(Moderators, Not sure if this is the right forum. Feel free to move the thread to where it belongs if it isn't. 
)
Question: If I want to use two 12 volt SLA's as a symmetrical PSU for an op-amp based preamp, would it be better to regulate the voltage from the batteries to a lower, stable voltage or to just leave it "as is" and let the voltage fluctuate as the batteries are charged and discharged? (I hope the meaning of the question is clear )
Maybe someone with experience in battery-PSU's can help?
/U.
)Question: If I want to use two 12 volt SLA's as a symmetrical PSU for an op-amp based preamp, would it be better to regulate the voltage from the batteries to a lower, stable voltage or to just leave it "as is" and let the voltage fluctuate as the batteries are charged and discharged? (I hope the meaning of the question is clear
)Maybe someone with experience in battery-PSU's can help?
/U.
I'll share the little experience I have... I've used precisely 2x12V SLAs to power a opamp buffered attenuator. Results have been way beyond expectation. and several DIY tube diehards have been quite complementary about it.
1) "SLA's as a symmetrical PSU". I decided not to leave GND to fate, and use a TLE2426 precision voltage splitter to define a ground between the 24V+/- terminals. All other grounds (reservoir caps, signal in, signal out) reference to this GND.
2) Sound: dead silent, smooth, rock solid. Any variations perceived between freshly charged batteries and 50% discharged are most likely in my mind. I've also driven the same preamp with 2x9V rechargeables, which are puny compared to the SLAs. Sound was essentially the same.
3) There is much potential to tune the preamp with good bypass caps right next to the opamp. I use 220-470uF per side as "main" caps, which aren't that critical; a good film cap (0.1-1.0uF) will influence the sound a lot.
Imho, adding regulators to a battery PSU is a step backwards, unless the opamp specifically needs a precise voltage value. The headphone amp community (headwize.com) should offer a lot of insight into battery powered designs. It will take a lot to convince me to move away from batteries; more of my friends are seriously looking at battery supplies for preamps and DACs.
mb
1) "SLA's as a symmetrical PSU". I decided not to leave GND to fate, and use a TLE2426 precision voltage splitter to define a ground between the 24V+/- terminals. All other grounds (reservoir caps, signal in, signal out) reference to this GND.
2) Sound: dead silent, smooth, rock solid. Any variations perceived between freshly charged batteries and 50% discharged are most likely in my mind. I've also driven the same preamp with 2x9V rechargeables, which are puny compared to the SLAs. Sound was essentially the same.
3) There is much potential to tune the preamp with good bypass caps right next to the opamp. I use 220-470uF per side as "main" caps, which aren't that critical; a good film cap (0.1-1.0uF) will influence the sound a lot.
Imho, adding regulators to a battery PSU is a step backwards, unless the opamp specifically needs a precise voltage value. The headphone amp community (headwize.com) should offer a lot of insight into battery powered designs. It will take a lot to convince me to move away from batteries; more of my friends are seriously looking at battery supplies for preamps and DACs.
mb
Nisbeth said:Question: If I want to use two 12 volt SLA's as a symmetrical PSU for an op-amp based preamp, would it be better to regulate the voltage from the batteries to a lower, stable voltage or to just leave it "as is" and let the voltage fluctuate as the batteries are charged and discharged? (I hope the meaning of the question is clear
No real need at all for regulators. The beauty part about batteries is that they don't have a bunch of ripple voltage like non-regulated AC supplies do. 'Bout the only thing a regulator would be helpful for in a battery situation is perhaps providing a bit lower source impedance from the batteries, which, unless you're using dry cells or something, isn't going to be terribly high to begin with.
se
mb said:
Leave GND to fate? You already have a perfectly good ground reference with your two SLAs. "Rail splitters" like the TLE2426 are just kludges to be used to provide a virtual ground when a split supply isn't available. A pair of SLAs is already a perfectly good split supply. Why turn them into a single supply and then use a kludged virtual ground reference instead of a real ground reference?
se
Nisbeth said:First of all thank you to all of you for the replies. I think I know what to do now.
You're welcome. Good luck! And remember:
<center>
<img src="http://www.q-audio.com/images/noac2.jpg">
</center>
That would be prudent. Using batteries doesn't change anything in that regard. The issue with bypass caps is inductance in the power supply lines. The (usually) internal compesnation capacitor references one of the supplies and if there's too much inductance, then at high frequencies the signal can be fed back to positively to the output stage by way of supply line modulation and the compesnation capacitor which can result in instability.
se
----------------------------mb said:
Why not just take 12V from a single unit?
Does anyone have a good auto charging circuit. My probelm with lead batteries is leaving the units on and discharging/ruining the whole thing. This is inspite of using 18Ah ones. The sound using batteries is much better.
sangram said:
That won't help in fmak's case. He said "My probelm with lead batteries is leaving the units on and discharging/ruining the whole thing."
Rod's charger senses current and DISENGAGES the charger when the unit being powered is turned on and draws current. So if fmak leaves his preamp on, Rod's circuit wouldn't engage the charger until the batteries were pretty much dead and no longer able to deliver current above whatever threshold was set.
se
sangram said:
Sure. But ultimately I still don't see it as needing to be any more complicated than a simple switch.
The way I read his comment, it's not like he's too lazy or forgetful. He just wants to keep the preamp powered up when he's not using it and instead of having that drain down the batteries, he wants something that would kick in at a certain time and keep the batteries topped up.
That being the case, all he really needs is a simple multipole switch that engages the charger when he's not listening. The preamp would still remain connected to the batteries so it would ultimately always be "on." You'd just have to remember to flip the switch when you were done listening.
se
fmak said:
Ah...
Hmmmm. Well that's a bit more complicated. A simple comparator could detect when you get down to +/- 10 volts, but once the charger kicks in, you'd be above the threshold and it would just disengage. So you'd need another comparator to monitor the current flowing from the charger. The outputs of the two comparators would then feed a logic circuit to determine when to engage and disengage the charger.
Hmmmm...
Ok, how 'bout a simple switch AND a string to tie around your finger to remind you to turn the charger on?
se
- Status
- This old topic is closed. If you want to reopen this topic, contact a moderator using the "Report Post" button.