about current consumption...

[waky]

hi again... i feel bad for making so much question around here... i spend hours reading the forum and i hope that someday im the helpfull guy giving the newb a hand, anyways... i have made a noisy cricket, but i tried to figure out its current consumption.. ( i puted the tester between +side of batery and 9v+ on the circuit in series of course, but i get no readings from the tester (and the amp doesnt even turn on with the tester on circuit), so all i can do its getting it in parallel. But thats useless for current right?

* is something wrong with my tester?, or am i doing the measuring wrong?
* in case i cant get to measure the current drain can someone tell me the aproximate current consumption?
* if i want to connect my cricket to a "9v" wall wart(the thing actually puts 13.7 volts out) could i add a zener 9.1v in paralel to the power line to get the tension down?
* even if i do this and i take the voltage down to 9.1volts could the circuit burn from too much current? or does it only drain what it needs from the wall wart?
* what wattage should the zener be? (if i had the current consumption  i could calculate this, that was the reason i was measuring it)

*is it normal that my cricket never gets quiet?, the volume pot works but when its fully down it doesnt mute... it still has  quite a bit of volume.
* What other transistors are good for this circuit? i have  a REAL hard time finding variety on my country... my cricket currently has some "k163" jfets.. wich i thought sounded great until i tested an mpf102 a friend showed me =/... but i cant get them here.. (neither j201's)


Off topic:
* do the voltage of a caps affect tone?, all i can find here are like 400 volts enourmous caps... for tvs i guess.. instead of the small ones i see in all ur photos, i builded a marshall bluesbreaker with those and it doesnt sound too good, wich leads me to:

* i cant get tl072 (bluesbreaker op-amp) so mine has a tl082, does the crappy tone come from the op-amp or from the caps?


Sorry if all these questions are boring or dumb =/, thx for any help

[Paul Perry (Frostwave)]

Note that when you use a multimeter to measure current, you plug the red lead in a different hole, from when you use it to measure voltage.
Yes, i still fall for it occasionally after 50 years..
Oh, and be sure to start with the current range on 'maximum'.
And, if you have an old or secondhand meter & it won't measure current - there might be a broken fuse. That's happened to me, too.

[waky]

  lol it worked, but i get 1 in all scales (10a, 200ma, 20ma, 2000ua), what does this mean?

[petemoore]

* is something wrong with my tester?, or am i doing the measuring wrong?
 Read the directions, maybe there's another lead jack for current on it?
* in case i cant get to measure the current drain can someone tell me the aproximate current consumption?
 Of a Bluesbreaker, about the same as a TS...not much 30ma? maybe the technical specs on a BB or TS type box is available, they'll all be close...
* if i want to connect my cricket to a "9v" wall wart(the thing actually puts 13.7 volts out) could i add a zener 9.1v in paralel to the power line to get the tension down?
 I would leave it at ~14...or use a 7809 regulator, which might also reduce PS ripple, each zener in series drops the voltage by 1 diode drop.
* even if i do this and i take the voltage down to 9.1volts could the circuit burn from too much current? or does it only drain what it needs from the wall wart?
 Circuits draw the power the need. Supplies supply power. Make sure your supply is rated for current above what the circuit will draw.
 What is the voltage rating of the chip [probably 15v or more?], other than a short [which can draw massive current/thermal runaway very quickly] the main problem with too much current draw is dissipating the heat from the chip, turn the volume down, lower the voltage [which reduces output/headroom], or use a *heatsink.
* what wattage should the zener be? (if i had the current consumption  i could calculate this, that was the reason i was measuring it)
 It's calculable, I'm the one that would recommend the regulator, more watts than the watts chip draws, which is a little more than the output, I think 1 watt would do it.
*is it normal that my cricket never gets quiet?, the volume pot works but when its fully down it doesnt mute... it still has  quite a bit of volume.
 If the signal path is connected to ground [which the CCW volume pot should probably do, I didn't look at the schematic], you should have 0.0 worth of voltage swing = zero output.
* What other transistors are good for this circuit? i have  a REAL hard time finding variety on my country... my cricket currently has some "k163" jfets.. wich i thought sounded great until i tested an mpf102 a friend showed me =/... but i cant get them here.. (neither j201's)
 2n5457...
 Try the circuit on almost perfect DC power source, a 9v battery, if the noise is the same, a regulator and filter won't improve the power supply.
 Off topic:
* do the voltage of a caps affect tone?,
No.
  all i can find here are like 400 volts enourmous caps... for tvs i guess.. instead of the small ones i see in all ur photos, i builded a marshall bluesbreaker with those and it doesnt sound too good, wich leads me to:  those caps are probably fine other than their physical size drawback.
* i cant get tl072 (bluesbreaker op-amp) so mine has a tl082, does the crappy tone come from the op-amp or from the caps?
 Probably neither one is bringing that. Small differences between those TLxxx opamps.  
  lol it worked, but i get 1 in all scales (10a, 200ma, 20ma, 2000ua), what does this mean?
  Not sure if polarity matters, reversing the leads.

