Waveform not symmetrical

[hagekay]

Quote: "Ideally you would connect the pre-amp out to the line in - that is, before the power amp. A speaker output is not designed to go into a line input, "

How does one connect to the pre-amp? There are no convenient jacks, like speaker jacks. So should I clip onto the internal wires coming from the pre-amp into the power amp?

Alternatively, there is a plug called "phones" on the front face of the stereo. Does this plug connection come from the pre-amp or power amp? Is this head phone plug 8 ohms?

[steve]

Some old record players had a "line out" or e "tape out" or some other output that was at "Line level", sometimes on a 5 pin DIN connector, but some did not. I'm guessing from your response that yours has not. Unless you're a bit keen on practical electronics I'd not recommend trying to hack into the circuits. So you are stuck with a speaker out and a headphone out. The headphone socket is still not ideal, though the expected load is slightly better (about 30 Ohms) - you could try it and see if it any better, but again, be careful to keep the volume low.

[kozikowski]

When you connect something to Audacity and you configure the system properly, you can click once inside the red record meters and they will wake up and monitor the level without you having to make a recording. Great for troubleshooting and level setting.

Koz

[alatham]

The puzzle is: why the sudden negative dip and then the gradual (exponential) curve to the centre (level 0).

Thanks for the picture, it's a great help. The picture strongly suggests that a capacitor somewhere within the stereo amp is either faulty or unhappy because it's running a load it wasn't designed for. My best guess is that it's a capacitor in the speaker output stage, but it may also be a capacitor in your sound card circuitry (though this seems unlikely to me). The capacitor is discharging and then exponentially rebuilding it's charge as the sound goes back to normal. There won't be a good way to fix the audio you've already recorded unless you take Koz's suggestion and re-draw the waveform yourself, but I think that will take oceans of time.

So, I agree with Steve. I also agree that it is not a good idea to hack into your stereo amp and tap into the pre-amp signal. There are capacitors in there that may be holding a several hundred volt charge right now (even if the thing is unplugged).

The way I see it, you have two options right now.
1) Tell us the model number of the stereo amp you have and we can try to find a manual online. You might have the output you want on there, but it may be labeled with an odd name. Audio electronics (especially older models) are like that.
2) Buy a dedicated phono pre-amp. Amazon.com sells plenty of them here. Many of these won't break the bank, but do shop around a bit, some of them are designed specifically for moving coil cartridges (which are rare) or moving magnet cartridges (which are not at all rare). If you don't know what kind of cartridge you have, then it's probably a moving magnet.

[hagekay]

"The way I see it, you have two options right now.
1) Tell us the model number of the stereo amp you have and we can try to find a manual online. You might have the output you want on there, but it may be labeled with an odd name. Audio electronics (especially older models) are like that."

Well, don't laugh, this stereo system is old. Old, yet still made in Taiwan. It was bought at Sears. Nameplate on the back: Model: 28843. Chassis: 132-10005. On the back:Speaker Output jacks "A" R & L 8 ohm. Speaker Output jacks "B" R & L 8 ohm. AUX Input jacks R & L.
On the front: Input jack "L-MIC". Input jack "R-MIC". Output jack "PHONES".
As reported above, I have been using the 8 ohm jacks, but probably need to clip onto the internal wires to get at the pre-amp.

[steve]

The options I see now:

1) Get a new record player
2) Use the "phones" output, but keep the volume really low. (Not ideal, but no worse than using the speaker out, and no financial cost as long as you don't blow up your sound card)
3) Intercept the signal directly from the cartridge and put it through a phono pre-amp, but it's probably not worth the hassle (and will not work properly with a "ceramic cartridge").
4) Intercept the signal directly from the cartridge and put it directly into your sound card, then use the RIAA Equalisation in Audacity effects. With a magnetic cartridge the signal level will be very very low, and with a ceramic cartridge it will sound very very tinny.