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Stream Operator
Joined: Oct 13, 2007 Posts: 6221 Location: near Austin, Tx, USA
Audio files: 267
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Cfish
Joined: Feb 24, 2016 Posts: 477 Location: Indiana
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Cfish
Joined: Feb 24, 2016 Posts: 477 Location: Indiana
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Posted: Fri Dec 23, 2016 10:05 pm Post subject:
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Also using the VCO on 9V with a 1/2v reference has the range down pretty low.
Everything I have dun up to now has been my own large format modules, actually a little larger than 5U, and 15v+-.
I'm enjoying a new set of peramiters to work within, but I'm not seeing a way to get much more span out of that specific VCO design.
Any suggestions? |
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Stream Operator
Joined: Oct 13, 2007 Posts: 6221 Location: near Austin, Tx, USA
Audio files: 267
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Posted: Fri Dec 23, 2016 10:29 pm Post subject:
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it will help if in the future the schematics have reference designators. R3, Q1, etc.
I'd suggest playing with a few component values. The resistor at the very top right of the diagram, the 10k could be reduced perhaps. You see, i'm thinking that the two 2N3906 transistors function as a current mirror. When you pull a current out of the left one, it shows up on the right one. so reducing that resistor to a 4.7kOhm might double the current into the charging capacitor.
Then also the 100kOhm and 1MEG Ohm resistors on coarse and fine can be reduced to half at 47kOhm and 470kOhm to better utilize the top and bottom end of the pot range.
Similarly the two 100 Ohm resistors that sense the charging cap's voltage can be played around with. I suggest using a 220 Ohm at the bottom end and/or a 47 Ohm at the top end just to see how it works.
I think the 2n2646 transistor is just dumping the charge off of the charging cap once the threshold is reached, so messing with the divider will alter it's threshold. Also the cap can be made bigger to increase the bottom end frequency range, I'd wager.
the transistor at the lower right seems to be an output buffer. Replacing it with a push-pull driver will melt your output mod into the buffer and remove a few resistors, i would think.
At least that's the best I can do with my limited knowledge of the circuit.
Les _________________ "Let's make noise for peace." - Kijjaz |
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Inventor
Stream Operator
Joined: Oct 13, 2007 Posts: 6221 Location: near Austin, Tx, USA
Audio files: 267
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Posted: Sat Dec 24, 2016 12:37 am Post subject:
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Regarding the pots and connectors subject, it seems rather strange to squeeze the entire user interface into the short side of one end of the card. Consider the mini 500 series - I/O on the backplane. I figure we can have a backplane or just a little bit of a backplane to distribute power, then wiring on the back. Leaves room for three items on the front.
Another option is to use the long side for the pots and jacks. Really though, we can make knobs to any size on the 3D printer, the alpha pots are 16mm in diameter each.
I like the creativity of the jack in the hole there, just don't think jacks and pots together really works in a small format. You tell me, we gotta learn how to think things through.
Les _________________ "Let's make noise for peace." - Kijjaz |
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Inventor
Stream Operator
Joined: Oct 13, 2007 Posts: 6221 Location: near Austin, Tx, USA
Audio files: 267
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Posted: Sat Dec 24, 2016 12:50 am Post subject:
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more facts to consider. when you think about it, designs are full of pots and jacks plus other I/O. the ratio of the space taken up by those items to the space taken up by circuitry is about equal. this means that cramming all the i/o in one little space will lead to inefficient utilization of the available space.
so we have four possible solutions:
pots on the short side, i/o on the back
pots on the long side, i/o on the the back
pots on the short side, i/o on the front
pots on the long side, i/o on the front
I'm really saying that the third option is the most space-cramped one of all.
you advise please.
Les
[/list] _________________ "Let's make noise for peace." - Kijjaz |
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Inventor
Stream Operator
Joined: Oct 13, 2007 Posts: 6221 Location: near Austin, Tx, USA
Audio files: 267
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Inventor
Stream Operator
Joined: Oct 13, 2007 Posts: 6221 Location: near Austin, Tx, USA
Audio files: 267
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Cfish
Joined: Feb 24, 2016 Posts: 477 Location: Indiana
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Posted: Sat Dec 24, 2016 7:02 am Post subject:
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Hi Les
last night while sleeping I realized that one resistor in the VCO would bring the span back.
I love it when I'm working with a simple enough schematic that I actually dream through solutions to problems.
Has to be a pretty simple schematic.
