It's hard to get these TO-99-type opamps here in EU, so I've ordered them from my supplier - US seller from ebay, with whom I have good experience from the past. Paid cca $30 for 3 pcs. They look genuine like many other LME49720HAs I can find on Google Images - shiny new/unused. But only the seller knows the truth
I have also thought about this, but if so, could it really make such drastic difference?
Have you tried seeing exactly which section of the O2 is the problem using these IC's. Try just the preamp IC with something else as the outputs and vice versa if that doesn't show an issue.
The words ebay and semiconductors aren't a happy combination judging by the many stories of fakes that make it onto these pages.
The words ebay and semiconductors aren't a happy combination judging by the many stories of fakes that make it onto these pages.
Okay, I don't intend to "spam" this thread with opamps switching results, that's for elsewhere
A friend of mine just told me that it could very possibly be the long legs of the TO-99 opamps acting like antennas and picking up interferences.
Will try to cut the legs and solder them onto DIP socket and see what happens then, will report back.
A friend of mine just told me that it could very possibly be the long legs of the TO-99 opamps acting like antennas and picking up interferences.
Will try to cut the legs and solder them onto DIP socket and see what happens then, will report back.
Okay, I don't intend to "spam" this thread with opamps switching results, that's for elsewhere
There's no problem looking for a "fault" or incompatibility if swapping the opamps proves it. I still have my suspicions on the provenance of your ebay purchase tbh.
Here is something else to try. Some TO99 op amps (like the OPA111) have the metal can tied to the chip substrate and tied to a pin. so the whole thing can be tied to either the signal shield ground or circuit ground to prevent RF pickup by the can.
The LME49720 data sheet doesn't seem to give any information here about how the "HA" TO99 case is tied, if at all. So do this. Take your ohmeter and measure from the metal case to all 8 leads to see if the case is tied to anything. I'm guessing probably not since the leads are all signal in, signal out, and V+/V-. Then put your meter on diode test and do that again, case to each lead, and do it in both directions to see if there are any diode junctions. If the case is tied to the chip substrate it can form a diode junction with some of the transistors. If none of this shows anything then, with the chip soldered in, try grounding the case to circuit ground but do it through a 1K resistor. If you don't notice any circuit problems reduce that ot 100R, and if all is still good then ground the case directly. See if that nukes some of the EMI.
Hi, I'm new to this forum and I really need help. I have just finish building my Objective2 amplifier and I was going through the tests and i failed at "Briefly Check The Supply Voltages". What happens is that I get 25V across the battery terminals when the power button is off and when it turns on, i get 19V. It's been 5 minutes and i haven't really felt anything get hot though. My electrical knowledge isn't all that great so I have no idea what went wrong.
Can any kind soul help, please?
Can any kind soul help, please?
Do you have batteries fitted ?
25 volts sounds OK with NO batteries fitted but it shouldn't fall when powered up. If it does then that suggests the unregulated supply to the regulators is dropping.
So measure across C4 and C5. Both should have at least 15 volts present under all conditions.
25 volts sounds OK with NO batteries fitted but it shouldn't fall when powered up. If it does then that suggests the unregulated supply to the regulators is dropping.
So measure across C4 and C5. Both should have at least 15 volts present under all conditions.
And do C4 and C5 have at least 15 volts across them when you turn it on and the "battery voltage" falls to 19 volts ?
If so then what is the voltage across C6 and C7 (the output of the regs) ? It should be plus 12 and minus 12.
Have you read the guide I put together ? There is a link at the end of post #1
If so then what is the voltage across C6 and C7 (the output of the regs) ? It should be plus 12 and minus 12.
Have you read the guide I put together ? There is a link at the end of post #1
Hi everyone,
I have built my own O2, my first DIY amp, a process I really enjoyed. However, something is not completely right with it. I've had some issues with getting it to work, as it is right now it works pretty well and the sound is awesome!
It works without any audible problems (that I've heard) on AC power, however when running on batteries and the batteries are partially discharged the amp starts turning on-off rapidly (constant LED though). I measured the batteries the last time it happened, they are discharged to 8.66 and 8.47V.
I think I've previously had a short from the outermost pin on J2 to the case, there were some buzzing on the left channel followed by the problem I'm having now when running on batteries when moving the amp and I don't think anything else were close enough to connect to the case. All pins near J2 are now cut almost flush to the board. R10 has also been touching S1 but is now clear both from S1 and R11.
What have I missed? I've been fiddling a lot with the amp to get it to work, I might have damaged some components just trying to get it to work properly. :-[
Philip
I have built my own O2, my first DIY amp, a process I really enjoyed. However, something is not completely right with it. I've had some issues with getting it to work, as it is right now it works pretty well and the sound is awesome!
