Think Portable.. 😉
I work with many portable battery powered devices that needs some touch up on the input. The amps usually don't have any type of input control but I'll install a volume control for obvious reasons. (If the source is not controlled).. *Stereo, of course..
I would like to discover a simple, portable line level tone control to "Tweak" the sound either from a straight line level source to an amp or to insert inline between a source and a Bluetooth transmitter. I vision a battery powered bass/treble/volume control operating from either from a 12 or 5 v.d.c. battery. (Trying to avoid dual +/- voltage supplies)
I have discovered a few tone control units that require an amplifier (Line Level) after the control to make up for the losses of the control. I could construct one but I may be missing something more simple. Guess I'm looking for a simple plug and play alternative or a single circuit that needs installed in some type of an enclosure..
Any suggestions are appreciated. Thanks in Advance!
I work with many portable battery powered devices that needs some touch up on the input. The amps usually don't have any type of input control but I'll install a volume control for obvious reasons. (If the source is not controlled).. *Stereo, of course..
I would like to discover a simple, portable line level tone control to "Tweak" the sound either from a straight line level source to an amp or to insert inline between a source and a Bluetooth transmitter. I vision a battery powered bass/treble/volume control operating from either from a 12 or 5 v.d.c. battery. (Trying to avoid dual +/- voltage supplies)
I have discovered a few tone control units that require an amplifier (Line Level) after the control to make up for the losses of the control. I could construct one but I may be missing something more simple. Guess I'm looking for a simple plug and play alternative or a single circuit that needs installed in some type of an enclosure..
Any suggestions are appreciated. Thanks in Advance!
Pretty much any audio orientated opamp data sheet gives a tone control example and these would readily translate to a single rail application in most cases.
This same tone control is found in a lot of popular equipment. It's simple and it works great.
For single ended operation, the non-inverting (+) input will have to be connected to a"virtual" ground that is half the supply voltage. This "ground" must be QUIET because any noise will be directly injected into the signal. This can be accomplished with a few resistors and a capacitor. In and out will have to be cap coupled too.
Very certain. I usually use 10K resistors between VCC and GND, shunted by a 100µF 16V capacitor in parallel to each resistor. May be a .1µF too.
Thanks guys!
I couldn't find much info on the Elektor. Is this unit just a preamp?
The LM833-N appears to be a neat project but I would need a little guidance on the specifics of the virtual ground. (I'm not an engineer but can follow a schematic) If I were to build one, I would be using a 12 v.d.c. LiPo battery with a voltage variance of 10.5/12.6 volts. (Hi/Lo Limits) Also, the values of the coupling capacitors..
I found the following unit in my ventures. It's the easy way out but I wasn't sure of the performance for my needs. It seems to have the functions that I need but I am afraid to pull the trigger. Perhaps an opinion from you folks?
https://www.aliexpress.com/item/NE5...32700058423.html?spm=a2g0s.8937460.0.0.rqViQG
I couldn't find much info on the Elektor. Is this unit just a preamp?
The LM833-N appears to be a neat project but I would need a little guidance on the specifics of the virtual ground. (I'm not an engineer but can follow a schematic) If I were to build one, I would be using a 12 v.d.c. LiPo battery with a voltage variance of 10.5/12.6 volts. (Hi/Lo Limits) Also, the values of the coupling capacitors..
I found the following unit in my ventures. It's the easy way out but I wasn't sure of the performance for my needs. It seems to have the functions that I need but I am afraid to pull the trigger. Perhaps an opinion from you folks?
https://www.aliexpress.com/item/NE5...32700058423.html?spm=a2g0s.8937460.0.0.rqViQG
It's easy, my dear. Put a 100K resistor in parallel to a 100µF 10 or 16V. Make a second net identical to the first. Then wire both in series, respecting the cap's polarity. Then, wire the + input of the opamp (LM833 or whichever you want o use, LM358 or any TL0x2 wil do the job. If power consumption is of primary need, thel TL272 is CMOS very low power drain. Then, the + remaining in teh series formed, to the pin 8 of the opamp, and the - to the pin 4. Please, to avoid entering DC voltages, add a 10µF non polar in series to the input, and another in series to the output.
Note also that this stage has no gain (Av = 1). I also suggest to use a buffer previous to this stage, also in this case, a quad opamp will do all the job. Here a TLC274 is also suggested.
Good luck.
Note also that this stage has no gain (Av = 1). I also suggest to use a buffer previous to this stage, also in this case, a quad opamp will do all the job. Here a TLC274 is also suggested.
Good luck.
Pretty much as Osvaldo says. In effect all you do is take the + input (the non inverting input) to a fixed voltage that is equal to half of the supply voltage. A simple resistive divider using say 100k resistors and with the lower resistor bypassed by a small cap (say 10uF) is all that is needed.
If battery operation is important then a FET opamp like the TL061 (dual TL062) would have low current consumption.
And don't forget to AC couple input and output as Osvaldo mentioned. That is vital.
Edit... hadn't spotted Eddies post above
I suggest to use both resistor bypassed capacitively, then the start time is lower (compensated attenuator).
This looks like fun! Thank You.. 😉
Question..
The thumb nail example uses 9 v.d.c. as the source voltage. The specs of the chip says it will handle up to 15 v.d.c. Would it be necessary for me to regulate my 12 volt LiPo to 9 v.d.c.?
Thanks in Advance..
Any of the opamps we have mentioned are rated up to -/+18 volts (so 36 volt in total).
12 volts is better than 9 because it allows more headroom.
12 volts is better than 9 because it allows more headroom.