The 1k resistor that gives 1/2 v reference to the bass of the first transistor in the current mirror needed increased in value to account for the decrease in actual cv swing.
3.3k worked pretty well.
I will post the amended schematic once I'm sure I'm done making fine adjustments. |
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Cfish
Joined: Feb 24, 2016 Posts: 477 Location: Indiana
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Posted: Sat Dec 24, 2016 7:27 am Post subject:
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I do agree on I.O. Placement.
I'm sort of merging 2 projects at the moment, so I decided I would build my first credit card modules with things placed on the short side, and power supply on the back, because they will fit in a case I have in mind for them.
I think the direction you are heading is much better for a real format.
I'm doing this one synth with the odd size constraint just because I'm enjoying the challenge.
Will be a baby credit card modular with 2 VCO modules 2 VCA modules, an LFO module, sequencer module, Mixer module and a VCF module.
Will look like my 2 racks of home built 6u modules got friskie with my rack of purchased 5u modules and made a baby LOL |
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Stream Operator
Joined: Oct 13, 2007 Posts: 6221 Location: near Austin, Tx, USA
Audio files: 267
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Posted: Sat Dec 24, 2016 8:39 am Post subject:
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you know, CFish, I sai to decrease that resistor by half, then when I thought about it later I wondered if increasing it would help more. Sure enough, your understanding was a practical answer. Shows what I know, lol.
I 3D printed the partially done layout of the twisty leads wire form of the VCO. It's over there all ready for me to get when the next opportunity arises. I'm dealing with pain and healing issues, prevents me from doing much at a time.
Les _________________ "Let's make noise for peace." - Kijjaz |
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Cfish
Joined: Feb 24, 2016 Posts: 477 Location: Indiana
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Posted: Sat Dec 24, 2016 2:10 pm Post subject:
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Hi Les.
Sorry to hear your not feeling well.
Your knowledge of electronics is far beyond my own. I however have several working 15v +- versions of this working to compare to.
Finally tore in to my scope today and got it half working. Still only have about half the time values working, but after cleaning the rotary switch it's at least somewhat usable.
Using the scope I determined that making the little VCO work correctly on a single power supply may be beyond my knowledge. Yes it's working. But not well.
The FET in the circuit acts as a buffer when being used on a dual supply. I actually wound up bypassing it and using the NPN drawn at the output to buffer and amplify. I had to add the blocking cap to stop the bias voltage for the NPN from affecting the oscillator. The first problem that arose is that the blocking cap changes the capacitance in the RC circuit, so I had adjusted for that.
Real problem is that the blocking cap also turns the saw wave in to a short Puls. Which makes since seeing it is basicly acting like a high pass filter
It can be usable on 9v but I think it may be more trouble than it's worth. |
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Stream Operator
Joined: Oct 13, 2007 Posts: 6221 Location: near Austin, Tx, USA
Audio files: 267
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Posted: Sat Dec 24, 2016 2:34 pm Post subject:
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Hi CFish,
I did not realize you were going for a single 9V supply. Yes, I can see how challenging it would be to do that. Really a +/- 9V supply would be nice. I feel that would be reminiscent of all the age-old synths and still be battery-practical. With two LEDs indicating charge, they can discharge at different rates and still be serviced. A box of 12 industrial 9V batteries on Amazon is only $16, and they should last a while plus the minus supply side generally uses a lot less charge so it's doubly OK. Let's go with that if you agree.
Les _________________ "Let's make noise for peace." - Kijjaz |
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Cfish
Joined: Feb 24, 2016 Posts: 477 Location: Indiana
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Posted: Sat Dec 24, 2016 3:17 pm Post subject:
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I agree
Was a good exercise trying to pull it off. I felt pretty close until I got the scope on it.
It actually works good up to the point where you try to buffer and amplify the UJT output.
To bias the buffer without affecting the RC circuit??? Guess the only way would be to adjust the supply voltage and ground reference of the buffer transistor around the bass input of the buffer.
Or would that even work???
I like to experiment. It's the only way I seem to really learn anything. |
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Stream Operator
Joined: Oct 13, 2007 Posts: 6221 Location: near Austin, Tx, USA
Audio files: 267
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Posted: Sat Dec 24, 2016 4:51 pm Post subject:
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One idea might be to try a Darlington Pair:
https://en.wikipedia.org/wiki/Darlington_transistor
It's a BJT with a BJT on it's input, lowers current draw by multiplying gain. Or use a MOSFET. Both approaches may eliminate the need for a cap on the input. Just guessing.
