After many years of not using turntable I tried to listen to my records but experienced loud hum output along with the music. My turntable is input to a preamp. I tried connecting the output of my peamp to many input areas of my audio receiver and the hum followed. I disconnected the input from the turntable and the hum is still there. I umplugged the A/c for the preamp the hum is gone. when i replug the A/c the hum is back. I have other devices plugged to my audio receiver and there is no problem....Would this mean that the preamp went bad from not being in use for many years.
Things to check:
1. There should be a "ground wire" from the turntable to a ground connection on the preamp.
2. Does the hum change with the volume control or not?
3. Disconnecting the input AND shorting the input is better for testing.
1. There should be a "ground wire" from the turntable to a ground connection on the preamp.
2. Does the hum change with the volume control or not?
3. Disconnecting the input AND shorting the input is better for testing.
Try connecting the turntable earth directly to the mains earth (via the earth pin in a 3 pin mains plug) see if that stops the hum.
If you get a lot of hum even with inputs shorted, then there's something wrong with the preamp. It could be power supply or other.
I hope so. it is nice to hear my old recordings again even with the hum. I'll wait swhile to see if there is any more feed back. If not i'll purchase another preamp. My existing amp is way is close if not more to 40 years old.... I haven't used my turntable in perhaps 20 plus years..... tks for your input.... if you come up with something else would appreciate your update.
Hi,
Possibly an earth loop, the turntable should only
be grounded by the phono inputs earth post.
The turntable should not have a mains earth connection.
rgds, sreten.
Possibly an earth loop, the turntable should only
be grounded by the phono inputs earth post.
The turntable should not have a mains earth connection.
rgds, sreten.
if your talking ground loop then why is it that with the turntable not connected to preamp input there is still a hum unless I disconnect the power to the preamp. Keep in mind the turntable is also powered down.
If pre-amp has hum with inputs shorted then you have a faulty pre-amp, possibly earthing issues but could also be pre-amp power supply - dodgy smoothing caps.
thanks ....looks like there are 2 of you that have the same reasoning.... I'll wait awhile and see if there is another like yours and then i will purchase another preamp.
Are there any switches or controls on the preamp (is this a phono preamp, or a general-purpose preamp?)? It is possible that some swich contacts have corroded a bit and need a good cleaning. Similarly, some internal connector, or even screw, could have corroded and prevents a good connection somewhere. Have you opened up the preamp to clean out dust and dead critters? I would go through it and unplug/replug every connector, clean all switches and controls, re-seat socketed components, and even back off and re-tighten all the screws and bolts. After that start looking at power supply components like capacitors.
Tried all that today and no success. cannot dismantle pre amp. it is a sealed unit with small clamps that i cannot dislodge. looks like the bottom is made of steel.
check the Power amp by shorting the two inputs and measuring the hum+noise at the output.
Now short the two input barrels together.
Measure the hum+noise. Is it the same or different?
Attach two input interconnects.
Short the remote ends of each interconnect.
Measure the Hum+noise.
Short the barrels of the remote ends together.
Measure the Hum+noise. Is it the same as the first test?
Connect the preamp.
Repeat the whole set of tests but this time using the pre-amp inputs and their interconnects.
Are all the hum+noise measurements the same?
Now short the two input barrels together.
Measure the hum+noise. Is it the same or different?
Attach two input interconnects.
Short the remote ends of each interconnect.
Measure the Hum+noise.
Short the barrels of the remote ends together.
Measure the Hum+noise. Is it the same as the first test?
Connect the preamp.
Repeat the whole set of tests but this time using the pre-amp inputs and their interconnects.
Are all the hum+noise measurements the same?
Tossing in another 2 cents, step one is always plugging both the preamp and turntable into the same wall receptacle. Not into a surge protector or power strip, but the same wall receptacle.
You might try looking at the connections to the pickup cartridge in the tone arm, dust might have collected.
At the same time check for a grounding conductor to the cartridge, there might or might not be one. Either way leave it the way it is, but make sure all connections are secure. As always, the way to do this is to wiggle them--remembering that cartridges are delicate.
You might try looking at the connections to the pickup cartridge in the tone arm, dust might have collected.
At the same time check for a grounding conductor to the cartridge, there might or might not be one. Either way leave it the way it is, but make sure all connections are secure. As always, the way to do this is to wiggle them--remembering that cartridges are delicate.
Ok, if your preamp is 40 years old then quite likely the electrolytic caps have dried out. Keeping it in an attic or out in the garage wouldn't help it any during that time.
When those caps dry out you aren't filtering the ripple from the supply voltage, which will cause "hum" on your output. Keep in mind that a phono preamp has to amplify very small signals coming from your cartridge, so that hum will be amplified as well. That's what you are hearing.
Either you can, or someone with soldering skills can, replace the power supply caps in the preamp and it will probably be fine for another few decades. Also, if it is using old carbon composition resistors, it can't hurt to replace those as well since either you or a tech will have it apart anyway.
Do that and you will be enjoying music in no time at all.
When those caps dry out you aren't filtering the ripple from the supply voltage, which will cause "hum" on your output. Keep in mind that a phono preamp has to amplify very small signals coming from your cartridge, so that hum will be amplified as well. That's what you are hearing.
Either you can, or someone with soldering skills can, replace the power supply caps in the preamp and it will probably be fine for another few decades. Also, if it is using old carbon composition resistors, it can't hurt to replace those as well since either you or a tech will have it apart anyway.
Do that and you will be enjoying music in no time at all.
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