Hi. Im making my 4th amplifier, this time with a tda2040.
My problem is when I want to test AC voltage I get very low voltage. For example, when I test 220v from the outlet I get 15v. When I test a 12v transformer i get like 1 volt, and so on.
I tried with a dmm that a friend gave me I have the same readings!
I haven't tried amps. Any idea for an easy/accurate way to test this?
Also... Do you have any idea why this could happen so I don't make the same mistake?
thanks
I do lot of testing and I've never seen that.
For main frequency voltages you shouldn't see any weird stuff (eg. low or high voltages due to the high frequencies.)
QuoteDo you have any idea why this could happen so I don't make the same mistake?
My first impression is you are consistently doing something wrong. Whatever that is isn't coming through in your question.
Sorry if these sound silly but:
-Are you setting the multimeter to the *AC* *voltage* range? *DC* voltage will not work.
-Are you connecting both probes?
-Are you getting a good contact.
-Are the leads good?
- Try a different transformer.
You could generate a full-height sinewave 100Hz using your sound-card.
Remove your speakers & headphones.
Measure the output with a multimeter. You should get around 1 to 2V rms.
It's not a very reliable method the advantage is you can change the frequency
and see if the voltage is relatively constant (say 5% variation at 1kHz).
A known transformer with say a 100ohm load is often more precise. (It will usually be about 10% high, as the rated voltage is at full load.)
A sanity check to get a rough idea of the voltage would be to connect a rectifier to the AC then use a DC measurement on the multimeter.
[Oh, flat batteries and sometimes blown fuses in the meter can cause weird problems.]
Quote from: Rob Strand on August 30, 2018, 04:21:33 AM
I do lot of testing and I've never seen that.
For main frequency voltages you shouldn't see any weird stuff (eg. low or high voltages due to the high frequencies.)
QuoteDo you have any idea why this could happen so I don't make the same mistake?
My first impression is you are consistently doing something wrong. Whatever that is isn't coming through in your question.
Sorry if these sound silly but:
-Are you setting the multimeter to the *AC* *voltage* range? *DC* voltage will not work.
-Are you connecting both probes?
-Are you getting a good contact.
-Are the leads good?
- Try a different transformer.
You could generate a full-height sinewave 100Hz using your sound-card.
Remove your speakers & headphones.
Measure the output with a multimeter. You should get around 1 to 2V rms.
It's not a very reliable method the advantage is you can change the frequency
and see if the voltage is relatively constant (say 5% variation at 1kHz).
A known transformer with say a 100ohm load is often more precise. (It will usually be about 10% high, as the rated voltage is at full load.)
A sanity check to get a rough idea of the voltage would be to connect a rectifier to the AC then use a DC measurement on the multimeter.
[Oh, flat batteries and sometimes blown fuses in the meter can cause weird problems.]
Hi.
Dc readings are fine. If I use a rectifier voltages are ok. When I switch to ac and test the ac input I have this problem.
I measured AC with this dmm before and it was fine. Now I'm using two different dmm and show the same faulty readings. Im testing it in every power outlet on the walls, and I did it like 50 times by now. I tried even on the solder terminals of a chassis interlock connector with alligator clips to be sure its not a bad connection and moved the dial from ac to dc and back to ac again to be sure.
With the 100Hz test it reads .068v on the 2v scale of the dmm and like .05 on the 20v scale.
When the probes aren't touching anything the voltage floats a little bit, I guess that's ok because rf,emp or something.
No expert here but could it be a dead fuse?
Quote from: swever on August 30, 2018, 05:12:41 AM
No expert here but could it be a dead fuse?
It only has 1 fuse, so if that fuse is dead nothing in the dmm should work.
Also, I already tested it.
Thanks anyway
Quote from: swever on August 30, 2018, 05:12:41 AM
No expert here but could it be a dead fuse?
Some DMMs are weird. Mine wouldn't measure current with a dead fuse, with all other features working.
The fuse in a DMM is normally just for the current ranges.
Test probes can have a fuse built in.
AC ranges above mV can demand more current from the circuit under test than DC ranges, this can make even a little contact resistance anywhere give an under-reading in those AC ranges.
Usually, if the AC reading is suspiciously low, it's actually reading stray induced current from EM radiation and something isn't making contact or the AC supply is actually switched off.
can you tell us the make and model number? meters these days don't need the lead moved from one jack to another for AC voltage measures, like some for current ranges, do they?
