Regards.
I own a DACT CT-100 phono preamp module card. Its installed inside a diy preamp metal cased along with a DACT ct-101 line stage module, a DACT CT-2 10k attenuator and Dact CT-102 power supply. Sort of a kit.
Currenty my turntable has a Sumiko SHo moving coil cartridge, 1.8mV wired with 1 meter of Discovery cable from cartridge pins to male RCA for connection at the phone stage case RCA’s.
I believe the hum issues are related to CT-100 installation or operation, not the tonearm wires or cartridge.
To identify cause I have done the following:
I.
The hum is on both channels when I select the phono for playback, even if the turntable motor is off.
With unit powered, cartridge output cables disconnected from CT100 input RCA’s I get white noise if volume is turned up. The white noise goes down with volume and its much lower than music playback. All OK.
If I open the case and put my finger near, or touch, the center wire connection inside the case input RCA (where RCA center pin is soldered to same wire as connected to CT100 IN1) I get a hum that varies with the distance between my finger and the solder point. The wire connecting the RCA to the board is shielded, and shielding is soldered together with cable return wire to CT100 board connection point.
The same happens with the other channel IN2.
I this hum normal?
II.
The RCA connector installed to chasis IN1 and IN2 is a WBT Nextgen (which has an insulated plastic body fixed from the outside by a metal collar acting as a nut. Said collar nut does not touch any metal at all as it is screwed to the RCA plastic body).
If I touch the RCA metal collar outside the case, I get the same hum as I described when my finger is near the female RCA solder point inside the case. I believe it is due to the metal collar acting as "antena" for my finger near the same center pin of female RCA for IN1 and IN2.
Again… I this hum normal?
III.
When I connect the cables coming from the cartridge to RCA IN1 and RCA IN2 and the tonearm ground cable to the case uninsulated ground post ( as stated to do in the phono card installation instructions), I get hum. Less than describe before but hum.
The rest of the CT100 installation includes a ground cable connected to the same CT100 ground lug as the case ground post for tonearm. That cable is fixed to the same point in the case as the ground wire connected to the CT-101 line stage pre board.
Any advise on how to deal with this?
Thanks to all.
I own a DACT CT-100 phono preamp module card. Its installed inside a diy preamp metal cased along with a DACT ct-101 line stage module, a DACT CT-2 10k attenuator and Dact CT-102 power supply. Sort of a kit.
Currenty my turntable has a Sumiko SHo moving coil cartridge, 1.8mV wired with 1 meter of Discovery cable from cartridge pins to male RCA for connection at the phone stage case RCA’s.
I believe the hum issues are related to CT-100 installation or operation, not the tonearm wires or cartridge.
To identify cause I have done the following:
I.
The hum is on both channels when I select the phono for playback, even if the turntable motor is off.
With unit powered, cartridge output cables disconnected from CT100 input RCA’s I get white noise if volume is turned up. The white noise goes down with volume and its much lower than music playback. All OK.
If I open the case and put my finger near, or touch, the center wire connection inside the case input RCA (where RCA center pin is soldered to same wire as connected to CT100 IN1) I get a hum that varies with the distance between my finger and the solder point. The wire connecting the RCA to the board is shielded, and shielding is soldered together with cable return wire to CT100 board connection point.
The same happens with the other channel IN2.
I this hum normal?
II.
The RCA connector installed to chasis IN1 and IN2 is a WBT Nextgen (which has an insulated plastic body fixed from the outside by a metal collar acting as a nut. Said collar nut does not touch any metal at all as it is screwed to the RCA plastic body).
If I touch the RCA metal collar outside the case, I get the same hum as I described when my finger is near the female RCA solder point inside the case. I believe it is due to the metal collar acting as "antena" for my finger near the same center pin of female RCA for IN1 and IN2.
Again… I this hum normal?
III.
When I connect the cables coming from the cartridge to RCA IN1 and RCA IN2 and the tonearm ground cable to the case uninsulated ground post ( as stated to do in the phono card installation instructions), I get hum. Less than describe before but hum.
