A
Alun
- Jan 1, 1970
- 0
I don't have the TL071 op-amp used here, do you think it'll be ok to use a CA3140?
I don't have the TL071 op-amp used here, do you think it'll be ok to use a CA3140?
audioguru2
- Apr 6, 2004
- 12,026
- Joined
- Apr 6, 2004
- Messages
- 12,026
Hi Alun,
The old CA3140 is too noisy for a high gain microphone preamp. There are lots of different low-noise audio opamps you could use.
The old CA3140 is too noisy for a high gain microphone preamp. There are lots of different low-noise audio opamps you could use.
audioguru2
- Apr 6, 2004
- 12,026
- Joined
- Apr 6, 2004
- Messages
- 12,026
Hi Sasi,
That 60W RF amp in our projects section doesn't even say what frequency it amplifies. Since it mentions QRP which is for ham or amateur radio, and it has a very high-value tuning cap and a coil with a core, it is probably for short-wave, certainly not for the FM broadcast band. ???
Have you seen the tiny size of the MAX2206? 1mm by 1mm! But it has only 4 connections while your circuit shows an IC with 6 connections. Wrong IC. :
That 60W RF amp in our projects section doesn't even say what frequency it amplifies. Since it mentions QRP which is for ham or amateur radio, and it has a very high-value tuning cap and a coil with a core, it is probably for short-wave, certainly not for the FM broadcast band. ???
Have you seen the tiny size of the MAX2206? 1mm by 1mm! But it has only 4 connections while your circuit shows an IC with 6 connections. Wrong IC. :
audioguru2
- Apr 6, 2004
- 12,026
- Joined
- Apr 6, 2004
- Messages
- 12,026
Yeah,
You got the correct IC, I got the wrong one!
Those guys at Maxim must have tin ears. The high-value cap at pin 3 will cut high audio frequencies, and the circuit doesn't have pre-emphasis capacitors across R3 and R4.
An FM radio receiving a transmission from that transmitter will probably sound worse than an AM radio, especially in North America with our severe de-emphasis! :'(
You got the correct IC, I got the wrong one!
Those guys at Maxim must have tin ears. The high-value cap at pin 3 will cut high audio frequencies, and the circuit doesn't have pre-emphasis capacitors across R3 and R4.
An FM radio receiving a transmission from that transmitter will probably sound worse than an AM radio, especially in North America with our severe de-emphasis! :'(
audioguru2
- Apr 6, 2004
- 12,026
- Joined
- Apr 6, 2004
- Messages
- 12,026
Hi Sasi,
If you could find a cheap cable TV amplifier that isn't overloaded all the time like most of them, an antenna could be connected to its output.
In the olden days, my cable had about 78 channels and the cable company gave just barely enough signal for one TV set. When you added a splitter for a second TV set, it cut the signal level in half for both of them, looking weak. You could order a splitter from the cable company, pay for it over and over every month as a fee, then all they would do is turn up the level a little for their splitter.
So I bought a cheap cable TV amplifier. It was overloaded on nearly every channel! I read up about them and discovered that with a few channels they are fine, but with many channels the signals intermodulate each other. Since the picture of TV is AM, it made a mess with my 78 channels. I changed its single microwave transistor and biased it strongly (it got fairly hot) so that it worked pretty well. It would make a good transmitter for you. ;D
If you could find a cheap cable TV amplifier that isn't overloaded all the time like most of them, an antenna could be connected to its output.
In the olden days, my cable had about 78 channels and the cable company gave just barely enough signal for one TV set. When you added a splitter for a second TV set, it cut the signal level in half for both of them, looking weak. You could order a splitter from the cable company, pay for it over and over every month as a fee, then all they would do is turn up the level a little for their splitter.
So I bought a cheap cable TV amplifier. It was overloaded on nearly every channel! I read up about them and discovered that with a few channels they are fine, but with many channels the signals intermodulate each other. Since the picture of TV is AM, it made a mess with my 78 channels. I changed its single microwave transistor and biased it strongly (it got fairly hot) so that it worked pretty well. It would make a good transmitter for you. ;D
audioguru2
- Apr 6, 2004
- 12,026
- Joined
- Apr 6, 2004
- Messages
- 12,026
Sorry, Sasi.