It works without any audible problems (that I've heard) on AC power, however when running on batteries and the batteries are partially discharged the amp starts turning on-off rapidly (constant LED though). I measured the batteries the last time it happened, they are discharged to 8.66 and 8.47V.
I think I've previously had a short from the outermost pin on J2 to the case, there were some buzzing on the left channel followed by the problem I'm having now when running on batteries when moving the amp and I don't think anything else were close enough to connect to the case. All pins near J2 are now cut almost flush to the board. R10 has also been touching S1 but is now clear both from S1 and R11.
What have I missed? I've been fiddling a lot with the amp to get it to work, I might have damaged some components just trying to get it to work properly. :-[
Philip
Have you followed my faultfinding guide (link in post #1)
You need to understand how the PSU works... then you should be able to determine the issue.
The LED is used as a reference voltage... so that means in absolute terms that it fixes the on/off points. Different LED's have different forward voltages.
The voltage on pin 2 of U2 set the trip point. So if the LED is different to the original design spec then modifying R5 or R9 will alter the trip point (the low battery cut off)
R25, the 1.5meg is a vital component because it introduce "hysteresis" into the operation. This means that the comparator output should switch cleanly and not dither or jump between two states (which yours sounds to be doing).
Also, the comparator type will be critical to the circuit working correctly with the specified values, so make sure it is a genuine and correct device.
(link in post #1)You need to understand how the PSU works... then you should be able to determine the issue.
The LED is used as a reference voltage... so that means in absolute terms that it fixes the on/off points. Different LED's have different forward voltages.
The voltage on pin 2 of U2 set the trip point. So if the LED is different to the original design spec then modifying R5 or R9 will alter the trip point (the low battery cut off)
R25, the 1.5meg is a vital component because it introduce "hysteresis" into the operation. This means that the comparator output should switch cleanly and not dither or jump between two states (which yours sounds to be doing).
Also, the comparator type will be critical to the circuit working correctly with the specified values, so make sure it is a genuine and correct device.
Yeah, I must have read that page more than 20 times now, but I still learn something new everytime I do. I've followed the testing steps several times without finding anything outside the error margin.
Is the low battery cut-off voltages and imbalance normal, or is the imbalance a symptom of something wrong? According to the blog, it's not uncommon for the amp to behave the way mine do, but the problem should have been remedied by R25 being revised from 2.7M ohms down to 1.5M ohms and R9 from 40K down to 33K, which they are in my amp.
I've already ordered a new comparator, hoping that will solve the issues, but I don't think it's that simple due to the imbalance.
I've followed the testing steps several times without finding anything outside the error margin.Is the low battery cut-off voltages and imbalance normal, or is the imbalance a symptom of something wrong? According to the blog, it's not uncommon for the amp to behave the way mine do, but the problem should have been remedied by R25 being revised from 2.7M ohms down to 1.5M ohms and R9 from 40K down to 33K, which they are in my amp.
I've already ordered a new comparator, hoping that will solve the issues, but I don't think it's that simple due to the imbalance.
The low battery cut off point you can determine by measuring the LED voltage and then calculating the voltage needed to bring pin 2 of the comparator to that point. Once that threshold is crossed then the comparator should change state and stay put. It shouldn't oscillate between the two.
One thought... I wonder if poor batteries (high internal resistance) could cause something like this, as the load of the O2 is removed then the battery voltage jumps up more than might be expected.
I would doubt the comparator is faulty tbh, and assuming its the correct type and is what it is supposed to be.
You can always experiment with those resistor values a little more.
One thought... I wonder if poor batteries (high internal resistance) could cause something like this, as the load of the O2 is removed then the battery voltage jumps up more than might be expected.
I would doubt the comparator is faulty tbh, and assuming its the correct type and is what it is supposed to be.
You can always experiment with those resistor values a little more.
Did the new batteries fix the problem ?
That voltage doesn't sound right but it depends where you measure from. The comparator looks at both batteries in series and non of the comparator circuitry is ground referenced.
With the IC out of the socket you should have approximately 18 volts between pins 4 and 8 (total battery voltage) and approximately 2 volts on pin 2 when measured between pins 4 and pin 2.
That voltage doesn't sound right but it depends where you measure from. The comparator looks at both batteries in series and non of the comparator circuitry is ground referenced.
With the IC out of the socket you should have approximately 18 volts between pins 4 and 8 (total battery voltage) and approximately 2 volts on pin 2 when measured between pins 4 and pin 2.