TZFM SAW VCO

Luka · Joined: Jun 29, 2007 Posts: 1003 Location: Melb.

can we use 2sa798s i have a bunch of those?

frijitz · Posted: Thu Nov 13, 2008 8:21 pm Post subject:

Yes, that's what I was using originally. You will get a bit of the drift I mentioned, but it may not be an issue for you. The board is layed out to take a 798 or a dil chip.

Ian

zthee · Joined: Feb 20, 2008 Posts: 414 Location: Stockholm

Been working on my panel design for this over the weekend.. That's how excited I am about this project! Smile

phdinfunk · Joined: Jun 04, 2008 Posts: 119 Location: Taiwan

Hi, I am planning a spot in my system for four of these oscillators. I'm still excited about them. Thanks, Ian.

frijitz · Posted: Sat Nov 29, 2008 9:34 am Post subject: Subject description: update

Time for another update.

I'm still beavering away at this. As soon as the PCBs came in I stuffed one, and everything worked right off. The problem I mentioned with a slight tendency for the VCO to try to sync with the modulation source was actually a bit worse with the PCB than it was on the whiteboard -- nothing like wires for low resistance. Laughing

How does this spurious syncing work? It happens when the system is near the point where a frequency reversal occurs very close to a Saw reset point. The system can either (1) reverse frequency or (2) switch, then reverse frequency, then switch back. It is very important to understand that ideally it makes no difference to the final output which path is taken! This is because to derive the final Saw from the raw Saw, the positive segments are shifted down and the negative segments are shifted up, so either path produces the same output waveform.

In practice, however, because of the finite reset time the two paths lead to slightly different frequencies (two extra switches for path (2) above). This means the system can adjust its frequency slightly by varying the ratio of how often it chooses one path over the other. Since the circuit deriving the final Saw waveform has a pair of comparitors that fire when the modulating signal induces a frequency reversal, the modulation signal ends up (indirectly) putting some spikes on the PS lines, which allows the syncing.

Don't worry if you don't follow all this -- it took me days to figure out. It is actually a very minor problem, but I wanted to clear it up. So most of my time lately has been spent figuring out this mechanism and working at cleaning up the PS noise. This has required making several changes, none of which worked by itself, but together have reduced the problem to a negligible level. Right now I've got it to where it is very difficult to tune the system to see the effect, and it now occurs only occassionally when the system has the conflict successively at the positive and negative crossover points. This would very rarely happen in normal operation, and in fact it takes me several minutes to dial in the problem area.

Right now I'm working on updating my "official" schematics, after which I am going to redo the board layout to incorporate the changes that had to be made and to further improve the decoupling between the circuit segments. I hope I can get the next prototype boards within a couple of weeks.

Thanks for all the interest in this project!

Very Happy

Ian

frijitz · Posted: Sat Nov 29, 2008 10:10 am Post subject:

johans121 · Posted: Sat Nov 29, 2008 12:09 pm Post subject: Subject description: update

neandrewthal · Joined: May 11, 2007 Posts: 672 Location: Canada

Do you think this would make a good companion for the double deka, or should I have at least 2 of these? I have 8u in my next cabinet reserved for VCOs. I`m thinking of doing 2x Tri core TZOs at 2U each, then cramming this and the double deka on 4U(basically 2.5U for the Deka, 1.5U for this)

frijitz · Posted: Thu Dec 11, 2008 1:50 pm Post subject:

The new board layout is finished and in to get prototypes made. I had to make the board a bit bigger to put in the improved circuitry. Here's a lores look to give you the basic idea. I'm shooting for the end of next week to get the new build finished. Stay tuned!

Very Happy

Ian

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mono-poly · Posted: Thu Dec 11, 2008 3:06 pm Post subject:

You rule!

johans121 · Posted: Thu Dec 11, 2008 3:39 pm Post subject:

fluxmonkey · Joined: Jun 24, 2005 Posts: 708 Location: cleve

whoo-hoo! thanks for persevering on this one, Ian, i'm sure it'll be a winner!

b

Rykhaard · Joined: Sep 02, 2007 Posts: 1290 Location: Canada

Many thanks and respect, Ian, for continuing to put out new things here on EM for all of us to enjoy. Smile

That, is greatly appreciated.

Waiting ...... still patiently, thankfully. Wink

zthee · Joined: Feb 20, 2008 Posts: 414 Location: Stockholm

TekniK · Joined: Aug 10, 2008 Posts: 1059

10 ic's on this vco!

frijitz · Posted: Fri Dec 12, 2008 7:33 am Post subject:

phdinfunk · Joined: Jun 04, 2008 Posts: 119 Location: Taiwan

Having followed the developement of this design, and hearing your developement issues, I just want it for my system. Alternatives be damned!

--Jonathan

krisp14u · Joined: Nov 11, 2006 Posts: 206 Location: uk

I have been following this closely as a TZFM VCO is something that I just need to have a play with but I just can’t stretch my funds to the Cynthia ZO

Funky40 · Posted: Fri Dec 12, 2008 11:51 am Post subject:

frijitz · Posted: Fri Dec 12, 2008 2:47 pm Post subject:

fluxmonkey · Joined: Jun 24, 2005 Posts: 708 Location: cleve

frijitz · Posted: Sat Dec 13, 2008 12:27 pm Post subject:

Sine · Joined: Sep 10, 2007 Posts: 111 Location: Netherlands

No need for low-drop, simple 7812/7912 regulators should do nicely, they are more than happy with 3 volts.

frijitz · Posted: Mon Dec 15, 2008 2:08 pm Post subject:

frijitz · Posted: Sun Jan 04, 2009 5:40 pm Post subject:

Latest results:

As I mentioned before, there was a small tendency for the system to rattle and/or phase lock a bit when the modulation frequency was very close to the carrier frequency, and when the waveform reversal level was very close to the switching level, and when the modulation depth was in a certain small range. This would rarely occur in practice, but I wanted to get rid of the problem as much as possible.

When I got the second prototype board hooked up there was still sometimes a bit of jittering. I eventually figured out that the cause was a slight difference in the voltage range of the up and down ramps. Readjusting the special charge injector circuit for better compensation of the reset charge injection got rid of the problem. So I think the circuit is quite reliable now.

I also found that I could have problems when there was noise pickup on the CV input leads and when the two VCOs were on different power circuits. The user will have to deal with these effects on an individual basis. But I imagine that if you want the two VCO frequencies to be the same, you will use the sycn feature anyway.

Yesterday I started measuring the temperature stability. First I looked at just the core oscillator. Surprisingly, the core drift is very small -- something around -60 ppm/K. This will probably depend somewhat on the properties of the actual components used. Anyway, it looks like this is going to be a nice stable unit. Next I'm going to test the drift of the whole circuit. With an accurate tempco resistor it should be very good. The OTA modulation block shouldn't add any drift, since I have the linearizations diodes biased on. But we will see ...

I don't think there are any other issues to address. The schematic drawings and the board layout need some minor changes, but I'll check all that carefully so I don't have to do another prototype run. (This gets expensive!)

Hope everyone had a good Holiday season!

Very Happy

Ian