The C451 and C452 are for bypassing RF interference present on the cable shield to the chassis.
The coils are not in the schematic.
The coils are not in the schematic.
The input RCA ground shells are directly connected to the audio board common (sometimes called "ground")
It is not necessary to connect the chassis to the audio ground for the circuit to work.
The chassis functions as a shield, and for protection against being able to touch a live circuit.
It also functions as a low inductance dump for input conducted RF in this case.
The chassis is normally connected to the utility ground, through the IEC outlet and power cord, for safety.
Usually the audio ground is connected to the chassis at one point, but that part of the schematic is not shown.
You could have the pcb just laying on the bench, connected to a power supply, and it would
work just the same, perhaps with a little noise pickup from the lack of shielding.
The RCA jacks are often isolated from the chassis in an attempt to avoid 60Hz ground loops.
It is not necessary to connect the chassis to the audio ground for the circuit to work.
The chassis functions as a shield, and for protection against being able to touch a live circuit.
It also functions as a low inductance dump for input conducted RF in this case.
The chassis is normally connected to the utility ground, through the IEC outlet and power cord, for safety.
Usually the audio ground is connected to the chassis at one point, but that part of the schematic is not shown.
You could have the pcb just laying on the bench, connected to a power supply, and it would
work just the same, perhaps with a little noise pickup from the lack of shielding.
The RCA jacks are often isolated from the chassis in an attempt to avoid 60Hz ground loops.
Last edited:
I can't guess which are the answers.Post No 4 above answers all your questions.
Of course you are right. I don't know how I missed it. One more option to listen to. It also comes as a dual, certainly slightly worst in specs.I see the OPA192 listed with a price of €3,75 for 1 piece.
Yes, the RCA ground has to be isolated from the input point, but it should go to the star ground. The pcb I bought already has the ground paths, but I can those I want to modify.The input RCA ground shells are directly connected to the audio board common (sometimes called "ground")
It is not necessary to connect the chassis to the audio ground for the circuit to work.
The chassis functions as a shield, and for protection against being able to touch a live circuit.
It also functions as a low inductance dump for input conducted RF in this case.
The chassis is normally connected to the utility ground, through the IEC outlet and power cord, for safety.
Usually the audio ground is connected to the chassis at one point, but that part of the schematic is not shown.
You could have the pcb just laying on the bench, connected to a power supply, and it would
work just the same, perhaps with a little noise pickup from the lack of shielding.
The RCA jacks are often isolated from the chassis in an attempt to avoid 60Hz ground loops.
First I will use them as it is, checking if there's no blatant mistake, and listen to it. And look for any hum at maximum volume.
The advantage of the LT1792 is that the inputs are FET, which eliminates the need to use an input cap with some opamps.To prevent too big DC @ your output I recommend replace LT1792 with 800 uV DC offset to OPA192 with 5 uV offset [ I have only 1.5 uV with it - see https://www.patreon.com/posts/64958853 ].
please highlight, its difficult to see.the relevant ground returns are separately routed to a single point on the RIAA PCB
Which Amplifier is this from ?
thanks.
The designer has kept L and R grounds separate all the way to the Phono RCA jacks, except the RF cross-connect to two 0.01uFd caps and the phono green-wire screw.why are the grounds sent off board as LG and RG?
Is that necessary? I do not know. Is it an affordable thing to do on a fairly expensive box? Certainly. Another 5 minutes on the layout table, after that it is print, etch, repeat, repeat, repeat.... no added labor and only penny parts.
well it still doesn't reconcile Extreme Boxy's claim that the grounds are brought to a star point on that pre-amp board...
not all grounds are equal (or should be termed grounds!!) nor should they be connected together.
not all grounds are equal (or should be termed grounds!!) nor should they be connected together.
Star grounding is good in pre amps but most difference is found in power amps where the currents are much higher and modulate the pcb tracks more.
For the pre amp I would star ground power supply grounds separate from audio signal grounds.
For the pre amp I would star ground power supply grounds separate from audio signal grounds.
It is not advantage LT1792 vs OPA192 because OPA192 is also with JFET input 🤓The advantage of the LT1792 is that the inputs are FET, which eliminates the need to use an input cap with some opamps.
Attachments
You are wrong. I have OPA192 for no more 4$ each @arrow.com [ https://www.arrow.com/en/products/opa192id/texas-instruments?q=OPA192ID ]Nick, you are suggesting a chip that Mouser sells for more than $500 each. Isn't that a bit too much?
Nice touch to add 10R isolation to the input ground.Your idea is good. I actually use the same concept. But it is not absolutely needed, only if you experience input related hum.
The 2 power supply caps get grounded to the star point. Put 0.1uf caps in their place on the board and the 100uf caps onto the power supply outputs.
- Home
- Source & Line
- Analogue Source
- Silent & noisy grounds on a RIAA preamp