Electronics > Beginners
Positive Feedback in Amp?
eev_carl:
Hi,
I'm building a bass guitar preamp and am starting with the input and output stages. I have a pair of op amps on a single 1455 IC, both unity-gain followers. The circuit is powered by a split power supply. There are 0.1 caps on +V to GND and -V and GND.
After about 90 seconds of playing or not playing, a repeating sound gets increasingly loader. You can hear it in the attached link to a WAV file. I'm on US power.
https://www.bekwam.net/audio/simple_audio_buffer_noise.wav
I was wondering if someone could help me identify the problem. I killed the lights and extra gear besides the power supply and amp.
Thanks,
Carl
Benta:
Where's your DC bias? The first amp is floating completely.
schmitt trigger:
The circuit is no preamp. With the feedback as shown, you have two unity gain stages in series.
In addition to the lack of bias.
eev_carl:
--- Quote from: schmitt trigger on September 15, 2018, 06:09:52 pm ---The circuit is no preamp.
--- End quote ---
I'm going to add a gain stage, a clipping stage, and a tone control stage. I figured I'd start with the input and output.
eev_carl:
For the first stage, should I put a resistor to GND. If so, what's a good value? I was confused because most of the schematics I read that had a bias were single supply and needed to account for the negative input.
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