Muff's Modules & More

felix · Posted: Sun Jun 07, 2009 1:54 pm Post subject: voltage to resistance

So, other than Vactrols, how would one use voltage to alter resistance?

dougcl · Posted: Sun Jun 07, 2009 1:56 pm Post subject:

Isn't this what transistors do?

felix · Posted: Sun Jun 07, 2009 2:13 pm Post subject:

flight · Posted: Sun Jun 07, 2009 2:54 pm Post subject:

Bipolar transistors are really current-control and have a logarithmic transfer ratio (in/out). They are commonly used for voltage control but have some other drawbacks such as the addition of the base current to the output.
For a more precision application, FET transistors (such as the MPF102 JFET) are better. Some are even specified as Voltage-Controlled Resistors (VCR). Like bipolar transistors, FETs require a bit of calculation (or trial and error) to set up the biasing network to get the exact behavior you are looking for, but they work quite well. They have no base current effects and behave much more like a true resistance.

wetterberg · Posted: Sun Jun 07, 2009 3:28 pm Post subject:

Hey Flight, I wonder if you, or other brainiac geniuses, could help out in designing like a breadboard layout for this?

A voltage controlled resistor pcb is one of the most useful devices for modding just about any circuit.

- just something simple; an input, a control input and an output... boom. Could probably be laid out more or less based on the datasheet diagrams even?

flight · Posted: Sun Jun 07, 2009 4:04 pm Post subject:

Sounds good to me. For now though, here's some links:

http://graffiti.virgin.net/ljmayes.mal/comp/vcr.htm

An excellent Siliconix App Note

LinearSystem's VCR11N datasheet

Vishay-Siliconix VCR2N/4N/7N datasheet

Discussions and Lab projects about VCRs:
http://www.edaboard.com/ftopic201952.html
http://www.nhn.ou.edu/~bumm/ELAB/Labs/lab11_FET_Lab.htm
http://www.electro-tech-online.com/general-electronics-chat/91272-volt age-controlled-resistor-jfet.html

Detailed descriptions of FET operation:

http://aries.ucsd.edu/najmabadi/CLASS/ECE60L/03-S/NOTES/FET.pdf
http://www.electronics-tutorials.ws/transistor/tran_5.html

Not FET-related, but damn interesting:
http://www.avtechpulse.com/papers/vres/

Aaand... that oughta be unough for y'all for the nonce!
razz

DGTom · Posted: Sun Jun 07, 2009 4:24 pm Post subject:

Felix,

Take a look at the 2nd schem. posted here;

http://deathlehem.com/php/viewtopic.php?f=21&t=34

Don't worry about tracking, altho I've not played with the dual transistor set-up much, you can also do it with another CMOS chip, the 4007;

Thanks for all the proper info flight!

Luka · Posted: Sun Jun 07, 2009 6:46 pm Post subject:

you can also use ota's like 3080
and transistors in current sink formation

wetterberg · Posted: Sun Jun 07, 2009 7:01 pm Post subject:

@flight: Most of those FETs are obsolete... I found one of them for like 20usd...

@DGtom... I've never seen a schematic like that... ever. What chip is that? Are those the pins of the 4007? I assume you're talking about the CD4007? I'd love to see a "proper" schematic for it... (hides)

@Luka I'm sorry, but I at least am going to need a little more than the mention of a methodology for doing this... help

Could we n00bify this thread a bit? Cheers much ambulance

panda30y · Posted: Sun Jun 07, 2009 7:36 pm Post subject:

Wow, great thread for us DIY'ers. Thanks for the info everyone.

Luka · Posted: Sun Jun 07, 2009 8:05 pm Post subject:

i heard about current sinks here
http://www.homebuilthardware.com/index.php/projects/pt239x-delay/

felix · Posted: Sun Jun 07, 2009 10:09 pm Post subject:

Wow, cheers guys! Lots of useful stuff here!

flight · Posted: Sun Jun 07, 2009 10:12 pm Post subject:

@ wetterberg:
Aside from the VCR-specific FETs, general-purpose FETs will work as replacements. Like the aforementioned MPF102.

