Yes, any of those diodes will work OK.
Just try and understand what is happening and I would be surprised if the diode was faulty tbh. If D5 were faulty then you would still get minus 12 volts on the "stripey" end. That is the end that goes to the regulator. Is it in the right way around ?
At the left of the circuit you have AC voltage coming in. D3 generates a positive DC voltage from this and D4 a negative voltage.
So are they present ? With the meter connected as we mentioned earlier, there must be at least plus 15 volts going into pin 1 of the 7812 and at least minus 15 volts going into pin 2 of the 7912.
Are those voltages present and OK ?
If they are then measure on pin 3 of both regulators and make sure that the plus and minus 12 volts are present.
Its as likely that there could be a break or damage to the print on the board as a faulty component at this stage.
Just try and understand what is happening and I would be surprised if the diode was faulty tbh. If D5 were faulty then you would still get minus 12 volts on the "stripey" end. That is the end that goes to the regulator. Is it in the right way around ?
At the left of the circuit you have AC voltage coming in. D3 generates a positive DC voltage from this and D4 a negative voltage.
So are they present ? With the meter connected as we mentioned earlier, there must be at least plus 15 volts going into pin 1 of the 7812 and at least minus 15 volts going into pin 2 of the 7912.
Are those voltages present and OK ?
If they are then measure on pin 3 of both regulators and make sure that the plus and minus 12 volts are present.
Its as likely that there could be a break or damage to the print on the board as a faulty component at this stage.
D3 measures +24DCV and D4 measures -24.7DCV.
7912 measures -22.7VDC, and 7812 measures +24VDC.
Pin 3 on 7812 measures +11.9 and 7912 measures +1.1. I have checked several times and got the same result each time.
I have one last set if questions.
I am planning to add the low power option op amps into my amplifier because the higher run time is more appealing to me then power i'll never use. I am set on changing the output impedance to 3.4 ohms as suggested by NwAvGuy, but i'm wondering about any other modifications that must be done.
The low power option kit came with the 6.8ohm resistors for R10, R11, R15 and R19, two BC101, two 2k and 3k ohm resistors (that double the value of R17, R21, R16 and R22 if i'm not mistaken) and 2 RN550. Are all of these neccessary to add or can I leave them out (especially the gain resistors to keep the gain at 1x)?
I am planning to add the low power option op amps into my amplifier because the higher run time is more appealing to me then power i'll never use. I am set on changing the output impedance to 3.4 ohms as suggested by NwAvGuy, but i'm wondering about any other modifications that must be done.
The low power option kit came with the 6.8ohm resistors for R10, R11, R15 and R19, two BC101, two 2k and 3k ohm resistors (that double the value of R17, R21, R16 and R22 if i'm not mistaken) and 2 RN550. Are all of these neccessary to add or can I leave them out (especially the gain resistors to keep the gain at 1x)?
I've not seen the low power option for this design (and I've never built the amp either, but just seem to have ended up answering most of the questions lately 
)
Do you have a link to the low power option ?
As regards power consumption, non of the gain setting resistors or those output resistors will alter the current draw under quiescent conditions. That's because there is no DC voltage present across any of these. Only under dynamic conditions does voltage appear (the signal) and power savings by altering the feedback and gain setting values will be minimal imo. The big power savings would come from the replacement opamps (whatever they are)
What is a BC101 and RN550 ?
)Do you have a link to the low power option ?
As regards power consumption, non of the gain setting resistors or those output resistors will alter the current draw under quiescent conditions. That's because there is no DC voltage present across any of these. Only under dynamic conditions does voltage appear (the signal) and power savings by altering the feedback and gain setting values will be minimal imo. The big power savings would come from the replacement opamps (whatever they are)
What is a BC101 and RN550 ?
The link doesn't show the extra parts it comes with, but the op amps it uses are OPA2277 to replace the NJM2068, and 2 TLE2062 to replace the NJM4556.I've not seen the low power option for this design (and I've never built the amp either, but just seem to have ended up answering most of the questions lately
Do you have a link to the low power option ?
As regards power consumption, non of the gain setting resistors or those output resistors will alter the current draw under quiescent conditions. That's because there is no DC voltage present across any of these. Only under dynamic conditions does voltage appear (the signal) and power savings by altering the feedback and gain setting values will be minimal imo. The big power savings would come from the replacement opamps (whatever they are)
What is a BC101 and RN550 ?
BC101 is a ceramic capacitor that I believe replaces C6 and C7, and the RN550 I have no information on as I don't know what the part is suppose to replace. Google searches list it as a metal film resistor.
OK...
So C6 and C7. These are just local rail decoupling caps for the regulators. On battery they do nothing and are out of circuit (isolated by D1 and D5).
I've no idea on the resistor either tbh, at least not without knowing its circuit reference.
Your power saving gains all come from the opamps... the TLE2062 is an interesting choice.
So C6 and C7. These are just local rail decoupling caps for the regulators. On battery they do nothing and are out of circuit (isolated by D1 and D5).
I've no idea on the resistor either tbh, at least not without knowing its circuit reference.
Your power saving gains all come from the opamps... the TLE2062 is an interesting choice.
Okay so now that I know the other components are optional, what about the 6.8 ohm resistors?
In NwAvGuy's blog he claimed they reduced the dc offset to increase the battery life, I am just trying to understand how they increase the battery life. I am also noticed a larger turn off transient using the low power op amps which is why I am asking if any of these parts were necessary.
In NwAvGuy's blog he claimed they reduced the dc offset to increase the battery life, I am just trying to understand how they increase the battery life. I am also noticed a larger turn off transient using the low power op amps which is why I am asking if any of these parts were necessary.