Quote from: duck_arse on August 30, 2018, 10:55:44 AM
can you tell us the make and model number? meters these days don't need the lead moved from one jack to another for AC voltage measures, like some for current ranges, do they?
This is the one https://www.hobby-hour.com/electronics/m890g.php (https://www.hobby-hour.com/electronics/m890g.php)
Quote from: anotherjim on August 30, 2018, 10:10:29 AM
The fuse in a DMM is normally just for the current ranges.
Test probes can have a fuse built in.
AC ranges above mV can demand more current from the circuit under test than DC ranges, this can make even a little contact resistance anywhere give an under-reading in those AC ranges.
Usually, if the AC reading is suspiciously low, it's actually reading stray induced current from EM radiation and something isn't making contact or the AC supply is actually switched off.
This is just a generic one. I'll be amazed if there's more than one fuse in the whole thing hehe.
Maybe I can try to resolder all through hole components
QuoteMaybe I can try to resolder all through hole components
While meter do get faults, two different meters with a similar problem points to a common external cause:
(- the meter settings)
- the meter leads
- the circuit
- the environment
If you have a Wall-wart/Plug-pack with an AC output measure the voltage at home then take it to work or a friends house and re-measure it there.
Quote from: Rob Strand on August 30, 2018, 06:17:29 PM
QuoteMaybe I can try to resolder all through hole components
While meter do get faults, two different meters with a similar problem points to a common external cause:
(- the meter settings)
- the meter leads
- the circuit
- the environment
If you have a Wall-wart/Plug-pack with an AC output measure the voltage at home then take it to work or a friends house and re-measure it there.
I know, right? It can't be only the dmm
(- the meter settings) I triple mega hyper double checked that
- the meter leads I have spare probes and its the same deal.
- the circuit Everything in my house works with 220v and everything is working. I can even test dc fine so I guess that means the ac is fine.
- the environment I don't know what you mean by that
Is there a chip that's responsible for measuring ac? (I've read that cheap dmm transforms the ac to dc and measure that, so I guess when you test dc the dmm bypass the rectifier)
Where in the world do you live? What type of socket/plug standard is used?
https://en.wikipedia.org/wiki/Mains_electricity_by_country
There is a link on the hobby-hour page that shows a circuit diagram. IC2A (TL062) seems to be of interest.
However you stated that another meter shows exactly the same fault (I think), which points towards a manufacturing production error - wrong part installed. Probably a resistor.
If the meter is under warranty - take it back as it is faulty. A low voltage reading on the AC mains could lead you to falsely believe that the voltage is low enough to be safe to work on without isolating the circuit. Not good.
QuoteIs there a chip that's responsible for measuring ac? (I've read that cheap dmm transforms the ac to dc and measure that, so I guess when you test dc the dmm bypass the rectifier)
If you have an averaging meter (ie. *not* a true rms meter) then you will find the AC to DC converter is very much like the circuit surrounding IC1 in the circuit below. Basically R15 through to the output at the cathode of D6/R20. There two very common and similar circuits, this is one of them.
https://www.eleccircuit.com/wp-content/uploads/2015/02/the-full-circuit-diagram-of-digital-multimeter.jpg
This one is a slight variant in that the circuit is around IC2A and the DC output comes off a smoothing cap,
http://www.frankshospitalworkshop.com/electronics/projects/voltage_reference/M890G.jpg
Opamps are almost always TL06x. Occasionally LM358.
Some really dodgy meters might only have a diode.
You really should start with a meter that works and an AC that produces a known correct voltage. From that point you can start isolating the problem ie. what works and what doesn't and take it from there.
The main issue I see in assuming the meter has a fault is you have two meters doing the same thing. If they are not the same make and model it unlikely both meters have the same fault (although not impossible). The last thing you want to do is assume the meter has a fault. There's a risk you will break something when you pull the meter apart and if you start messing with it you might upset the calibration. If you have no reference meter or known AC source you cannot re-calibrate it.
