Noise from Batteries

[booangler]

Help!!!

OK, I am not drowning but I am confused and need some clarification. I have been reading some new posts to a Quickie thread I started on another web site. Suddenly, there is talk that batteries are noisy. Are they? If so, why, and what would you do about it.

Cheers, Alan

[porcupunctis]

I'm not the most qualified to answer this question but here is what I would say:

First, everything has noise.  Resistors, caps, wires, solder joints, etc. all have some noise even if it is virtually imperceptible.  So, in that sense, I suppose that even a battery will exhibit some noise.

That being said, anything else you use to provide power will almost certainly have at least that amount of noise, plus other issues like ripple, spikes, and other fluctuations that won't be an issue with batteries.

Also, since there are many different types of batteries, I suppose some would have more noise than others.  But again, for the smoothest DC around.  The battery will be the way to go.

You probably get as much noise from solar flares and cosmic background radiation as you do from the batteries in a Quickie.

[Paul Joppa]

A high-impedance load (a PJCCS or a choke) will isolate any battery noise voltage. This happens two ways:

1) As with all parallel feed circuits, the voltage divider of the load plus tube will reduce power supply noise voltage proportionately.

2) I believe battery noise is largely associated with the fluctuating (signal) current that flows through the power supply. A high tube-load impedance reduces that current, forcing it to flow through the output instead.

This analysis also applies to capacitor noise - some people say that electrolytic capacitors are noisy in the same way that batteries are noisy. Naturally, different battery technologies are likely to have different noise characteristics. You can place a capacitor across a battery to shunt the noise current - but the capacitor itself may generate or pick up noise, so it's hard to interpret the results of such an experiment.

Do be aware that any current source, including the PJCCS, will itself generate noise. A choke will also generate a little noise from it's resistance, but is more likely to produce noise by picking up magnetic field noises from the environment. Also remember that the tube makes some noise itself ("tube rush") which may swamp out battery or other power supply noises.

I expect the only way to deal with this issue practically is to experiment. Connect the Quickie to increasingly sensitive amplifiers and speakers until you can hear some noise with the Quickie level control all the way off. Then try different plate loads in the quickie to see if any particular arrangement is quieter than another. The engineers will be happy to know what makes the system quiet, and the scientists will enjoy speculating about why it is quieter. Neither  of them an do anything until there is some data, though.

[Doc B.]

As always PJ has presented a very thoughtful and useful response. I on the other hand have to say that my initial thought was suggest that you to ask the poster on the other forum to support his comment with an experiential reference or otherwise just be considered another one of those guys who posts on the internet that "I heard third hand that someone somewhere said that something was something to be concerned about so you should be worried!!!!"

[Grainger49]

The greatest benefit of battery power is that there is no component of 60 Hz or 120 Hz hum.  The plate and heater supplies can not hum from rectified AC.  

The most noise from the batteries is likely to come from the fluctuating voltage after a battery starts to run down.  Sadly many users are not aware the batteries have crossed the knee.  I probably wouldn't either.

[porcupunctis]

Here is a good analogy:  Batteries, like fire are a chemical reaction.  Think about a campfire that has inconsistent fuel  and oxygen supply (wind).  A campfire is very chaotic and noisy.  Now think of a butane torch.  This is much more controlled and you can see that in the resulting flame.  The fuel is much more controlled and you have to look really close to see any aberrations (noise). 

The batteries are going to get you closest to the butane torch than anything else for DC.  Period.

You can say there is noise in those batteries and be technically correct but if they don't have a better alternative, I say just shut up and listen.

I really loved the way Doc put it.  "Show me the noise!"

[booangler]

So he showed me the noise, but is it really noise? Or to put it differently, are these numbers that significant?

"To cut the very long story short, according to a 1995 IEEE paper on "measurement of voltage noise in chemical batteries",

Ni-Cd battery gets the lowest noise - -195dBV/Hz at 1Hz & -204dBV/Hz at 6.5KHz , (measaured spectrum 1Hz - 75KHz),
followed by D alkaline, then AA alkaline, then AA lithium..."

Thanks for the help, I am trying to figure out what is real and what is less than real (just a math and physics exercise) with all this.

Cheers, Alan

[Paul Joppa]

Excellent - real numbers!

OK, the most audible noise will be in the midrange, so let's take the -204dBV/Hz at 6.5KHz value. (It's actually square-root Hz, incidentally.) Over a 20000Hz band, that's 43dB more than -204, or -161dBV. (That translates to 8.9 nanovolts.) Assuming that the signal level at the output of the Quickie is 1 volt (0.0dBV), and the Quickie in stock form has about 6dB rejection of power supply noise, the signal to noise ratio is about 167dB, which is about 23dB better than a perfect 24-bit digital stream with no dithering. I think you can safely ignore it. 

:^)

[booangler]

Paul, thank you, this is what I thought, but I do not know the math well enough to prove it out.

As always this is one of the best support forums on the web. You guys, and the Queen, all rock!

Cheers, Alan

[earwaxxer]

Noise from batteries is just crazy. I have been using batteries with my t-amp for some years now. I have several types of 30V battery supplies for my dual TP2050's in the t-amp. It doesnt seem to matter much which one is used. All are better than the SMPS, but not by a ton. More "musical" is the way I would describe it. Its funny, as we speak here I am listening to my system with the Quickie of course. I have been in the habit of subbing in a "fresh" pair of AA NMH after the amps warm up (30 min or so). I am starting to notice more "ring" with the fresh charged batteries, vs. the ones from the previous session. The warmers that were more quiet measured at 1.3V, whereas the fresh ones are 1.45. Not sure what that is about if anything!