2. amps-preamps
  3. 1286429954

moving coil pre-preamp hum

Hi all,

I am having a bit of a problem with a moving coil head amp. I am using an Ortofon MCA 76 and getting the horrid low level 40-60hz vibrating hmmmmm. at moderate-to-loud listening levels it is extremely faint, but at high listening levels it is apparent.

My old man is using the same headamp with a maplenoll turntable in a high end system and he swears by it and has never had any issues. Did I get a lemon?

Here is a little background: Tried a Madrigal carnegie one and a Supex Super 901 Low output. They sound incredible to say the least and are in very god condition, however the hum is driving me nuts. Using a VPI HW 19, Jelco arm. Bryston 4B amp. Dual Mono Tube phono section that no one has ever heard of but is amazing -Soundtech Preamp one. Have used a number of moving magnet carts with great results and NO NOISE, Grace f9 Ruby, Ortofon 2M Red (booo)...Totem sttaf speakers. Kinber 4tc speaker cables.

Okay so you have the background, lets hear the diagnosis and recommended course of action that will place me in moving coil heaven.

Does the headamp need a recap, is it mismatched in terms of load, does it need a flu-shot? I am dying to hear it, so please guys help me out.



dfelkai
dfelkai OP
89 posts
 
0-07-10: Rwwear
Make sure the ground wire is connected first of all.

>>The ground wire from the turntable is connected, there is no ground for the ortofon mca 76.

Then make sure the headshell is firmly connected

>>Done

and all wires to the cartridge are good and connected. Also be sure the head amp has enough gain for a low output cartridge.

>> I do not know how to check this but I will provide some specs, and maybe someone can tell me.

SO:
1) Ortofon MCA 76
Frequency response: 20Hz to 50kHz
Voltage gain: 34dB
Input impedance: 75ohms
Output impedance: < 140ohms
Maximum input: 6mV RMS
Harmonic distortion: 0.04% (2nd harmonic)
Hum level: 120dB below max output
Signal to noise ratio: >69dB
Sub sonic filter: -20dB
CD-4 filter: -20dB
Power requirements: 90-132 or 180-264V AC

2) Madrigal Carnegie one
Output Voltage 0.28mV
Frequency Response20Hz -
Tracking Force1.5-1.8g
Mass 6.5g
Channel Separation > 30db
Channel Balance < 1db
Load Impedance 30-47k ohms
Output Impedance ?

3) Supex SD Super 900 E+

Type
moving coil
Output Voltage 0.20 mV
Frequency Response 5Hz - 45kHz
Tracking Force 1.5-2.0g
Mass 9g
Channel Separation > 27db
Channel Balance < 0.5db
Load Impedance 2-20 ohms
Output Impedance 3.5 ohms
dfelkai OP
89 posts
 
Anybody?
hdm
1,062 posts
 
My suggestion is simple. Try experimenting with, very carefully, moving the head amp around. It may simply be picking the hum up from another nearby component or cable.

Not unusual with phono preamps or head amps. Many have issues like this.
dfelkai OP
89 posts
 


Ortofon MCA 76 is fixed... wow that was easy :) There was nothing wrong with it in the first place, it was the tubes in my pre . Swapped out a pair of RCA tubes and replaced with some Magnavox tubes noise is gone!!!!

BTW this headamp is awesome, and dead quiet, I am in love with it again.
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