Updated SSI2130 VCO Datasheet available...

[KSS]

Didn't David Dixon use this method for his Freq Shifter?

I know its -all pass- been used for quadrature before.

[KSS]

You can call it the "Johnson Oscillator" or "Johnson Configuration"

How about the "Johnson Circumference"?

[devinw1]

[neil.johnson]

Didn't David Dixon use this method for his Freq Shifter?

No, I don't believe so.

I know its -all pass- been used for quadrature before.

Do you have a link? This specific application is a voltage-controlled all-pass filter that tracks the VCO. To that extent you could do further interesting things like changing the phase shift by a second control voltage.

Neil

[KSS]

Quote from the lower of a few possibly pertinent posts on page 19 of the "Something New from Doc sketchy" thread.
https://muffwiggler.com/forum/viewtopic ... &start=450

-- The 90-degree PDN is especially awesome. I tested it by feeding it a sine wave from my Rubicon and scanning the frequency from 15Hz to 15kHz by playing octaves and turning the octave selector switch, and measuring the two outputs on my oscilloscope in XY mode. If the PDN is working well, one should get a circular Lissajous figure across the entire frequency range. I got a perfect circle and it didn't budge at all as I changed the octaves -- it was only very slightly deformed at the highest frequency of 15kHz. I compared this with my previous PDN, and I think that maybe this one is just a little bit better than that one. I hand-selected the 12 film capacitors (four each of 102, 103 and 104) to get virtually perfect values. The resistors are 1% tolerance, just randomly pulled from the bags (I have a little kit of resistor values just for this PDN design -- 22 very specific values which, when combined with the three cap values, give 12 allpass filters with very precise corner frequencies

[dksynth]

Quote from the lower of two pertinent posts on page 19 of the "Something New from Doc sketchy" thread.
https://muffwiggler.com/forum/viewtopic ... &start=450

-- The 90-degree PDN is especially awesome. I tested it by feeding it a sine wave from my Rubicon and scanning the frequency from 15Hz to 15kHz by playing octaves and turning the octave selector switch, and measuring the two outputs on my oscilloscope in XY mode. If the PDN is working well, one should get a circular Lissajous figure across the entire frequency range. I got a perfect circle and it didn't budge at all as I changed the octaves -- it was only very slightly deformed at the highest frequency of 15kHz. I compared this with my previous PDN, and I think that maybe this one is just a little bit better than that one. I hand-selected the 12 film capacitors (four each of 102, 103 and 104) to get virtually perfect values. The resistors are 1% tolerance, just randomly pulled from the bags (I have a little kit of resistor values just for this PDN design -- 22 very specific values which, when combined with the three cap values, give 12 allpass filters with very precise corner frequencies

The Dixon FS uses a dual core Rubicon VCO set up in a way that keeps the outputs in quadrature. The allpasses mentioned later are not part of the driving VCOs.

[KSS]

True.

[Funky40]

are there NICE DIY ( TZFM plus phase modulation) VCOs to expect to come based on that chip ?
i´d guess thats the case, right ?
how long might this take, 6 months, 9 months ?

Q2: is soft sync possible ? ....adjustbale softsync ?
if so, you DIY kits manufacturers: add in any case (adjustable! ) softsync to your VCOs ! please !
it can do wonders when patchong VCOs together who have TZFM AND Phase modulation.

( i did just recently some supergreat patching with a Fritz Teezer and the joranalogue G3.
the softsync can REALLY change things here, in complex patchings)

[neil.johnson]

are there NICE DIY ( TZFM plus phase modulation) VCOs to expect to come based on that chip ?
i´d guess thats the case, right ?
how long might this take, 6 months, 9 months ?

Q2: is soft sync possible ? ....adjustbale softsync ?
if so, you DIY kits manufacturers: add in any case (adjustable! ) softsync to your VCOs ! please !
it can do wonders when patchong VCOs together who have TZFM AND Phase modulation.

