Why are you limited to 36v?
Looking at the datasheet, it states that it has differential analog inputs. That may eliminate the need for an isolated supply.
Why not try it in the vehicle with the negative of the LiPO grounded with the engine running to see if it has any engine noise. Install it in the trunk so there is plenty of ground length so nothing is masked.
Looking at the datasheet, it states that it has differential analog inputs. That may eliminate the need for an isolated supply.
Why not try it in the vehicle with the negative of the LiPO grounded with the engine running to see if it has any engine noise. Install it in the trunk so there is plenty of ground length so nothing is masked.
If I used lipos I wouldn't need to hook up to the vehicles power supply. I have used an amp before in my truck powered from some RC car lipo packs and it worked excellent. Not something I can do permanently unless I found a way to charge the packs in an 8s configuration. (I used 4 2s packs in series and had to take them out and charge them with mains power.) I used some 12v relays that would switch the power from the batts to the amp using the radios remote wire as the trigger. Worked good and eliminated any pops when turning it on or off. I'm limiting myself to 36v so that I can use tda7498e boards or tpa3255s as well as being easier to achieve 36v vs something higher. I theoretically would use only need 4-6 amps max current at any time at 36v per board.
I'd like to use 1 or 2 tda7498e for 2 or 4 tweeters(pair on each board), a tpa3255 2 channel board for 2 front speakers, and a 2nd tpa3255 for rear speakers(2).
I'd like to use 1 or 2 tda7498e for 2 or 4 tweeters(pair on each board), a tpa3255 2 channel board for 2 front speakers, and a 2nd tpa3255 for rear speakers(2).
If you want to use a switching supply that's not isolated, it will have a grounded output. I want you to simulate the same grounding scheme by grounding your LiPO packs.
Oh ok gotcha, I'd have to put it all back together because I tried the lipo packs awhile ago. The amps negative power supply terminal and the audio input ground are connected so there's a pretty good chance of issues.
For those who don't know, the floor-pan as a ground is not a perfect conductor. If you use a multimeter to measure the resistance from the front of the vehicle to the rear, it may appear perfect (using a standard meter) but it's far from perfect. If you used a signal tracer amplifier and did the same thing, you would hear noise from the front ground point to the rear ground point.
When you have a head unit grounded in the front of the vehicle and the amp grounded in the rear you have to allow for that difference in ground. If you only sent the signal (no RCA shield ground) to the amp, the amp (with its audio ground taken from the rear ground) would amplify the difference between the audio and the rear ground and you'd get a lot of noise.
When you send a signal (normally) with a shield ground and signal, you get a clean signal at the rear but if the amp has its input shield grounded at the rear, the amplified signal has a mix of shield grounds and noise is introduced.
In a standard/common amplifier, the amplifier shield ground is about 1000 ohms from being connected directly to the rear ground. The shield from the head unit has a low enough impedance so that noise introduced through a 1k resistance would have no ability to introduce noise.
For a differential input, the signal and shields are treated the same by the input so if there is a difference from the front ground point and the rear, the difference would be on both the signal and head unit's shield and the differential input would cancel them out. It sees the signal line and the shield both as signals. Noise that's common to both (the difference in the ground points) is cancelled out.
When you have a head unit grounded in the front of the vehicle and the amp grounded in the rear you have to allow for that difference in ground. If you only sent the signal (no RCA shield ground) to the amp, the amp (with its audio ground taken from the rear ground) would amplify the difference between the audio and the rear ground and you'd get a lot of noise.
When you send a signal (normally) with a shield ground and signal, you get a clean signal at the rear but if the amp has its input shield grounded at the rear, the amplified signal has a mix of shield grounds and noise is introduced.
In a standard/common amplifier, the amplifier shield ground is about 1000 ohms from being connected directly to the rear ground. The shield from the head unit has a low enough impedance so that noise introduced through a 1k resistance would have no ability to introduce noise.
For a differential input, the signal and shields are treated the same by the input so if there is a difference from the front ground point and the rear, the difference would be on both the signal and head unit's shield and the differential input would cancel them out. It sees the signal line and the shield both as signals. Noise that's common to both (the difference in the ground points) is cancelled out.
Tthank you x a million Perry Babin!! I've never heard that before and 100% explains noise issues I had 2 years ago when I first got the truck I have now.
Hi @Perry Babin
Just to understand, this discussion of need for isolated power supply for auido amps in a car are related to noise only or is there any other concern?
