Just opened a new GB thread: Omicron 3rd GB. I took the liberty of signing up @Brakspear75 and @drof - feel free to correct the sign-up list if I made a mistake. The GB will close on Sunday, June 2, 2024. Be sure to sign up before then.
That's not a difficult load. Omicron's through-hole version in its stock version runs at 50mA quiescent current. It will stay in Class A while delivering 200mW peak into 25 ohm. The SMT version runs at 25 mA. It will leave Class A at about 60mW peak into 25 ohm, but even then Omicron will stay more linear than the vast majority of headamps.
Here are link to the updated Mouser projects for Omicron TH and SMT versions:
Omicron TH - Mouser shared project
Omicron SMT - Mouser shared project
The projects have been updated to the current availability of the parts. Note that all relays are currently available from Mouser.
I added these links to the first post of this thread as well.
Omicron TH - Mouser shared project
Omicron SMT - Mouser shared project
The projects have been updated to the current availability of the parts. Note that all relays are currently available from Mouser.
I added these links to the first post of this thread as well.
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Shared Mouser project for the PSU board
Does not include the power transformer (see post #174). Also, the project includes the heatsinks and the (optional) thermal pads, but not the hardware (2x M3x8 screws, 2x M3 nuts and washers) to attach the TO-220 regulators to the heatsinks.
Does not include the power transformer (see post #174). Also, the project includes the heatsinks and the (optional) thermal pads, but not the hardware (2x M3x8 screws, 2x M3 nuts and washers) to attach the TO-220 regulators to the heatsinks.
The Omicron power supply PCB has its own LCR filter on the primary side of the transformer, so filtered IEC inlet is not necessary.
The maximum power drawn by the Omicron (under somewhat unrealistic condition of delivering 30Vpp into a 32 ohm load) is about 10W. With 110VAC primary, a 0.5A or even 0.25A slow-blow fuse should be ok. It is also possible to omit a separate fuse and use fusible resistors in that primary-side filter, or to use short-circuit-protected transformer (e.g. BLOCK FLD).
The maximum power drawn by the Omicron (under somewhat unrealistic condition of delivering 30Vpp into a 32 ohm load) is about 10W. With 110VAC primary, a 0.5A or even 0.25A slow-blow fuse should be ok. It is also possible to omit a separate fuse and use fusible resistors in that primary-side filter, or to use short-circuit-protected transformer (e.g. BLOCK FLD).
R3,R4 are missing in shared mouser project and i saw this.
Please let me know the value of R3, R4 for Talema 70054K?
Attachments
Hi ,
I just completed about half of the build. When I powered on the amp board for the first time, the LED dimmed and then started to blink. I immediately shut off the power.
After a few seconds, I powered on the amp again. This time, the LED was bright initially but dimmed after 2-3 seconds.
And then, I tried again, the LED stayed dim. Now, it remains dimmed consistently.
Not sure if any part has cooked, but there's no magic smoke or any sound, all the part seems cold.
Not sure if I solder the wrong part or wrong position, maybe some clever guy will help me out of this.
I just completed about half of the build. When I powered on the amp board for the first time, the LED dimmed and then started to blink. I immediately shut off the power.
After a few seconds, I powered on the amp again. This time, the LED was bright initially but dimmed after 2-3 seconds.
And then, I tried again, the LED stayed dim. Now, it remains dimmed consistently.
Not sure if any part has cooked, but there's no magic smoke or any sound, all the part seems cold.
Not sure if I solder the wrong part or wrong position, maybe some clever guy will help me out of this.
Nice build!
Dim LED means DC at the output of one of two channels. Check voltages at the point where R15 R16 connect, and where R35 R36 connect. Both should be a couple of millivolts, but in your case one will be high. Since the voltage drop across R15 R16 is normal and U21 is hot, I suspect the voltage at the connection of R35 R36 will be high.
Pins 3 and 7 on U21 are connected on the board - see the schematic. Pin 7 is the output of one half of the chip, pin 3 is the non-inverting input of the other half. So the connection between them should be there by design and is not a problem.
With power off, check the board visually and/or with a DMM for shorts, esp. between pins 1 and 7 of the opamps (their outputs) and power rails. I suspect a short between pins 7 and 8 of U21. Also, check the power supply voltages (without Omicron connected). We will take it from there.
Dim LED means DC at the output of one of two channels. Check voltages at the point where R15 R16 connect, and where R35 R36 connect. Both should be a couple of millivolts, but in your case one will be high. Since the voltage drop across R15 R16 is normal and U21 is hot, I suspect the voltage at the connection of R35 R36 will be high.