( i did just recently some supergreat patching with a Fritz Teezer and the joranalogue G3.
the softsync can REALLY change things here, in complex patchings)

I'm sure there will be

As regards to soft sync: yes it is possible with the SSI2130. It's an interesting little feature in its own right, so I'm sure the designers out there will have plenty of fun with it

Cheers,
Neil

[neil.johnson]

Quote from the lower of a few possibly pertinent posts on page 19 of the "Something New from Doc sketchy" thread.
https://muffwiggler.com/forum/viewtopic ... &start=450

You missed the pertinent post. Allow me:

Mathematically, it's a Bode frequency shifter (I tried building a Weaver shifter once and failed miserably). However, all of the circuit components are of my own design. The TZFM VCO is a dual-core simplified Rubicon set up so that the two cores are always 90 degrees out of phase, the multipliers are linearized 2164 circuits of my own design, and the 90-degree phase displacement network is my own design based on the free software QuadNet (for a 12-filter unit creating 90 degree phase displacement between 15 and 15,000 Hz). There are no trimmers in the PDN or the multipliers, only on the VCO (one for 1V/octave tuning and four for sine and cosine wave shaping). The secret to trimmer-less multipliers is to a) hand-select the gain resistors, and b) to AC couple all the inputs.

The all-pass PDNs that you pointed out in your post are used to split the incoming audio signal into the I/Q pair.

I must admit the approach Dave took is rather brave (two oscillators, keeping them in sync) and I take my hat off to him for it. I would have taken a different approach, but as he points out in his youtube vid you get the advantage of a variety of waveforms, not just sine/cosine.

Neil

[KSS]

Thanks for the replies.
@neil.johnson
I didn't "miss" the pertinent post, I mentioned it but quoted the one with the words "all pass" instead. Since that's the thing we were talking about and I'd said there were other posts to read on that page.

But again, thank you for the replies!

[Funky40]

As regards to soft sync: yes it is possible with the SSI2130. It's an interesting little feature in its own right, so I'm sure the designers out there will have plenty of fun with it

I hope they follow you / Great ! Much Thanks !

[forestcaver]

are there NICE DIY ( TZFM plus phase modulation) VCOs to expect to come based on that chip ?

Yes :-)

[DozenCrows]

Got my test board up and running today - core waveforms worked first time! Need to test tuning, mixing and sync.

I created my own Kicad symbol and "hand soldering" footprint (both in attached zip) with longer pads, and was able to successfully drag-solder the QFN. I started by putting down some flux on the corner with pins 15 & 16, then adding some solder on the iron to those so it wicked up against the pins. I then proceeded to flux and drag solder each side in turn, with several short passes of the iron on each until I could just see solder on the QFN pins on the edges and no bridges on the PCB pads.

The QFN shifted very slightly sometime during the drag solder, but not enough to break any contacts that I've tested so far.

I'll be putting up board files, schematic and BOM in Github once I've tested all of it.

[neil.johnson]

Got my test board up and running today - core waveforms worked first time! Need to test tuning, mixing and sync.

I created my own Kicad symbol and "hand soldering" footprint (both in attached zip) with longer pads, and was able to successfully drag-solder the QFN. I started by putting down some flux on the corner with pins 15 & 16, then adding some solder on the iron to those so it wicked up against the pins. I then proceeded to flux and drag solder each side in turn, with several short passes of the iron on each until I could just see solder on the QFN pins on the edges and no bridges on the PCB pads.

The QFN shifted very slightly sometime during the drag solder, but not enough to break any contacts that I've tested so far.

I'll be putting up board files, schematic and BOM in Github once I've tested all of it.

IMG_20201101_162133.jpg

Nice!

Neil

[trip]

Hi Neil, I'm curious if there is trick that can be used to get quadrature functionality from a pair of SSI2130. This would be very useful in a frequency shifter.

Tricky to get a seamless sync between the two oscillators. Have you considered a voltage-controlled all-pass filter to provide a 90 degree phase shift that tracks the VCO? You could do it with 1/4 of an SSI2164 and a couple of op-amps.
Neil

Something like this:


Details to come in the SSI2130 datasheet.

