TH VCO-1 and XR-VCO?

[zthee]

Hi,

I've started to plan the building of my modular. Got some EFM-modules done already, just ordered som CGS PCBs. But when it comes down to VCOs I'm kinda lost.

For a long time I thought about the CGS VCO. It looks like it's a great VCO - though I haven't really read any reviews of it. So I don't know..

Anyway - my current thoughts lean towards using 2 VCO-1 and 2 XR-VCO.

Let me explain; They look kinda easy to build? They don't have like 20 ins and outs (This might be a downside aswell, but as for now I think it's a plus). They're simple and elegant VCOs. They cover the most basic needs - VCO-1 has PWM and XR has skew and sync.. and with the bugbrand mod you can have the XR as an LFO.

They are to be used mostley for bleeps, squeeks and sometimes melodies.

I guess my questions are:

Are they hard to build? (I did put together a x0xb0x in just about 3 days..)
Do they stay somewhat in tune over atleast some time? (not tuning every day..?) - I don't know why I really care about this

Or am I just being unimaginative here - and should I go for the CGS VCO instead?

(I mean it's a modular, I've got all the possibilities to expand it later) - but as a first choice..

I think this just turned into one of these dreadfull "Is this right for me"-threads. That wasn't my intention. I just wanted to know -

Should I reconsider or is it a cool idea?

[Coriolis]

I built the VCO-1 as my first module and it's worked fine ever since. Tuning stinks, but that's because I put an NTC thermistor in it instead of a PTC (so actually worsening the temp drift of the expo pair ).
The original layout only has space for an expo pair made of either discrete transistors or metal can duals, so DIP duals can't be used without a bit of kludging - could be a downside. I couldn't quite get a decent sinewave out of it, but it's my only vco sofar (building an XRvco right now as my second) and I don't have a scope, so what do I know?

If I got my shit together and corrected a few things, it would be a cool vco.
Although...the XR has a sync in, which the VCO-1 doesn't...

C

[zthee]

Oh, better becarefull with the thermistors then

About the matching of the transistors - It's just to match them by hand by the HFE numbers? If i go discrete (which I intend to do, I think).

I think the VCO-1 and the XR compliments each other in a nice way.

[Pehr]

The XR-VCO looks really nice with its skew-function. I'm at least going to build one.

Regarding the ins and outs, I often find myself using more than one CV-inputs. For example, you might want a VCO to be controlled by a keyboard, sequencer and a LFO at the same time, thus many CV ins could be usefull. However, that could be achieved with other DC mixer modules...

Also I very often use the saw-output of my oscillators, which the VCO-1 don't have.

I have built 4 MFOS VCOs and I pretty pleased. However, I have to trim them again now after the winter since the sine waves are 'popping'

Oh, and also, a sync input is very useful for sweeping effects

[zthee]

Pehr, The MFOS VCO looks good! I've been looking at some of the MFOS parts for a long time (I mean, everyone do need a WSG right?). It could be a good idea to have it as a project in the future..

And you're right about the ins and outs. I tend to use all my 4 inputs into the EFM filter module. But Since I'm trying to get as many modules as possible into the smalles space possible I have to make some sacrifices.. (I'm thinking of building a small DC-mixer break-out-box, it might be a good idea). But the possibilty to connect both sequencer, lfo and envelope to the input of oscillator is a must!

[RF]

I'd second Pehr on the MFOS VCO's.
They are very well documented, easy to set up and find parts.
I've got a bunch of those in my modular.

bruce

[crashlander42]

I'm a big XR VCO fan. I've built 3 of them now. They seem stable enough, are fairly cheap to build, and are simple to build. I've also built 2 VCO-1's and haven't had any problem with them. I was very careful about matching the transistors.

[numbernone]

I have a pair of MFOS and three of the XR. The MFOS oscillators have most of the options you are gonna need, lots of waveshapes, PWM. The XR is really pleasing to my ear, and the VC waveshape/rampoid is great fun, which Im only now 6 months later starting to really exploit. My philosophy is build a ton of everything. I am finishing up 4 8038 VCOs currently, the are pretty vanilla but I fit them into about 3 square inches each, and I like to build small. Yusynth will probably be next, then hopefully somebody will roll out a DIY thru zero model.

