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!!!
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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
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
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