Neil

This is very exciting!

I've always been intrigued by doing DX style "feedback" in an analogue VCO, but have never figured out how to do it without a dc offset. I remember hearing Rob Hordijk talking about using a cosine wave to achieve the sinewave tilt, but can't recall the details - I think it might have been for his OSC HRM, but can't find any info online on that now.

I'd be interested to see if something like that could be possible with a tracking all pass filter.

[BugBrand]

That'd be Chebyshev functions - think Rob discusses it here:

[Nick66]

I created my own Kicad symbol and "hand soldering" footprint (both in attached zip)

Thanks for that! Will be very helpful.

are there NICE DIY ( TZFM plus phase modulation) VCOs to expect to come based on that chip ?

I'm new to TZFM. I get the idea of maintaining the centre of pitch compared to exponential FM even for extreme modulation, so then would you ever need to have linear FM without the through zero part? Any musical value? I would you just implement the TZFM circuit and leave it at that

[neil.johnson]

I'm new to TZFM. I get the idea of maintaining the centre of pitch compared to exponential FM even for extreme modulation, so then would you ever need to have linear FM without the through zero part? Any musical value? I would you just implement the TZFM circuit and leave it at that

TZFM requires more components than linear FM. So it's a product definition question: higher price but TZFM, or lower cost for linear FM.

Neil

[lickspittle]

I'm new to TZFM. I get the idea of maintaining the centre of pitch compared to exponential FM even for extreme modulation, so then would you ever need to have linear FM without the through zero part? Any musical value? I would you just implement the TZFM circuit and leave it at that

Here's a YouTube vid demonstrating through zero linear FM using a software synth...
The comparison between through zero and non-through zero begins from about 18:00 onwards. You can decide whether you think it's worth it. Personally I think, if it's available, I'd want it. I've heard it described as "linear FM that just works".

[BugBrand]

Coming back to the Eagle package I put up (using footprint shared with me by ForestCaver)..
I finished up my test board design (quite a bit beyond the datasheet ) but now doing the gerbers it is noticeable that the 2130 part is giving some CAM issues.. [flags up extremely large plot data - so going to try editing the package again, perhaps deleting the central pad]

[edit - OK, tried plotting again &, while it did take some time & did make a larger file than usual, it did seem to work OK -- I also tried editing the package but would need to change the whole device inc symbol to now remove the pad... so won't bother for this time around]

[DozenCrows]

My test board checks out on all the essentials. BOM, schematic and Gerbers available at https://github.com/dozencrows/eurorack/ ... 0_vco_eval.

The components are all surface mount except headers and trimmers, resistors and caps using 0805 footprints. Values pretty much match the datasheet, with some tweaks from comments in this thread (e.g. 100K resistors on frequency input). I also added +5V and -5V references for external use.

I slightly tweaked it from the one pictured above to add a header for the regulated power rails, a test point for adding a pin to get a solid GND connection, and some mounting holes.

[Ayeh]

Hello peps,
I´m very pleased to write my first post in this forum about this incredible IC,
I´ve made a PCB following the schematics from the website and I´ve managed to solder this tiny QFN with a soldering iron, everything is working as expected, V/oct tracking and stability is very good after leaving the VCO on for a couple of hours, and TZ sounds pretty cool.
The only thing that bothers me is the sine shaper at low freq, it gets distorted as you can see in the pics, I did exactly what datasheet suggest. Is this normal behavior from the sinewave??

[DozenCrows]

One thing not explicitly mentioned in the datasheet is the expected signal amplitude from the mixer when a channel is set to unity gain. Unlike the tri, saw and pulse outputs, the mixer output is bipolar. When putting the indicated 100uA into one of the corresponding mixer channels, I get a ~1.6Vpp waveform on the output. The mix output is connected to GND via a 5K resistor as indicated in the datasheet.

[DozenCrows]

The only thing that bothers me is the sine shaper at low freq, it gets distorted as you can see in the pics

How low is low frequency here? My guess from your oscilloscope output is LFO range, around 1.5Hz?