R.G.'s sequencer

[Arno van der Heijden]

With the sequencer flu going round here a few weeks ago, I was wondering if anyone got R.G.'s sequencer to work.
(http://www.geofex.com/Article_Folders/udrand.htm)

I build one on a breadboard, and it works fine, except for the random part, which I can't get to work.
I hooked the 4051 up to 8 LED's for testing purposes. When I switch to random mode, all LED's are lit at the same time. :?
Any ideas why it won't work?

[Arno van der Heijden]

bump

[R.G.]

ACK.

There's a logic bug there. The load input is not edge triggered like the count up/down inputs, it's active low. I'll have a fix for you, perhaps tonight. There is one inverter section of the 74C14 that you're not using, right?

If so, you can break the line between the SP3T switch going  to the -LD input, and insert an capacitor/resistor/diode/inverter circuit to shape a negative going pulse for the load signal.

I'll post it as soon as I get the drawing done, perhaps tonight.

[R.G.]

I had a minute.

The fix is now illustrated on the web page.

Look at the new box with round corners next to the three way switch. The random sampling signal is now routed to a signal inverter that also makes a very short pulse on the load line.

Should work. Please let me know if it does not.

[Arno van der Heijden]

Thanks!!
I'm going to try it out right away, but just to let you know, the quality of the new picture is not as good as it was, the text being difficult to read.
I think it may have been slightly resized.

[casey]

if you have microsoft "picture it"  the text looks fine.

[Arno van der Heijden]

Yes, but meant when viewing with Internet Explorer.

Anyways, it works fine right now!!! Thanks again!!!!
One thing that strikes me is that it sometimes seems to stick in one position for a slightly longer time.

I'm going to hook it up to a twin-t style circuit now. The twin-t circuits that I have seen don't have the largish (100uF) capacitor from the frequency pot to ground. Is it needed to prevent switching glitches? Will it influence the wah circuit?

[Torchy]

Any chance of some component values on there sometime ?

I really want to try this out, some values (even just guideline values) would help thickos like me get started  :oops:

[Arno van der Heijden]

Look in the archives:

http://www.diystompboxes.com/sboxforum/viewtopic.php?t=22978&highlight=sequencer

http://www.diystompboxes.com/sboxforum/viewtopic.php?t=22999&highlight=sequencer

[Torchy]

Thanks, I had checked the archives but the threads were a little confusing. Looks like I got more reading to do than I did to build the firefly :lol:

[R.G.]

the quality of the new picture is not as good as it was, the text being difficult to read. I think it may have been slightly resized.

I'll go mess with that. It does look grainer.

Anyways, it works fine right now!!!

Hot Stuff!! I love it when I can nail down bugs like that.

I'm going to hook it up to a twin-t style circuit now. The twin-t circuits that I have seen don't have the largish (100uF) capacitor from the frequency pot to ground. Is it needed to prevent switching glitches? Will it influence the wah circuit?

It really needs that capacitor. It's to allow the outputs to sit at the bias voltage to minimize pops when switching from setting to setting. It wouldn't hurt to stick a 1M or greater from the top of the cap to the bias voltage so the selected output pins all sit at bias. Otherwise it'll pop once until the cap charges up through the input bias resistor. The cap needs to be large to keep the impedance low for any pot that happens to be set to a low resistance. You could just run a wire from the junction of the eight pots and 100uF cap to V+/2 bias voltage, too. In fact, that may be a better option.

The cap should have no effect on the wah circuit operation.

[Ry]

Hey cool!

I had the same problem when I tried building it a few years back.  I'm glad to see it's working now!

Ry

[Arno van der Heijden]

So I tested a basic twin-t filter today. It isn't connected to the sequencer yet, but powered from the same rails. Nasty ticking clock noises were the result.....  :?

I read that in Zach's seek/ooh wah "the audio wah circuit has its own filtered supply voltage".
How would I go about doing this here?

[Paul Perry (Frostwave)]

One thing that strikes me is that it sometimes seems to stick in one position for a slightly longer time.

It isn't a case of the same value turning up twice in a row, is it? Because there is nothing to stop that happening (in random mode).

