New OTA Phaser Design - “Causality 4”

[soggybag]

This sounds really good. I'm thinking about making a PCB from the layout above. What resolution should I use. As is the resolution is set to 72. Which is too large. I'm printing from photoshop.

[frequencycentral]

My perfboard is 50mm x 56mm approx. The PCB layout should be the same size.

I'm about to start a MkII when my parts arrive, as I sold my MkI, pretty exceted about it actually!

[soggybag]

Right on, I like the sound sample. I love the heavy sludge metal with phase shifter sound.

Looks like C3 sets the speed of the LFO. I really like the low speed. I switch for an extra cap in parallel with C3 might be good for a low and high speed option.

[frequencycentral]

C3 stops any clicks as the LFO switches from upsweep to downsweep. In fact the LFO will work almost the same without C3. C4 is really the timing cap, along with the value of the speed pot, I used a 1M for that 'is it on?' sound.

I love the heavy sludge metal with phase shifter sound.

Hey! That's my middle name!

[soggybag]

I etched up two boards for this. I just finished drilling them.

I was looking over the schematic and reading the notes here and an idea occurred to me. This phaser shifter is set up with two fixed stages and two modulated stages. I was wondering what it would sound like if the two modulated stages were modulated out of sync. What gave me this idea was coming across a sketch of this oscillator in my note book. Note that it provides both sine and cosine out. Which should be out of phase by 90 degrees.

Might have a unique sound or might not sound too different. I might give it a try if I can get this version built and working.

[soggybag]

Etched a PCB and soldered everything. I fired it up tonight and and got strange oscillator noises. Very cool, but not quite right. I used a tl074 in place of the TL084. I'll assume this is an OK substitution. I'll have to give it a debug tomorrow night.

Here's a picture: http://www.super-freq.com/?p=256

[soggybag]

After figuring out that I had forgotten to connect the ground wire from the jack to the board we have achieved phase shift!

I did a few tests with the scope. I think the shape pot is doing nothing. Testing from the wiper of the Range pot, turning the Shape pot produces no change. Turning the Width transforms the LFO wave form from a soft triangle to a sharp trapezoid.

The phase shift sound is pretty rich. I need to test some more to get a good idea of the sound. I used a TL072 for the quad op-amp. I'll assume that this shouldn't make much difference in the sound. I also used a 50K in place of 47K pot, and a 500K in place of the 470K.

Have to play around with this some more. Here's a post with a picture.

http://www.super-freq.com/?p=293

[frequencycentral]

I did a few tests with the scope. I think the shape pot is doing nothing. Testing from the wiper of the Range pot, turning the Shape pot produces no change.

Have you got the diodes the right way around? I added a on/off/on toggle switch to my 3 knob MkI before I sold it. The upsaw and downsaw were more noticable at slower speeds than they were at fast speeds. I still haven't built a MkII, got all the parts but keep getting tied up in builds for other people (£££'s   ). When I get round to building a MkII I'm going to experiment with different values for the shape pot. But it definately works.

[soggybag]

My mistake, the shape pot is indeed working. I think the Width pot seems to square off the LFO wave form as it is turned up. Which starts to eliminate the effect of the shape pot.

Sounds good. There's a lot of adjustment with 5 knobs.

[frequencycentral]

The MkII was designed 'at a distance', doc_drop breadboarded the MkI and I suggested the changes to make the MkII. There may still be some fine tuning to be done - I'll find out when I build my MkII in a couple of weeks. I *think* I'll use 220K for R5 (as in the MkI) and use a higher value for R33, possibly 22k, 33k or 47k, increasing R33 will reduce the amplification of the LFO so hopefully it won't lop off the tops of the waveform.

[frequencycentral]

Here's my new MkII:

[soggybag]

Nice work! I like the way the board is sort of suspended off the ground wire that runs across the bottom of the box. The ribbon cable is a great idea also. I was thinking about trying this. Where do you get it? Of course you're in the UK and I'm in the states so I may have to find a different source. When I see old computer stuff I try and salvage any ribbon cable, though I have yet to use any.

Speaking of the bare bus wire. I was talking to a friend who had made a pedal for a big name rock star. They like the pedal but their sound tech wouldn't let the person use it on stage. Because it had a bare wire running to the LED. I guess the guy was worried about it breaking or shorting on stage on front of 10,000 people.

[frequencycentral]

Thanks! I particularly like the grounding in this build.

After playing about with my MkII I've done the following tweaks to get it how I like it:

• R5 = 220K
• C4 = 47uF

R5 at 220k appears to me to keep the LFO symettry. I increased the value of C4 (the timing cap) because the addition of the shape control has the effect of approximately doubling the minumum available speed. I like very slow phase sweeps, so I played around with paralleling different value caps with the existing C4, I really liked the sweep with a 33uF in parallel, so I'm going to sub a 47uF for the existing 10uF. The fastest speed is now slower though, so it's a trade off.

[soggybag]

I'll give these a try when I get a chance. It would be great if the schematic had part numbers on it.

I would redraw it in Eagle, but I don't have a part in my library for the OTA. The best I've been able to do is use a 16 pin DIP which is not very easy to understand. If anyone has a library for the 13600 let me know.

[keto]

Geez..I'm intimidated, and I haven't applied heat to it yet  



Actually, this has been on my 'to-do' list right from when I first saw it.  My LM13700's should land this week, so I'm going to go at the circuit.

2 questions, both my show off my ignorance but hey!  don't ask, don't learn    By the way, working off the Mark2 perf layout as reference.

1.  Orientation of the chips.  I know it has to do with the square solder pad in one corner - is that the end that usually has the little 'u' or divot in the chip & socket? **EDIT** looked at Rick's build and that seems to be confirmed, I have my sockets oriented the same way /**EDIT**
2.  Diodes aren't specified.  914's?  4001's?