[neandrewthal]

I'm enjoying my MFOS VCOs, though I kinda wish I had used the Temp-co resistors as they are kinda drifty. I didn't think this would be a problem for me, but after using my modular (my first true modular experience) I realize the benfeits of stable oscs. Mainly for making finely tuned cross mod sounds that are consonant(not that a little dissonance is a bad thing though)

The CGS VCO can be as fancy or simple as you want it, as evidenced by the 4U width! Motm version shown in the Modular Synth Panels Yahoo group (I wish I could link to the file, but you have to be a member) and Richard Brewster minimalistic layout here: http://www.pugix.com/cgs-vco.htm

[Thomas Henry]

I just delivered a keynote presentation for our STEM Summit (Science, Technology, Engineering and Mathematics) today to 350 highschool students considering a career in the sciences. My topic was mathematics and music, with an emphasis on Fourier series and synthesis.

Anyway, I used the VCO-1 for all of my demonstrations. It was rock solid for all of the demos, and sounded superb through the one dozen Mackie speakers in the auditorium at a very loud volume.

That's the VCO I turn to when tuning accuracy matters more than anything.

And, oh, I made the local television news---the first time I've been on the tube. I feel just like Brittney now, but I'm not going to shave my head (or anything else, for that matter).

Thomas Henry

[zthee]

I was hoping you'd make it easier for me, but instead I feel like I just want to scream: Give me more of everything!! I need atleast 20 XR-VCO! 40 MFOS VCO and 10 CGS VCO with 20 ins and outs!

And instead of a small modular I've got this huge modular wall in my head. I really have to make it go away.

But I think I'll start out with the XR and VCO-1 and see. If they don't appeal to me after playing with them for a while, I guess I'll go for the MFOS instead..

[zthee]

[Pehr]

I use SSM2210. Abt 50 kr on electrokit.se

http://electrokit.se/item_show.php?code_no=40352210



EDIT: Oh, you mean PNP.

See SSM2220 http://electrokit.se/item_show.php?code_no=40352220

[zthee]

Thanks!

I think'll use that instead

[numbernone]

I have also used the SSM2210 with tempco on the MFOS and XR boards. The 8038 was a nice cheap treat with the 2sa798 at $.45 each!

[23isgood]

I built three XR2206 VCO's and they are rock solid. I used tempco's from MFOS. These have been the easiest VCO's to build, and I use them exclusively. They sound clean and great, though you can get grungy sounds if you like too. The only thing is, I wish they had PWM. Other than that I highly recommend them. Oh and they where dirt cheap. I think I spent around $40.00 on each of them.

pete

[Scott Stites]

VCO-1 is more of a classic, straightforward VCO, while the XR gives you some really spiff stuff (not least of which is that uniquely implemented sync portion) - at least one of each would do it.

Cheerio,
Scott

[zthee]

Thanks guys! You're help is really appreciated!

Damn, I want my PCBs now!

Good thing I got other projects to keep me occupied..

[numbernone]

What differs in the functioning between VCOs and LFOs in terms of sync? The sync on the XR is great, however when I kick it down to LFO territory, and try to reset the cycle, no dice.

What gives??

I am working on the Yusynth VCLFO to remedy this situation.

[Scott Stites]

The XR VCO sync is a bit different than a standard VCO sync - it actually takes advantage of the FSK function of the XR2206 - it's not resetting the VCO per se, but rather shifting it way off frequency each time a pulse arrives (as I understand it) - that's the weirly unique thing about it.

I use Rene Schmtiz's VCO3 a lot - that is a VCO with such a wide frequency range, it's not even funny. It easily goes to cycle/coffee break range, but the sync still works down there - makes a great syncable LFO in that mode.

Cheerios,
Scott

[frijitz]

[fluxmonkey]

[Thomas Henry]

With regard to the sync, yes, it's using the FSK capability of the XR chip. But just as important are these two properties:

1. The period of the reset pulse is much more narrow than the period of the dummy second (super high frequency) FSK signal , and

2. The XR chip always starts the alternate FSK signal from wherever the other leaves off. (It's phase continuous).

Put these together, and in effect the output signal is always being reset to some value close to 0. It may not be exactly 0, but it will be consistent from cycle to cycle, and is indistinguishable to the ears.

I've never seen this used before, but that's because I've never seen a chip like the XR which has switchable dual current sources.

Thomas Henry

[zthee]

Finnished my first XRVCO yesterday. And it works (and sounds) like a charm!

Also completed a VCO-1. But it didn't produce any sound. I need to look at it today and see what could've gone wrong with it.. (I wasn't surprised though. I built it on the copperside of a mirrored pcb).

[numbernone]

OOOO neat, can you post a forward shot of that panel???

Looks kinda like a Harvestman style.

Isnt the XR awesome?? Do yourself a favor and dont sleep on the VC Skew like I did for months, it is so so sweet.