Pins 3 and 7 on U21 are connected on the board - see the schematic. Pin 7 is the output of one half of the chip, pin 3 is the non-inverting input of the other half. So the connection between them should be there by design and is not a problem.
With power off, check the board visually and/or with a DMM for shorts, esp. between pins 1 and 7 of the opamps (their outputs) and power rails. I suspect a short between pins 7 and 8 of U21. Also, check the power supply voltages (without Omicron connected). We will take it from there.
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Hi Alex,
Thanks for the help!
To apology that, I'm totally green hand when reading the schematic and using DMM... Found that you are right, the pin 3 and pin 7 are connected.
But I measured the pin3 and pin7 on U1, is not connected. Should be the problem of the parts?
Measured Pin 7 and 8 on U21 it seems not shorted.
I measured the power supply voltage, whichc is +16.4V and -16.28V. Seems normal to me.
But now I wonder, when using continuity test mode on dmm, I got all the lead shorted on both R15, R16 and R35, R36. Is this normal?
The attached pic shows the simplified schematic, I can have shorted on any two of these leads. Is that normal?
Thanks for the help!
To apology that, I'm totally green hand when reading the schematic and using DMM... Found that you are right, the pin 3 and pin 7 are connected.
But I measured the pin3 and pin7 on U1, is not connected. Should be the problem of the parts?
Measured Pin 7 and 8 on U21 it seems not shorted.
I measured the power supply voltage, whichc is +16.4V and -16.28V. Seems normal to me.
But now I wonder, when using continuity test mode on dmm, I got all the lead shorted on both R15, R16 and R35, R36. Is this normal?
The attached pic shows the simplified schematic, I can have shorted on any two of these leads. Is that normal?
Attachments
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On U1, pins 1 and 5 are connected instead - it is oriented differently on the board, so its halves are connected differently.
You're right, power supply voltages are normal.
R16 R16 R35 R36 are small value resistors. They should measure 2.2ohms when measuring resistance, but in the continuity testing mode, most DMMs will consider then small enough to a short and will beep, indicating continuity.
If you have U21 smoking, it means it draws too much current. This usually happens if one of its outputs is shorted to a power rail. (Shorting it to the ground is safe, plus there are no ground traces close by on the board.) This can happen, for example, if there is a small ball of solder between pins 7 and 8 - 7 is an output and 8 is the positive supply. There are other possibilities, e.g. one of the output transistors is wrong polarity - if you install PNP instead of NPN or vice versa, the opamp output will be connected to the power rail via a small resistor, an diode, and the emitter junction of that transistor. Note that NPNs (Q1 and Q21) are closer to the edges of the board while PNPs (Q2 and Q22) are closer to the middle.
Try checking the board for shorts.
You're right, power supply voltages are normal.
R16 R16 R35 R36 are small value resistors. They should measure 2.2ohms when measuring resistance, but in the continuity testing mode, most DMMs will consider then small enough to a short and will beep, indicating continuity.
If you have U21 smoking, it means it draws too much current. This usually happens if one of its outputs is shorted to a power rail. (Shorting it to the ground is safe, plus there are no ground traces close by on the board.) This can happen, for example, if there is a small ball of solder between pins 7 and 8 - 7 is an output and 8 is the positive supply. There are other possibilities, e.g. one of the output transistors is wrong polarity - if you install PNP instead of NPN or vice versa, the opamp output will be connected to the power rail via a small resistor, an diode, and the emitter junction of that transistor. Note that NPNs (Q1 and Q21) are closer to the edges of the board while PNPs (Q2 and Q22) are closer to the middle.
Try checking the board for shorts.
It turns out that I use too much flux. After the power up, the U21 is getting hotter, the flux gradually melt and connect the pins, lead to malfunction.
Replace both of the NE5532 did help and the DC offsec now is 1.3 and 1.7 mV which is pretty low.
Here's some pictures of the build, the alumium case is custom made(R&F panel) from China and it is relatively checp ~25 USD(volume knob & IEC jack & CNC processing fee included)
Some parts are 3D printed, especially the toggle switch, there's no bracket for that.
The Omicron is a fantastic headphone amp and preamp, the background is more black and bass is more deeper and puncher. Also the clearity is absoluly amazing, the vocal is no doube much clear from the track "Mistakes from Lake Street Dive" than before.
And the crossfeed did something, especially from older track or some track that the musical instrument sounds are more biased toward the left and right channels. Toggle on the crossfeed makes the soundstage a bit wider and the sound is no more at the front but a bit lay back, more natural.
Thanks to bring this great project for us, Alex!