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ARP 4027-1 VCO Saw Core
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mrmrshoes



Joined: Feb 19, 2011
Posts: 73
Location: Newcastle Upon Tyne
Audio files: 4

PostPosted: Wed Jun 26, 2013 3:15 am    Post subject: ARP 4027-1 VCO Saw Core Reply with quote  Mark this post and the followings unread

I've just finished Breadboarding the Arp 4027-1 Saw-Core and this thing is pretty cool so I thought I would post my findings. I must say that I’m no expert I’ve just been following the resources on the internet and hoping for the best.
When I come to building this VCO I didn't want to use any hard to get parts so after consulting Andy1960 ARP VCO thread I replaced the ca3046 with unmatched 2n3904 transistors.
Check out the pictures of the VCO core on the breadboard and the resulting Ramp wave form using 2n3904/2n3906 and 2n5457 transistors.

Sure you can still get the ca3046 but a 100 2n3904 is about the the same price as a couple of chips and a lot easier to get hold of, this fact sells it to me every time.

The only hard to get part will be the JFET's seeing that someone thought it was a good idea to cease production. The good news is that I tried every JFET I had to hand and the circuit kept purring away.

Here is a list of JFET's I used with no noticeable differences

2n5457
2n5485
2n3819
J201

I couldn’t test the BF245 because the batch of 50 I bought are duds which I must say is pretty disappointing. I do believe this JFET should work because I’ve seen people stating these fellas as a working substitute.


The main resources I used for this project are found here:

4027-1 VCO schematic
http://www.till.com/arptech/modmain.htm

Bergfotron Basic VCO
http://hem.bredband.net/bersyn/VCO/vco_basic.htm


I breadboarded the original schematic first of all. The wave-shape was nice looking and sounded good. They was a little offset when testing. I then implemented Bergfotron resistor value changes to the vco core. They are about 5 value changes. These changes seem to correct the DC offset on the Ramp output.

I decided to implemented Bergfotron triangle wave-shaper. This wave-shaper uses commonly available parts which is a bonus. I decided to leave out the CV controlled switch circuity on the Bergfotron basic VCO. but the addition of a square, sine saw and ramp output + - 5V would be very useful. For the square and sine shapers I decided to use Thomas Henry circuits from his VCO-1 design. The triangle output is the correct amplitude for the wave-shaper inputs.

The sine wave-shape might need a bit of tweaking. If so you will want to read details on TH VCO-1 page, I've just left the value stated on the vco-1 schematic.
http://www.birthofasynth.com/Thomas_Henry/Pages/VCO-1.html

I've added my redrawn schematics

I’m planning on laying out a single sided PCB and I’ll post it here when it's built and tested.


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Last edited by mrmrshoes on Thu Jun 27, 2013 10:27 am; edited 2 times in total
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elmegil



Joined: Mar 20, 2012
Posts: 1524
Location: Chicago
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PostPosted: Wed Jun 26, 2013 6:18 am    Post subject: Reply with quote  Mark this post and the followings unread

NICE Smile
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mrmrshoes



Joined: Feb 19, 2011
Posts: 73
Location: Newcastle Upon Tyne
Audio files: 4

PostPosted: Fri Jun 28, 2013 7:03 pm    Post subject: Reply with quote  Mark this post and the followings unread

Cheers man Wink

I've tested the waveshapers over the pass couple of days and they work well.
Wave forms look good but I did have to make one change to the sine output. R64 & R65 were changed from 12k to 15k because i using + / - 12V supply and the resulting output was a bit weak.
Also I'm getting a wee bit of bleed on the triangle output from the saw core but I'm putting this down to the state of my breadboard and a lack of de-coupling caps. I'm going to push on and see how a clean build works outs. I've designed this single sided PCB. I need to refine it abit but it's getting there.

Last edited by mrmrshoes on Tue Jul 02, 2013 7:58 am; edited 1 time in total
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mrmrshoes



Joined: Feb 19, 2011
Posts: 73
Location: Newcastle Upon Tyne
Audio files: 4

PostPosted: Sat Jun 29, 2013 9:59 am    Post subject: Reply with quote  Mark this post and the followings unread

Ha, I'm such a dumb ass sometimes.

