Voltage controlled amplifier - Electronic Circuits Projects Diagrams Free

Thunderchild · 14th November 2005, 12:11 PM

I need to make a voltage controlled amplifier to put in a theremin. unfortunately the IC specified in the diagram is impossible for me to getso i must find another IC or make a VCA with an op amp. can anybody help me in this. i was also woundering: the theremin will probably have a log or exponential reaction so could this be neutralised with an op amp in expo or log configuration ? :roll:

Optikon · 14th November 2005, 02:29 PM

Quote:

Originally Posted by Thunderchild

I need to make a voltage controlled amplifier to put in a theremin. unfortunately the IC specified in the diagram is impossible for me to getso i must find another IC or make a VCA with an op amp. can anybody help me in this. i was also woundering: the theremin will probably have a log or exponential reaction so could this be neutralised with an op amp in expo or log configuration ? :roll:

Texas Instruments & National Instruments make VCA's. They also provide versions with linear gain control. Also, I believe one can be made with opamps & a JFET (as variable resistor). Operational transcondcutance amplifiers might also work.

You say you can't get the IC you wanted, so how can someone recommend something, we don't know what you can get?

chemelec · 14th November 2005, 05:02 PM

What IC are you not able to get?

Maybe someone here can Supply it.

4electros · 14th November 2005, 05:03 PM

Quote:

Originally Posted by Thunderchild

I need to make a voltage controlled amplifier to put in a theremin. unfortunately the IC specified in the diagram is impossible for me to getso i must find another IC or make a VCA with an op amp. can anybody help me in this. i was also woundering: the theremin will probably have a log or exponential reaction so could this be neutralised with an op amp in expo or log configuration ? :roll:

My friend, i want you to explain the principle with more clarify, could you please do that?!

for example , what is VCA?!
thanks!

Optikon · 14th November 2005, 05:12 PM

Quote:

Originally Posted by 4electros

Quote:

Originally Posted by Thunderchild

I need to make a voltage controlled amplifier to put in a theremin. unfortunately the IC specified in the diagram is impossible for me to getso i must find another IC or make a VCA with an op amp. can anybody help me in this. i was also woundering: the theremin will probably have a log or exponential reaction so could this be neutralised with an op amp in expo or log configuration ? :roll:

My friend, i want you to explain the principle with more clarify, could you please do that?!

for example , what is VCA?!
thanks!

A VCA is a Voltage controlled amplifier. It operates similar to a voltage feedback opamp but with an extra terminal for externally setting the open loop gain. One applies an external voltage usually between -1V & +1V to establish the gain. Useful in oscillators for stabilizing the amplitude and also used in audio applications (AGC circuits)

Thunderchild · 14th November 2005, 09:02 PM

i do not know what i can and can't get util i ask for it. here in italy there is not that much of a hobbiest marcket. my supplyer is a local TV repairer that gets me what he can or there is another shop two towns away that supplies tv repaireres and the likle and has a bit more range but he told me that the SSM-2018 I weant is not available but the SSM-2017 is. this is funny because on analouge devices web site it said that the 2017 is obsolete and is replaced by the 2019 that anyhow is only a normal preamp and not a VCA.
i have come us with an idea: i can supply the control voltage as pulse widdth modulation (PWM) so for example if i want half the control voltage i will supply a 50 % duty cycle. if this is done at like 100-200 KHz then it will not be audible and can control the actual RMS of the signal i want to control and finish in a low pass filter to make it a bit more normal again.
so any ideas on PWM circuits simple if possible so the whole is not two complex.
btw as i do not use credit card or any stuff like that i have a problem with getting anything of the net. does anybody know a supplyer that has alternatives ?

Dr.EM · 14th November 2005, 09:15 PM

I have one of these:

http://www.rapidelectronics.co.uk/rk...0724&XPAGENO=1

I haven't actually used it yet, but it should be very good looking at the specs.

You may also find the attached circuit useful, again though, I have no personal experience with it.

Thunderchild · 14th November 2005, 09:20 PM

the theremin i am building is the one i posted on this page http://www.electro-tech-online.com/v...remin&start=15 if that helps. can anybody advise a suitabe IC to substitute the SSM-2018 ?

