I have two class D amps, both using the TDA7297 chip. One is a Chinese pre-made board from eBay with 50k dual pot.
Pre-made circuit
The other I've made following the details listed on the electro-dan website, which is a similar circuit.
Electro-Dan website
Electro-Dan circuit
I need to be able to mount the dual pot within a radio, so the pot can't be mounted on the PCB due to available space.
Testing the pre-made board with pot mounted on the board, and being powered by a 12v CCTV PSU, generates no noise and is pretty good clean output.
However, when desoldering the 50k pot and extending using cat5 wire, it creates a clicking noise and faint hum. Low and high ends of the pot have no noise, just everything in-between is noise.
I've tested with a new 47k dual pot and get the same noise issues. This is marginally reduced when touching the metal back of the tda7297 with my finger.
The home-built circuit (I'll upload a circuit diagram later) has the same noise issue when using the 47k log pot or a 10k linear pot (both extended using the cat5 wire).
I have un-twisted the cat5 pairs and shortened the wire, which hasn't made that much of a difference.
Do I need to use shielded wire to the pot?
Any other recommendations please?
Pre-made circuit
The other I've made following the details listed on the electro-dan website, which is a similar circuit.
Electro-Dan website
Electro-Dan circuit
I need to be able to mount the dual pot within a radio, so the pot can't be mounted on the PCB due to available space.
Testing the pre-made board with pot mounted on the board, and being powered by a 12v CCTV PSU, generates no noise and is pretty good clean output.
However, when desoldering the 50k pot and extending using cat5 wire, it creates a clicking noise and faint hum. Low and high ends of the pot have no noise, just everything in-between is noise.
I've tested with a new 47k dual pot and get the same noise issues. This is marginally reduced when touching the metal back of the tda7297 with my finger.
The home-built circuit (I'll upload a circuit diagram later) has the same noise issue when using the 47k log pot or a 10k linear pot (both extended using the cat5 wire).
I have un-twisted the cat5 pairs and shortened the wire, which hasn't made that much of a difference.
Do I need to use shielded wire to the pot?
Any other recommendations please?
TDA7297, AMP, AUDIO, BTL15W, AB, MULTIWATT15; Output Power:15W; Amplifier Class:AB; No. of Channels:2 Channel; Supply Voltage Range:6.5V to 18V;
Use shielded wire or twisted pair. Select the correct connection locations for the common signal wire. Avoid earth loops.
Attachments
You apparently pick up noise and RF via the pot wiring.
The fact that it is worst in mid setting is because in mid setting there is the max resistance between the top and bottom wires.
Use a good quality screened cable and it will probably be fine.
Jan
The fact that it is worst in mid setting is because in mid setting there is the max resistance between the top and bottom wires.
Use a good quality screened cable and it will probably be fine.
Jan
That's screened to the pot and screened back from the pot.... Perhaps a lower valued pot would be better too, 10k or so?
Thanks everyone for your replies.
I have some shielded mic cable on order.
With regards to the ground on the pot, I'm assuming I'm ok to tie this to the shielding of the cable and connect the shielding to the ground on the board?
Re: 10k pot. I have already tried a 10k, admittedly it is linear rather than logarithmic, but get the same issue.
I have some shielded mic cable on order.
With regards to the ground on the pot, I'm assuming I'm ok to tie this to the shielding of the cable and connect the shielding to the ground on the board?
Re: 10k pot. I have already tried a 10k, admittedly it is linear rather than logarithmic, but get the same issue.