How do I make an amplifier for an old turntable?

[Brisance]

depends on your amp, tubes generally won't get fried like that, however some trannies will.

[guidoilieff]

depends on your amp, tubes generally won't get fried like that, however some trannies will.

So I suppose I have to make a voltage divider to send an amp to a pre amp?

[Brisance]

stick a volume knob there Make sure you calculate the cutoff frequency though.

[guidoilieff]

Should I use a small fixed resistor to prevent transistors from frying? I have no idea how to do that calculation. Ill search it.

After that I could connect the amp directly to the input jack of the pc with no problems?

[ashcat_lt]

I like this amp design. I just don't want to burn my bass combo amp. The output is 10v DC. Wouldn't that fry something?

Probably not.  It'll distort all to hell, but it's not really likely to destroy anything.  A line level signal can get to greater than 20V peak-to-peak, but I wouldn't really hesitate to plug a mixer output into a guitar/bass amp.

Then again, being solid state (and no transformer), it'll probably survive a much bigger resistance in place of the speaker.  Put a 10K pot with the outside lugs to the respective speaker wires and the wiper to the tip of a jack and you've got an output volume control.  Put a 10K resistor in series with the "top" of that pot and the most you'll ever get out of it is 5V.

[guidoilieff]

Probably not.  It'll distort all to hell, but it's not really likely to destroy anything.  A line level signal can get to greater than 20V peak-to-peak, but I wouldn't really hesitate to plug a mixer output into a guitar/bass amp.

Then again, being solid state (and no transformer), it'll probably survive a much bigger resistance in place of the speaker.  Put a 10K pot with the outside lugs to the respective speaker wires and the wiper to the tip of a jack and you've got an output volume control.  Put a 10K resistor in series with the "top" of that pot and the most you'll ever get out of it is 5V.

I should use a protection diode just in case right? It is connected to a regulated and rectified +12/-12 transformer.

The mc7909 regulators have this protection circuit inside anyway right?

[ashcat_lt]

I'm so sorry.  I thought you were worried about the peak-to-peak voltage of the actual output signal even though you quite clearly said it was DC.  Got it now.

Your amp should be AC coupled already, and as long as its input cap can handle 10V plus whatever the positive excursions of the signal are, you're fine.  It probably can, but...

If you want to be sure, then stick a cap in series with the tip of whatever jack you're using for output.  Before the volume pot I described would be best.  The value kind of depends on how big that pot is, but somewhere in the 1-10u range is almost always overkill.