They ain't no bleed through from the VCO Core on the triangle output, it's harmonic content generated from the glitch in the waveform. I increased R77 from the schematic above to 82k and this considerable reduced this effect.

The input resistor for the PWM control (R53) needs tweeked aswell. I used 560K to set the pots range.

I think i'll add the opiton on the PCB for a trim pot for the triangle glitch resistor seeing that the value needed will change depending on the JFETS used within the circuit.
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LFLab



Joined: Dec 17, 2009
Posts: 195
Location: Rosmalen, Netherlands

PostPosted: Sat Jun 29, 2013 11:01 am    Post subject: Reply with quote  Mark this post and the followings unread

Looks great!
Interesting footprint for the potmeters, is that for both 16mm and 9mm pc-mount pots?
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mrmrshoes



Joined: Feb 19, 2011
Posts: 73
Location: Newcastle Upon Tyne
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PostPosted: Sat Jun 29, 2013 11:40 am    Post subject: Reply with quote  Mark this post and the followings unread

cheers dude, glad you dig it like.

The footprint is a 16mm pot with a 0.1 header lumped together. It will give me the option of PCB mounted pots or the use of headers depending on how i choose to mount the PCB to a panel. It seemed like a good idea at the time, I don't even think about it anymore when I'm laying out a board.

To be honest i haven't paneled anything up yet so I not sure how useful it will be. Laughing
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mrmrshoes



Joined: Feb 19, 2011
Posts: 73
Location: Newcastle Upon Tyne
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PostPosted: Tue Jul 02, 2013 8:31 am    Post subject: Reply with quote  Mark this post and the followings unread

Below is the finished Single sided PCB I’ve been working on.

I've added the sync circuity from Bergfotron Basic VCO, The PCB has Sine, Saw, Ramp, Square, and Triangle outputs.
The square wave has one PWM CV input
One Header accommodates 1-V/Oct, and 2 FM Inputs.
The Low Frequency Switch will require a 3PDT switch. (When all Switch are closed the VCO will operate in Low Frequency mode. The LF switch Headers are labelled SW-A, SW-B and SW-C, Header SW-B will require shielded cable that is grounded at one end)

I've deleted picture in the earlier post in favour of this one to save space.

Once this is built and tested I’ll upload the PCB layout. if anyone is brave enough and can't wait until this is done I can send you the eagle files.


Thanks all

mrmrshoes


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steffensen



Joined: Jul 11, 2012
Posts: 95
Location: Sweden

PostPosted: Tue Jul 02, 2013 8:52 am    Post subject: Reply with quote  Mark this post and the followings unread

Pure Awesomeness!!! too much coffee
Cant wait to get my hands on that!

I have made the ARP 2600 AD/ADSR on a dual sided board in Eagle as well, just awaiting the boards to arrive. (about 4 weeks i guess)

Soon we'll have the many ARP parts yes.
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mrmrshoes



Joined: Feb 19, 2011
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PostPosted: Wed Jul 03, 2013 10:58 am    Post subject: Reply with quote  Mark this post and the followings unread

Quote:
Pure Awesomeness!!!
Cant wait to get my hands on that!


Thanks alot dude. If other people find this useful, it make the effort worth while Wink

I've just put in an parts order so if all goes well the files will be up in a couple of weeks or so.

Your work on the ADSR/AD Envelope sounds interesting like. Could you supply more info on that if possible. Have you used substitute Transistors in your build. If the transistors and Jet’s in this build could be subbed for more common parts I’m defos up for building this and other ARP modules.

Also I've read somewhere that you can't sub the LM301 OP-AMP because of the way it functions, but you can still get hold of these so shouldn't be a problem.