Thunderchild · 14th November 2005, 09:29 PM

ok but i need the data sheet for that part. how does that circuit work there are no pins specified or transistor numbers

Dr.EM · 15th November 2005, 11:53 AM

http://www.thatcorp.com/datashts/2180data.pdf

That is the datasheet for the part. I'd suggest that using it is the easiest way to approach this problem, its a nice one IC package.

In the other circuit, the transistors you mention are actually inside the 1/2 LM13700; http://www.rapidelectronics.co.uk/rk...4498&XPAGENO=1

Thats why that whole area is surrounded with the dotted box. Ictl is the control current, it will be voltage controlled using a suitable resistor.

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14th November 2005, 12:11 PM	(permalink)
Thunderchild	Voltage controlled amplifier I need to make a voltage controlled amplifier to put in a theremin. unfortunately the IC specified in the diagram is impossible for me to getso i must find another IC or make a VCA with an op amp. can anybody help me in this. i was also woundering: the theremin will probably have a log or exponential reaction so could this be neutralised with an op amp in expo or log configuration ? :roll: __________________ I AM the exeption that disproves the rule in many ways but the rules still apply (unfortunately) my site:www.simons-photography.com http://rushdenrotaract.org.uk

14th November 2005, 05:02 PM	(permalink)
chemelec	What IC are you not able to get? Maybe someone here can Supply it. __________________ I No Longer accept Private Messages on here. All Emails to me Must Contain the Word \"Electronic\" in the \"Subject Line\" or they go Directly to my Junk Mail Folder. Email me at: chemelec@hotmail.com Website: http://www3.telus.net/chemelec

14th November 2005, 09:02 PM	(permalink)
Thunderchild	i do not know what i can and can't get util i ask for it. here in italy there is not that much of a hobbiest marcket. my supplyer is a local TV repairer that gets me what he can or there is another shop two towns away that supplies tv repaireres and the likle and has a bit more range but he told me that the SSM-2018 I weant is not available but the SSM-2017 is. this is funny because on analouge devices web site it said that the 2017 is obsolete and is replaced by the 2019 that anyhow is only a normal preamp and not a VCA. i have come us with an idea: i can supply the control voltage as pulse widdth modulation (PWM) so for example if i want half the control voltage i will supply a 50 % duty cycle. if this is done at like 100-200 KHz then it will not be audible and can control the actual RMS of the signal i want to control and finish in a low pass filter to make it a bit more normal again. so any ideas on PWM circuits simple if possible so the whole is not two complex. btw as i do not use credit card or any stuff like that i have a problem with getting anything of the net. does anybody know a supplyer that has alternatives ? __________________ I AM the exeption that disproves the rule in many ways but the rules still apply (unfortunately) my site:www.simons-photography.com http://rushdenrotaract.org.uk

14th November 2005, 09:20 PM	(permalink)
Thunderchild	the theremin i am building is the one i posted on this page http://www.electro-tech-online.com/v...remin&start=15 if that helps. can anybody advise a suitabe IC to substitute the SSM-2018 ? __________________ I AM the exeption that disproves the rule in many ways but the rules still apply (unfortunately) my site:www.simons-photography.com http://rushdenrotaract.org.uk

14th November 2005, 09:29 PM	(permalink)
Thunderchild	ok but i need the data sheet for that part. how does that circuit work there are no pins specified or transistor numbers __________________ I AM the exeption that disproves the rule in many ways but the rules still apply (unfortunately) my site:www.simons-photography.com http://rushdenrotaract.org.uk

15th November 2005, 11:53 AM	(permalink)
Dr.EM	http://www.thatcorp.com/datashts/2180data.pdf That is the datasheet for the part. I'd suggest that using it is the easiest way to approach this problem, its a nice one IC package. In the other circuit, the transistors you mention are actually inside the 1/2 LM13700; http://www.rapidelectronics.co.uk/rk...4498&XPAGENO=1 Thats why that whole area is surrounded with the dotted box. Ictl is the control current, it will be voltage controlled using a suitable resistor. __________________ Angry!? I'm absolutely electrolytic! Will have to make do with myspace now I guess...