Should this work?

[digi2t]

Hi all,

I've got this on the breadboard right now;



The VCF part IMHO isn't working. I've studied a few similar Steiner VCF layouts, and ones I've seen are fed negative and positive voltage from a bipolar source. Looking at this one, I only have the the single source. What's really throwing me off is just below the 2SC1583 dual transistor, there is a "(-Vcc)" marked just below it.

I've got a bald spot where I've been scratching my head.....

[Mark Hammer]

I salute you for going the extra step.  I've had that schematic and layout for a decade, and been tempted, but never gone the whole way.

Japanese schematics can have some weird stuff on them, sometimes.  This one, as you can see, is over 30 years old.  Looking at the PCB layout, it looks like the two bases ought to connect to ground.  And looking at this Steiner schematic it seems they do also: http://yusynth.net/Modular/Commun/STEINERVCF/VCF-2SC1583-sch.gif

BTW, is the TA7125P that thick SIP chip that Radio Shack used to carry as a 5W power amp?  I must have 6 or 8 of those in my bin.

[digi2t]

The more I look at it, the more I'm convinced that the Steiner section need a bipolar supply. I've looked at your link, plus a bunch of others, and I haven't found one yet that uses a single sided power supply.

Think I'll rig up a bipolar for this section with a couple of 9v batteries, and see what happens.

BTW, is the TA7125P that thick SIP chip that Radio Shack used to carry as a 5W power amp?  I must have 6 or 8 of those in my bin.

Dude... if I'da known, I would have buzzed ya. Fortunately, I managed to find some on the net, though I never did manage to find a datasheet. Even dropped Toshiba a line, but no reply. Yup, 7 pin SIP. Thems the ones.

[Mark Hammer]

My mistake.  What I have a stack of is TA7205P.  THOSE are the ones Rat Shack used to sell.  TA7125P is entirely different.  My bad.

[slacker]

The op amp bit should be fine, I think Mark is right the bit round the transistors looks wrong. In my experiments with making a single supply Steiner I had to connect the base of the right hand transistor to a positive voltage in order to get it to work, as shown below.

http://www.eskimo.plus.com/fxstuff/slackfilter_lite.png

Connecting it to 1/2 vcc might work.

[jaapie]

I got the filter portion of that schematic working a couple months ago, but its been long enough that I don't remember any specifics. I redrew that part of the schematic, I'll see if I can find it if it'd be helplful

[jaapie]

if i recall, there are two different ground symbols (the rake-looking thing and the triangles). I think the triangles represent Vcc/2, so the "rake" could be thought of as -4.5V and the triangles as 0v.

[jaapie]

Here's my redrawn schematic, probably with errors:
http://imgur.com/XCqQM37

sorry if the "triangle/rake" differentiation was already obvious, it threw me for a loop when i tried to get this filter working though,

[tca]

Going to simulate the filter part... report later.

[digi2t]

OK, I got it working. Just really tough sometimes keeping track of where evrything is going on the breadbaord. I had a couple of components, and a jumper plugged into the wrong holes on the TL074 end of things. That's why the VCF part wasn't reacting as expected.

This is one ornery critter. It sounds like doom. Very prehistoric sounding. Puts out a nasty fuzz tone, with loads of octave overtones, glitching all over the place. Naturally. It sounds like a cat driving a Ferrari, out of control.

It's very.... ummm.... primitive. More of a noise maker than anything else. I'll try and do a video. It's like.... woah!

@tca - let us know what you get.

[tca]

Well as it is, does not work. I don't get the typical frequency response graphs of a LPF and the harmonics showing up as the resonance varies. I agree that the right hand side transistor should be biased correctly... and there are some components missing if one compares the filter section with the original Steiner circuit. The HP input has been removed and the 1k resistor to ground also... there is something fishy about the circuit.
ah, had an error o the schematic! It does work!



You should adjust the pot BPF-ADJ 50K to get symmetric resonances on both parts of the signal (positive/negative). Probably due to the grounded transistor. Notice also that the amplitude of the signal is smaller than the input amplitude and it changes with the cut of frequency. Probably not the best Steiner filter implementation but I guess you have found a one battery 9V Steiner filter, have to breadboard this! Thanks.