I found this:
https://www.eevblog.com/forum/testgear/dangerous-multimeter-mastech-m890g-m890g2-(aka-dc-electronics-dc03)/?PHPSESSID=36ia6cni50duvbsb4hchc94j03
Quote from: Tony Forestiere on August 30, 2018, 06:49:51 PM
Where in the world do you live? What type of socket/plug standard is used?
https://en.wikipedia.org/wiki/Mains_electricity_by_country
I'm from argentina
Type I (Australian AS/NZS 3112); Argentinian version has reversed polarity compared to Chinese and Australian versions ( I don't know what they mean by polarity... phasing? idk. The thing is that I don't know any house that has a conductive rod driven into the ground because its expensive.)
My house has these outlets: So-called "universal socket" which meets no standard[5] but accepts a number of different plug types.(criticized as unsafe)
Quote from: duck_arse on August 31, 2018, 10:46:38 AM
I found this:
https://www.eevblog.com/forum/testgear/dangerous-multimeter-mastech-m890g-m890g2-(aka-dc-electronics-dc03)/?PHPSESSID=36ia6cni50duvbsb4hchc94j03
I'll check for a transistor...
A forum user posted:
"From my understanding, the NPN transistor "Q4" will blow up if in ohms mode with 240VAC"
I mean... I already opened it and nothing seems burnt but I have no idea what could it be.
Your mains is 220Hz - that meter's rated range for AC voltage is: "Frequency Response: 40Hz - 200Hz".
Quote from: guidoilieff on August 31, 2018, 03:49:09 PM
Quote from: Tony Forestiere on August 30, 2018, 06:49:51 PM
Where in the world do you live? What type of socket/plug standard is used?
https://en.wikipedia.org/wiki/Mains_electricity_by_country
I'm from argentina
Type I (Australian AS/NZS 3112); Argentinian version has reversed polarity compared to Chinese and Australian versions ( I don't know what they mean by polarity... phasing? idk. The thing is that I don't know any house that has a conductive rod driven into the ground because its expensive.)
My house has these outlets: So-called "universal socket" which meets no standard[5] but accepts a number of different plug types.(criticized as unsafe)
Polarity in this context means which pin is connected to the hot AC, vs. the neutral. See the "polarization" section of the wiki article.
Quote from: GGBB on September 01, 2018, 01:19:03 AM
Your mains is 220Hz - that meter's rated range for AC voltage is: "Frequency Response: 40Hz - 200Hz".
Thanks. I'll try to find how higher frequency can damage a circuit.
I'm pretty sure argentina has 50/60Hz. Why you say its 220?
Quote from: reddesert on September 01, 2018, 04:46:25 AM
Quote from: guidoilieff on August 31, 2018, 03:49:09 PM
Quote from: Tony Forestiere on August 30, 2018, 06:49:51 PM
Where in the world do you live? What type of socket/plug standard is used?
https://en.wikipedia.org/wiki/Mains_electricity_by_country
I'm from argentina
Type I (Australian AS/NZS 3112); Argentinian version has reversed polarity compared to Chinese and Australian versions ( I don't know what they mean by polarity... phasing? idk. The thing is that I don't know any house that has a conductive rod driven into the ground because its expensive.)
My house has these outlets: So-called "universal socket" which meets no standard[5] but accepts a number of different plug types.(criticized as unsafe)
Polarity in this context means which pin is connected to the hot AC, vs. the neutral. See the "polarization" section of the wiki article.
Isn't that called phasing?
Quote from: guidoilieff on September 01, 2018, 09:28:28 AM
Isn't that called phasing?
That's different, though related. Phase usually refers to single-phase: https://en.wikipedia.org/wiki/Single-phase_electric_power (https://en.wikipedia.org/wiki/Single-phase_electric_power) versus 3-phase: https://en.wikipedia.org/wiki/Three-phase_electric_power (https://en.wikipedia.org/wiki/Three-phase_electric_power).
A typical US home installation has split-phase: https://en.wikipedia.org/wiki/Split-phase_electric_power (https://en.wikipedia.org/wiki/Split-phase_electric_power). There will be three wires coming into the house: positive hot, neutral, and negative hot. Neutral should be tied to ground at a central location. This is not 3-phase: the positive and negative are 180 degrees out of phase. That allows attaching a large appliance (usually a clothes dryer) across positive and negative to get 220 VAC. All of the small appliances in the house run off a connection between neutral and one or the other hot wire, receiving 110 VAC (closer to 120 these days).
Appliances like lamps use a polarized plug (one blade wider) to make sure that the outer thread connection of the lightbulb is connected to neutral, not hot, to minimize the risk of accidental shock. This is also why you hear about people getting shocks from old amps with un-polarized reversible 2-prong plugs; if you plug it the wrong way round and the amp has a fault, hot voltage can leak onto the chassis.
