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post #316 of 556
Quote:
Originally Posted by Avro_Arrow View Post

It's here.
 



 


thanks for the link. i checked the circuit, it is too big for portable use. my pimeta case barely have the space for something like that

 

@tangent: how do i check the opamp functionality? i'm afraid there is some problem with the opamp or the buffers. it all started after the opa827 left channel suddenly died, then i switched to ad8610, then the buzzing sound and run out of battery happened

 

post #317 of 556

There is a simpler one in Tangents site that just turns off the LED

which should fit. I don't remember off hand which amp it is

associated with.

post #318 of 556
Quote:
Originally Posted by i_djoel2000 View Post

i checked the circuit, it is too big for portable use

 

There are at least two mentioned in that thread. The one I posted above the one Avro's link takes you to requires a dual op-amp, a handful of resistors, and a reference. Even with thru-hole, you could probably pack that into a corner somewhere. Do it with SMT, and it should be easy.
 

Quote:

how do i check the opamp functionality?

 

The best way is to plug them into a separate, known-working circuit.

 

Lacking that, you can build this or something like it.

 

I doubt your low-battery problem killed the op-amps, by the way. I think it's more likely that your initial successes with the DC-DC conversion circuit were a matter of insufficient testing, and that you're now finding the downsides.

 

Try temporarily bypassing the conversion circuit and powering from a good linear power supply.

 

Quote:
Originally Posted by Avro_Arrow View Post

There is a simpler one in Tangents site that just turns off the LED

which should fit. I don't remember off hand which amp it is

associated with.


You're thinking of the zener/CRD cut-off circuit in the META42.

 

You don't have to have a CRD. You can replace it with any constant current source. There are many in my op-amp biasing article, but easiest would be to use the one the PIMETA v2 already gives you, in its class A biasing circuit.

 

If you put a zener in series with LED2, you get the META42 circuit. The downside of that is that when the LED cuts off, it also cuts off class A biasing, though that's a small matter. You could even spin it as a positive thing, since it's a way to save on battery power.

 

If you don't like that, you could just add another transistor to the current mirror and run your zener-limited cut-off LED from that.


Edited by tangent - 4/24/11 at 3:11pm
post #319 of 556

tangent, thank you for your respond. i think voltage indicator would not be necessary for my pimeta. the dc-dc converter simply won't turn on when voltage supply is below 4v

 

now i'm running the amp on another set of 4 aaa batteries, still no problem so far. i'll turn it on for 5 hours and see what happens, i hope the previous problem was only a small glitch and nothing goes wrong this time. what is the capacitance of normal aaa batteries? i'm trying to predict the hours of the run-time


Edited by i_djoel2000 - 4/25/11 at 1:25am
post #320 of 556

i think i just found the problem..

 

well, it is not really a concerning problem but it is the downside. it turns out that the dc-dc converter consumes some heavy current as well as the pimeta. i measured the current draw on the battery socket and i got reading of around 150mA (more than twice of normal pimeta!!), the volume pot was set to 9AM, hence you pretty much get the idea of how power-consuming this converter in normal usage. i checked the murata datasheet but i couldn't find any current consumption of this converter, then i thought it only consumes very little current if does not consume them at all

 

when the voltage across battery drops below 4V, the converter produces really low voltage (below 1V), then the buzzing noise comes out of the headphone jack, i guess this explains everything.

 

now i'm out of idea on how to utilize this pimeta, 4 hours of run time with 300mA 9v battery is pretty much useless for portable use. someone please enlighten me! frown.giffrown.gif anybody knows a good dc-dc step up converter that does not consume much current?


Edited by i_djoel2000 - 4/25/11 at 3:36am
post #321 of 556

There's no such thing as a free lunch, dJoeL.

 

5 V divided into 12 V is 2.4, which is how much output current must be multiplied to get input current, if the converter is 100% efficient.  The actual efficiency is closer to 80%, so the multiplier is closer to 3.

 

If it were otherwise, power in would be less than power out. In other words, you would be creating power.

 

The actual situation: P=IV, so if current out is 50 mA and voltage out is 12 V, then P_out = 0.6 W. Likewise, P_in is approximately 0.75 W, or 125% more than P_out, as expected. The law of conservation of energy is preserved.


Edited by tangent - 4/25/11 at 5:57am
post #322 of 556
Quote:
Originally Posted by tangent View Post

There's no such thing as a free lunch, dJoeL.

 

5 V divided into 12 V is 2.4, which is how much output current must be multiplied to get input current, if the converter is 100% efficient.  The actual efficiency is closer to 80%, so the multiplier is closer to 3.

 

If it were otherwise, power in would be less than power out. In other words, you would be creating power.

 

The actual situation: P=IV, so if current out is 50 mA and voltage out is 12 V, then P_out = 0.6 W. Likewise, P_in is approximately 0.75 W, or 125% more than P_out, as expected. The law of conservation of energy is preserved.


i know there is efficiency takes place in the equation. but still, almost 100mA current consumption for the converter alone is way beyond my expectation!

 

i thought about the dc-dc converter after local member made a cmoy with cheap dc-dc converter. with ad8397 opamp, it gets the amp to run around 10 hours, meaning the converter does not consume current that much. the converter simply looks like a miniature transformer, unlike mine. based on that experience, i figured using more expensive dc-dc converter will get you the same result plus better efficiency. i guess i was wrong..