[GibsonGM]

Check the fuse on the meter! And replace it with the same volt/amp rating, or the thing will burn out.  There's a chance that part of the meter DID burn out, maybe.
I prefer the old-fashioned needle type of meter (D'Arsonval meter) to measure current, they just seem to respond better (for me).  And they are very inexpensive! 

The 'red' or + lead goes to your + power supply output...the black, "-" lead goes to the + input of the circuit you are measuring - sometimes that seems odd, but if you think about it, it is like a diode...

Sometimes the scale will screw you up, too.  If you start off on 200mA, and the circuit draws 300mA, you will blow the fuse.  But if you try 10A for that circuit, you may get a nonsense reading like "3.2A" or something.  So you know that is not true, and you turn the scale to "200mA', and blow the fuse again, ha ha!  That's why I like the needle type.

Some circuits seem sensitive, and can't operate with the meter in series...I guess that is just how it goes - I'd like to know why, also.  The meter draws nearly nothing, so it doesn't make much sense.

It is better to use caps (electrolytic type) near their rated voltage since that is 'good for' their dielectric, although you will get away with using larger-rated caps if you have to.  Don't think it matters with poly or ceramic caps.     

[Ripthorn]

As far as your power supply putting out 13 ish volts, they do that because when they say 9V, they mean that the supply will provide at least 9V when drawing the max current it is rated for.

[waky]

* if i want to connect my cricket to a "9v" wall wart(the thing actually puts 13.7 volts out) could i add a zener 9.1v in paralel to the power line to get the tension down?
  I would leave it at ~14...or use a 7809 regulator, which might also reduce PS ripple, each zener in series drops the voltage by 1 diode drop.

i did that once and burned the cricket... i guess it was too close to the max voltage rating  of my lm386(aparently mine is rated for 12 volts), thats why i wanna use a zener =/.

* What other transistors are good for this circuit? i have  a REAL hard time finding variety on my country... my cricket currently has some "k163" jfets.. wich i thought sounded great until i tested an mpf102 a friend showed me =/... but i cant get them here.. (neither j201's)
  2n5457...
  Try the circuit on almost perfect DC power source, a 9v battery, if the noise is the same, a regulator and filter won't improve the power supply.

thx, it doesnt have noise, its the tone what sucks.

[petemoore]

thx, it doesnt have noise, its the tone what sucks.
  Kudos for honesty !
  The lm386 and 9v is barely enough power to wiggle a speaker cone.
  Using a boost-o-distorter to drive larger output from the amplifier will make the amplifier distort more, perhaps in a way that is desired. However if something else is preferred for the amplifer...you could find that you have waning interest in the Cricket tone.
  Asking an amplifier do surpass itself and it's power supply may offer diminishing returns.
  http://www.national.com/mpf/LM/LM386.html
  • Wide supply voltage range: 4V-12V or 5V-18V
  'Almost' like they're talking about two completely different chips, the 5-18 looks like it'd be more fun for driving current consuming components like speakers.

[earthtonesaudio]

I built my multimeter from a kit (with no instructions!) and the current side has never worked (nor do I care to debug the thing), so here's my workaround:

Add a 10 ohm resistor (at an appropriate power rating) in series with the V+ line, measure the voltage drop across it.  According to good ol' Georg, V=IR so you divide the voltage reading by 10 to get the amperage.

[petemoore]

  Voltage is like a water pressure, the higher you fill the glass the more pressure develops.
 Spring a leak and current flows, voltage may drop...for a while...not at all...permanently...depending on if there's a supply, and how much current flows into the glass to replenish what flows out.
 Fill the glass too full [overvoltage] and water goes everywhere, the chip or cap lets out some of it's magic blue smoke it needed to work right.
 RG keeps telling me data sheet, sometimes I even listen and read, other times I ask again 'why-woe-nit', or ask for interpretation of what it is I don't understand about the data sheet.
 Behind every data sheet is some chip or other part, and, being a component, it is bound to sound somewhat like a component....how much sometimes depends on how you hook it up.