Hello, I have built this simple op-amp tone control/ premap.
Im satisfied with the bass and treble frequency " cut/ add " , but it doesnt sound so " clean / crisp " I mean, using the same op amp in an preamplifier sounded " better " than in this tone control circuit, I've used TL072-NE5532 .
Should I add a buffer before the "tone control " ? i have seen most op amp bandaxall tone controls use a buffer at the front.
I dont want to build Rod's tone control ( it uses 3 op amps ) I want to use 1 or 2 max.
Im satisfied with the bass and treble frequency " cut/ add " , but it doesnt sound so " clean / crisp " I mean, using the same op amp in an preamplifier sounded " better " than in this tone control circuit, I've used TL072-NE5532 .
Should I add a buffer before the "tone control " ? i have seen most op amp bandaxall tone controls use a buffer at the front.
I dont want to build Rod's tone control ( it uses 3 op amps ) I want to use 1 or 2 max.
Attachments
Also , maybe the caps that im using make it sound not so good comparing to the simple pre amplifier with the same op amps that sound better.
What
What
It is scaled for high impedance, it would probably sound better using a lower impedance pots of 10k ohms and scaling the capacitors accordingly. What are the source and load? See fig 5.... http://sound.whsites.net/articles/eq.htm
Last edited:
Thank you, source is pc ,mp3 player, mobile phone. load is input to any amplifier , but i make it for my " boombox " that has an tda7375
Also, for the schematic from post 1
If I ad a resistor 20-100k from output to gnd , that changes the output impedance right? .
If I ad a resistor 20-100k from output to gnd , that changes the output impedance right? .
A buffer op amp after the volume pot would help. A resistor at the output to ground would be in parallel to the amp's input impedance and lower it.
NEVER drive this circuit directly from the potentiometer center tap. The parameters constantly change as the potentiometer is rotated. You would know this if you had calculated your Norton-Thevenin equivalents correctly.
The obvious solution is a buffer after the volume control tap.
This is a very simple circuit and has been widely used. Although not as precise as other tone control circuits, it should sound "clean/crisp"as you say. What kind of capacitors did you use in the tone shaping circuit? You should be using some kind of film capacitor, NOT ceramic. MKP is great for this application, but more humble film capacitors should work fine.l
The obvious solution is a buffer after the volume control tap.
This is a very simple circuit and has been widely used. Although not as precise as other tone control circuits, it should sound "clean/crisp"as you say. What kind of capacitors did you use in the tone shaping circuit? You should be using some kind of film capacitor, NOT ceramic. MKP is great for this application, but more humble film capacitors should work fine.l
What does this mean?
That you set it to a given position and never again touch it or that it´s simply not in the circuit?
The circuit is fine, parts used also, and compared to relatively Lo Fi signals (MP3 and such) provided by
it has flawless response.
Maybe you expect too much from it 🙂
As of adding an output ground reference resistor, it does not need it since Op Amp out is both DC coupled and low impedance.
What did you use for power supply bypassing? Did you build it on a small dedicated board? Do you have a 0.1 uF ceramic capacitor soldered directly to the power supply pins of the chip? On board electrolytic bypass? Every board needs local bypassing.
Non inverting input should be connected to noise ground, not power ground. The two grounds shouldn't even be connected together on this board - should be connected together somewhere else in the circuit and only at one point. Sloppy ground schemes can introduce some "grit" to the sound - especially at lower volumes. That's because connecting signal ground and power ground together at more than one point in the circuit can introduce nasty ground loops. If you're sticking this circuit in a device or using it with another board, then failure to get the grounding right can seriously degrade performance.
Finally, this circuit will interact with the output impedance of the circuit driving it. So if the circuit has a relatively low output impedance (say 47 ohms) then the interference should be negligible. But if the output impedance is higher, or not linear with respect to frequency, then you will get some unwanted results.
Non inverting input should be connected to noise ground, not power ground. The two grounds shouldn't even be connected together on this board - should be connected together somewhere else in the circuit and only at one point. Sloppy ground schemes can introduce some "grit" to the sound - especially at lower volumes. That's because connecting signal ground and power ground together at more than one point in the circuit can introduce nasty ground loops. If you're sticking this circuit in a device or using it with another board, then failure to get the grounding right can seriously degrade performance.
