Battery properties as power source for preamps/ options.

[lagoausente]

I want to supply the Supergreen/9098 with batteries.
I know that internal Z of batteries is an issue, I will have to check, but is not the only issue, I think, there are more problems like space, price, charging method..
It´s suppose the preamp comsumption is around 40 ma/channel. I have two channels, but will use most times only one.
I have been considering all types and options. I resume my conclusions.

To get a good performance of the preamp, and since consumption seems not high, I think on suppling something between +/-15V and +/-20V.

NIMH: The problem on this type of battery,is that I would need a lot of batteries to get a voltage , let´s say +-18V would need 30 batteries. To get +-12V woud need 20 batteries. In any case I think I´ll have not space enough inside the preamp case. Aditionally, I´m not sure about if this holders allow a proper way to conect the pack, and I¨m not sure how about the internal Z of a pack like that:

Li-ion, are unsufe, and expensive, and specially to get those voltages.

Although I have found this Li-ion 9V batteries, 400 mah. They come with an integreated protection IC. Seem atractive, low space (4x9V= +-18V).
Cost 8$ each, so the cost would be 32$, near the same than with a NIMH package. http://www.batteryspace.com/index.asp?PageAction=VIEWPROD&ProdID=2644
That bad thing here, is that I would need to charge (I think), each battery separately, and life time would be around 10 hours in theory.

And finally LIfePO4:
They are 3.2 volt, so I would need 2x5 to get +/-16V.
The problem is the cost.
The advantages, they don´t explode and non fire, 10 units probably could fit in the preamp box, and the last advantage is that could charge the hole 32volt at one time, with a LI-ion charger+LIfePO4 cable adapter.
The problem again the cost, that charger cost 32$.
This LifePO4 batteries have between 1100 and 1600mah and cost around 6$ and 7$ each unit.

I would like to know your opinions, suggestions, and technical considerations.

 

[JohnRoberts]

A long time ago I went through the mental exercise of making a battery powered high performance audio path, and while battery technology was much cruder back then, I was thinking in terms a few car batteries for a console. The play would have been to build in a trickle charger and rely upon the battery to act as a huge ripple filter.

This never advanced beyond the mental masturbation stage since it would be just about impossible to completely eliminate AC power from a studio, so it was far more practical to just properly engineer the power supply to be clean.

YMMV

JR

 

[Gus]

IIRC Brad posted a power supply link here in the past, good reading about noise from power supplies and batteries.

 

[lagoausente]

This never advanced beyond the mental masturbation stage since it would be just about impossible to completely eliminate AC power from a studio, so it was far more practical to just properly engineer the power supply to be clean.

Well, in my case I need the batteries for portability. I carry my laptop, a Magma chassis (PCI to PCMCIA converter), and the AD.
Probably a good clean AC PSU may give a clean power, but I think many times doesn´t. I have compared that on my Presonus Mp20. It´s not ideal since it requires around +-170ma, but just with four 9V alkaline batteries, I can tell you that the improvement is very high, more than what should be expected. Much more clean. With the AC supply, the noise added is not just 50hz, it´s like the preamp have more distorsion, metallic sound.
I have not a technical explanation of it. But I don´t trust on regulators, even I know some noise come from the diodes.

 

[bcarso]

Batteries are not noiseless, although they can be pretty good. The link I posted in the thread Gus mentioned was some website about regulator noise; toward the end the author showed some noise spectra from batteries. Maybe someone can find it.

The isolation properties of batteries are cool though, and the avoidance of conducted and probably mostly common-mode noise is probably the basis of the difference in "sound" perceived, not something mysterious about voltage regulators, unless the latter are particularly poor. But bear in mind that as the pack gets bigger its capacitance to the environment goes up---you are not really isolated anymore to that extent at least. One has a similar issue with any electronics that looks out into the environment and "sees" potentials that differ from its own internal "ground" reference.