The 6.8 ohm are just "series output resistors" and have no direct effect on battery life.
They do isolate the opamp output from the load and help in keeping the opamps stable with any capacitive loading that may be present. Its common for opamps to oscillate at very high frequency when loaded by a small capacitance at the output. Perhaps that is what he was thinking of.
Also, they reduce the efficiency of the design. Because they are in series with the headphone it means some signal is lost across the resistors (like ohms law). The advantage of that is that the intrinsic noise level from the amp is subjectively attenuated too. So perhaps he was thinking along those lines as well.
The DC offset should be non existent with the TLE2062 because its a FET device and doesn't suffer from offset caused by input bias currents (like the original opamps). You could measure that for interest.
They do isolate the opamp output from the load and help in keeping the opamps stable with any capacitive loading that may be present. Its common for opamps to oscillate at very high frequency when loaded by a small capacitance at the output. Perhaps that is what he was thinking of.
Also, they reduce the efficiency of the design. Because they are in series with the headphone it means some signal is lost across the resistors (like ohms law). The advantage of that is that the intrinsic noise level from the amp is subjectively attenuated too. So perhaps he was thinking along those lines as well.
The DC offset should be non existent with the TLE2062 because its a FET device and doesn't suffer from offset caused by input bias currents (like the original opamps). You could measure that for interest.
And what about the turn off transient? I have no way of measuring how loud it is, but instead of a soft thump like on the original opamps its a louder distorted noise. I don't think it is enough to damage my headphones, but paired with another noise it might be a different story. Could the high frequency oscillation be related to this noise or am I misunderstanding?
I know I am asking a lot of questions, but i'm not an engineer and have little to no understanding of these relatively common things.
I know I am asking a lot of questions, but i'm not an engineer and have little to no understanding of these relatively common things.
No problem... ask as many questions as you want
Switch on/off noises can be problematic and there is no quick fix for this unfortunately because its inherent to the design and it happens because of a number of reasons. When the power is applied, the rails don't rise at the same rate, and when its powered off they don't collapse at the same rate either. That means that for an instant the opamp sees one or other rail at a value that is to low for it to work correctly with. You get a significant offset, and you hear that as a pop or thump.
Don't confuse that with "unbalanced rails" though. A rail of +10 and -5 or +5 and -10 won't cause any DC offset. We are talking about the milliseconds the rails take to rise from zero to a high enough voltage for the device to work and the time for the rails to collapse... the time the opamps see a voltage to low to work with.
So I'm afraid there is no easy answer or fix short of building an add on muting circuit (to clamp the output to ground), but that would be no small design challenge to do it with essentially zero power consumption.
Bottom line is that the switch on/off behaviour hasn't been considered in the original design.
I'll be back later on today (8am here) if you think of anything else
Switch on/off noises can be problematic and there is no quick fix for this unfortunately because its inherent to the design and it happens because of a number of reasons. When the power is applied, the rails don't rise at the same rate, and when its powered off they don't collapse at the same rate either. That means that for an instant the opamp sees one or other rail at a value that is to low for it to work correctly with. You get a significant offset, and you hear that as a pop or thump.
Don't confuse that with "unbalanced rails" though. A rail of +10 and -5 or +5 and -10 won't cause any DC offset. We are talking about the milliseconds the rails take to rise from zero to a high enough voltage for the device to work and the time for the rails to collapse... the time the opamps see a voltage to low to work with.
So I'm afraid there is no easy answer or fix short of building an add on muting circuit (to clamp the output to ground), but that would be no small design challenge to do it with essentially zero power consumption.
Bottom line is that the switch on/off behaviour hasn't been considered in the original design.
I'll be back later on today (8am here) if you think of anything else
Is there a way to test the output of a dac using a dmm? I want to optimize the gain on my amplifier to have enough output for my ipod but not clip into my dac on ac power. The specifications of my Audioquest Dragonfly say 2vrms output, but I had to lower the volume on my pc to 90% so it won't clip. I'm not sure if you've heard of this dac but it claims to control volume by hijacking the volume control on your computer and use its 64 bit volume chip, but the creator only used 60 of the 64 steps causing the last 4 steps to clip into high impedance loads like my amplifier. Don't ask me how that works, i'm just quoting AudioQuest DragonFly USB D/A converter Measurements | Stereophile.com but I can say for certain that I notice noise above 90% volume which could be something else for all I know.
You bet! Play a sine wave from the internet, like this one
1000 Hz / 1 kHz Sine Wave Audio Frequency Test Tone - YouTube
into the DAC while measuring the output on the Volts AC setting of your DMM.
A few things to note though. The frequency of the sine wave has to be within what your meter can measure on the AC range. The link above is for 1kHz, which may be higher than some meters can accurately measure. You specifications table in the meter instructions will say. If you need a lower frequency just Google - there are sine wave tones for just about anything out there.
If your meter is capable of reading true RMS on the AC range then you can multiply that reading by 1.404 to find the peak level of the sine wave (top and bottom of the sine wave). If your meter is average reading rather than true RMS multiply by 1.56 for the peaks.
I have a pretty low quality dmm so I am assuming mine can only accurately measure 60-100hz? Also do I just put both probes connected to a headphone wire or directly on the output jack of the dac, or do I only use the red probe and ground the black probe?
I have never done measurements like these, and my dac already has problems so I don't want to make any of them worse.
Most meters should be good for at least 400Hz but a bigger problem could be the resolution at low levels. Its meter specific and so you would have to try it. You won't damage any small signal circuitry by measuring voltages, even if you accidently short it to ground. Assuming the DAC is a single ended (a normal) output then black lead on ground and red on the output.
I can measure it from a headphone cable right? connecting the probe to the dac in the back of my computer is difficult