuse any mistakes I am still learning!)

Thank you for your help!
 

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I am at work so this will be quick. The TL072 is not a rail to rail op amp so the output will not swing to the power rails. I am not sure but a TLC2262 may be a good rail to rail op amp replacement. That is a quick off the cuff guess. Another member will hopefully see this and add to it. I don't have circuit wizzard so doubt I could open the file. If you can, try a simulation with the TLC2262 or a rail to rail op amp and see if that helps.

Ron
 
Thanks Ron.

Currently in the simulation I am using an 'Ideal' Op amp. But I shall give it a go..

I have TL072's and Tba820m's for the/a build. (If these are any help?!). I wont build until I have everything 110% stable and safe.
The plan is to use 5v instead of 9v as I am using a 16*2 LCD and a PIC in the final design. (I may end up splitting the voltage with regulators so I can achieve maximum power output from the OSC stages).

I have successfully run a simulation where I get a 0v return. (On a single stage). I think I may messed up a few times here as certain things don't add up.

If I can get this sorted (and possibly add more channels) then I will be stoked.
I am aiming for a total of 6 Oscillators to mix in pairs (3 x 2 pairs). Or possibly even more if this is possible? (I have seen that it is, but cant seem get them to SIM?).

I am using the schematics below as a reference:

http://all-electric.com/schematic/simp_mix.htm

**broken link removed**

I hope this makes my mission more clear?

Again, thanks for the fast reply and any help!
 
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I'll look more into this tomorrow. Didn't want you to think I fell off the planet. Interesting as the links show basic summing amp circuits they do not mention op-amp part numbers that I read or if they are using dual or single ended power supplies. I need to read them more when I am less tired. :)

Also, the guy in these forums really good with this stuff is AudioGuru and it would be cool if he found this thread. He breathes audio stuff,

Ron
 
Interesting as the links show basic summing amp circuits they do not mention op-amp part numbers that I read or if they are using dual or single ended power supplies.

No need to mention either really, the opamp type is pretty well whatever you want (even lowly 741's are absolutely fine, but TL0xx series would be better), and you can use either a spilt supply, or generate your own with two resisters and a cap.

However, I fail to see what the OP is trying to do, and why he would want rail-to-rail opamps?.
 
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