I'll keep you updated with progress man

take it easy

mrmrshoes
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jackdamery



Joined: Apr 26, 2010
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PostPosted: Thu Jul 04, 2013 4:55 am    Post subject: Reply with quote  Mark this post and the followings unread

super awesome-o 5000
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steffensen



Joined: Jul 11, 2012
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PostPosted: Thu Jul 04, 2013 9:31 am    Post subject: Reply with quote  Mark this post and the followings unread

mrmrshoes wrote:


Your work on the ADSR/AD Envelope sounds interesting like. Could you supply more info on that if possible. Have you used substitute Transistors in your build. If the transistors and Jet’s in this build could be subbed for more common parts I’m defos up for building this and other ARP modules.

Also I've read somewhere that you can't sub the LM301 OP-AMP because of the way it functions, but you can still get hold of these so shouldn't be a problem.

I'll keep you updated with progress man

take it easy

mrmrshoes


I of course meant the ADSR and AR (not AD). Working long hours until the vacation kicks in on Saturday. Then ill have the time/energy to try my design - when it arrives from the factory that is.
As im planning on doing it on 12v, i suspect i will have to do some tweaks to it. It might work straight off however, hoping for that.

I have implemented a Schmitt-trigger in the circuit to make sure the input trigger is above 10v, as thats the threshold for this circuit to work.
I am using 2N3906/3904's all the way thru, besides for the 2N5459 & 2N5460. Also sticking with the LM301 as i like that old grit. These parts are perhaps not to most available ones, but still pretty easy to get hold of.
I know several other IC's that would work too, but as said, i like to stick with the original path as much as i can.

Once ive made it work, i will experiment with some easier to find FET's, to really make this thing as easy to make as possible.

Gonna stop hogging up this thread now. I'll let you know if/when this thing is up and running. Smile
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Jerry_100



Joined: Nov 18, 2011
Posts: 6
Location: Bavaria

PostPosted: Tue Jul 09, 2013 9:29 am    Post subject: Reply with quote  Mark this post and the followings unread

Excellent Job ! I like your board, keep on rolling.....
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mrmrshoes



Joined: Feb 19, 2011
Posts: 73
Location: Newcastle Upon Tyne
Audio files: 4

PostPosted: Tue Jul 09, 2013 2:51 pm    Post subject: Reply with quote  Mark this post and the followings unread

Thanks alot fellas.

I've been having computer problems the pass 3-days. My laptop decided to die on me. I had feared for my hard drive. It contained all my PCB work. I got sloppy and didn't back up regularly. The Good news is that i have managed to pull all of my work onto another computer aswell as a stick/ external drive.

hopefully i'll have a prototype PCB made up in the next couple of days. Just need to double check the schematics and we should be ready to rock.
Please bear with me chaps. Wink
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Baloo



Joined: Jul 09, 2013
Posts: 15
Location: France

PostPosted: Tue Jul 09, 2013 4:40 pm    Post subject: Reply with quote  Mark this post and the followings unread

Nice work.
I am working in ARP Odyssey MK3 VCA & VCF
When I wil finish I will upload pictures of them. I even don´t know if they will work !!
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Paradigm X



Joined: Feb 15, 2011
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PostPosted: Fri Jul 12, 2013 2:42 am    Post subject: Reply with quote  Mark this post and the followings unread

Hey mrmrshoes!

Hope youre well.

Glad to see youre still on it!

Cheers
Ben
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mrmrshoes



Joined: Feb 19, 2011
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PostPosted: Fri Jul 12, 2013 4:35 pm    Post subject: Reply with quote  Mark this post and the followings unread

Paradigm X

Hows tricks like? all good i hope. yeah man I'm still plodding away with this stuff, I've got a fair few circuit finished but nothing boxed and paneled up like.
Rolling Eyes Rolling Eyes Rolling Eyes Rolling Eyes Rolling Eyes

Steffensen

Your plan for the ADSR sounds spot on like. I don't think you'll have much trouble subbing in JFET's. ARP designs seem pretty forgiving spec wise.
I'm looking forward to seeing the finished thing.


