Hi Folks, Yesterday I quickly did up a basic Guitar amp design useing a LM3886 and a Dual op amp which I thought was pretty basic but for the life of me I can"t get it to work.....
The basic idea was I would use the Input opamp to add gain in an inverting config with some Clipping diodes in the feedback loop to add an Overdrive sound , The second opamp would be used as an active inverting One knob tone controll , and after this it would go into a Non inverting LM3886 in the Basic datasheet implementation.....
The PCB I did has the PSU on the same board ,It puts out an unregulated +/-26v for the LM3886 and a regulated +/-15v for the TL072 opamp useing LM7815/7915 regulators with 10,000uF per rail and 2200uF on each rail close to the LM3886 and 10uF per rail for the tlo72 close to the IC.....
I have tested the PSU part and it puts out the correct Voltages and I am getting the correct Voltages at the pins of the IC"s , I am not getting anything at all at the output ,Not even DC and the LM3886 isn"t getting hot at all but I know it is getting the correct voltages at the power pins.....
I have attached the schematic and the PCB design and I weas wondering if someone could tah=ke a look at it and see if they can see any Glareing errors that i might have missed that would cause the amp to put out nothing....
I"m hopeing I just made a stupid mistake and another few sets of eyes might help me find the problem....
Thanx a Lot!!!
The basic idea was I would use the Input opamp to add gain in an inverting config with some Clipping diodes in the feedback loop to add an Overdrive sound , The second opamp would be used as an active inverting One knob tone controll , and after this it would go into a Non inverting LM3886 in the Basic datasheet implementation.....
The PCB I did has the PSU on the same board ,It puts out an unregulated +/-26v for the LM3886 and a regulated +/-15v for the TL072 opamp useing LM7815/7915 regulators with 10,000uF per rail and 2200uF on each rail close to the LM3886 and 10uF per rail for the tlo72 close to the IC.....
I have tested the PSU part and it puts out the correct Voltages and I am getting the correct Voltages at the pins of the IC"s , I am not getting anything at all at the output ,Not even DC and the LM3886 isn"t getting hot at all but I know it is getting the correct voltages at the power pins.....
I have attached the schematic and the PCB design and I weas wondering if someone could tah=ke a look at it and see if they can see any Glareing errors that i might have missed that would cause the amp to put out nothing....
I"m hopeing I just made a stupid mistake and another few sets of eyes might help me find the problem....
Thanx a Lot!!!
An externally hosted image should be here but it was not working when we last tested it.
Thanx a Lot....You solved my problem(s)...i knew it had to be something simple...
I just soldered a 10K resistor to the bottom of the PCB between the Mute and -V pin and I am getting a pretty good sound...
I think this will also solve a problem I am haveing with another LM3886 amp I built but this time a 100w Br amp....
Anyone can feel free to Use this design if they want, I just played with the amp for a few minutes and I has a Really nice sound and no Hum, just remember to add the Un-Mute resistor.....
Thanx again....😀
I just soldered a 10K resistor to the bottom of the PCB between the Mute and -V pin and I am getting a pretty good sound...
I think this will also solve a problem I am haveing with another LM3886 amp I built but this time a 100w Br amp....
Anyone can feel free to Use this design if they want, I just played with the amp for a few minutes and I has a Really nice sound and no Hum, just remember to add the Un-Mute resistor.....
Thanx again....😀
The output stage’s input should have a ground reference to prevent floating of the DC level. I guess a Zobel network in the output would do no harm either.
Is guitar going to connect directly to P1? If yes, this is a serious impedance mismatch.
The PCB traces carrying rail and ground return currents are awfully thin.
Is guitar going to connect directly to P1? If yes, this is a serious impedance mismatch.
The PCB traces carrying rail and ground return currents are awfully thin.
this circuit is bleeding from many wounds...
1. P1: 5k gives very low input impedance, and this potentiometer is put there with wrong pinout (the source is shorted at zero volume level)
2. U1: the input impedance of this stage is approximately 10k, which is low...
3: P2: wrong pinout... (see (1))
4: U2: pin 6 should have been connected to ground by a resistor, because of two reasons:
a, this one-band eq isn't working properly
b, bias problems...
5: LM3886: pin 10, so the non-inverting input is floating, this aplifier has serious DC-offset issues, if it's working at all
regards
1. P1: 5k gives very low input impedance, and this potentiometer is put there with wrong pinout (the source is shorted at zero volume level)
2. U1: the input impedance of this stage is approximately 10k, which is low...
3: P2: wrong pinout... (see (1))
4: U2: pin 6 should have been connected to ground by a resistor, because of two reasons:
a, this one-band eq isn't working properly
b, bias problems...
5: LM3886: pin 10, so the non-inverting input is floating, this aplifier has serious DC-offset issues, if it's working at all
regards
6: lack of capacitors (~100nF) at voltage regulators, and LM3886. danger of high frequency oscillation...
7: lack of zobel-network and inductur at the output gives unstable operation
8: grounding on the pcb...
7: lack of zobel-network and inductur at the output gives unstable operation
8: grounding on the pcb...
LM3886: pin 10, so the non-inverting input is floating, this aplifier has serious DC-offset issues, if it's working at all
Maybe there are problems But I don"t notice them...I got about 10mv of Dc offset at the output and amp sounds great and goes really damn Loud...
1. P1: 5k gives very low input impedance, and this potentiometer is put there with wrong pinout (the source is shorted at zero volume level)
Don"t opamps work better with a Low input impedance, Like in Mic preamps that deal with 200 Ohm source impedances??
3: P2: wrong pinout... (see (1))
and I fixed the pot, I allways work with Trial and error with pots...
and I usually put a Pedal in front of it...
a, this one-band eq isn't working properly
Seems to be working for me....
The output stage’s input should have a ground reference to prevent floating of the DC level...
How do I fix that???
And there is an Inductor at the output....
Thanx
Maybe there are problems But I don"t notice them...I got about 10mv of Dc offset at the output and amp sounds great and goes really damn Loud...
1. P1: 5k gives very low input impedance, and this potentiometer is put there with wrong pinout (the source is shorted at zero volume level)
Don"t opamps work better with a Low input impedance, Like in Mic preamps that deal with 200 Ohm source impedances??
3: P2: wrong pinout... (see (1))
and I fixed the pot, I allways work with Trial and error with pots...
and I usually put a Pedal in front of it...
a, this one-band eq isn't working properly
Seems to be working for me....
The output stage’s input should have a ground reference to prevent floating of the DC level...
How do I fix that???
And there is an Inductor at the output....
Thanx
Can I fix the Dc and Bias problems by adding a resistor to ground after the input caps?? Is that what is meant by a DC return path??
Thanx
Thanx
return path??
Simple run a 22K resistor on the + input pin to ground, that is if your using 22K for your NFB, The NFB creates an offset and the input to ground offsets it by the same ratio.
Simple run a 22K resistor on the + input pin to ground, that is if your using 22K for your NFB, The NFB creates an offset and the input to ground offsets it by the same ratio.
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