 

now i'm thinking to use buf634 (min. 2.25V supply voltage) as buffer, LM4562 (min. 2.5V supply voltage) in signal, and lt1364 (min. 2.5V supply voltage) in ground without the converter. i tested the same configuration but with the LMH6321 buffer, works great, got reading of 0.5mV dc offset.but the music is still distorted when bass impact is involved, otherwise fine. i thought the problem was the insufficient buffer, LMH6321 (requires 5V supply voltage, while the battery only gives around 3V after rail splitter). what do you think, tangent? do you think the distortion was caused by the opamp, or buffer?

 

note: my power supply is 3x aaa rechargeable batteries (around 4.8V max)

 


Edited by i_djoel2000 - 4/25/11 at 9:34am
post #323 of 556
Quote:
Originally Posted by i_djoel2000 View Post
now i'm thinking to use buf634 (min. 2.25V supply voltage) as buffer, LM4562 (min. 2.5V supply voltage) in signal, and lt1364 (min. 2.5V supply voltage)


You need to check those voltages again as they are incorrect without some signs in front of them (which changes things significantly).

 

post #324 of 556
Quote:
Originally Posted by i_djoel2000 View Post

I know there is efficiency takes place in the equation. but still, almost 100mA current consumption for the converter alone is way beyond my expectation!

 

 

This is not about efficiency.  It is about power and the convertor is not consuming 100mA.

 

Let say you amp is drawing 50mA @ 12V

 

12V x 50mA = 0.6W.

 

So we need 0.6W of power.

 

0.6W / 4.8V = 125mA.

 

So 4.8V @ 125mA is the *same power* as 12V @ 50mA.

 

And a DC-DC convertor uses the same *power*, but converts the voltage.  Now a DC convertor is not 100% efficient.  Let's say it is only 80% efficient, so 20% or 25mA is wasted in the conversion, make the total draw 150mA

 

Don't forget that the situation gets worse as the batteries discharge, as 4.8V is fully charged.  As the the voltage drops in the cells, the current demand goes up, hasten the death of the battery.

post #325 of 556
Quote:
Originally Posted by cobaltmute View Post




You need to check those voltages again as they are incorrect without some signs in front of them (which changes things significantly).

 


it has plus minus sign in front of them, i just don't know how to type them with the keyboard. if i'm not mistaken, 2.5V supply voltage needs at least 5V in single supply operation

 



Quote:
Originally Posted by cobaltmute View Post



 

This is not about efficiency.  It is about power and the convertor is not consuming 100mA.

 

Let say you amp is drawing 50mA @ 12V

 

12V x 50mA = 0.6W.

 

So we need 0.6W of power.

 

0.6W / 4.8V = 125mA.

 

So 4.8V @ 125mA is the *same power* as 12V @ 50mA.

 

And a DC-DC convertor uses the same *power*, but converts the voltage.  Now a DC convertor is not 100% efficient.  Let's say it is only 80% efficient, so 20% or 25mA is wasted in the conversion, make the total draw 150mA

 

Don't forget that the situation gets worse as the batteries discharge, as 4.8V is fully charged.  As the the voltage drops in the cells, the current demand goes up, hasten the death of the battery.


thanks for the explanation. but, maybe you got me wrong? my pimeta is drawing 150mA after the conversion, meaning it was already in 12V. if the amp is really drawing 150mA, i wonder why i still need to crank up the volume to the same level as when i used 9V battery, which in fact only gives around 60mA current draw?


Edited by i_djoel2000 - 4/25/11 at 10:35am
post #326 of 556

btw, can i solder the buf634 SOIC's pins on the LMH6321 pad? i looked at the buf634's data sheet and pin 5 is not connected anywhere, while in pimeta v2 pin 5 is connected to ground.

 

but i do remember tangent used buf634 on pimeta v1, that is why i'm asking this


Edited by i_djoel2000 - 4/25/11 at 9:49pm
post #327 of 556

You could get adapters, but that will make your amp non-portable.

 

And read my comment about the voltages again.  The minimum supply voltages are the same.

 

And if you are really concerned, you could consider another case.  Unless I'm reading the dimensions wrong, the Hammond 1455J1202 is the same size as the Serpac H-65 and I have 12xAAA in my Hammond case.  14.4V with 800ma capacity.

post #328 of 556

My solution was to use 3 x 1500mah Iphone 1G batteries that I got off of Ebay. I wired them in series with a protection PCB (see link below). On the second charge I got 17 hours of running time. You will also dedicated Li-poly charger. I have installed a jack so that I can charge the battery witout removing it from the amp.

 

http://www.batteryjunction.com/prcimopcbfor1.html 

 

http://www.tenergybattery.com/index.php?option=com_virtuemart&page=shop.product_details&flypage=shop.flypage&category_id=17&product_id=85&Itemid=1&vmcchk=1 

 

RC

post #329 of 556
Quote:
Originally Posted by cobaltmute View Post

You could get adapters, but that will make your amp non-portable.

 

And read my comment about the voltages again.  The minimum supply voltages are the same.

 

And if you are really concerned, you could consider another case.  Unless I'm reading the dimensions wrong, the Hammond 1455J1202 is the same size as the Serpac H-65 and I have 12xAAA in my Hammond case.  14.4V with 800ma capacity.


wait, i'm still confused..if i want to use buf634 in pimeta v2 pcb, i need to use adapter??

 

post #330 of 556
Quote:
Originally Posted by i_djoel2000 View Post




wait, i'm still confused..if i want to use buf634 in pimeta v2 pcb, i need to use adapter??

 


This is my mistake - for some reason I was thinking of the Buf634 in DIP, not SOIC.

 

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