<edited> 'cause it needed it... hmmm.....

flight · Posted: Mon Jun 08, 2009 10:21 am Post subject:

I was too tired last night to go into any detail, so here's a bit more:

There are thousands of different transistors, bipolar and FET, and they go in and out of production on a regular basis. Many of them exist because some manufacturer wants a specific set of properties and orders a custom run (this is often due to military projects). Afterwards, the semiconductor company now has the dies and setup so they do runs of the unit to see if there is any demand. If there is, it stays as a product line. If not, it is discontinued.
Other times, a part is discontinued because of advances in manufacturing processes, sometimes re-appearing under a different part number.

Parts that are successful and not patented in time are subsequently cloned by other manufacturers, often under the same part number but also under a different part number that conforms to regional standards - hence the various prefixes such as: 2N, BC, MPF, etc..

So, when using any schematic that is more than a couple years old, you will often come across transistors that are obsolete. You then just need to find the specs for that part and select a replacement unit that has the same or similar. Since transistors usually require a biasing network of some kind, the specs aren't too restrictive. You will just need to play with the bias component values a bit.

DGTom · Posted: Mon Jun 08, 2009 3:52 pm Post subject:

Navs · Posted: Wed May 23, 2012 2:59 am Post subject:

Bumping this thread for help with a specific circuit.

I've breadboarded an all-pass filter which I'd like to VC at audio rates (i.e. vactrols out of the running):

I bought what I thought was a JFET - the BSN10A. Can this also be used as a resistor and, if so, how do I hook it up? Do I need further resistors on the input and output?

I've tried using a CD4049 as per the ETI 447 phaser, but this was noisy. Can I expect better performance from the discrete transistor or is the filter circuit itself just not capable of being VC-d at audio rate?

Help a noob to trannies please!

Thanks, Navs

Refs:
http://www.pa.msu.edu/courses/2007fall/PHY440/Problems/P1_3.pdf
http://synthdiy.com/show/?id=1068
http://ecircuitcenter.com/Circuits/JFET_Variable_Res/JFET_Variable_Res 1.htm
http://english.electronica-pt.com/db/cross-reference.php?ref=BS&page=9

frijitz · Posted: Wed May 23, 2012 3:15 am Post subject:

diablojoy · Posted: Wed May 23, 2012 3:54 am Post subject:

Navs · Posted: Wed May 23, 2012 10:52 am Post subject:

Thanks, diablojoy, I'll take a look.

Any other thoughts on the suitability of the circuit and BSN10A for audio-rate VC?

Navs · Posted: Thu May 24, 2012 9:38 am Post subject:

The Ray Wilson circuit worked, thanks. It's just as noisy as the CMOS trick, tho, so will have to find another alternative.

DGTom · Posted: Thu May 24, 2012 9:58 am Post subject:

Navs, have you seen Neil Johnsons All Pass?

http://www.milton.arachsys.com/nj71/index.php?menu=2&submenu=0&subsubm enu=3

I'd bet the 2164 will be alot cleaner & easier than a FET.

In my experiance starting with something that sounds the way you want & adding VC can be a PITA, better to start with something that is VC'able & get it to sound the way you want.

Navs · Posted: Thu May 24, 2012 11:15 am Post subject:

Yes! Found that today after I changed my usual google search to 'voltage controlled all-pass' lol

Way too much information for me - I'll have to mail you for help!

Dr. Sketch-n-Etch · Posted: Thu May 24, 2012 11:24 am Post subject:

I use the 2164 quad exponential VCA almost exclusively as a voltage-control element. It takes a current in (at virtual ground) and attenuates it (with positive voltages) or amplifies it (with negative voltages) depending on the voltage at the control pin. Hence, the ratio between input and output current is determined by a voltage. It is a "voltage-controlled current source" -- in other words, a voltage-controlled resistor.

2164 VCAs must terminate to virtual ground, which means that you must feed each 2164 VCA into the inverting terminal of an opamp with its positive terminal grounded. An opamp wired as an inverter with a resistor in the feedback loop, but with no input resistor, is a "current-to-voltage" converter, and this is what typically follows a 2164 VCA. However, you can also put a capacitor in the feedback loop of the opamp, and now you have an integrator. 2164 + resettable integrator = VCO. 2164 + integrator with feedback to the 2164 input = 6dB LPF. Neither of these require exponential converters, since the 2164 does that already.

lysander · Posted: Thu May 24, 2012 11:32 am Post subject:

Navs · Posted: Tue May 29, 2012 10:43 am Post subject:

Thanks, Dave! Now, where do I get 2164s in Europe? hyper

russma · Posted: Tue May 29, 2012 10:54 am Post subject:

I think Dave uses CoolAudio 2164 clones. See if you can find a CoolAudio distributer in Europe. Behringer uses CoolAudio 2164's in some of their "vintage" knockoffs.

