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 Forum index » DIY Hardware and Software » Rob Hordijk DIY Designs
Benjolin schematics
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slabman



Joined: Sep 01, 2005
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PostPosted: Sun Mar 21, 2010 12:57 am    Post subject: Reply with quote  Mark this post and the followings unread

Thanks Rob - that's saved me going down a wrong track.
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macumbista



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PostPosted: Mon Sep 06, 2010 3:18 am    Post subject: Reply with quote  Mark this post and the followings unread

I'm interested in what kind of CV controls would be available in this design. I see the Rungler Speed CV, and I think there is also a Filter CV, right? What else could be externally controlled or in some other way patched into my larger modular system (to create larger feedback loops)? Also, would it have enough headroom to handle +/-5V signals, seeing that it uses a +/-9V PSU?

Thanks!
D.

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Rob



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PostPosted: Mon Sep 06, 2010 7:49 am    Post subject: Reply with quote  Mark this post and the followings unread

macumbista wrote:
I'm interested in what kind of CV controls would be available in this design. I see the Rungler Speed CV, and I think there is also a Filter CV, right? What else could be externally controlled or in some other way patched into my larger modular system (to create larger feedback loops)? Also, would it have enough headroom to handle +/-5V signals, seeing that it uses a +/-9V PSU?

Thanks!
D.


Actually the CV inputs have a much bigger headroom as they feature a CV input processor that limits the gain cells to their proper operating range. The 51k Ohm input resistor roughly gives a 1V/Oct range.

There can be one more and quite interesting 'input': connecting a 10kOhm resistor to the base of the transistor can 'hold' the pattern in the rungler shift register with a +5V or -5V CV. A three position toggle switch with the center tap connected to this resistor and the outer taps connected to the + and - power supply voltages will 'hold' the pattern, one position will play forward only and the other alternates between forward and inversed forward. The middle position will give normal operation.
This can also be a pulse from a LFO pulse output, the pattern will change slightly on the flank of a pulse and hold the pattern while the pulse is positive or negative. Again use a 10kOhm resistor between the input connector and the base of the transistor.

The transistor and its associated opamp together form an analog XOR port, or in fact a +.5 or -.5 gain amp, depending on if the transistor conducts to ground or isolates. Adding the extra 10kOhm resistor makes it possible to force the transistor into permanent conducting or isolating mode, resulting in a negative or a positive gain. In fact, this analog XOR circuit is sort of a poor man's ringmodulator when the transistor is driven by a pulse waveform and any kind of analog waveform is fed to the two opamp input resistors.
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macumbista



Joined: Sep 12, 2007
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PostPosted: Mon Sep 06, 2010 7:54 am    Post subject: Reply with quote  Mark this post and the followings unread

Thanks Rob! I enjoyed the Leonardo article, and wondered also if there is any kind of block diagram for the Benjolin similar to the one you made for the Blippoo Box in that article. Then it might be easier to map the different points of intervention (both by knobs and CV).
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Dr. Sketch-n-Etch



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PostPosted: Sun Feb 12, 2012 2:01 am    Post subject: Reply with quote  Mark this post and the followings unread

Hi, all. Sorry I'm a bit late to this party, but...

I've built a couple of Benjolins, and I'm having a problem with the filter circuit. It doesn't seem to put out much of a signal. Both units are exactly the same. I've also simulated the filter part of the schematic, and the simulation shows the same thing: an output signal from the filter of only +/- 300 mV or so. The oscillators are putting out very strong signals, but I have to crank my audio mixer way up to hear the output of the filter.

Has anyone else had this problem?
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fluxmonkey



Joined: Jun 24, 2005
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PostPosted: Sun Feb 12, 2012 9:48 am    Post subject: Reply with quote  Mark this post and the followings unread

Dr. Sketch-n-Etch wrote:
Hi, all. Sorry I'm a bit late to this party, but...

