Hi everyone!
I'm working on my first DIY audio project - the Objective2 amplifier.
I've done all the soldering and moved on to the initial testing section (NwAvGuy: O2 Details). I found a couple of issues and I'm not confident I'll be able to figure things out for myself, so any tips you can give me would be much appreciated!
The first thing I did was to check the resistances. I noticed that R16 was around 1.48kOhm instead of the 1.3kOhm it should have been, but I figured that might be within tolerance and moved on... All other resistances seemed close enough to what they should be.
Next I checked the wall transformer which seems to deliver 18.5V AC. I then checked the supply voltages by connecting my DMM across the outermost battery terminals and, with the power switch off (out), I connected the AC wall transformer. The DMM read 20V, when it should have read 23-24V. NwAvGuy says this is no good, so I disconnected the power supply again and scratched my head...
I had a look at the troubleshooting section, but it seems that most of it is concerned with O2s that have passed the stage I'm stuck at. The thing I'd like to check for is solder bridges, but I can't see any on the bottom of the board and on the top the larger components don't allow me to see underneath them to check what's going on.
If anyone can give me a hint on how to figure out what's gone wrong I'd be eternally grateful! My electronics/circuits knowledge is regrettably poor - my undergrad in physics touched on these things in a more fundamental than practical way, unfortunately. As it stands, I don't even know if the R16 issue and the 20V issue are likely to be related or not. Seems to me, naively, that R16 is quite far from the power management circuitry, but what the heck do I know...
Apologies for the wall of text! If I can provide any more information that might help you guys help me, do give us a shout.
Many thanks in advance for any input you're able to give!
-db
I'm working on my first DIY audio project - the Objective2 amplifier.
I've done all the soldering and moved on to the initial testing section (NwAvGuy: O2 Details). I found a couple of issues and I'm not confident I'll be able to figure things out for myself, so any tips you can give me would be much appreciated!
The first thing I did was to check the resistances. I noticed that R16 was around 1.48kOhm instead of the 1.3kOhm it should have been, but I figured that might be within tolerance and moved on... All other resistances seemed close enough to what they should be.
Next I checked the wall transformer which seems to deliver 18.5V AC. I then checked the supply voltages by connecting my DMM across the outermost battery terminals and, with the power switch off (out), I connected the AC wall transformer. The DMM read 20V, when it should have read 23-24V. NwAvGuy says this is no good, so I disconnected the power supply again and scratched my head...
I had a look at the troubleshooting section, but it seems that most of it is concerned with O2s that have passed the stage I'm stuck at. The thing I'd like to check for is solder bridges, but I can't see any on the bottom of the board and on the top the larger components don't allow me to see underneath them to check what's going on.
If anyone can give me a hint on how to figure out what's gone wrong I'd be eternally grateful! My electronics/circuits knowledge is regrettably poor - my undergrad in physics touched on these things in a more fundamental than practical way, unfortunately. As it stands, I don't even know if the R16 issue and the 20V issue are likely to be related or not. Seems to me, naively, that R16 is quite far from the power management circuitry, but what the heck do I know...
Apologies for the wall of text! If I can provide any more information that might help you guys help me, do give us a shout.
Many thanks in advance for any input you're able to give!
-db
Hi dasburnd and welcome to diyAudio.
Have a read at this that I put together. It should cover pretty much everything relating to the O2 (post#3775)
http://www.diyaudio.com/forums/head...eadphone-amp-diy-project-189.html#post3806667
Also, you can not measure resistances in circuit... its a totally non valid test method 🙂
Have a read at this that I put together. It should cover pretty much everything relating to the O2 (post#3775)
http://www.diyaudio.com/forums/head...eadphone-amp-diy-project-189.html#post3806667
Also, you can not measure resistances in circuit... its a totally non valid test method 🙂
DC voltage after rectifiers= your source voltage AC*1.3 E.g.: 18*1.3=23.4V
I use 18V AC source and 7815\7915 voltage regs without any problems.
So just to confirm, that means there's a problem, right? I should be seeing 23.4V and am only seeing 20V. Does that mean there's something wrong with the rectifiers, or is it not as simple as all that?
Thanks for the swift reply and the link - that thread looks like it's gonna be very helpful!
As for measuring resistances in circuit: yeah, I can see how you won't get the "right" (as in specified) resistance out, but I figured NwAvGuy knows this too and accounted for this in his diagram showing what resistances one should get when measuring them on the board. I was using this as a reference.
Follow the tests I set out. With S1 set to off and no batteries fitted you should see +12 volts dc across C6 and -12 volts dc across C7. That's keeping the black meter lead on ground for both measurements.
The readings in circuit will vary from meter to meter because of the different test currents and voltages that appear across the probes when measuring resistance. Its a totally non valid method. Also differences between the IC's from one batch to another will influence the results enormously.
And is it crucial that the regulators are removed from the circuit? I've soldered them in place, and my desoldering experience is rather limited... I think I could probably manage it, as I have access to one of those solder pump thingies, but if it's avoidable I'd rather not risk it.
Thanks for explaining that about the meters. Makes sense once you read it, but it would never have occurred to me spontaneously.
Don't remove anything at this stage. Just power it up and measure the voltages across those two caps (with S1 off). If you have -/+ 12 volts then all is well.
Right... well... All is definitely not well, it would seem...
