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BYO preamp anyone?


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Has anyone every built their own preamp? I've got a problem...


I'm trying to record music on my PC and my laptop. On my PC I have a nice creative card and in general it works great. My laptop has a cheapy card and it gives me tons of noise, so I thought I'd build a preamp to boost the signal a bit and hopefully decrease the signal to noise ratio.


I built a simple non-inverting amplifier using a simple CMOS Op amp (LM324N). The circuit gives a simple ~4x amplification. When I say simple non-inverting I mean basic textbook. 3 resistors and the CMOS chip. Nothing fancy - I wanted to use this as a starting point.


On my PC it works -great-. It totally eliminates noise even if I crank the mic volume enough to clip at my sound recorder.


However on my laptop it sounds -much- -much- worse. If I play quietly, I get nothing. If I turn it up and play hard, I get cracking.


My guess at this point is only that some DC offset is causing clipping, and the only reason I get sound when I play loud is because the trough of the wave is dipping below the clip point. How can this be, though? The circuit source is a 9V, and I split it evenly and ground everything at 4.5V so the amp should be swing at max from -4.5 to 4.5 and center at 0.


Any clues as to why this is happening?

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You might check the input settings on the laptop.


Some laptops have built in mic's that pick up the ambient sound around the laptop. It might have a setting that needs to be changed so the laptop is switched to use the signal coming from the cord that is plugged into the laptop.


On a Mac it's in the system preferences. It's either what they call the internal mic as opposed to the audio line in port.


Internal mic picks up sound around the computer.


Audio line in is the sound from the cord that is plugged into the computer.


Hopefully I've explained it....... cause now I've confused myself.

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Unfortunately my laptop has only the one mic input. I should have mentioned it works when I don't use the preamp, it's just got a lot of white noise. When I attach the preamp it all goes to hell.

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Hello L_Mo,

I know you are recording an Epiphone guitar so I hope this response will not get deleted due to my talking about "recording".


Laptop recording can be convenient, moble and frustrating. Laptop sound cards are...well...cheap. Even an inexpensive external sound card such as a soundblaster usb can be a vast improvement.


For 1 or 2 channels at a time a Behringer 802 coupled with an external sound card can offer an inexpensive solution. Other alternatives that offer a combination of input devices (sound card) and mixing capabilities are made by companies such as Line 6, Lexicon, M-Audio, Pre Sonus and many others. Most basic setups can cost as little as $100, although they can escalate into the thousands. Other alternatives include mixing boards that have their own interface built in: Mackie, Alesis, Phonic Helix, Allen and Heath, Soundcraft to name a few.


Other considerations are usb v.s. firewire. Usb is dependable but, due to data transfer rates are usually limited to 2 or 4 channels. Firewire devices can offer more simultaneous inputs but the manufacture often do not tell you that some of them will only work with certain firewire inputs. Interfaces that were developed using one brand of fire wire port often do not "play well with others".


Another consideration can be hard drive speed. Most stock laptops come with slow hard drives.


Technique can also be a factor. Do you want to record directly from your guitar, from a mic in front of an amp, through a D.I. box, or maybe a line out from an amp? The later can be an issue as some amps with a headphone/ emulated line out often produce poor results.


Entire books have been written on this "simple" subject so I will not bore this forum with details. The best starting point is to do your homework.


A good reference for recording is the Adobe forum as it provides a plethera of imformation on recording. Go to Adobe.com and click on communities/ forums. You will see a list of forums. Go to the Audition forum.


The best place to start is right here as I am now asking other members to please post some of the interfaces that they use on their laptops.

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