I've built a couple of Benjolins, and I'm having a problem with the filter circuit. It doesn't seem to put out much of a signal. Both units are exactly the same. I've also simulated the filter part of the schematic, and the simulation shows the same thing: an output signal from the filter of only +/- 300 mV or so. The oscillators are putting out very strong signals, but I have to crank my audio mixer way up to hear the output of the filter.

Has anyone else had this problem?


from a different thread:

Rob wrote:
oscilloclast wrote:
Rob,
oscilloclast wrote:
2. The filtered out is a lower volume then the other outs. If this is the way it was designed is there any way to increase the filtered output to the level of the others? I’m going to be running these kits with my modular so the more signal I can get out the better. If there is nothing on the PCB I can do I’ll just increase the signal with an opamp.


Totally correct, the filter output is at line level so you can plug it into a line level input amplifier. All other outputs swing roughly between +5V and -5V and can so be used as input signal for a modular system.

The filter output is directly connected to the last pole output of the filter, so there is nothing to do there. Increasing the filter input level would overload the filter and also drastically explode the all harmonic distortion in the filter. So, a preamp to amplify it to analog synth input level would be the way to go. An amplification of roughly 20dB should do the trick.

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Dr. Sketch-n-Etch



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PostPosted: Sun Feb 12, 2012 2:11 pm    Post subject: Reply with quote  Mark this post and the followings unread

Hey thanks, fluxmonkey! If that's the way it's supposed to be, then I guess that's the way I'll leave it. It's just a bit of a nuisance, since these will probably be used as modules. Oh well!
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jean bender



Joined: Feb 21, 2010
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PostPosted: Tue Feb 14, 2012 3:06 pm    Post subject: Reply with quote  Mark this post and the followings unread

Hi everybody...

I'm going to build my own benjolin, and trying to connect it to my lunetta stuff, but...

i really don't know how to read one schematic part.
On the first pdf schematic given here by Rob, on the fourth page, there's a schema of J2 / HDR16, with some 100k resistors... I really don't see what it is...
Could somebody help me to understand this ...

thanks for any response... It's a bit Infuriating for me since the whole schematic is really easy to understand... Confused Confused

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Dr. Sketch-n-Etch



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PostPosted: Tue Feb 14, 2012 4:34 pm    Post subject: Reply with quote  Mark this post and the followings unread

deadbeat wrote:
On the first pdf schematic given here by Rob, on the fourth page, there's a schema of J2 / HDR16, with some 100k resistors... I really don't see what it is...

Those are just 100-ohm output resistors leading to the 16-pin output header (HDR16). There are 8 different output signals: the two triangles (T1, T2), the two pulses (P1, P2), the filtered output at line level (OUT), the PWM comparator output (PWM), the rungler CV (RUNCV), and the exclusive OR output (XOR). All of these can be tapped for use in other modules, etc. (The other 8 pins of the header are grounded.)

Having said that, this is a particularly difficult schematic to read and make sense of, mostly because the grounds are all tied together rather than just shown with little ground symbols (my pet peeve). Indeed, I had to redraw the filter section (page 4) in Multisim myself just to understand the signal flow.

Last edited by Dr. Sketch-n-Etch on Tue Feb 14, 2012 4:38 pm; edited 1 time in total
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jean bender



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PostPosted: Tue Feb 14, 2012 4:36 pm    Post subject: Reply with quote  Mark this post and the followings unread

THANKS a lot a lot... now it make sense... almost so easy to understand... Well, i'm done, i can try build mine now.
GREAT !! Razz

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macumbista



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PostPosted: Thu Apr 12, 2012 1:06 pm    Post subject: Reply with quote  Mark this post and the followings unread

Just finished a build over Easter weekend, posted to the Show Us Your Benjolin thread. Working on a demo video now.

I would encourage people to bring all the input/outputs to the panel, it gives a much bigger range of feedback/self-modulation possibilities. I also like seeing the Rungler bits as LEDs (thx to Casperelectronics' docs).

