New here, and pretty new to electronics too. I've been working on a guitar humbucker active preamp based on the LM4250 X5 difference amplifier design.
I've gotten so far as to get a working breadboard done and ordered couple board prototypes from JLCPCB.
Here's the design:
C2 is a ceramic cap, I wonder if this is causing issues? What happens, it that the preamp basically does nothing. I get the same sound out of it with or without power connected to 9V+, which is slightly less volume than without the preamp from the humbucker. I tried replacing the diode with a wire and that changed nothing.
I've gotten so far as to get a working breadboard done and ordered couple board prototypes from JLCPCB.
Here's the design:
C2 is a ceramic cap, I wonder if this is causing issues? What happens, it that the preamp basically does nothing. I get the same sound out of it with or without power connected to 9V+, which is slightly less volume than without the preamp from the humbucker. I tried replacing the diode with a wire and that changed nothing.
Hi. Measure dc voltages on ic pins with reference to gnd and post them there. Maybe you got fake remarked or broken ic from bad source like ali* ? Also , resistor divider R1 R2 connected in a way , that all the power supply ripple is applied to input and amplfied with signal, need to add another resistor and capacitor. This may be an issue ,if powering from weak battery or badly filtered power source.
Look at lm4250 datasheet, there must be resistor for current setting , according to supply voltage. Your schematic lists pin8 as not connected to anything, maybe that's is the problem.
Also , in your pcb design not all connections are complete, that's already indicated by software used , by tiny lines. These points should be connected.
Look at lm4250 datasheet, there must be resistor for current setting , according to supply voltage. Your schematic lists pin8 as not connected to anything, maybe that's is the problem.
Also , in your pcb design not all connections are complete, that's already indicated by software used , by tiny lines. These points should be connected.
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Thanks guys, I'll check the suggestions later when I have better time. Here are some answers.
Input is grounded to the pickup frame. Chips should be fine, they were sourced by JLCPCB.
Here are the voltages from the chip:
1=0
2=0
3=4.07
4=0
5=0
6=dissipates from 6V to 0 slowly
7=8.7V
8=8.0V
Input is grounded to the pickup frame. Chips should be fine, they were sourced by JLCPCB.
Here are the voltages from the chip:
1=0
2=0
3=4.07
4=0
5=0
6=dissipates from 6V to 0 slowly
7=8.7V
8=8.0V
According datasheet internal ic schematic, pin 8 must have resistor to pin4 , without it ic is off. While you measured voltage at pin8 , you turned ic on for some time ,through voltmeter input resistance, and after you disconnected dmm from pin8 , voltage on output pin6 started decreasing. Put a high resistance resistor between pin 8 and pin4 , several megaohms. Look at datasheet.
In your schematic, the two inputs are floating. Is one of them grounded to the supply ground shown in the schematic?
If so, which one?
Jan
I think he uses a some kinda guitar sensor with two signal wires ,maybe magnetic or piezoelectric, with metal shield case , which is connected to gnd. Signal is wired differential, without ground i think.
Inputs are the two coils from a humbucker. I'll try to hotwire a resistor to the suggested place, thanks a lot! Hopefully that does it.
Yeah but the signal must be referred to gnd somewhere to make sure it stays within the common mode of the power supply.
There is a reason why a multimeter has two probes although you only measure one voltage.
Jan
Input have ac coupling by two capacitors, so it would stay at supply ranges already. Another thing , if input has some very high lets say rf reception, common mode , then yes, it would overload inputs. Differential mode is working only if resistors values for inputs are balanced, in this schematic this is not true. May ears ago I've used cassette recorder to record talk from wired phone line, and only ac coupled balanced schematic with opamp worked to completely remove hum. But there all four resistors had same values.
According to table ,lets assume you have not new battery , so +-3V suppy line is actual , from 544k to 55,6 megaohms values usable.
According to table ,lets assume you have not new battery , so +-3V suppy line is actual , from 544k to 55,6 megaohms values usable.
Now it works like it should! Big thanks!
Hotwired 4 1M resistors in series between pins 8 and 4. 😀 Looks very pro.
Reason for unbalanced inputs is sound tweaking. EMG uses similar method for the 81. This results in an audible peak at 2kHz.
Hotwired 4 1M resistors in series between pins 8 and 4. 😀 Looks very pro.
Reason for unbalanced inputs is sound tweaking. EMG uses similar method for the 81. This results in an audible peak at 2kHz.