The rest of the CT100 installation includes a ground cable connected to the same CT100 ground lug as the case ground post for tonearm. That cable is fixed to the same point in the case as the ground wire connected to the CT-101 line stage pre board.
Any advise on how to deal with this?
Thanks to all.
Pictures of the build would be helpful.
Are the RCA jacks grounded directly to the chassis or to a star ground.
I don't know what discovery cable is - is it shielded?
Does it hum with the inputs shorted at the RCA jacks?
Are the RCA jacks grounded directly to the chassis or to a star ground.
I don't know what discovery cable is - is it shielded?
Does it hum with the inputs shorted at the RCA jacks?
I. This hum is perfectly normal.
II. This hum is not normal if the metal collar is connected to the ground of the amplifier.
II. This hum is not normal if the metal collar is connected to the ground of the amplifier.
Physically getting near inputs will always cause hum.
Having wide open inputs will cause hum, and hiss.
Employing grounding in multiple areas will cause ground loops and hum.
Not knowing how you built the whole system, including physical relationship of components will prevent quality answers and only cause speculation.
Having wide open inputs will cause hum, and hiss.
Employing grounding in multiple areas will cause ground loops and hum.
Not knowing how you built the whole system, including physical relationship of components will prevent quality answers and only cause speculation.
Just short the inputs (with shorting plugs) like Kevin said, and the proximity hum should be gone.
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Thanks all.
I will post pictures when I get to my house, but the responses are already very helpful...
To reply some comments...
Kevinkr and rayma
Are the RCA jacks grounded directly to the chassis or to a star ground.
Not to chasis directly, to one point.
I don't know what discovery cable is - is it shielded?
Discovery cable is a brand, their tonearm cable is 28ga. not shielded.
Does it hum with the inputs shorted at the RCA jacks?
I have not tried shorting plugs. I will try.
MarceldG and wiseoldtech.
Thanks, I will verify all solders, and grounding to see if a better implementation for all components of the built (boards and RCA connectors can be achieved)
Also maybe using shorting plugs for unused female RCA's.
I will post pictures when I get to my house, but the responses are already very helpful...
To reply some comments...
Kevinkr and rayma
Are the RCA jacks grounded directly to the chassis or to a star ground.
Not to chasis directly, to one point.
I don't know what discovery cable is - is it shielded?
Discovery cable is a brand, their tonearm cable is 28ga. not shielded.
Does it hum with the inputs shorted at the RCA jacks?
I have not tried shorting plugs. I will try.
MarceldG and wiseoldtech.
Thanks, I will verify all solders, and grounding to see if a better implementation for all components of the built (boards and RCA connectors can be achieved)
Also maybe using shorting plugs for unused female RCA's.
Normally the RCA jack's "ground" terminal goes directly to the audio pcb ground.
Most audio equipment does not have the RCA jack's body directly mounted on the chassis as a ground.
It is instead insulated from the chassis, and grounded elsewhere. Most audio circuits do not use
star grounding, but rather a hierarchal grounding system. There are good reasons for this.
Most audio equipment does not have the RCA jack's body directly mounted on the chassis as a ground.
It is instead insulated from the chassis, and grounded elsewhere. Most audio circuits do not use
star grounding, but rather a hierarchal grounding system. There are good reasons for this.
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"Normally the RCA jack's "ground" terminal goes directly to the audio pcb ground."
Yes. the documentation for the phono board indicates as its connected... RCA terminal to a terminal at the PCB which has "Two capacitors "C" on the CT100 PC board are already connecting GND to common at the inputs IN 1 / IN 2 in order to secure high frequency stability".
Yes. the documentation for the phono board indicates as its connected... RCA terminal to a terminal at the PCB which has "Two capacitors "C" on the CT100 PC board are already connecting GND to common at the inputs IN 1 / IN 2 in order to secure high frequency stability".