If it is just noise caused by the small voltage differences along the car ground plane, if we run separate cables for positive (fused) and ground just for the audio system, wouldn't it resolve the problem? We would not use car ground for any connection. We would follow a kind of star topology where we take ground from a single point, in this case the 12V battery negative connector.
We would run cables from car battery directly to the audio system (player, amplifier etc) regardless of their position in front or rear of the car.
Typical class D output are bridged, so speakers don't have any common ground - we need to run 2 isolated cables (positive and negative) from the amp to the speakers and none are ground anyways.
Just to understand, this discussion of need for isolated power supply for auido amps in a car are related to noise only or is there any other concern?
If it is just noise caused by the small voltage differences along the car ground plane, if we run separate cables for positive (fused) and ground just for the audio system, wouldn't it resolve the problem? We would not use car ground for any connection. We would follow a kind of star topology where we take ground from a single point, in this case the 12V battery negative connector.
We would run cables from car battery directly to the audio system (player, amplifier etc) regardless of their position in front or rear of the car.
Typical class D output are bridged, so speakers don't have any common ground - we need to run 2 isolated cables (positive and negative) from the amp to the speakers and none are ground anyways.
I'm not 100% sure about the question so I'll cover what I (think you're asking).
If you have any connection to the vehicle ground for the audio, there is a problem because there are no perfect conductors.
You can have the amp grounded and even its audio shield grounded if there is no ground for the signal source (cell phone operating from battery power). You could also use a ground loop isolator (isolation transformer type) to break the shield ground from a conventional head unit. Many people claim that the GLIs are garbage but I'd bet that no one could pick a system with or without a GLI in line 10 times out of 10.
I've not kept up with the various class D boards for home audio but many had their shield ground connected to their power supply grounds and that caused no problem for home systems because there is isolation from ground in the power transformer. You can get the same in a car switching power supply but a 'boost converter' type power supply has no isolation. The 'flyback' variant can have isolation but the pure 'boost' does not. Using a board with no special input circuit with a grounded shield is a problem in a car.
If you were to use the vehicle grounds and had all components grounded to the same point (for systems without special isolation for audio), it could result in noise free operation but it's not good to have all amplifiers in the same place as the head unit. Running large cables to the rear of the vehicle that are grounded to the same point as the head unit could possibly work as long as the amplifier grounds had no contact with the rear of the vehicle. This means mounting the amps on wood or some other insulator because many amps have their heatsinks connected directly to the primary (battery) ground.
If you have any connection to the vehicle ground for the audio, there is a problem because there are no perfect conductors.
You can have the amp grounded and even its audio shield grounded if there is no ground for the signal source (cell phone operating from battery power). You could also use a ground loop isolator (isolation transformer type) to break the shield ground from a conventional head unit. Many people claim that the GLIs are garbage but I'd bet that no one could pick a system with or without a GLI in line 10 times out of 10.
I've not kept up with the various class D boards for home audio but many had their shield ground connected to their power supply grounds and that caused no problem for home systems because there is isolation from ground in the power transformer. You can get the same in a car switching power supply but a 'boost converter' type power supply has no isolation. The 'flyback' variant can have isolation but the pure 'boost' does not. Using a board with no special input circuit with a grounded shield is a problem in a car.
If you were to use the vehicle grounds and had all components grounded to the same point (for systems without special isolation for audio), it could result in noise free operation but it's not good to have all amplifiers in the same place as the head unit. Running large cables to the rear of the vehicle that are grounded to the same point as the head unit could possibly work as long as the amplifier grounds had no contact with the rear of the vehicle. This means mounting the amps on wood or some other insulator because many amps have their heatsinks connected directly to the primary (battery) ground.
Ok! Thank you! That clears things up.
Problem is when any part of audio system touches the car ground plane, which is noisy.
So what I thought is to have all audio equipment grounded by exclusive cables (positive and negative).
But care must be taken, specially when fixing amps to the car structure, which is car ground - something like the wood as an isolator you mention would be needed.
And regarding the DC-DC, yes, it dependes on how we design it. The isolated DC-DC must use a transformer with isolated primary and secondary windings instead of just an inductor to boost voltage.
Problem is when any part of audio system touches the car ground plane, which is noisy.
So what I thought is to have all audio equipment grounded by exclusive cables (positive and negative).
But care must be taken, specially when fixing amps to the car structure, which is car ground - something like the wood as an isolator you mention would be needed.
And regarding the DC-DC, yes, it dependes on how we design it. The isolated DC-DC must use a transformer with isolated primary and secondary windings instead of just an inductor to boost voltage.