Trapezoid VCO

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ashleym
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Post by ashleym » Tue Aug 20, 2019 3:29 pm

Exciting. How many modules legitimately have TZ controls? When the time comes I’ll ask for or try to figure out the mods to get this working in a 12v :sadbanana:

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Haralds:Werk
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Post by Haralds:Werk » Wed Aug 21, 2019 8:02 am

ashleym wrote:Exciting. How many modules legitimately have TZ controls? When the time comes I’ll ask for or try to figure out the mods to get this working in a 12v :sadbanana:
No mods needed. It'll work with 12V out of the box.
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Post by Haralds:Werk » Wed Aug 21, 2019 8:08 am

B0bcat wrote:I want to express interest in a Euro version :)
Building a Euro version is just replacing the bananas with 3.5mm jacks and and adapting the power connector. Both is easily done with the wiring. The VCO is running on 12V without changes.
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Isaiah
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Post by Isaiah » Wed Aug 21, 2019 8:36 am

Haralds:Werk
This looks great!
Do the Alfa 3280s work in this circuit?
What other waveshapes are you adding?

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B0bcat
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Post by B0bcat » Wed Aug 21, 2019 9:07 am

Haralds:Werk wrote:Building a Euro version is just replacing the bananas with 3.5mm jacks and and adapting the power connector. Both is easily done with the wiring. The VCO is running on 12V without changes.
fantastic!
FS:
WMD/SSF Blender ($80), AMSynths AM8109 ($170), Alesis Midiverb-2 ($100), Yamaha SPX-90 ($150), all prices shipped from and to US

WTB:
Malekko/Wiard Oscillator (Gargoyles),
Sputnik Dual Oscillator,
Plan B / SubCon Model 15 VCO, Plan B Model 12 VCF,
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ashleym
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Post by ashleym » Wed Aug 21, 2019 9:48 am

Haralds:Werk wrote:
No mods needed. It'll work with 12V out of the box.
Fantastic news. I thought there would have been something complicated with the original/inspiration need 8v.

All I/we need is a nice Loudest Warning panel for the Sergeratti and Robert is your father’s brother.

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Post by Haralds:Werk » Thu Aug 22, 2019 1:18 am

Isaiah wrote:Haralds:Werk
This looks great!
Do the Alfa 3280s work in this circuit?
What other waveshapes are you adding?
According to the datasheet the AS3280 should work as a direct replacement for the CA3280. The AS3280 comes in SOIC so you need a adapter to use it or change the PCB. The guys from Alfa refused to send me samples so I was not able to make tests.

The other waves are triangle, sine, ramp up, ramp down and voltage controlled pulse.

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Post by whoop_john » Thu Aug 22, 2019 2:10 am

Great work, thanks for sharing. I am very interested in making a eurorack version of this. I can work with Julian on a euro panel. Of course I'd only work with the blessing of Harald Antes.
Ⓞⓝⓔ ⓓⓐⓨ ⓨⓞⓤ ⓦⓘⓛⓛ ⓦⓐⓚⓔ ⓤⓟ ⓐⓝⓓ ⓕⓘⓝⓓ ⓨⓞⓤⓡⓢⓔⓛⓕ ⓓⓔⓐⓓ ⓐⓝⓓ ⓨⓞⓤ ⓦⓘⓛⓛ ⓢⓣⓐⓨ ⓛⓘⓚⓔ ⓣⓗⓐⓣ ⓕⓞⓡ ⓣⓗⓔ ⓡⓔⓢⓣ ⓞⓕ ⓨⓞⓤⓡ ⓛⓘⓕⓔ

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Haralds:Werk
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Post by Haralds:Werk » Thu Aug 22, 2019 5:31 am

ashleym wrote:
Haralds:Werk wrote:
No mods needed. It'll work with 12V out of the box.
Fantastic news. I thought there would have been something complicated with the original/inspiration need 8v.

All I/we need is a nice Loudest Warning panel for the Sergeratti and Robert is your father’s brother.

Keeping the 8V regulators is the reason for working on 12V and 15V.
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Haralds:Werk
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Post by Haralds:Werk » Mon Aug 26, 2019 9:12 am

The documents and Gerber files are online now. Download here:

https://www.haraldswerk.de/VCO/Trapezoi ... d_VCO.html
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Post by guest » Mon Aug 26, 2019 12:06 pm

thank you once again for sharing a well designed and documented project! i noticed you kept the dual-capacitor per integrator aspect of tillmans original design. i never quite understood what this did. could you share your insights?
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Post by smrl » Mon Aug 26, 2019 2:53 pm

i thought it was just a capacitance matching thing, increasing the similarity between the two integrators, since any imbalance will create asymmetrical waveforms. But then I noticed they're connected to + and - supplies. Balancing charge injection spikes between the supplies rather than coupling to ground?