I measured from ground to the striped end of D3 and got 22.5V, which seems ok according to your post. I then measured from ground to the non-striped end of D4 but got only -10.5V... I also noticed a strange hissing/bubbling sound emanating from the board, and when I investigated I found that C3 had started bulging and leaking. Bad times. But the good news is, I think I found my problem: Apparently after installing C4, C5, and C6, my brain decided this was easy and switched to auto pilot, resulting in me installing C3 backwards...
Now the question is: am I likely to have damaged anything else by having the board powered up with C3 installed the wrong way round, or will it be ok once I replace that cap?
Measure the voltage on the legs of one of two large resistors then add to it the voltage that you see.
Never mind about the voltage at the point where you measure it. If your opamp is not soldered into the board, then take them off and measure the voltage at pins 4 and 8. You will see the full scope of the supply voltage. In order to measure the voltage on the positive or negative bus you should measure the voltage between ground and terminal circuit 4 or 8 of any of the operational amplifiers. The supply voltage must be equal to the voltage regulator (7812 or 7912).
So I replaced that capacitor with an equivalent one and rechecked the voltages on the diodes. I'm getting -/+ 13.5V instead of -/+ 12V. Does that mean my regulators are faulty? D1 and D5 are definitely fitted the way they ought to be.
EDIT: The voltage across the outermost battery terminals is now 24V as it ought to be.
Last edited:
Ok so I now have the full 23.6V across between pins 4 and 8 of U2, but according to my BoM that's the comparator, not the op amp). U1, U3 and U4 all have 9.3V between pins 4 and 8. So does this mean my regulators are providing 9.3 volts? Is that acceptable? what should these values be at?
🙂 That's that little drama fixed... we've all done it 😀
-/+13.5 is out of tolerance but its strange that both supplies are out by the same amount... so we'll come to that later. (Two possibilities come to mind, firstly check the calibration of your meter, secondly, and this shouldn't really happen, the voltage is high with no load being present (yet))
Lets be exact... it helps with your understanding of it all. And it all sounds OK tbh so far.
D1 and D2 will drop around 650 millivolts each when conducting so that means if you have 23.6 volts across pins 4 and 8 of U2 then you should see (23.6 +0.65 + 0.65) which is a total of approximately 24.9volts across the two caps C6 and C7.
Up to now it all seems fine with the regulators. (U2 is a dedicated comparator but the symbol and basic operation is the same as an opamp. In fact you can use an opamp as a comparator with very little if any change to many circuits)
Next problem... you only have 9.3 volts between pins 4 and 8 of the other opamps.
So with S1 ON recheck the voltage between ground and pin 8 of U2 (should be around 12 volts) and between pins 4 and ground (should be around -12 volts). If that's OK then check the voltage across either C8 or C17. What is it ? Also check the voltage across C9 or C18. What is it ?
Right, with U2 in place and S1 ON, I get -/+11.8V between ground and pins 4 and 8 (respectively) of U2.
Across C8 I get 11.78V and across C9 I get -11.84V (although I might have got the signs wrong on those). Is that what I ought to be seeing?
I also just remeasured my voltages across pins 4 and 8 of the other IC sockets and I got 23.6V now. Popped U2 out again, and (with S1 on) it was 13.6V, then a little later it was down to 12V and seemed to be decaying slowly... I'm guessing this is capacitance at work, but I don't know if it's normal or not. In any case, with U2 in place it's at 23.6V, which sounds decent, no?
I did some more of the tests NwAvGuy suggests here, and there are "only" two discrepancies I found: ground to pin 7 of U2 (Q2 gate) reads 8.4V instead of 9.8V, and ground to pin 2 of U2 is at -8.9V instead of -8.4V... Any clues on how well/badly this bodes for my baby?
Thanks a ton for your help, btw, don't know what I'd do without you!! 😀
Those voltages sound fine. We'll assume they are the correct polarity 😀 The 79 series of regulators can do strange things with no or light loading so there is a good chance that accounts for the odd readings you have seen at times. With all the parts fitted that situation doesn't arise.
The outputs from the comparator sound OK so I would carry on with testing it all as a complete unit checking as you go by following the fault finding guide I linked to earlier. That also gives a couple of tests you can perform on the comparator action to prove its all working.
The outputs from the comparator sound OK so I would carry on with testing it all as a complete unit checking as you go by following the fault finding guide I linked to earlier. That also gives a couple of tests you can perform on the comparator action to prove its all working.
So I completed the testing and everything seems to check out so far.
Now I'm just waiting on a male to male 3.5mm cable to go on my maiden voyage. I tried to buy one in ye local audio shoppe, but they only had high-end £5 cables, so I think I'll try somewhere else with less extortionate cables.
Thanks once again for all your help!
Now I'm just waiting on a male to male 3.5mm cable to go on my maiden voyage. I tried to buy one in ye local audio shoppe, but they only had high-end £5 cables, so I think I'll try somewhere else with less extortionate cables.
Thanks once again for all your help!
Just now listening for the first time through my lovely O2! Sounds a treat!!
Many thanks for all your help - this has been a really fun project, and I doubt I'd have been able to do it without you. Call me a DIYaudio convert. 🙂
Many thanks for all your help - this has been a really fun project, and I doubt I'd have been able to do it without you. Call me a DIYaudio convert. 🙂
- Status
- Not open for further replies.