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PostPosted: February 28th, 2019, 11:10 pm 
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Roscoe Primrose wrote:
OK, I'm gonna reply out of context to several of the comments...

1. They're not filters, they're energy storage. I didn't use NiMH/LiPo etc because the charging requirements are much more of a pain in the butt, and the supercaps should be good for >500K charge cycles.
2. As for the current surge when charging, the power supply is going to have a 15ohm output impedance, so the surge will be quite small.
3. OK, you guys have convinced me, I'll use TL431s with pass transistors, one per rail, and individual LC (yeah Stuart, wire wound resistors with LOTS of inductance) filter between the regulators and each op-amp.
4. Line noise? What line noise? The charger will be switched out when the phono stage is operating, and only connected when recharging.

Roscoe


And "they" say audio electronics is not rocket science. 8-)

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PostPosted: March 1st, 2019, 1:49 am 
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SoundMods wrote:
And "they" say audio electronics is not rocket science. 8-)


More like brain salad surgery ;)


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PostPosted: March 1st, 2019, 10:13 am 
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Well maybe they relate it to rocket science because you need a lot of hot air escaping at high velocities to get things moving forward. :roll:


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PostPosted: March 1st, 2019, 10:16 am 
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tomp wrote:
Well maybe they relate it to rocket science because you need a lot of hot air escaping at high velocities to get things moving forward. :roll:



Hmmm. I guess we are "rocket scientists" because as a collective group there is an abundance of "hot air." :crazy:

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PostPosted: March 1st, 2019, 11:20 am 
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Maybe you're thinking about this all wrong -- all that capacitance would give you a time constant of something like months or years, so the resulting ripple using them just as filter capacitors would be pretty tiny!

Mark


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PostPosted: March 1st, 2019, 11:28 am 
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At the expected 30mA/side, more like 6.7hrs... And, used as filters, there's ripple current which Walt correctly pointed out these are not really good at handling...

Roscoe


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PostPosted: March 1st, 2019, 11:30 am 
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Roscoe,

Your use of supercapacitors got me reading a few thing online concerning the tradeoff between super capacitors and batteries for energy storage:

https://batteryuniversity.com/learn/article/whats_the_role_of_the_supercapacitor

From what I read, supercapacitors better in fast charge/discharge applications, but energy delivery (particularly voltage) falls off much steeper than batteries as the capacitor bank discharges, and only can deliver part of its stored energy before the voltage drops significantly. Batteries have a more linear discharge maintaining voltage over its discharge range and can deliver most of its stored energy.

Probably not an issue with the low current demand you are using, you probably would not have much discharge over the timescale you are playing. Since they charge up quickly anyway, it would not take much time to recharge the capacitor bank. Even between queueing up records ;) .

David


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PostPosted: March 1st, 2019, 11:45 am 
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David McGown wrote:
Roscoe,
. . .

Probably not an issue with the low current demand you are using, you probably would not have much discharge over the timescale you are playing. Since they charge up quickly anyway, it would not take much time to recharge the capacitor bank. Even between queueing up records ;) .

David


Exactly. It's probable with the power supply I'm building for charging that if you turned the charger on every time you flipped a record, you could play records forever without the voltage ever dropping below the input voltage the regulators need to maintain proper operation. Fully charged the caps will be at 31.4V/rail, the regulators should work fine down to about 20V in...

Roscoe


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PostPosted: March 1st, 2019, 1:09 pm 
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Roscoe,

So, if you had a way of monitoring the signal output, you could have a circuit that would detect a low signal (lifted stylus), which would actuate a relay that would engage the charging circuit. As soon as the needle hits the groove, the relay would disengage.

One thing about battery charging. Charging circuits for NiHM batteries are actually pretty simple, basically the same a NiCd, and there are loads of examples out there. You could trickle charge to keep them topped off. Li-ion are another matter...

David


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PostPosted: March 1st, 2019, 1:15 pm 
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David McGown wrote:
Roscoe,

So, if you had a way of monitoring the signal output, you could have a circuit that would detect a low signal (lifted stylus), which would actuate a relay that would engage the charging circuit. As soon as the needle hits the groove, the relay would disengage.


It'd be easier to put an optical sensor on the tonearm lift ;) Of course, I'll have to wait and see what kind of transient connecting/disconnecting the charger generates at the phono stage output...

Quote:
One thing about battery charging. Charging circuits for NiHM batteries are actually pretty simple, basically the same a NiCd, and there are loads of examples out there. You could trickle charge to keep them topped off. Li-ion are another matter...

David


Batteries are so 1990s ;)

Roscoe


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