A quick update on this VCO

I've got the board etched and drilled. Hopefully get it built tomorrow.
If all goes well i'll have the build documentation up soon.

here are some picture in the mean time


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isak



Joined: Dec 13, 2009
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PostPosted: Sat Jul 13, 2013 12:22 pm    Post subject: Reply with quote  Mark this post and the followings unread

Great looking board Smile

I'm watching this post for awhile now, happy to see you have progressed.
I etched a board of the vco 2 of the arp2600, it's with waveshapres to tri and sine, didn't built it yet.
I really can't find the post of the vco 2, sorry, but I have all the documents if you want me to upload Smile

Cheers.

Posted Image, might have been reduced in size. Click Image to view fullscreen.

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Baloo



Joined: Jul 09, 2013
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PostPosted: Sun Jul 14, 2013 2:38 am    Post subject:   Reply with quote  Mark this post and the followings unread

@Isak- Could you upload the layout for the Arp2600 vco-2 ?
I would like try to build it.
Wink
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isak



Joined: Dec 13, 2009
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PostPosted: Sun Jul 14, 2013 3:17 am    Post subject: Reply with quote  Mark this post and the followings unread

Baloo wrote:
@Isak- Could you upload the layout for the Arp2600 vco-2 ?
I would like try to build it.
Wink


i actually found the original post Smile
http://electro-music.com/forum/topic-39973.html

roll down Wink

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Baloo



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PostPosted: Sun Jul 14, 2013 2:25 pm    Post subject:   Reply with quote  Mark this post and the followings unread

Thanks!!
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mrmrshoes



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PostPosted: Wed Jul 17, 2013 4:12 pm    Post subject: Reply with quote  Mark this post and the followings unread

Sorry for wait fellas

I finally managed to finish the documentation for this VCO like, It took longer than I thought but its done now.
I've tested the majority of the circuit: VCO Core, LF mode, Saw, Ramp, Triangle, Square and Sine Wave-shaper circuity and all looks good. I should state that I’ve not had time to test external input functions of the VCO like 1V-Oct, FM and Sync but saying that I don't really see any issues arising from these things. Just be warned, if you build this project it at your own risk.

If you want extra documentation on calibrating the wave shapers or general back ground reading check out all of these sites:

4027-1 VCO schematic 
http://www.till.com/arptech/modmain.htm 

Bergfotron - Basic VCO 
http://hem.bredband.net/bersyn/VCO/vco_basic.htm 

Thomas Henry - wave-shapers schematics
http://www.birthofasynth.com/Thomas_Henry/Pages/VCO-1.html 

AndyR1960 - great thread – ARP Odyssey Oscillators
http://electro-music.com/forum/topic-28604.html

Also a VERY big thank you to ARP, Bergfotron, Thomas Henry and Andy1960 for the resources related to this great VCO.


I'll probably update Build doc PDF with a basic run down of trimming the various wave-shaper parts of the circuit. I won't be able to do that for a few days, So keep an eye out.

enjoy!


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isak



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PostPosted: Sat Jul 20, 2013 12:25 pm    Post subject: Reply with quote  Mark this post and the followings unread

thank you very much my friend, great job!
i hope it sounds good as it look Wink

did you matched any of the transistor?
the sync... is it in or out?


thanks again Smile

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mrmrshoes



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PostPosted: Sat Jul 20, 2013 1:24 pm    Post subject: Reply with quote  Mark this post and the followings unread

Cheers pal.
You are more than welcome.

It sounds good like Wink (good old ARP)

I didn't match a single transistor (It can't hurt if you do) and I got the waveform outputs shown in the VCO Build Doc PDF.

The Sync is Input. I just added Bergfotron's sync from his Basic VCO design.
Check out the schematic to get a feel for it.

The Triangle ain't a 100% clean, but you can trim it pretty close.

take it easy man

shoes
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isak



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PostPosted: Sat Jul 20, 2013 3:29 pm    Post subject: Reply with quote  Mark this post and the followings unread

Thank you Smile
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koenpepping



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PostPosted: Wed Jul 09, 2014 4:33 am    Post subject: Reply with quote  Mark this post and the followings unread

Hi,

first of all thanks for sharing the vco Smile
I was looking at the BOM and noticed the ST3P switch.

my question is:
what does it do? and where can i find one?

thanks again and already!
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