Anyway, long story, if you have a 3-prong plug the plug can't be plugged the wrong way around, but from the website it sounds like Argentina uses an opposite convention for which is the hot/neutral wire, vs China/Australia.
I am sure that the previous poster misread the table and you have 220 V power at 50 Hz, not 220 Hz.
The remaining problem of why you don't measure AC voltage - are you sure you're measuring it off the proper pins? Need to measure hot vs neutral or ground, not neutral vs ground. Do you have a wallwart that outputs say 9 VAC or 12 VAC that you can try measuring with the DMM? [Never mind, I guess you mentioned trying a 12VAC transformer in the original post.]
QuoteThat's different, though related.
It does affect safety if you use equipment from other countries:
- equipment with single pole power switches will still pass live wires through the circuit when the switch is off. The device is obviously switches off as far as the user goes.
- fusing would be on the neutral will is highly undesirable (and usually illegal).
Quote from: reddesert on September 01, 2018, 02:35:59 PM
Quote from: guidoilieff on September 01, 2018, 09:28:28 AM
Isn't that called phasing?
That's different, though related. Phase usually refers to single-phase: https://en.wikipedia.org/wiki/Single-phase_electric_power (https://en.wikipedia.org/wiki/Single-phase_electric_power) versus 3-phase: https://en.wikipedia.org/wiki/Three-phase_electric_power (https://en.wikipedia.org/wiki/Three-phase_electric_power).
A typical US home installation has split-phase: https://en.wikipedia.org/wiki/Split-phase_electric_power (https://en.wikipedia.org/wiki/Split-phase_electric_power). There will be three wires coming into the house: positive hot, neutral, and negative hot. Neutral should be tied to ground at a central location. This is not 3-phase: the positive and negative are 180 degrees out of phase. That allows attaching a large appliance (usually a clothes dryer) across positive and negative to get 220 VAC. All of the small appliances in the house run off a connection between neutral and one or the other hot wire, receiving 110 VAC (closer to 120 these days).
Appliances like lamps use a polarized plug (one blade wider) to make sure that the outer thread connection of the lightbulb is connected to neutral, not hot, to minimize the risk of accidental shock. This is also why you hear about people getting shocks from old amps with un-polarized reversible 2-prong plugs; if you plug it the wrong way round and the amp has a fault, hot voltage can leak onto the chassis.
Anyway, long story, if you have a 3-prong plug the plug can't be plugged the wrong way around, but from the website it sounds like Argentina uses an opposite convention for which is the hot/neutral wire, vs China/Australia.
I am sure that the previous poster misread the table and you have 220 V power at 50 Hz, not 220 Hz.
The remaining problem of why you don't measure AC voltage - are you sure you're measuring it off the proper pins? Need to measure hot vs neutral or ground, not neutral vs ground. Do you have a wallwart that outputs say 9 VAC or 12 VAC that you can try measuring with the DMM? [Never mind, I guess you mentioned trying a 12VAC transformer in the original post.]
Thanks for the explanation! I got it.
In my country it's a roulette witch is the hot and which is neutral. I think that's why there are problems with electricity all the time at gigs or why sometimes you can "feel" electricity in the chassis of some electric products while you're barefoot.
I made like 5 or 6 of these http://www.generalguitargadgets.com/effects-projects/power-supplies/ultra-clean-power-supply/ (http://www.generalguitargadgets.com/effects-projects/power-supplies/ultra-clean-power-supply/) with transformers I alredy meassured and labeled. Now I'm trying to rewire this amp I made a long time ago http://www.generalguitargadgets.com/effects-projects/amps/tda2030-amp/ (http://www.generalguitargadgets.com/effects-projects/amps/tda2030-amp/) but I dont know wich cable is negative and wich is positive of a similar transformer like this http://www.electronicagimeno.com/sites/default/files/007581_0.jpg (http://www.electronicagimeno.com/sites/default/files/007581_0.jpg), or does th circuit doesnt know wich is wich?
(I blew a tda7294 because I thought the heatsink was connected to ground instead of negative and now I'm scared to blow another one)
Quote from: Rob Strand on September 01, 2018, 06:34:19 PM
QuoteThat's different, though related.