Finally, this circuit will interact with the output impedance of the circuit driving it. So if the circuit has a relatively low output impedance (say 47 ohms) then the interference should be negligible. But if the output impedance is higher, or not linear with respect to frequency, then you will get some unwanted results.
made it on breadboard just to test it ( one channel ) bypass caps on the power supply board 4400uf or so per rail + 0.1uF non polar,
That's perfect. Does it go up and down when you rotate the bass control? It should.
Do you have this assembled on one of those solderless prototype boards? Audio circuits do not work well on these boards. They're very noisy with lots of stray capacitance. The "experimenter" PC boards from Radio Shack work much better and right now they're practically giving them away. Have you used them? They're laid out perfectly for op amp circuits.
Where do you have the non-inverting input grounded? Lots of noise and distortion can be introduced here. It should be grounded right at the audio input ground. I always have the input and output grounds right next to each other on my modular boards, and any critical signal ground goes right there. Signal ground should only be connected to power ground at one point in the whole circuit, typically at the input/ volume control ground.
The non-inverting input bias current is an unavoidable DC ground loop which can be minimized by using high input impedance op amps like the TL07x or OPA2134 devices. But even a 5532 with its higher input bias current works fine in a circuit like this.
Do you have this assembled on one of those solderless prototype boards? Audio circuits do not work well on these boards. They're very noisy with lots of stray capacitance. The "experimenter" PC boards from Radio Shack work much better and right now they're practically giving them away. Have you used them? They're laid out perfectly for op amp circuits.
Where do you have the non-inverting input grounded? Lots of noise and distortion can be introduced here. It should be grounded right at the audio input ground. I always have the input and output grounds right next to each other on my modular boards, and any critical signal ground goes right there. Signal ground should only be connected to power ground at one point in the whole circuit, typically at the input/ volume control ground.
The non-inverting input bias current is an unavoidable DC ground loop which can be minimized by using high input impedance op amps like the TL07x or OPA2134 devices. But even a 5532 with its higher input bias current works fine in a circuit like this.
Last edited:
Try this circuit with a 10k volume control at the output. You will probably like it better.
Getting the grounds right is crucial in a line level circuit. I build modular boards that can be used stand alone or cascaded together in various configurations. I have a system I use to get the grounds right.
Every board has the power ground and signal ground connected together at one point. This connection is made with a conspicuous jumper wire. I use a black wire and green shrink tube to make stripes. This wire sticks up off the board and is twisted.
You can take any one of these boards and stick it in a case with a power supply. If you're making a preamp (like I am) and want to cascade a few boards together (like volume/balance + voltage amplifier, bass and treble, and baffle step correction), you can cut this jumper wire on two of the three boards (in this case you would cut the jumper on the bass and treble, and baffle step correction boards) and avoid a couple of local ground loops. And for your circuit, there is essentially no signal ground anyway except for the non-inverting input bias, which isn't really a signal ground but can introduce noise and distortion exactly like a signal ground.
Every board has the power ground and signal ground connected together at one point. This connection is made with a conspicuous jumper wire. I use a black wire and green shrink tube to make stripes. This wire sticks up off the board and is twisted.
You can take any one of these boards and stick it in a case with a power supply. If you're making a preamp (like I am) and want to cascade a few boards together (like volume/balance + voltage amplifier, bass and treble, and baffle step correction), you can cut this jumper wire on two of the three boards (in this case you would cut the jumper on the bass and treble, and baffle step correction boards) and avoid a couple of local ground loops. And for your circuit, there is essentially no signal ground anyway except for the non-inverting input bias, which isn't really a signal ground but can introduce noise and distortion exactly like a signal ground.
Probably so. It would work best if the power amplifier were in the same case and the signal leads were short.
I would recommend using a 5532 (or 2134) in this case. The op amp is not only driving the pot, but also the resistors in the tone control circuit. This is even more relevant if the second circuit (with smaller value resistors) is used. The 5532 would be best in that circuit and would drive everything at 1 volt RMS with ease.
- Status
- Not open for further replies.