Has you know I've made a non-VCF Steiner filter with a pot controlled frequency cut off but with +-9V, I can't thank you enough for posting this.

If you are interest, I can put the sim file (TINA-TI) for download for you to play with it.

[digi2t]

If you are interest, I can put the sim file (TINA-TI) for download for you to play with it.

Thanks for simming this. I'm still too technically challanged to do stuff like that, but if could see I would really appreciate it. I'm really a visual creature. Will I need some associated app to run the sim, or is Java enough?

You know, it might be the best application of a Steiner, as you point out, but there's always a way to make it better. With a MAX chip, I could produce +/-9v, and reconfigure the filter. I just need to figure out how to make it less glitchy right now. It's quite primitive sounding, but then again, I think that's part of it's charm. That, I to think that someone actually came up with this so long ago. I wonder if any commercial units exist...

[tca]

It's quite primitive sounding, but then again, I think that's part of it's charm.

I would love to ear it!

[digi2t]

I'll try and put something up on Youtube today.

On another note, the TA7125P is integral to it's operation. I tried the CA3080/4558 combo replacement, and I lose filtering, not to mention a great deal of volume. Seems to me like the 7125 is more of a sort of voltage controlled tone control, as well as amplifier. With the 3080/4558 combo, even by pulling the 11K to ground, I still can't get the same volumne as I can with the 7125, and the working the sensetivity and cut-pff controls yields no changes in the sound.

I'm glad I found those 7125 chips. Think I'll order some more, they were tough to find. Who knows, maybe some other obscure hen's tooth will need it. 

[digi2t]

OK, had time to shoot a quick video. This thing had me up late last night when it stopped working properly. Found that my breadboard is starting to get dodgy. This is the biggest thing I've ever had on the bb, and there was a lot of tracing required to pin down the culprit. Here's a shot of my "rat's nest";



Another thing that had me baffled was the quad opamp. I could not get a TL074 to work properly, but an LM324 does the job though. For some reason, when I pop an 074 in there, the VCO running through the filter get really weak. Plucking a string yields a very low, to none, output. The 324 is loud and proud. Weird, and beyond my comprehension. I know it's not a question of a bad chip either, I have plenty of both, and I tried several, with the same result. I have some RC4136's on hand as well, I'll try that as well, who knows.

Finding the right "zones" for the trimmers was an adventure in itself. My hand got sore cranking those trimmers, but that was more of a result of ignorance than anything else. I'm not really knowledgeable on synth terms, but with time, my ears began to understand what each trimmer did. As I mention in the video, I didn't play with the Resonance, Duty, VCF adjustments et al, they do vary the sound of the unit, but I really wanted to bring you a peak (and listen) this monster.

So there it is, in all it's synthy cacophony. 

[Thecomedian]

with all those exposed resistor wires, do you ever worry about shorting or parasitics damaging the active parts like op amps or transistors?

[digi2t]

with all those exposed resistor wires, do you ever worry about shorting or parasitics damaging the active parts like op amps or transistors?

I haven't had a problem to date. But, to quote Elmer Fudd, "Be wary, wary cwarefulll". 

Seriously though, I have had the occasional resistor or cap wires short, but luckily, without consequence other than the circuit not working. I've found IC's to be pretty robust in general. I'm not using the typical precautions i.e. antistatic mat, grounding strap, etc., and I have yet to blow a chip. Call me lucky. I try to ensure that everything is kosher before applying power. The problem I have had of late is my breadboard not making good connections between rows due to dodgy clips in some holes. This was a huge headache for me last night (and into the wee hours of the morning  ).

[Thecomedian]

on a side note, i love those little blue box trimmer pots. They can get very precise resistance values.

[digi2t]

on a side note, i love those little blue box trimmer pots. They can get very precise resistance values.

Also indispenable for breadboarding, for general hacking of circuits.

[zetamkiii]

I'm curious to see how you're going to get THAT into a box. This one looks very interesting, patiently awaiting vero.