I’m fond of RGB LEDs, so it would be RGB led with 3 trimer pots to adjust any color that’s in fashion.
I expect that some of those that decided to build this buffer, could receive PCBs soon. Here are comments on assembly, that I hope could be of some help.
4 layers PCB absorbs more heat than ordinary 2 layers one. Soldering iron temperature should be elevated by +30 degrees Celsius from your standard value for all components except ICs. OPA828 should be soldered at standard non-elevated temperature.
OPA551 and LME use PCBs’ copper area as heatsink. Therefore, there are no thermal reliefs around them for easy soldering. For soldering TO-263 metal tab, use fat chisel or knife tip with at least 400 degrees temperature. Even with that, it is expected to take 5 -10 seconds to melt solder properly. It is perfectly enough to solder only upper edge of TO-263 metal tab. While soldering OPA551 and LME, first solder their legs(with ‘standard’ temperature) for all three chips. Than exchange soldering iron tip, crank up the temp. and solder their metal tabs. Flux is necessary.
Parts soldering order: all resistors, OPA551 & LME, OPA828, ceramic capacitors, film capacitor (220 pF), LM329, electrolytic capacitors, RCA socket.
4 layers PCB absorbs more heat than ordinary 2 layers one. Soldering iron temperature should be elevated by +30 degrees Celsius from your standard value for all components except ICs. OPA828 should be soldered at standard non-elevated temperature.
OPA551 and LME use PCBs’ copper area as heatsink. Therefore, there are no thermal reliefs around them for easy soldering. For soldering TO-263 metal tab, use fat chisel or knife tip with at least 400 degrees temperature. Even with that, it is expected to take 5 -10 seconds to melt solder properly. It is perfectly enough to solder only upper edge of TO-263 metal tab. While soldering OPA551 and LME, first solder their legs(with ‘standard’ temperature) for all three chips. Than exchange soldering iron tip, crank up the temp. and solder their metal tabs. Flux is necessary.
Parts soldering order: all resistors, OPA551 & LME, OPA828, ceramic capacitors, film capacitor (220 pF), LM329, electrolytic capacitors, RCA socket.
Is hot plate + smd paste + hot air station intended soldering method?
Those large TO-263 SMD parts are soldered easily with soldering iron. It only takes some time for metal tab. I have hot air station and both low and standard temperature SMD paste, but decided to solder in classic way.
For hot plate I use old Teflon coated frying pan and portable cooking plate.
Those large TO-263 SMD parts are soldered easily with soldering iron. It only takes some time for metal tab. I have hot air station and both low and standard temperature SMD paste, but decided to solder in classic way.
For hot plate I use old Teflon coated frying pan and portable cooking plate.
If you really must, three corners could be drilled with no harm. Lower right corner has one track too close. However, nonconductive standoffs and screws must be used to avoid short circuiting three PCB layers. I would rather make PCB revision with mounting holes if that is more convenient mounting method. Using RCA socket for putting PCB in place also provides that no input cable is required and minimizes EMI noise pickup.
Yeah, my plan would be to use plastic shoulder washers to insulate the machine screw from the internal copper layers. But, I’m too concerned the actual drilling could cause issues with the internal copper layers. I’ve decided not to drill them.
Maybe for future builders you could modifiy the Gerbers and add M3 holes for additional mounting options.
Some progress……
Maybe for future builders you could modifiy the Gerbers and add M3 holes for additional mounting options.
Some progress……
Attachments
I have already prepared modified PCBs. It’s a minor modification.
One remark on LM329. They have up to 0.3 V tolerance. So, you could end with 0.6 V difference between rails. It is of absolutely no consequence. All published measurements were done on buffer with 0.5 V rails difference. Afterwards, checking batch of 10 LM329, I easily found 3 pairs that had only several mV difference.
One remark on LM329. They have up to 0.3 V tolerance. So, you could end with 0.6 V difference between rails. It is of absolutely no consequence. All published measurements were done on buffer with 0.5 V rails difference. Afterwards, checking batch of 10 LM329, I easily found 3 pairs that had only several mV difference.
As only 30 minutes more is required to finish both input buffers, I suspect that first test is imminent.
Don’t connect both buffer grounds. You can chose to connect ground to the PS, along with positive and negative rail input. In that case, connect only single output wire to the transformer input.
Or, connect both outputs - signal and ground, to the amp PCB, and only supply input rails to the amp PS. Ground will be provided through amplifier board.
Don’t connect both buffer grounds. You can chose to connect ground to the PS, along with positive and negative rail input. In that case, connect only single output wire to the transformer input.
Or, connect both outputs - signal and ground, to the amp PCB, and only supply input rails to the amp PS. Ground will be provided through amplifier board.
Hmmm…. 30 minutes? I must be a dilly dallier 😂
Thanks for confirming the GND connection without me asking, and also about the possibility of voltage difference between rails due to the Lm329 tolerance.
I’ve been thinking about a way to use this buffer with single rail power supply amps, like MoFo. A DC/DC converter could be used to output
+/-V required for the buffer from a +V amplifier supply.
Thanks for confirming the GND connection without me asking, and also about the possibility of voltage difference between rails due to the Lm329 tolerance.
I’ve been thinking about a way to use this buffer with single rail power supply amps, like MoFo. A DC/DC converter could be used to output
+/-V required for the buffer from a +V amplifier supply.
Yeah, I'm a bit longer than 30 minutes. I got most of it finished today with a few caps for tomorrow. Soldering the opamps wasn't hard at all.
I think my Aliexpress RCA jacks are in town. Here's hoping they get delivered in the next couple of days so I can finish and try out the buffers.
I think my Aliexpress RCA jacks are in town. Here's hoping they get delivered in the next couple of days so I can finish and try out the buffers.