[Arno van der Heijden]

It isn't a case of the same value turning up twice in a row, is it? Because there is nothing to stop that happening (in random mode).

It could be, but the probability for that situation is less than 2 % (if it's really random) and it happens pretty often. Also I don't think there was a switching moment visable halfway.

Anyway, I got rid of the LED's and connected it to a twin-t filter based on Tim E's ghost dance (http://www.geocities.com/tpe123/folkurban/fuzz/ghostdance.gif).

It works pretty good, if you like a built in drum computer.  

[The Tone God]

Anyway, I got rid of the LED's and connected it to a twin-t filter based on Tim E's ghost dance (http://www.geocities.com/tpe123/folkurban/fuzz/ghostdance.gif).

It works pretty good, if you like a built in drum computer.  

Umm why don't you read my post in one of the threads you quoted above ? That might give you some answers.

http://www.diystompboxes.com/sboxforum/viewtopic.php?t=22978

Andrew

[gez]

I read that in Zach's seek/ooh wah "the audio wah circuit has its own filtered supply voltage".
How would I go about doing this here?

Could be as simple as a RC lowpass filter from the positive terminal of your supply to the +ve connections of the audio circuit.  Ground connections should connect to -ve terminal and shouldn't share a common connection with the rest of the circuit.

Start with something like a 51R resistor and 330u cap, increase the resistor if ticking still persists (though you'll cut into headroom by doing this).  

It's a primitive approach, but it does work at reducing/eliminating clicking.  Haven't read all of this thread, but if this is on a breadboard your layout might be partly responsible.

[R.G.]

So I tested a basic twin-t filter today. It isn't connected to the sequencer yet, but powered from the same rails. Nasty ticking clock noises were the result.....

Yep, there's going to be some ticking if the power supplies are not ust right. By the way - that was a very insightful first step. Good job thinking about that as part of your build.

Normal twin t's with transistors have zero power supply rejection. Try this:
1) isolate both logic and analog from the battery + with separate 100 ohm resistors, and use a 22 to 47uf cap on each one, with a 0.1uF ceramic on the logic side. This is to keep the current pulses in the logic local. You can also split the collector resistor in a transistor twin T and decouple it to 0V locally at the transistor.
2) ensure that the logic and analog signals do not share a power carrying path for ground; otherwise the logic ground pulses are impressed on the ground line. The decoupling in (1) will help, but not eliminate the ground ticking.

Integrating logic and transistor analog stuff requires sincere attention to power supply routing paths. I can well imaging that ZV had to use a second power supply. That is one solution, albeit an expensive one.

It may be that using opamp based twin t's will help.

One thing that strikes me is that it sometimes seems to stick in one position for a slightly longer time.
...

It could be, but the probability for that situation is less than 2 % (if it's really random) and it happens pretty often. Also I don't think there was a switching moment visable halfway.

I would guess that the "random" oscillators are not 50% duty cycle. While CMOS schmitts are supposed to have equal + and - threshold voltages, sometimes they don't. If they preferentially spend more time down than up, or vice versa, you get a higher probability of one side or the other, and a higher likelihood of certain states.

Of course, three unrelated oscillators are not really random. They are just quick and easy. And depending on the exact component values, there may be some "locking" happening. I'm guessing that could well be layout dependent.

I'll see if I can piece together a good power supply practice for this puty some thought into the randomness.

If you happen to have some CD4013's handy, try running each "random" oscillator through a 4013 to generate a truly 50% duty cycle signal. That will test the preferential stat hypothesis.

[Arno van der Heijden]

I found some time to work on this thing again.
I think/hope I solved the ticking problems (need to do some more testing), but I ran into another strange thing when I was testing the random mode in the dark last night. (Different coloured LED's make for a cool spectacle )

When I run the master clock at a slower speeds (in the order of 1 hz), the randomness gets worse and worse, up to the point where it only cycles between 2 of the 8 positions. :?
Is there anything simple I can do to improve this (without having to use an extra 4013, my breadboard is crowded enough already... )?

[Arno van der Heijden]

bump