Hi,
Yes, but It is possible that the voltage goes to 29.9 but really the amplifier is in saturation. There is just a low volume sound coming from the amp. I do not know if you tried another speakers. You said that you have two in series. I built the LM3886 to find out why so many people have so much problems building the LM3886. If you follow the schematic from National you will not have any problem if you built it as it is in the schematic they provided. That is what I said go back I double check the wiring. It is possible that you have a bad chip.
Yes, but It is possible that the voltage goes to 29.9 but really the amplifier is in saturation. There is just a low volume sound coming from the amp. I do not know if you tried another speakers. You said that you have two in series. I built the LM3886 to find out why so many people have so much problems building the LM3886. If you follow the schematic from National you will not have any problem if you built it as it is in the schematic they provided. That is what I said go back I double check the wiring. It is possible that you have a bad chip.
'Saturation', eh?
We all assumed he measured 29.6VAC
Again, even if the chipamp is working correctly, there is not enough gain to amplify an electric guitar - it needs a preamp.
It does not matter with small input signal the amplifier output should not goes to 29.9 volts. Unless he has something wrong in the input. The national schematic specified that rf1 = 20k and ri = 1k this will be a gain of 20. You mean by putting the output from the guitar the output goes to 29.9 noway. It is possible if the input is floating then the output may goes to 29.9volts.
The only different is that he is using for rf1 33k and I am using for rf1 20K with r1 equal to 1K same as he is using. If you built the amplifier using the National spec with so few components that the only thing can go wrong is bad wiring or wrong components. He is missing the 220pf capacitor between pin 9 and pin 10 to prevent oscillation. Must people recommended to add this capacitor. Other than that my schematic same as he is.
Please bare in mind that I am not trying to offend nobody. What I am trying to point out is that if your are building a design that somebody already successfully assembled it and now you are experiencing some problems you should concentrate in what you may have done wrong. My advice to him is to try to make amplifier work with the Ipod , CD player or any other device he has available and then once is working try interface the guitar.
Tauro0221
Tauro0221
I finished building the preamp. Now with the volume controls all the way up I get about 10-29V (depending on if I pick a single note or strum a chord) at the speaker terminals. But now theres another problem. At first I ran the preamp of a 9V battery but the battery fell down to 7V. So I used a 9V regulator connected to the +33VDC rail (I will post the schematic below). But this gave me an awful 100Hz hum even when the volume on the preamp and amp was turned all the way down. However there was not hum when I tried it with an external 9V regulated power supply I use for my effects. Does anyone know why this is happening and maybe how i can fix it.
Thanks
Thanks
Attachments
Ground loop. Very difficult to avoid ground loops in a high gain preamp / power amp combination, that's why it's best if you can do the preamp on a battery supply.
What schematic did you use for the pre? Something simple with the right amount of gain would last a looong time on a 9V battery.
What schematic did you use for the pre? Something simple with the right amount of gain would last a looong time on a 9V battery.
Do you mean something like that below. I will also post the preamp schematic I used and the connection diagram.
Attachments
Says in your block diagram that the reg is attached to the metal chassis. Did you isolate it with an insulating washer? The tab of positive LM78xx regs is at ground potential and you want to have only one ground connection to a device. Ground through the circuit or ground through the chassis, not both - both potentially creates a loop.
Hi,
you need to install a dedicated Main Audio Ground (MAG).
This must not be located on the junction between the smoothing caps.
Find the locations of the Speaker Return Terminal, the PCB Power Grounds, the Signal Ground at the input RCAs, the PCB Signal Ground/s.
Now try to find a location (in mid air if necessary) that is roughly in the middle (centroid) of that group.
Bring all your ground references to this MAG. Bring the PSU Zero Volts to this MAG.
Before you connect Chassis to MAG or just as good Chassis to PSU Zero Volts, check that Chassis to MAG indicates open circuit.
Now connect Chassis to MAG.
you need to install a dedicated Main Audio Ground (MAG).
This must not be located on the junction between the smoothing caps.
Find the locations of the Speaker Return Terminal, the PCB Power Grounds, the Signal Ground at the input RCAs, the PCB Signal Ground/s.
Now try to find a location (in mid air if necessary) that is roughly in the middle (centroid) of that group.
Bring all your ground references to this MAG. Bring the PSU Zero Volts to this MAG.
Before you connect Chassis to MAG or just as good Chassis to PSU Zero Volts, check that Chassis to MAG indicates open circuit.
Now connect Chassis to MAG.
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