Hi guys,
I have a problem with the preamp that I can't understand.
The situation is like this, by chance I have two preamps and I have the same problem on both (Pro-Jectphono box mm/mc and Pro-Jectphono box mm), when I connect a pream to an amp (at any input) there is no noise/hum, but as soon as I connect the RCA cable to the preamp, to connect turntable, noise/hum occurs.
So the turntable is not connected and the noise only appeared due to the RCA cable.
Noise remains even when I connect the turntable which is grounded.
I tried 4 different RCA cables and they all come up with the same problem, while with the same cables there is no problem when they are connecting CD player to an amp (ded silent), so I believe the cables are OK.
I just don't understand, please help
I have a problem with the preamp that I can't understand.
The situation is like this, by chance I have two preamps and I have the same problem on both (Pro-Jectphono box mm/mc and Pro-Jectphono box mm), when I connect a pream to an amp (at any input) there is no noise/hum, but as soon as I connect the RCA cable to the preamp, to connect turntable, noise/hum occurs.
So the turntable is not connected and the noise only appeared due to the RCA cable.
Noise remains even when I connect the turntable which is grounded.
I tried 4 different RCA cables and they all come up with the same problem, while with the same cables there is no problem when they are connecting CD player to an amp (ded silent), so I believe the cables are OK.
I just don't understand, please help
That suggests the ground/screen connection to the RCA socket isn't reliable, so that noise is being picked up by the cable screen and coupled to the signal wire.
Proper grounding of the screen would divert capacitive pickup straight to ground
Proper grounding of the screen would divert capacitive pickup straight to ground
bad pre-amps?
when you say the turntable is grounded you are talking about a separate ground lead attached to the ground lug on the back of the preamp?
what make and model turntable?
when you say the turntable is grounded you are talking about a separate ground lead attached to the ground lug on the back of the preamp?
what make and model turntable?
"Bad preamps??"
No chance. By experience both phonoamps are totally silent when connected properly with proper cables 🙂
No chance. By experience both phonoamps are totally silent when connected properly with proper cables 🙂
My first guess was that it was TT, after I opened it and checked everything (bad soldier joints, wires...) I hooked it up (the ground wire and RCA cables) and the power cord wasn't plugged in, I turned on the amp and there was hum/noise.
After that i disconnected RCA cable from the TT and the noise was even stronger.
So:
1. amp+preamp connected and powered =silence
2. amp+preamp+cable=noise
3. amp+preamp+grounded TT=less noise but not acceptable
Situation the same on both preamps and cables silent when connected to CD player.
I'll try shielded cables next week, but if there are any other suggestions I am ready to try them out, just to get rid of that annoying hum
After that i disconnected RCA cable from the TT and the noise was even stronger.
So:
1. amp+preamp connected and powered =silence
2. amp+preamp+cable=noise
3. amp+preamp+grounded TT=less noise but not acceptable
Situation the same on both preamps and cables silent when connected to CD player.
I'll try shielded cables next week, but if there are any other suggestions I am ready to try them out, just to get rid of that annoying hum
In my experience hum is usually caused by earthing problems.
No earths is bad for hum.
2 or more earths is bad for hum through earth loop.
1 earth is good.
No earths is bad for hum.
2 or more earths is bad for hum through earth loop.
1 earth is good.
Nothing fancy, Technics sl dd333, but I don't see any correlation between my problem and make/model of TT
These Technics typically come with a short RCA cable (check for continuity of both shields and inner conductors) plus an extra ground wire coming from the tonearm shell. Both are hooked up, right?
Are you using the stock ~0.7 m RCA cable that came with the Technics? That should normally do the business. You need some ordinary coaxially constructed audio cable. As long as it's that and not e.g. twisted pair, you should be fine.
If the phonopre hums a lot with just an RCA cable connected, I would tend to suspect that the whole setup is floating with regard to its surroundings with some small capacitive coupling across the mains transformers, and may need to be earthed to keep its ground potential from flapping around in the breeze. If you happen to have both an ordinary PC and an RCA to 3.5 mm adapter cable and can spare e.g. a recording output on the amp, that would be one way. Otherwise run a second wire from the preamp's ground terminal to something known to be earthed, like mains protective earth, the case of a device connecting to it (like a PC) or the heating.
If I'm right with my hunch, you may even detect a change in hum levels when you turn around the amp's mains plug... that is, if you aren't in polarized mains plug territory, of course.
Are you using the stock ~0.7 m RCA cable that came with the Technics? That should normally do the business. You need some ordinary coaxially constructed audio cable. As long as it's that and not e.g. twisted pair, you should be fine.
If the phonopre hums a lot with just an RCA cable connected, I would tend to suspect that the whole setup is floating with regard to its surroundings with some small capacitive coupling across the mains transformers, and may need to be earthed to keep its ground potential from flapping around in the breeze. If you happen to have both an ordinary PC and an RCA to 3.5 mm adapter cable and can spare e.g. a recording output on the amp, that would be one way. Otherwise run a second wire from the preamp's ground terminal to something known to be earthed, like mains protective earth, the case of a device connecting to it (like a PC) or the heating.
If I'm right with my hunch, you may even detect a change in hum levels when you turn around the amp's mains plug... that is, if you aren't in polarized mains plug territory, of course.
I've had similar, and it was due to a cheap RCA lead which turned out to not be actually shielded. Keep in mind a phono preamp has very high gain, any small amount of induced noise (which will be predominantly mains hum) or ground loop hum at the input will become very prominent at the output. Try a known high quality shielded cable, make sure the turntable ground wire is connected, and there's only one path to ground through the system.
Solved the problem, DIY cables made from shielded microphone cable came up very good, but guitar cable did it even better.
There is a hum while not connected to a TT, but when connected they are silent, which wasn't the case with other cables.
Thank you all for hep and suggestions
There is a hum while not connected to a TT, but when connected they are silent, which wasn't the case with other cables.
Thank you all for hep and suggestions
I'd say too much electromagnetic interference around these days, and it's going to be much worse in the future
You can't compare apples with oranges:
TT pickup - 2-5mV (grounded)
CD player - 500mV-2V (probably not grounded plug).
Check if the head-shell wires are correct (White & Red go to RCA Tips) and for proper grounded RCA cables.
Correct. It happens with all pre-amps when You attach a wire, but it should no occur if You short the non connected RCA ends.