preamp output voltage clipped!

[bobon721]

our preamp uses the this schematic but with the potentiometer only rated at 100k or 250k ohms.

what's causing the output voltage to be clipped at higher input frequencies? can this be prevented without a redesign of the schematic? if it can, how?
our group's just not satisfied with a working preamp. we want it to work to its full potential.

[danny]

anong klaseng mic ginamit nyo

[bobon721]

nevermind the mic. we didn't notice any distortion when we first tested it with a mic. we noticed the clipping when we tested the pcb using a function generator and oscilloscope.

[Johannah Aleksandria]

anong silbi nung R1? saka ano ba values nito? low output yung mic kaya cguro ok lang, pero ang function gen kung set mo rin output kagaya nung sa mic (milivolt ) baka di mag-clip.

[Johannah Aleksandria]

The gain is set at R5/R2 + 1. Kaya kung maximum yung R5 kailangan yung voltage gain ay di lalagpas sa 1/2 supply voltage. Magkapareho value nung R3 at R4 di ba? ginawang voltage divider dahil single supply.

[Woots29]

anong silbi nung R1? saka ano ba values nito? low output yung mic kaya cguro ok lang, pero ang function gen kung set mo rin output kagaya nung sa mic (milivolt ) baka di mag-clip.

ang silbi ng R1 is to supply the mic. ngaun ang ginamit nyang mic sa schem is condenser

mic which requires supply. ang problema eh inverting input ung pinaglagyan ng signal

since kapag bumaba ang impedance ng input tataas ang gain

IMHO

[insomartin]

 

[Johannah Aleksandria]

Wla na si ts.

[Born2BeWired]

The maximum output swing a LM358 can generate without clipping is approximately Vcc-2, or 7Vp-p for a 9V supply voltage. One thing worth noting is, the LM358, being designed for single supply operation, has an asymmetrical output swing range. That is, it can swing low to practically 0 volt, but can swing up to Vcc-2V only. You will see this effect (using sine function gen and a scope) as high side of the waveform clipped harder than the low side (or high side clipping earlier).

You can improve your circuit a little by adjusting values of R3/R4- instead of using R3=R4, adjust the value of R3 a tad greater higher than R4.

If you are looking for a still greater unclipped output voltage swing, use higher Vcc. 30VDC will be good.

[Born2BeWired]

BTW, too much input voltage (from function gen) will drive your preamp to clipping, even with 30VDC supply voltage.

If 'clipping' occurs only at high frequencies, it may well be that you have exceeded the slew rate limit of the OPAMP. In this case, use a faster OPAMP.

[bobon721]

Our function generator input voltage was 500 mV peak-to-peak at 60 Hz, 500 Hz, and 1 kHz. We never change the input voltage from that value. Clipping generally started at near-max volume (through potentiometer) at 500 Hz except for one mic module which never experienced any clipping at all frequencies even though it used the same schematic.

[Johannah Aleksandria]

Mic output is in the range of 5mV-20mV. So pwede yung circuit nyo sa microphone at di pwede sa line out ng mga audio equipment. Pwede rin sa line out kung babaan nyo R5, bababa din kasi yung gain.

[eirol_99]

taas ng input mo, eh mic pre-amp lang yan,mag clip nga yan. attenuate your source then try measuring it again

[bobon721]

Thanks. Napilitan kami sa 500 mV input kasi yun lang minimum na nabasa sa oscilloscope.