I don't have the circuit of my old cable TV amplifier anymore. :'(
I don't have the circuit of my old cable TV amplifier anymore. :'(
Kevin Weddle
- Feb 23, 2004
- 1,620
- Joined
- Feb 23, 2004
- Messages
- 1,620
Hey Audioguru. How are you? What keeps Q2 and Q3 from creating too large a signal. Couldn't you use a parallel resistor to keep the gain down? We must know that the signal is constantly modulating a carrier and anytime the carrier is thrown into cutoff or saturation the meaning of the signal is lost. Although the square wave produced contains the rate of change, the higher amplitudes of the signal will not affect the
Last edited by a moderator:
audioguru2
- Apr 6, 2004
- 12,026
- Joined
- Apr 6, 2004
- Messages
- 12,026
Hi Kevin,
My FM transmitter circuit badly overmodulates when a loud sound or talker is too close to its microphone. I made its preamp gain high enough to pickup conversations about 2m away.
I built the original circuit of a defective transmitter to see everything that was wrong with it and when its preamp was working (it was very affected by supply voltage changes and had much more gain and distortion) it would overmodulate like crazy!
I think its overmodulation wouldn't be so bad if its RF oscillator produced only FM, since it would simply produce bad distortion in an FM radio, or cause interference to an adjacent RF frequency. Bad overmodulation does cause the AFC in my Walkman radio to work backwards and push the signal away. But since its RF oscillator produces AM in addition to the FM, overmodulation causes its RF carrier to stop momentarily whenever the RF oscillator is saturated and cutoff by overmodulation of its AM component.
Adding a parallel resistor somewhere to reduce the gain would mess it up. If I add a resistor in parallel with the collector resistor of the preamp transistor then it would be cutoff and need rebiasing.
My FM transmitter circuit badly overmodulates when a loud sound or talker is too close to its microphone. I made its preamp gain high enough to pickup conversations about 2m away.
I built the original circuit of a defective transmitter to see everything that was wrong with it and when its preamp was working (it was very affected by supply voltage changes and had much more gain and distortion) it would overmodulate like crazy!
I think its overmodulation wouldn't be so bad if its RF oscillator produced only FM, since it would simply produce bad distortion in an FM radio, or cause interference to an adjacent RF frequency. Bad overmodulation does cause the AFC in my Walkman radio to work backwards and push the signal away. But since its RF oscillator produces AM in addition to the FM, overmodulation causes its RF carrier to stop momentarily whenever the RF oscillator is saturated and cutoff by overmodulation of its AM component.
Adding a parallel resistor somewhere to reduce the gain would mess it up. If I add a resistor in parallel with the collector resistor of the preamp transistor then it would be cutoff and need rebiasing.
audioguru2
- Apr 6, 2004
- 12,026
- Joined
- Apr 6, 2004
- Messages
- 12,026
Hi Mp,
Thanks, I completely forgot about that one. I have an NE572 stereo one in my stock that I could try. Philips' "Compandor Cookbook" is full of applications for them:
http://www.semiconductors.philips.com/acrobat/applicationnotes/AN176.pdf
Thanks, I completely forgot about that one. I have an NE572 stereo one in my stock that I could try. Philips' "Compandor Cookbook" is full of applications for them:
http://www.semiconductors.philips.com/acrobat/applicationnotes/AN176.pdf
A
Alun
- Jan 1, 1970
- 0
How about the LF351? then ?audioguru said:
audioguru2
- Apr 6, 2004
- 12,026
- Joined
- Apr 6, 2004
- Messages
- 12,026
Hi Alun,
Happy Birthday soon!
You are not very old like me so why are you selecting old parts?
The LF351 hasn't been manufactured for about 7 years by National its inventor, but some shops might still have one. Its noise is lower than a 741 but not nearly as low as a TL071.
Just rip apart an audio mixer, most have TL071 opamps inside.
I don't know where you are, but don't use New Japan Radio's 1st version copy of the TL071. They tried to make their copy better than TI's original and ended up with it oscillating all the time. They had a big appology and warning about it on their website, but it's gone now.
Happy Birthday soon!
You are not very old like me so why are you selecting old parts?
The LF351 hasn't been manufactured for about 7 years by National its inventor, but some shops might still have one. Its noise is lower than a 741 but not nearly as low as a TL071.
Just rip apart an audio mixer, most have TL071 opamps inside.
I don't know where you are, but don't use New Japan Radio's 1st version copy of the TL071. They tried to make their copy better than TI's original and ended up with it oscillating all the time. They had a big appology and warning about it on their website, but it's gone now.
Alun,
I can see using an older op-amp if you have a bunch of stock you want to get rid of, but not as something to purchase.
If you MUST use the LF351, I found about 28,000 of them around with my parts search. You should not have a problem getting one. But like audioguru has stated, go for the low noise op-amp in a new design. You will be much happier in the long run.
MP
I can see using an older op-amp if you have a bunch of stock you want to get rid of, but not as something to purchase.
If you MUST use the LF351, I found about 28,000 of them around with my parts search. You should not have a problem getting one. But like audioguru has stated, go for the low noise op-amp in a new design. You will be much happier in the long run.
