I run my DAC (RME ADI-2 DAC) on a 12V sealed AGM battery, and I use a microRendu as streamer that runs on 6V sealed lead acid battery. The DAC acts as a preamp to power amplifiers that use the regular mains grid.
However, it seems that the DAC and microRendu don’t live totally isolated, there is a connection between the batteries zero, I assume through grounding over USB. There is also a connection between the DAC and the power amp, which I would assume comes over the balanced XLR cables.
Finally, there is a 17 ohm and 4V connection between the 12V battery zero and grounding on the power amp, which feels worrying!
So how to best solve this? Should I simply connect battery zeros to mains grid ground? Or try to isolate every part by cutting ground connection for XLR or USB?
Appreciate some help, because I am over my head right here
First, are you experiencing an issue, ground loop, noise, hum? Second, there are two earths, safety ground and signal ground. So, what’s your concern: getting zapped, or reducing noise? With a balanced system, signal ground is less of an issue, but you still may be concerned about safety ground. Perhaps just strapping the neg. battery terminal to a metal chassis is enough.
I am just not sure its optimal, and also one of the reasons to use batteries is to isolate but its still grounded. But I am not concerned about safety (everything on mains grid is grounded properly), its more to try and increase sound quality.
Maybe just unplug the pin1 in XLR on the DAC side (which is safe since the DAC runs on 12v battery) and remove the GND and +5V from USB. That should make both the microRendu and DAC isolated and freely floating on their batteries only (no stray currents, etc)
Connecting grounds between components is not necessarily a bad thing, and is usually required unless you are running balanced connections. Batteries are used mainly to provide a clean source of power, not as a ground isolation technique. Unless you are experiencing symptoms of ground loops like humming, etc. it’s best to leave things as they are. You will get no sonic benefit from isolating the USB ground to your DAC (in fact, it may not even work).
I am running balanced XLR connection, and I cut the pin1 (ground) on XLR on the DAC side, so now the DAC is isolated from mains grid ground. The sound feels a little calmer and more fluid. But now the DAC and its battery is isolated, so no strange 4V 17ohm between battery zero and ground (well, 4V is still there, but infinite ohm).
Now its time to fix USB between DAC and microRendu …
Amazing. I think you’re finding your own solutions.
Google and some common sense: pin 1 is return for signal, and if its connected to ground on the amplifier side it makes sense it can be cut to the dac. But still, always a little scary with XLR
You will need ground on the usb as it relies on it for the data signal reference. The +5v on the usb should be ok to remove or isolate
I can confirm this, microRendu didn’t see the DAC if I disconnected both +5 and GND, but disconnecting only +5 worked.
I guess I have to live with batteries sharing “ground”, at least both DAC and microRendu is isolated from mains grid power and ground.
Sealed Lead Acid (SLA) batteries are among the noisiest power supplies you can get. Any modern PSU produces less noise. Besides that, they have pretty high internal resistance in higher frequencies. They have a pretty slow transient response which also changes over time and with the amount of charge. Noise generated by SLA batteries is usually very high-frequency noise, this is caused by the electrochemical reactions when a current flows in the battery itself. This noise is very difficult to filter and is exactly the kind of noise you were trying to get rid off by using batteries in the first place. They should only be used in combination with a large low-ESR capacitor bank and some very wide bandwidth low noise regulators which happen to be difficult to work with because of instability. Just because it is a battery doesn’t make it a good power supply. There are better batteries out there, SLA are not good for audio applications at all. I have no experience with AGM batteries you also mentioned but I have a gut feeling they will not be performing much better either, but I could be wrong on that one.
That’s not my experience, I have preferred SLA batteries over the LPS I have tried. And the internal resistance of a battery is lower than impedance of most LPS (my 12V battery has 12 mOhm), which means better transient response.
But more important: they isolate from mains grid. For example, I got better sound when I cut pin1 on XLR on the DAC side, which means even ground from mains grid caused problems.
Having said that, lithium-ion or similar (LiFePO4) is probably better, but expensive to get with the capacity needed, and often comes with switched DC-to-DC electronics inside them.
Btw, I recently listened to Bayz speakers and very high-end electronics, which was powered by Stromtank ( https://stromtank.com/s5000/ ). The demo was showcasing the Bayz speakers, so I doubt they would have used battery power unless it was actually good.
Here is a picture, it sounded pretty amazing but so is the cost I would imagine:
Well, the Stromtank is not a SLA battery, it’s a mains generator running on LiFePO4 which is a completely different story. They have absolutely nothing in common other than the word “battery” involved.
The internal resistance you mentioned is only for DC, this is not the wideband internal resistance. Unfortunately, I don’t have all the measurements available at home but we did extensive measurements on all kind of power supplies in the past (12 years ago but still actual) and we coclude that bare SLA batteries suffer from bad transients response. Yes they can deliver a huge amount of energy in a short time due to their very low DC internal resistance but that is again a completely different story than wideband behaviour. They are pretty noisy. When you measure them static state, that is with no current flow they are absolutely silent but due to electrochemical process noise is becoming an issue ones you draw current out of them, the higher the current the higher the noise. Non-biased listening test on using SLA’s on a preamp also confirmed that they sound slowish, grey, flat and uninvolving unless you parallel them with enough low esr capacitors up to a point that the battery becomes only a energy supplier to the capacitor bank. By then you are actually running of capacitors. Without such measures all other power supplies we tested actually sounded better than a bare SLA battery.
This information is all meaningless off coarse as long as you like what your hearing more when running SLA batteries, enjoy the music
Googled some and there seem to be fairly cheap LiFePo4 alternatives without any protection-electronics inside them, for example this:
Or maybe 4 of these (which is probably what the above battery has inside):
Just have to make sure not to drain them to much, because then they are damaged.
@Nyquist I ordered the 12V LiFePo4 battery for the DAC and 2 LiFePO4 cells for the microRendu, all with capacity 20Ah. Will be interesting to see how it sounds. And if it sounds worse than the SLA I have I will bill you €300
If you read my messages completely you could have read that I have never adviced you on using LiFePo4 batteries.
But if you really insist on using batteries the LiFePo4 is a much better choice than a SLA battery for sure . Personally I would not run the microrendu of batteries, when the voltage goes low on the threshhold of just not enough for the microrendu there is a big change to corrupt the SD card in it.
Happy experimenting and enjoy the music,
I charge at night, and with 20Ah the DAC and the mR will consume less than 50% of the capacity. I don’t want to over-drain LiFePo4 batteries because then they become damaged (they have no safety-electronic). I will report back once I have tested.
Got my LiFePo4 cells now (each 3.2V 20Ah), 4 for the DAC and 2 for the microRendu. And yes, it sounds better, increased clarity and details, and music feels more fluid.