EDIT: Here is the article. Look as well at the preceding pages for additional voltage regulator noise material.

http://www.tnt-audio.com/clinica/regulators_noise4_e.html

 

[JohnRoberts]

[quote author="lagoausente"]

Well, in my case I need the batteries for portability. I carry my laptop, a Magma chassis (PCI to PCMCIA converter), and the AD.
Probably a good clean AC PSU may give a clean power, but I think many times doesn´t. I have compared that on my Presonus Mp20. It´s not ideal since it requires around +-170ma, but just with four 9V alkaline batteries, I can tell you that the improvement is very high, more than what should be expected. Much more clean. With the AC supply, the noise added is not just 50hz, it´s like the preamp have more distorsion, metallic sound.
I have not a technical explanation of it. But I don´t trust on regulators, even I know some noise come from the diodes.[/quote]

My comment was why "I" didn't pursue battery for a stationary application. I did one battery powered mixer at my last gig and we used 3x 9V batteries as I recall. +/- 9V with 18v phantom. But that whole mixer probably used much less than your 170 mA.

It should not be that difficult to make a reg PS that is sonically neutral, but if there is low mains voltage and the PS drops out of regulation, that can introduce lots of garbage into the rails. It may be something simple.

JR

 

[lagoausente]

Bcarso, I have read that page before, but also have read a thread were was disussing that the method and conclusions of the guy made on that web, was not very reliable.

Both mention regulators. I´ll try to avoid them because they would add an extra consumption I think.
I remember a guy on other DIY forum that told that he became acostumed to "that strangulated sound that give regulators".

When I tried the 9V batteries on the Mp20, I conected that after the regultators, and haven´t noticed more noise.
I have read also about the Z of the batteries, that could make the voltage drop. I´ll have to check that when I´ll have finished the Supergreen, withing this next week. I have read also about this issue, that the batteries Z could be minimized with caps, so with diferent type of caps to act along the diferent frequencies.
I guess if this method could be ok: put a square wave at the preamp input, with variable frequency from 20hz to 20khz. And then measure if there is any AC on the batteries output, due to posible dropouts. Then if found those dropouts, add caps trying to correct them. I assume, they would provide a quicker power source if battery voltage drops with some transients.
That´s something I will have to check. I would you like to know your opinions if my testing idea is well oriented.


Regarding to the battery options I posted, have you any advice for what way should I go?

 

[jdbakker]

[quote author="lagoausente"] NIMH: The problem on this type of battery,is that I would need a lot of batteries to get a voltage , let´s say +-18V would need 30 batteries. To get +-12V woud need 20 batteries. In any case I think I´ll have not space enough inside the preamp case. Aditionally, I´m not sure about if this holders allow a proper way to conect the pack, and I¨m not sure how about the internal Z of a pack like that[/quote]
I'd go with NiMH: cheap, mature technology, available from multiple sources, with reasonable energy density (both by weight and volume).

You can buy pre-made packs, like this one (if the link is broken, go to www.conrad.de and search for order code 227908-12). These are used for radio-controlled cars; I am sure that appropriate chargers are available for little money. Other battery packs come with a connector, so you can take spare sets with you if you like, or charge one pack while you're using another.

The holders you show aren't very mechanically secure; you have to clamp or tape the packs up to keep the batteries from falling out if you use or transport them in high-vibration environments, such as on the back of a bicycle (as I found out the hard way). The RC car battery packs are made to withstand a moderate amount of abuse.

[quote author="bcarso"]http://www.tnt-audio.com/clinica/regulators_noise4_e.html[/quote]
To put it mildly, I cannot reproduce his findings. It would have been helpful had he named battery brands and part #s. In my test (Duracell AA cells, noname NiCD and NiMH AA packs) I'm seeing lower noise levels than he reports.

JDB.
[TODO: clean up battery noise measurements and post them online]

 

[Samuel Groner]

I cannot reproduce his findings.

As far as I've seen he does neither mention FFT resolution nor window type. So it seems rather difficult to do comparable measurements. How did you came to the conclusion that your measurements show different results?