It does affect safety if you use equipment from other countries:
- equipment with single pole power switches will still pass live wires through the circuit when the switch is off. The device is obviously switches off as far as the user goes.
- fusing would be on the neutral will is highly undesirable (and usually illegal).
Never thought of that. I think I'm doing both things in the amp I'm making.
Since in this country there is no polarization in the connectors how do I avoid this?
> Your mains is 220Hz - that meter's rated range for AC voltage is: "Frequency Response: 40Hz - 200Hz".
1) It is highly UN-likely he gets 220Hz power. It is not suitable for even urban power distribution. (The stray capacitance means higher losses, which are already problematic at 50/60Hz.) That's gotta be some typo or mis-read.
2) I would not expect large error reading some 220Hz source with a "40Hz-200Hz" meter. The filtering is gentle. It might not meet a 1% spec but should be within 5%. Errors will climb so when you poke your 400Hz large airplane system it may read 20%-30% down.
Quote from: GGBB on September 01, 2018, 01:19:03 AM
Your mains is 220Hz - that meter's rated range for AC voltage is: "Frequency Response: 40Hz - 200Hz".
!!! I need to avoid posting after midnight - can't even keep Volts and Hertz straight. Now that is hilarious! :-[
"Live" and "Neutral" *should NOT* matter inside your appliance (power unit). The transformer is amply insulated from ground/chassis on both sides. (Over 10KV is different, but none of our business.)
The fact that switch or fuse may be on the "wrong" side does not matter because you should NOT be sticking your hand inside unless the power cord is UN-plugged. (Yes, we sometimes flirt this rule when trouble-shooting, but *very carefully*!!)
The fact that 3-phase power can be delivered at least 6 ways (wYe, Delta, grounded, high-leg) normally does not matter in small audio because we only use one pair of current-carrying conductors.
> I dont know wich cable is negative and wich is positive of a similar transformer
Both legs of an AC transformer swing both + and - of each other.
The polarity which matters when blowing-up chips and cap is determined by the *rectifier*.
Quote"Live" and "Neutral" *should NOT* matter inside your appliance (power unit). The transformer is amply insulated from ground/chassis on both sides. (Over 10KV is different, but none of our business.)
The fact that switch or fuse may be on the "wrong" side does not matter because you should NOT be sticking your hand inside unless the power cord is UN-plugged. (Yes, we sometimes flirt this rule when trouble-shooting, but *very carefully*!!)
I'm pretty sure if you submitted a product for safety testing that (only) switched neutral and/or (only) fused neutral it would not pass.
I believe if the assignment of active and neutral is ambiguous there are cases in the safety standard where you need to fuse both lines. There's also some statements in the standard with a wider net regarding not creating unnecessary safety risks. Medical device standards actually enforce fusing both lines as a means of reducing risk.
What is interesting is integrated power inlet modules (IEC inlet + fuse + maybe switch) will have the fuse on a specific line. I've never looked for or come across modules with fuses on the other line.
For what is is worth, the IEC cable should correctly translate the wall socket pins assignments to the IEC pin assignments. At the IEC connector the Active and Neutral orientation should be standardized.
As far as Active being on the left or right (say when looking into the power socket on the wall) there's also the issue of the earth pin being up or down.. In AU the earth pin is normally considered to be down.
Here's some cables, the L and N lines are looking into the faces of the cable ends, on the IEC cable.
http://www.yunhuanelectric.com/Clkj_Images/upfile/Brazil-14136-to-IEC-C13-Power-Cord.jpg
http://www.yunhuanelectric.com/Clkj_Images/upfile/AS-NZ-3112-to-IEC-60320-C13-Mains-Cable.jpg
"Back in the day"...for US equipment at least...it didn't matter which line you fused because the power cords had non-polarized 2-prong plugs, and could be inserted either way. For power switches, Fender usually switched one line only with a SPST toggle, while Marshalls tended to have DP power switches. Might have been a British requirement, but not a bad idea anyway.
Quote"Back in the day"...for US equipment at least...it didn't matter which line you fused because the power cords had non-polarized 2-prong plugs, and could be inserted either way.
There's a few countries where you can still do that. Basically those with US style plugs or the two round prongs.
Over time the rules for importing products weeds-out the bad practices.
These days the products either break or go obsolete before two versions of the safety standard go by so we don't have to worry about the old stuff not complying to the new rules ;D.