Rod Serling Fan Club · Posted: Tue May 29, 2012 1:37 pm Post subject:

daverj · Posted: Tue May 29, 2012 4:22 pm Post subject:

Dr. Sketch-n-Etch · Posted: Tue May 29, 2012 8:20 pm Post subject:

daverj · Posted: Wed May 30, 2012 1:44 pm Post subject:

Those are cool building blocks. I may have to take a closer look at that chip (some day in the future if I ever have spare time again).

It's been a while since I read the data sheet on the 2164, but I vaguely remember it having a similar temperature drift on the gain input to the classic bipolar expo converter. If that's the case then it would need some kind of temperature compensation network on the gain input to cancel the drift, like the tempco resistor used on the classic circuit.

J3RK · Posted: Wed May 30, 2012 1:56 pm Post subject:

Nice information! Makes me want to play with this chip too! This and the THAT 218Xes. Thanks Dr.!

Navs · Posted: Wed May 30, 2012 3:50 pm Post subject:

Dr. Sketch-n-Etch · Posted: Wed May 30, 2012 9:37 pm Post subject:

Moog$FooL$ · Posted: Wed May 30, 2012 9:54 pm Post subject:

time for a 2164 group buy!

hyper

daverj · Posted: Fri Jun 01, 2012 12:43 am Post subject:

Dr. Sketch-n-Etch · Posted: Fri Jun 01, 2012 5:02 am Post subject:

iopop · Posted: Fri Jun 01, 2012 5:52 am Post subject:

Moog$FooL$ · Posted: Fri Jun 01, 2012 1:32 pm Post subject:

Rod Serling Fan Club · Posted: Fri Jun 01, 2012 1:38 pm Post subject:

Thanks for all the great info Dr. Etch

J3RK · Posted: Fri Jun 01, 2012 1:53 pm Post subject:

Yes, thanks once again! Very nice stuff! Also, I'd be in for some of them if a group buy were to be arranged.

CLee · Posted: Sat Jun 02, 2012 10:33 am Post subject:

Dr SnE, thanks for the tip on the 2164 VCO. I'm working on a circuit that needs a VCO that tracks 1 v/oct but doesn't need to be perfect, or fully temperature stable. This looks like a nice small circuit that I could use without building a whole expo converter.

Craig

Dr. Sketch-n-Etch · Posted: Sat Jun 02, 2012 4:14 pm Post subject:

CLee · Posted: Sat Jun 02, 2012 10:42 pm Post subject:

Actually I searched for Roman Sowa, whose name you mentioned, and and the 2146 and came accross this,

2146 oscillator

this is a complete VCO, right?

iopop · Posted: Sun Jun 03, 2012 4:16 am Post subject:

Sorry for completely OT, but I couldn't help smiling reading this,
"PS It's only 5K file. Hope you don't mind... "

Ailurophilia · Posted: Sun Jun 03, 2012 7:02 am Post subject:

Dr. Sketch-n-Etch · Posted: Sun Jun 03, 2012 12:37 pm Post subject:

CLee · Posted: Sun Jun 03, 2012 3:56 pm Post subject:

Ailurophilia · Posted: Mon Jun 04, 2012 3:01 am Post subject:

neil.johnson · Posted: Mon Jun 04, 2012 6:36 am Post subject:

neil.johnson · Posted: Mon Jun 04, 2012 6:50 am Post subject:

neil.johnson · Posted: Mon Jun 04, 2012 6:53 am Post subject:

neil.johnson · Posted: Mon Jun 04, 2012 7:19 am Post subject:

CLee · Posted: Mon Jun 04, 2012 7:21 am Post subject:

Dr. Sketch-n-Etch · Posted: Mon Jun 04, 2012 9:34 am Post subject:

Navs · Posted: Mon Jun 04, 2012 10:49 am Post subject:

Navs · Posted: Sun Oct 21, 2012 3:04 am Post subject: