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 Forum index » DIY Hardware and Software » Les Hall's Projects including eChucK
emSynth
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Stream Operator


Joined: Oct 13, 2007
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PostPosted: Fri Dec 23, 2016 9:28 pm    Post subject: Reply with quote  Mark this post and the followings unread

three pots fit with a width of 48mm. the short dimension of the card is 54mm so there is a 3mm space on top and bottom end.

jacks on the back panel?

Les


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Cfish



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PostPosted: Fri Dec 23, 2016 9:51 pm    Post subject: Reply with quote  Mark this post and the followings unread

I'm working on the 3 pots on the sequencer right now. Seeing I only need 1 cv output on it, I was thinking of using 10mm knobs and trying to slide it in the front panel right in the v between the pots.

Will half to use a panel mount jack. I really prefer them anyway. No undue stress on the board that way.


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Cfish



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PostPosted: Fri Dec 23, 2016 10:05 pm    Post subject: Reply with quote  Mark this post and the followings unread

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


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PostPosted: Fri Dec 23, 2016 10:29 pm    Post subject: Reply with quote  Mark this post and the followings unread

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

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PostPosted: Sat Dec 24, 2016 12:37 am    Post subject: Reply with quote  Mark this post and the followings unread

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

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PostPosted: Sat Dec 24, 2016 12:50 am    Post subject: Reply with quote  Mark this post and the followings unread

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]

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PostPosted: Sat Dec 24, 2016 1:46 am    Post subject: Reply with quote  Mark this post and the followings unread

my progress, slow with all the alignment and all that schtuff.

Les


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PostPosted: Sat Dec 24, 2016 4:34 am    Post subject: Reply with quote  Mark this post and the followings unread

been at it for hours and hours, about an 8 hour day's worth of work. getting tired, time for a break!

Les


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Cfish



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PostPosted: Sat Dec 24, 2016 7:02 am    Post subject: Reply with quote  Mark this post and the followings unread

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



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PostPosted: Sat Dec 24, 2016 7:27 am    Post subject: Reply with quote  Mark this post and the followings unread

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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PostPosted: Sat Dec 24, 2016 8:39 am    Post subject: Reply with quote  Mark this post and the followings unread

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

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PostPosted: Sat Dec 24, 2016 2:10 pm    Post subject: Reply with quote  Mark this post and the followings unread

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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PostPosted: Sat Dec 24, 2016 2:34 pm    Post subject: Reply with quote  Mark this post and the followings unread

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

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PostPosted: Sat Dec 24, 2016 3:17 pm    Post subject: Reply with quote  Mark this post and the followings unread

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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PostPosted: Sat Dec 24, 2016 4:51 pm    Post subject: Reply with quote  Mark this post and the followings unread

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

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PostPosted: Sat Dec 24, 2016 6:50 pm    Post subject: Reply with quote  Mark this post and the followings unread

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

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PostPosted: Sat Dec 24, 2016 7:28 pm    Post subject: Reply with quote  Mark this post and the followings unread

Yes the Lm386 is a wonderful IC.

Great little amplifier.
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PostPosted: Sun Dec 25, 2016 3:09 am    Post subject: Reply with quote  Mark this post and the followings unread

Here is the form for the credit card synth VCO.

Les


Credit Csrd Synth.jpg
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credit card synth, VCO Form 3D Printed
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PostPosted: Sun Dec 25, 2016 7:59 am    Post subject: Reply with quote  Mark this post and the followings unread

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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PostPosted: Sun Dec 25, 2016 1:39 pm    Post subject: Reply with quote  Mark this post and the followings unread

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

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PostPosted: Sun Dec 25, 2016 1:45 pm    Post subject: Reply with quote  Mark this post and the followings unread

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

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PostPosted: Sun Dec 25, 2016 6:01 pm    Post subject: Reply with quote  Mark this post and the followings unread

This image shows the VCO frame that I'm working on. It has most of the parts and it does not quite work out right, but that's a given. It's more of an idea sketch than a final image. What I'm thinking is as follows.

We will use the conductive adhesive available at Radio Shack (what's left of it) and other sources. The leads will wrap around those posts of which two are illustrated near the potentiometer mounts. The transistor and capacitor mounts (with three holes each (caps use two of the three provided depending on their lead spacing)) will be rotated 90 degrees so they are on their sides.

That and more traces with possibly trace guides along their lengths and connectors on the back (if we go with that approach). I like the pots on front and wires on back approach because it keeps the control panel clean and allows more room for labeling of the connectivity panels. Also the cards are small enough, at exactly credit card size, that the whole synth can (usually) fit in one hand. So it's easy to turn it around for wiring or tuning.

That's about it for now, more to follow I hope!

Les


little VCO 12.png
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Here is the latest "solderLes" form for assembling the VCO.
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PostPosted: Mon Dec 26, 2016 1:52 am    Post subject: Reply with quote  Mark this post and the followings unread

Here is a closeup of the VCO fixture. The idea is to wrap wire around the posts in such a way that a drop or two of conductive glue will make a reliable connection. the troughs are for resistors, the brick-things on their side with three holes are transistors or caps, and the can thing is a can transistor. Three pots on left side are not visible in this image.

Les


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closeup of VCO fixture
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PostPosted: Mon Dec 26, 2016 3:45 am    Post subject: Reply with quote  Mark this post and the followings unread

I've noticed that in this type of work, the going is slow at first then it gets faster near the end. That's the case here in which the posts and leads are quickly added due to hierarchical design.

This is much closer to the goal.

Les


little VCO 14.png
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rapid progress - tie posts and grounds plus wires even!
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PostPosted: Mon Dec 26, 2016 11:15 am    Post subject: Reply with quote  Mark this post and the followings unread

Ahhhh, now I see what you are driving at Smile

This is a very, very clever way of working around the problem of not being able to solder in your living situation, Les Smile
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