Edit: looks so
" C1 through C4 are the ramping capacitors. The capacitors are split between the ±8V power supply instead of being connected to ground to avoid sudden current changes in the ground line. "

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Post by J3RK » Mon Aug 26, 2019 2:57 pm

smrl wrote:Balancing charge injection spikes between the supplies rather than coupling to ground?
Not sure, but it could be. I believe Don's original article did mention attempting to reduce this. (including going with the higher-end switches)
Are you lemon? Does your head come to a nub?

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Post by guest » Mon Aug 26, 2019 8:14 pm

ill give this some thought. it doesnt seem like there would be large ground spikes on a triangle core, as the current doesnt change rapidly. particularly in this core, which goes from positive current, to no current, then to negative current. maybe it helps with charge injection from the switches? although i dont quite see how at the moment. the powersupply rails are the same as ground to a capacitor.
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Post by Haralds:Werk » Wed Aug 28, 2019 3:43 am

guest wrote:ill give this some thought. it doesnt seem like there would be large ground spikes on a triangle core, as the current doesnt change rapidly. particularly in this core, which goes from positive current, to no current, then to negative current. maybe it helps with charge injection from the switches? although i dont quite see how at the moment. the powersupply rails are the same as ground to a capacitor.
I am with you here. In this configuration no large ground spikes should occur. But if there are any spikes they are isolated or buffered through the additional 8V regulators from the main PSU.
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Post by Haralds:Werk » Thu Sep 05, 2019 5:46 am

smrl wrote:i thought it was just a capacitance matching thing, increasing the similarity between the two integrators, since any imbalance will create asymmetrical waveforms. But then I noticed they're connected to + and - supplies. Balancing charge injection spikes between the supplies rather than coupling to ground?

Edit: looks so
" C1 through C4 are the ramping capacitors. The capacitors are split between the ±8V power supply instead of being connected to ground to avoid sudden current changes in the ground line. "
From personal communication with Don I know this was his intention. But by now he has improved the circuitry further and moved away from the double capacitors.
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Post by Haralds:Werk » Thu Sep 19, 2019 4:22 am

The quad waveshaper for the trapezoid quadrature VCO is now online. You can find it here: https://www.haraldswerk.de/VCO/Trapezoi ... _Wave.html

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J3RK
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Post by J3RK » Thu Sep 19, 2019 5:05 pm

Those wave shapes are looking really good! Nice work!
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Post by appliancide » Fri Sep 20, 2019 7:19 am

This is very impressive! I will definitely have to build this for myself at some point. Nice work!

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Post by Haralds:Werk » Thu Dec 05, 2019 11:33 am

I have a new version online now. With thanks to Don Tillman I could simplify the schematic. The level shifting in the address lines to the DG409 is removed and I switched to a two capacitor design. Some part values are changed as well. Docs and Gerbers are updated.

https://www.haraldswerk.de/VCO/Trapezoi ... d_VCO.html
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Post by tardishead » Fri Dec 06, 2019 2:00 am

This looks great
can we have some sound demos?

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Post by tardishead » Sun Dec 08, 2019 5:08 am

I have no idea what a trapezoid wave sounds like
Can anybody point me to a sample?

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Post by Haralds:Werk » Tue Dec 10, 2019 11:17 am

Sorry no soundfiles yet. The trapezoid wave sounds somewhere between triangle and sine. What makes this VCO interesting are the quadrature outputs and of course mostly the through zero capability. I highly recommend the waveshaper to get all the other waves as well.
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Re: Trapezoid VCO