One thing, the oscillators and Rungler don't really like to work with anything less than a full battery. Filter still works but nothing else once the batteries get drained even a bit. I have an LM386 driving a small speaker in the same circuit, so YMMV.

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macumbista



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PostPosted: Tue Apr 17, 2012 6:53 pm    Post subject: Reply with quote  Mark this post and the followings unread

So my standalone Benjolin rocks, but now I'm on to a different problem. I wanted to extract the Rungler circuit and build a synth module out of it.

Of course I made a few mistakes freehanding the circuit but I think I found them all. However, it just doesn't rungle and worse yet the 4021 IC starts to get hot. This happens even with the op-amps and transistor removed, and with no inputs or outputs connected to anything else on the synth.

I've banged my head against this thing all day now (4am now), and I just wanted to ask: are the values used in the schematic good for +/-15V operation? I mean specifically the Rungler, not anything with the SSM chip.

Also, the 4021 gets powered from positive and negative rails right? Not positive and ground. This isn't listed on the schematic AFAIK, but I see on the PCB that pins 8 an 9 are connected and they both go to negative there.

Thanks for any clues here.

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macumbista



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PostPosted: Wed Apr 18, 2012 4:56 am    Post subject: Reply with quote  Mark this post and the followings unread

OK, after some sleep.... Seems 30V of potential is too much for the 4021, so I connected pins 8 and 9 to ground instead of V-. I assume the parallel/serial bit doesn't mind GND instead of V-.... but it just don't rungle.

I'm wondering if the values of the XOR network should be changed. Or something. Somebody must have tried this before. It would seem silly to add a pair of voltage regulators to the board when it's probably a matter of one or two resistors. Any feedback y'all have would be especially appreciated.

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inlifeindeath



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PostPosted: Wed Apr 18, 2012 10:34 am    Post subject: Reply with quote  Mark this post and the followings unread

the CD4021 can only handle a total voltage swing of about 18 volts. That's why the benjolin uses 9v regs, because +/-9v equals 18 volts. 30 volts is over spec for the chip.
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macumbista



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PostPosted: Wed Apr 18, 2012 10:41 am    Post subject: Reply with quote  Mark this post and the followings unread

Yeah, I did some datasheet digging and had a friendly chat with casperelectronics where I learned a great many things. I'm redoing the board for +/-9V now, I should have realized it would be more complicated than copy/paste.
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macumbista



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PostPosted: Fri Sep 21, 2012 5:23 am    Post subject: Reply with quote  Mark this post and the followings unread

I've been trying to work out where on the schematic one could add an audio input to the filter. I see two points of interest:

1) Replace T2 as one of the inputs to comparator U6.C

2) Replace T2 as the input to P6

Has anyone tried either of these?

Best!
D.

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PostPosted: Sat Sep 22, 2012 3:32 pm    Post subject: Reply with quote  Mark this post and the followings unread

Once again, Casperelectronics to the rescue:

Posted Image, might have been reduced in size. Click Image to view fullscreen.

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Starspawn



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PostPosted: Sat Sep 06, 2014 9:46 am    Post subject: Reply with quote  Mark this post and the followings unread

Hey guys, Ive spent the last day sick doing a stripboard layout for this, but a few questions ...

The FCV inputs seems like they are connected to the output of the Tl072 in the schematic, or at least theyre all marked FCV ... are really both pin 3 and 6 connected and could they receive different CVs if I wanted to?
Or are they perhaps 1 CV for frequency and one for resonance, or for the low pass and hig pass?

Is P1-8 on the 4021 and pin 1 on the 2164 just floating?

Is the RunCV connected to all 4 points; 2xosc, 51k resistor and pot 7, directly from pin 14 of IC6?
And is the output another connection or one of those?

And most importantly, how is the 4021 powered when it has -9V on pin 9?
Positive and ground?
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