Les _________________ "Let's make noise for peace." - Kijjaz |
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Stream Operator
Joined: Oct 13, 2007 Posts: 6221 Location: near Austin, Tx, USA
Audio files: 267
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Posted: Sat Dec 24, 2016 6:50 pm Post subject:
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Speaking of scopes, I don't have one believe it or not, and I think I'll get one soon cause these days the low end audio models are so very affordable. However we cannot expect our target audience to have scopes. The will, however typically have smart phones.
So there are free scope apps that just listen to the microphone and display the resulting waveform. pretty cool and fun to use. All we have to do for that is provide hi impedance input to audio output in a module or on the chassis. In fact, there are piezo speakers that do the job all by their lonesome without even so much as a buffer. That could be one option and a proper LM386 "Little Gem" amplifier to an 8 ohm mini speaker would be another choice. We could offer both, gotta make sound somehow anyway right?
Then the phone becomes the scope and it's free (once you have the pricey phone).
Les _________________ "Let's make noise for peace." - Kijjaz |
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Cfish
Joined: Feb 24, 2016 Posts: 477 Location: Indiana
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Posted: Sat Dec 24, 2016 7:28 pm Post subject:
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Yes the Lm386 is a wonderful IC.
Great little amplifier. |
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Stream Operator
Joined: Oct 13, 2007 Posts: 6221 Location: near Austin, Tx, USA
Audio files: 267
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Cfish
Joined: Feb 24, 2016 Posts: 477 Location: Indiana
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Posted: Sun Dec 25, 2016 7:59 am Post subject:
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First off Merry Christmas.
The form looks awesome.
This is an awesome project. I feel like I'm doing more watching than helpful doing.
The single transistor VCA poasted several places on here would be a great VCA for this project.
I could test values with the dual 9v supplied VCO to optomize its function?? If you think it's good enough as at least a start VCA for the project.
I use it in my bass pedal synth. It takes a low pass filter to get rid of the noise. But works ok. |
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Stream Operator
Joined: Oct 13, 2007 Posts: 6221 Location: near Austin, Tx, USA
Audio files: 267
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Posted: Sun Dec 25, 2016 1:39 pm Post subject:
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Well, CFish, first off Merry Christmas! It's Christmas day and as I look about my small bedside table that I use as a desk, your gift is the one that I chose to have right here within arm's reach. That should tell us something!
Regarding who's doing what, I feel the same - that you are the one doing all the work and I am not. So maybe it's just a matter of perspective.
Certainly I think your work on the VCO is fundamental to our joint effort. All I've done is define the credit card format and the I/O structure plus some early beginnings of a printable (and injection moldable) VCO form. Maybe some other design thingies but that's it. You on the other hand, have actual working modules in physical form. So don't knock yourself down you're doing great!
To solder It will take a month to get a cold solder gun and batteries for it. Then I can play catch-up with you on assembly. Certainly what you are doing is fundamental to our efforts. When you think about it, A VCO is the flagship of our adventure. It is just one card and it makes sound. I'm doing very little and you are doing a lot on making the VCO. So well done and keep at it.
Les _________________ "Let's make noise for peace." - Kijjaz |
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Stream Operator
Joined: Oct 13, 2007 Posts: 6221 Location: near Austin, Tx, USA
Audio files: 267
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Posted: Sun Dec 25, 2016 1:45 pm Post subject:
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As for what to do next, CFish, I'd say follow your joy. This is the season for merriment and pleasantries so we should not be guided by the burdens of what is right or more efficient. I feel that if you do what's fun, everything will fall into place. So have at it!
Les _________________ "Let's make noise for peace." - Kijjaz |
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Stream Operator
Joined: Oct 13, 2007 Posts: 6221 Location: near Austin, Tx, USA
Audio files: 267
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Stream Operator
Joined: Oct 13, 2007 Posts: 6221 Location: near Austin, Tx, USA
Audio files: 267
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Stream Operator
Joined: Oct 13, 2007 Posts: 6221 Location: near Austin, Tx, USA
Audio files: 267
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AlanP
Joined: Mar 11, 2014 Posts: 746 Location: New Zealand
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Posted: Mon Dec 26, 2016 11:15 am Post subject:
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Ahhhh, now I see what you are driving at
This is a very, very clever way of working around the problem of not being able to solder in your living situation, Les |
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