MP
A
Alun
- Jan 1, 1970
- 0
audioguru2
- Apr 6, 2004
- 12,026
- Joined
- Apr 6, 2004
- Messages
- 12,026
Hi Guys,
Here is a pic of my FM transmitter circuit built on a copy of Veroboard. It is Mod4, but using the circuit board of Mod3, so a few of its parts are very close together and I have resistor R6 and little ceramic cap C2 underneath. I have a 680 ohm resistor at the lower left as a current-limiting resistor for its LED. I don't have any space on this board for the 5.1V zener diode in series with the LED that shuts it off when the batt gets down to about 5.3V as a low-batt warning.
Look at the tiny size of its trimcaps and electret mic. The mic has a thick rubber sleeve around it so is actually much smaller. The 1mm wire for my coils is so stiff that you can stand on them and they don't change.
View attachment 36747
Here is a pic of my FM transmitter circuit built on a copy of Veroboard. It is Mod4, but using the circuit board of Mod3, so a few of its parts are very close together and I have resistor R6 and little ceramic cap C2 underneath. I have a 680 ohm resistor at the lower left as a current-limiting resistor for its LED. I don't have any space on this board for the 5.1V zener diode in series with the LED that shuts it off when the batt gets down to about 5.3V as a low-batt warning.
Look at the tiny size of its trimcaps and electret mic. The mic has a thick rubber sleeve around it so is actually much smaller. The 1mm wire for my coils is so stiff that you can stand on them and they don't change.
View attachment 36747
Nice work audioguru ,
I always find it helpful to have a pic of the project I want to construct. I'll get started on it once I have finished the two projects I am working on now, or at least finish putting them together then comeback later to get them working properly as I often do ;D.
, I always find it helpful to have a pic of the project I want to construct. I'll get started on it once I have finished the two projects I am working on now
, or at least finish putting them together then comeback later to get them working properly as I often do ;D.
A
Alun
- Jan 1, 1970
- 0
Good job audioguru!
It would be nice if some administrator could add your project to this site. When I get the time I will build it with some of the modifications Iv'e talked about.
Could you tell me which is the least noisy pre-emphasis amplifier?
The one I sugested with the LF351 - I have a few lying around, or the transistor one you sugested, I'm far too cheap to go out an buy a TL071! ;D
It would be nice if some administrator could add your project to this site. When I get the time I will build it with some of the modifications Iv'e talked about.
Could you tell me which is the least noisy pre-emphasis amplifier?
The one I sugested with the LF351 - I have a few lying around, or the transistor one you sugested, I'm far too cheap to go out an buy a TL071! ;D
audioguru2
- Apr 6, 2004
- 12,026
- Joined
- Apr 6, 2004
- Messages
- 12,026
Thanks Dazza, ;D
Yours should also work fine.
Thanks Alun, ;D
Over here, a very popular TL071 costs less than a lousy old 741 or LF351. A TL072 dual costs even less! I always buy at least 10 and get a nice discount. Some experts like quieter audio opamps that cost an arm and a leg. This circuit is fine with just my transistor.
I'm still working on my FM transmitter, trying little ferrite chokes throughout it. I had the RF oscillator direct-coupled from the preamp but the preamp's bias went haywire. I didn't think that the oscillator's base voltage would be dragged down so low I guess by the oscillations. It works best with a little choke replacing C3, but I didn't bother changing the schematic yet.
I am also concerned with overmodulating it. A compressor/limiter would be too complicated for such a simple transmitter circuit. Because it has a lot of AM modulation, popping "P's" and other loud sounds cause its oscillator to stop for a moment. It will probably end up being modulated and tuned by a varicap for pure FM.
Then (if it is ever finished) I'll post it as a project! ;D
Yours should also work fine.
Thanks Alun, ;D
Over here, a very popular TL071 costs less than a lousy old 741 or LF351. A TL072 dual costs even less! I always buy at least 10 and get a nice discount. Some experts like quieter audio opamps that cost an arm and a leg. This circuit is fine with just my transistor.
I'm still working on my FM transmitter, trying little ferrite chokes throughout it. I had the RF oscillator direct-coupled from the preamp but the preamp's bias went haywire. I didn't think that the oscillator's base voltage would be dragged down so low I guess by the oscillations. It works best with a little choke replacing C3, but I didn't bother changing the schematic yet.
I am also concerned with overmodulating it. A compressor/limiter would be too complicated for such a simple transmitter circuit. Because it has a lot of AM modulation, popping "P's" and other loud sounds cause its oscillator to stop for a moment. It will probably end up being modulated and tuned by a varicap for pure FM.
Then (if it is ever finished) I'll post it as a project! ;D