Post by tardishead » Tue Jan 21, 2020 5:10 am

I am building the Trap VCO and Waveshaper boards from Harald. I thought I would document some of my experience in case it will help others.
Firstly the CA3280E. I mistakenly thought that if I buy an expensive CA3280 from a reputable seller then I would be guaranteed a part that works. I have never had a problem before with rare parts when I have done so. I was totally wrong. The CA3280 I bought was not working. CAVEAT EMPTOR. But a lot has been said about this. Indeed some people have bought fake ones which have ended up destroying other expensive parts. I was lucky that did not happen to me but the outputs were reading DC.
The good news is that the reissued AS3280 does work. I have yet to fully test out the circuit to see if there are any anomalies but the first impressions were very good. Very nice looking and sounding wave shapes from the main board.
A few technical issues/queries. I installed a couple of unmatched 2n3906 for the expo convertor just to check the build make sure everything was working ok. I have ordered an SSM2220. When I install is it better to not use an IC socket over the top of the tempo resistor and install the SSM2220 directly on top so that it is in direct physical contact with the tempco (and use transfer compound as well)? Or is it preferable to use a socket?
When trimming the DC offset for the waveforms I discovered that while you can trim one quadrature output exactly its opposite was a little off. This offset must be introduced by the inverting buffers on the outputs. I doubt this is a big deal.
The wave shaper PCB I had problems with to start with. On the TRAP comm outputs connecting cable between the two pcbs pin 5 on the VCO PCB needs to go to pin 4 on the Waveshaper PCB. This took me a while to figure out. I’m not sure this is a mistake as such because it is shown on the schematic but it threw me because everything else in the build was totally intuitive. I have to say the PCBs are a fantastic design and quality - otherwise very easy to build without making mistakes.
Somehow when ordering a BF245B from Farnell it took me to the BF256B page and I ordered them by mistake. However I do get a sine shape. It seems OK at first glance but I will look into this. I’m not sure what anomalies to look out for when using a different FET.
I am building mine in MU 5u. I will document the build further

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Re: Trapezoid VCO

Post by Haralds:Werk » Tue Jan 21, 2020 9:42 am

tardishead wrote:
Tue Jan 21, 2020 5:10 am
I am building the Trap VCO and Waveshaper boards from Harald. I thought I would document some of my experience in case it will help others.
Thank you. I am always happy to hear from other builders. Every feedback is welcome. This keeps me going and helps me to improve my designs and my website.
tardishead wrote:
Tue Jan 21, 2020 5:10 am
The good news is that the reissued AS3280 does work. I have yet to fully test out the circuit to see if there are any anomalies but the first impressions were very good. Very nice looking and sounding wave shapes from the main board.
I am still waiting for my AS3280 to arrive. I'll just swap them in and report back here.
tardishead wrote:
Tue Jan 21, 2020 5:10 am
A few technical issues/queries. I installed a couple of unmatched 2n3906 for the expo convertor just to check the build make sure everything was working ok. I have ordered an SSM2220. When I install is it better to not use an IC socket over the top of the tempo resistor and install the SSM2220 directly on top so that it is in direct physical contact with the tempco (and use transfer compound as well)? Or is it preferable to use a socket?
I am using a socket and put the tempco above the socket. Socket - tempco - SSM2220. So the tempco is below the SSM but above the socket.
tardishead wrote:
Tue Jan 21, 2020 5:10 am
When trimming the DC offset for the waveforms I discovered that while you can trim one quadrature output exactly its opposite was a little off. This offset must be introduced by the inverting buffers on the outputs. I doubt this is a big deal.
You are right. In the audio path when dealing with 10Vpp signals a few millivolts doesn't matter. I you want to optimize the DC offset you can us selected OpAmps. You have got the right answers in your other thread about DC offset.
tardishead wrote:
Tue Jan 21, 2020 5:10 am
The wave shaper PCB I had problems with to start with. On the TRAP comm outputs connecting cable between the two pcbs pin 5 on the VCO PCB needs to go to pin 4 on the Waveshaper PCB. This took me a while to figure out. I’m not sure this is a mistake as such because it is shown on the schematic but it threw me because everything else in the build was totally intuitive. I have to say the PCBs are a fantastic design and quality - otherwise very easy to build without making mistakes.
Sorry for the confusion. The naming of the connections are not very clear. BTW try to experiment with different connections. You can find unusual looking and sounding waveforms.
tardishead wrote:
Tue Jan 21, 2020 5:10 am
Somehow when ordering a BF245B from Farnell it took me to the BF256B page and I ordered them by mistake. However I do get a sine shape. It seems OK at first glance but I will look into this. I’m not sure what anomalies to look out for when using a different FET.
Good find. The BF245B is rare today. If the BF256B looks and sounds right for you, stay with it. Unless you have a decent audio measure equipment you can't tell the difference by looking at the scope when it is not way off.
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