Samuel

 

[lagoausente]

Hello jdbakker,
I would like know about your measurements and conclusions aswell.

I'd go with NiMH: cheap, mature technology, available from multiple sources, with reasonable energy density (both by weight and volume).

I´m still in doubts. With NiMH can get much more mah for the same price, but I have my doubts about the ability of the pack chargers. I already have one of that smart charger for packs between 9.6 and 18V, but my experience was not good. One reason is that the batteries I used come from china on a cheap Ebay offer, so I`m not sure about their quality.
But what I´m afraid of, is that if one cell, gets lower capacity then the others, will stop charging before, and so the smart charger would perceive that voltage drop, isn´t? Maybe I´m wrong, but at first, either chargin, or discharging a pack, if one cell is wrong, the hole pack doesn´t work ok. At least this happened to me with a walkie talkies I have.
I guess how is the behaviur of the pack regarding to the ability of providing the preamp "instant current". What would happen if one cell is not on proper current performance? would this affect the +- outputs? or would the other cells provide the current without the problem of that cell?

In the other hand, the 9V Li-ion 400mah, would cost near the same as the NIMH. I´m not sure if the capacity would be ok for the 40ma consumption of the preamp. The good point would be less cells, only two 9v batteries for 18, and other two for -18V.

 

[bcarso]

I'd avoid Li-ion.

Ideally you would charge NiMH cells in parallel and discharge in series (EDIT---with a small R in series with each during charging). EDIT again---even better a separate charger per cell...

As far as battery noise, "intuitively" they are going to have a lot of 1/f noise and one would expect that to be a function of current pulled. But I don't have the time to measure right now, interesting though the data would be. The website guy's NiCad data looks like something very wrong though, maybe a cell on its way out, or merely some bad contacts somewhere.

As far as regulators, I'm reminded of what the late Joe Weber, one of the pioneers of gravitational wave research said about the Heisenberg uncertainty principle: that it set a lower limit to the errors associated with measurements of certain conjugate variables, but it did not set an upper limit.*

By analogy there is no limit to how badly one can do voltage regulation, but I don't think that justifies its rejection.




*He was making a jab at his critics who all said they couldn't get anything approaching his claims of detection. As it turns out Weber was probably wrong about his detections, and may have been the victim of a disgruntled grad student programmer, but you had to love the guy, especially after he (quite late in life at that) married Virginia Trimble**, a woman with astonishing sexual appetites who had worn out more than a few previous partners...

See her popular book on Amazon, Visit to a Small Universe, ISBN 0883187922, for a picture of the woman. BTW the book description on the Amazon.com page is totally incorrect: "A select group of top Soviet and American specialists reports in this volume from the frontiers of chaos and nonlinear science." Say What??


** you can imagine what her nickname was.

 

[CJ]

the stomp box guys choose different batteries for different sounds, alkaline is too harsh, they like the cheap radio shack 9 volts, which are no nonger available now.
there is a new brand that theyswitched to, but the point here is that yes, people are into the sounds of batteries.
in the case of a pre amp, i do not think it matters.
you can hear noise from a battery, snaps, pops, crackles, plates moving, other weirdness....but there's this thing the just invented called a capacitor....

 

[lagoausente]

[quote author="CJ"]the stomp box guys choose different batteries for different sounds, alkaline is too harsh, they like the cheap radio shack 9 volts, which are no nonger available now.
there is a new brand that theyswitched to, but the point here is that yes, people are into the sounds of batteries.
in the case of a pre amp, i do not think it matters.
you can hear noise from a battery, snaps, pops, crackles, plates moving, other weirdness....but there's this thing the just invented called a capacitor....[/quote]

True? I have never heard about this type of obsession. And about the capacitors, can be heared their snaps, pops, crackles etc?

 

[JohnRoberts]

My suspicion about stomp boxes and preference for battery type relates to nominal battery voltage and high sensitivity to (unregulated) rail voltages in some nonlinear effects circuitry.

Or not...

JR