Thanks, Mooly..
I was afraid to add regulation because of possible noise. The battery has a voltage monitor circuit built in to avoid over charge and low voltage shut down as self protection. I hope this circuit doesn't hinder me..
I was afraid to add regulation because of possible noise. The battery has a voltage monitor circuit built in to avoid over charge and low voltage shut down as self protection. I hope this circuit doesn't hinder me..
The monitor circuit will not pose any problem. Ultimately it is just a very low resistance FET used as a switch to cut off the voltage at the battery terminals. No problem there 🙂
Most opamps have internal regulation. Unless you need several stages DC coupled, no regulation at power lines is needed. 9V is OK for use with a 9V cell battery and then, portable.
Fantastic!
I'm curious of how long this circuit would operate on a 9 volt battery. I could parallel 2 with no issue. This would cure my fear of a ground loop issue in the project that I'm planning to build..
The mention of "Headroom" is something I need to understand. Would this circuit be capable of reproducing the line level (or equal to) the input operating at 9 volts? Most all of my sources are ample but a little boost would be welcome as long as I can control it.
Most opamps do not drain more than a couple of milliamperes. Then, a 9V battery (I don't know the bat capacity, but let's suppose 500mAh), then the battery will work 250 hours in use or ten days of non stop running.
Headroom is the capacity of manage large signals. With 9V you can have a ±4.5V theoretical output excursion. Let's assume 1V drop in the final stage of the opamp. Then, your maximum output without distortion will be ±3.5Vpp or 2.5VRMS, more than sufficient to input in a standard power amplifier.
Headroom is the capacity of manage large signals. With 9V you can have a ±4.5V theoretical output excursion. Let's assume 1V drop in the final stage of the opamp. Then, your maximum output without distortion will be ±3.5Vpp or 2.5VRMS, more than sufficient to input in a standard power amplifier.
In general it's not the best idea to tie the non inverting input to a rail through either a resistor or capacitor. Noise can still get coupled into the signal; path. Remember that CMRR will not help you here - that's for the rails.
For a quiet power source (like a battery) this will probably prove adequate. But I challenged myself to build a hi fi quality basic preamp (volume/bass/treble) that could run off the worst power supply there is for audio - a laptop power supply. (It can also work off a conventional wall wart.) I will share my findings.
My first prototype worked great except for the laptop supply buzz and whine. I had used a conventional virtual ground with a resistor ladder and a capacitor.
The first thing I did was to bypass the ladder. I split the top resistor 10K into 9K + 1K. The 1K was connected to the rail. I then bypassed that junction to ground with another capacitor. This got me about a 30 dB reduction; certainly adequate.
But I am never satisfied. I had a couple of TLE2426 "virtual ground"chips laying around. This is a chip with three leads in a small signal transistor package, so it is compact and easy to use. First I used the 2426 directly to the rail. Still the noise was transmitted. Then I bypassed the 2426 with a 10K resistor in series with the rail and a 10 uF bypass capacitor to ground. On the 2426 output I used a 1uFcapacitor in parallel with a 0.1 uF capacitor (just like the datasheet). This was the magic combo.
Also, a 5532 might be a better op amp for this circuit. You can scale the resistors down (and the capacitors up) to work better with this device.
For a quiet power source (like a battery) this will probably prove adequate. But I challenged myself to build a hi fi quality basic preamp (volume/bass/treble) that could run off the worst power supply there is for audio - a laptop power supply. (It can also work off a conventional wall wart.) I will share my findings.
My first prototype worked great except for the laptop supply buzz and whine. I had used a conventional virtual ground with a resistor ladder and a capacitor.
The first thing I did was to bypass the ladder. I split the top resistor 10K into 9K + 1K. The 1K was connected to the rail. I then bypassed that junction to ground with another capacitor. This got me about a 30 dB reduction; certainly adequate.
But I am never satisfied. I had a couple of TLE2426 "virtual ground"chips laying around. This is a chip with three leads in a small signal transistor package, so it is compact and easy to use. First I used the 2426 directly to the rail. Still the noise was transmitted. Then I bypassed the 2426 with a 10K resistor in series with the rail and a 10 uF bypass capacitor to ground. On the 2426 output I used a 1uFcapacitor in parallel with a 0.1 uF capacitor (just like the datasheet). This was the magic combo.
Also, a 5532 might be a better op amp for this circuit. You can scale the resistors down (and the capacitors up) to work better with this device.
I've just finished making this:http://www.ti.com/lit/an/sloa042/sloa042.pdf
Needed some tone ctrl to go with a pair of TDA7295 chip amps I put together to install into some old passive peavey speakers to make them more convenient.
I chose this design because i'm still lacking a lot of knowledge to always understand the schematic i'm following so wanted one I could trust to be correct. I modified it somewhat to use parts I had on hand: tl072 OP amp instead of the TLC074 specified and a completely different method for the virtual ground supply.
But the original design as shown in PDF is probably ideal for your application.
I am very happy with the performance of this circuit and it wasn't hard to complete even as a beginner
Needed some tone ctrl to go with a pair of TDA7295 chip amps I put together to install into some old passive peavey speakers to make them more convenient.
I chose this design because i'm still lacking a lot of knowledge to always understand the schematic i'm following so wanted one I could trust to be correct. I modified it somewhat to use parts I had on hand: tl072 OP amp instead of the TLC074 specified and a completely different method for the virtual ground supply.
But the original design as shown in PDF is probably ideal for your application.
I am very happy with the performance of this circuit and it wasn't hard to complete even as a beginner
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