That circuit should be OK.
Check the DC conditions are correct, pin 1 should be around 6 volts DC.
Check the DC conditions are correct, pin 1 should be around 6 volts DC.
Pin 1 is about 6v. I checked the connections multiple times now. This is turning into quite a headache.
Its got to work 🙂
You need to check all the component values are correct now. If the input bias resistors were to low in value (but equal) then the DC conditions would be correct but it would load the source component excessively. If the feedback resistor (the upper) were to low then again, the DC is correct again but the gain is low.
Ideally you need to use a scope to confirm the audio is on pin 3 of the opamp. An open circuit coupling cap could give 'low gain'. Also make sure the 100k's are not something like 100 ohm or 10 ohm.
You have either a construction error or a wrong value somewhere.
You need to check all the component values are correct now. If the input bias resistors were to low in value (but equal) then the DC conditions would be correct but it would load the source component excessively. If the feedback resistor (the upper) were to low then again, the DC is correct again but the gain is low.
Ideally you need to use a scope to confirm the audio is on pin 3 of the opamp. An open circuit coupling cap could give 'low gain'. Also make sure the 100k's are not something like 100 ohm or 10 ohm.
You have either a construction error or a wrong value somewhere.
All of the values check out. A scope would be ideal, but... I'll use the next best thing - a diy signal tracer.
Edit: There is an audio signal at the input pin.
Edit: There is an audio signal at the input pin.
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We need to be able to compare amplitudes though, input vs output to be sure what is going on.
If you remove the opamp and link pins 1 and 3 then you should get the same audio on both input and output. That's worth checking as it would show excess loading or an open condition.
And it's impossible to do so. I hooked it up to a better stereo and it sounds like the higher frequencies are much quieter than the input and the bass is aboutthe same. Maybe I should try a higher gain?
A gain of 5 should be plenty, particularly considering the low supply voltage. Increase the gain too much and you will run into clipping. All audio frequencies should be amplified equally by this circuit.
If that correctly *drawn* circuit causes signal level loss instead of ~5X gain, then it was not properly *built* , period.
Or you are not correctly hooking it up: preamp signal should go into this gain booster and nowhere else, following power amp should be fed by this booster output and nothing else.
For basic checking you don't need a scope or signal tracer: feed it 100mV 400Hz and at the output you must have ~550mV AC
You can measure them with any cheapish Multimeter which has a minimum 200mV AC scale.
This one has a minimum scale of 399.9 mV AC , perfect:
The $10 ones with only 2 scales, 200V and 750V AC will not do.
Useless:
This one measures True RMS voltage, even better:
There is no excuse for delving into DIY Audio and not having at least a reasonable multimeter.
Or you are not correctly hooking it up: preamp signal should go into this gain booster and nowhere else, following power amp should be fed by this booster output and nothing else.
For basic checking you don't need a scope or signal tracer: feed it 100mV 400Hz and at the output you must have ~550mV AC
You can measure them with any cheapish Multimeter which has a minimum 200mV AC scale.
This one has a minimum scale of 399.9 mV AC , perfect:
The $10 ones with only 2 scales, 200V and 750V AC will not do.
Useless:
This one measures True RMS voltage, even better:
There is no excuse for delving into DIY Audio and not having at least a reasonable multimeter.
Well, after a week or so, I came back to it. Tested it again, and found a short. It works like a charm! On the bench atleast, powered by an ATX psu and connected to a home stereo. But when connected to the lexus factory radio, there's a detuned radio like whine when the preamp is turned on, which is quite audible. The radio's not in the car but on the bench, powered by an ATX psu, and the preamp is powered from a regulated 10v source inside the radio. I tried powering the preamp directly from the psu with 12v, still the same. Could this be a ground loop?
It could the radio picking the radiated hash from the ATX supply. Its possible it could be a ground loop to as there will be high frequency noise from the PSU.
A good chance it will all be fine when in the car.
A good chance it will all be fine when in the car.
It could be noise from power supply reaching amplifier input vis voltage divider R6 & R6 you may cure the problem using the circuit below.
I had already implemented something similar in my circuit, but thanks for the suggestion.
I tried it out in the car and it worked like a charm! Thank you all, for your suggestions and time!
pleased to hear its working OK in its intended application.I think you were testing with computer switching power supply ... switching power supply are often noisy ... eveen if they dont have noise in the output
they spread EMI all aroud ....
they spread EMI all aroud ....
I have had trouble with ATX PSU they induced noise or the ones I have used have, I would recommend trying a 12 V battery, car battery etc. to verify that the psu is not the problem.
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