I'm checking the sizes on the PCB again.
Look at the cluster of resistors at bottom left (R5, R28, R4). They measure only 7mm between drill holes.Now look at R19 and R13 just above and to the right. They are 10mm and would be fine. It hard to see on the picture which are 7 and which are 10 but there are a quite a few at 7mm.
The 0.22 ohms are 15mm spacing and that would "just" take the vitreous enamel type I used (and they are small) but would be a more comfortable fit with around 18mm or more for the larger "box" type low value resistor.
A good quality 1000uf/63v comes in at around 18mm diameter. The board is for 10mm.
Oh Alex
I really do feel awful coming out with that but it would be a real issue.
Look at the cluster of resistors at bottom left (R5, R28, R4). They measure only 7mm between drill holes.Now look at R19 and R13 just above and to the right. They are 10mm and would be fine. It hard to see on the picture which are 7 and which are 10 but there are a quite a few at 7mm.
The 0.22 ohms are 15mm spacing and that would "just" take the vitreous enamel type I used (and they are small) but would be a more comfortable fit with around 18mm or more for the larger "box" type low value resistor.
A good quality 1000uf/63v comes in at around 18mm diameter. The board is for 10mm.
Oh Alex
I really do feel awful coming out with that but it would be a real issue.
Talking out loud now while looking at the PCB...
Do we need fuses onboard ? These could be in the PSU/chassis and that would free up a lot of space.
The two mounting holes in the middle of PCB. Are they needed ? We could gain a millimeter or two there and increase the spacing between the 0.22 ohms a little.
The feedback resistor, output series resistor and coil. The important component is really the 0.22 ohm series output resistor. I would suggest the coil could be dispensed with for all practical purposes. The resistor alone should be sufficient to protect from capacitive loading which is really something that is done deliberately for testing purposes. Removing the coil would allow the resistor to be fitted and for the feedback (R14/22K) to straddle across the two tracks and connect to what would become a spur feeding the output series resistor.
A couple more millimeters board height would allow the grounds from the rail caps to have there own print run and ground terminal. The input ground could then be separate.
Most of the 7mm resistor spacings should be easy to increase to 10mm.
Do we need fuses onboard ? These could be in the PSU/chassis and that would free up a lot of space.
The two mounting holes in the middle of PCB. Are they needed ? We could gain a millimeter or two there and increase the spacing between the 0.22 ohms a little.
The feedback resistor, output series resistor and coil. The important component is really the 0.22 ohm series output resistor. I would suggest the coil could be dispensed with for all practical purposes. The resistor alone should be sufficient to protect from capacitive loading which is really something that is done deliberately for testing purposes. Removing the coil would allow the resistor to be fitted and for the feedback (R14/22K) to straddle across the two tracks and connect to what would become a spur feeding the output series resistor.
A couple more millimeters board height would allow the grounds from the rail caps to have there own print run and ground terminal. The input ground could then be separate.
Most of the 7mm resistor spacings should be easy to increase to 10mm.
Something like this
The output is a spur from the main line with the feedback sampling that point. Very few amplifiers get this point correct. The trouble with sampling on a "line"between the output devices is that the speaker feed has to be "somewhere else" and only the feedback take off point is a true representation of the amplifier output due to the resistance of the PCB print. Its a small detail that Doug Self outlined in his series on distortion mechanisms in amplifiers. The feedback resistor can straddle the two traces as shown.
The output is a spur from the main line with the feedback sampling that point. Very few amplifiers get this point correct. The trouble with sampling on a "line"between the output devices is that the speaker feed has to be "somewhere else" and only the feedback take off point is a true representation of the amplifier output due to the resistance of the PCB print. Its a small detail that Doug Self outlined in his series on distortion mechanisms in amplifiers. The feedback resistor can straddle the two traces as shown.
Attachments
What about the Power Ground, +ve & -ve connections?
Should they all be along the low level signal side, or should all three be moved to the other side of the PCB, alongside the high current level devices?
And even better, all three located next to the speaker output. Just where that silly speaker symbol is printed !
Should they all be along the low level signal side, or should all three be moved to the other side of the PCB, alongside the high current level devices?
And even better, all three located next to the speaker output. Just where that silly speaker symbol is printed !
Hi Andrew,
I don't forsee a problem with the connector position tbb. The space where the speaker symbol is, is where I would rotate the connector to allow for the alternate NFB feed. Can't see any electrical issue with having the -45v rail and a ground running together.
I haven't had chance to check it all pad for pad yet but it looks good thus far (particularly if Alex could tweak the speaker output thingy)
I don't forsee a problem with the connector position tbb. The space where the speaker symbol is, is where I would rotate the connector to allow for the alternate NFB feed. Can't see any electrical issue with having the -45v rail and a ground running together.
I haven't had chance to check it all pad for pad yet but it looks good thus far (particularly if Alex could tweak the speaker output thingy
)One rail, either positive or negative carries half wave versions of the output.
A single rail parallel to a ground return will cancel on those halfwaves. IF the currents in the two opposite directions are the same.
How do you make the current values equal and opposite with that layout?
Why put those unbalanced currents so close to the input stage?
Alex has not thought about the current flows in each of the circuits, while laying out his PCB. He has the same fault repeatedly in almost all his PCB layouts. Single current flows not associated (near) the return current flow in many of the circuits on the PCB.
A single rail parallel to a ground return will cancel on those halfwaves. IF the currents in the two opposite directions are the same.
How do you make the current values equal and opposite with that layout?
Why put those unbalanced currents so close to the input stage?
Alex has not thought about the current flows in each of the circuits, while laying out his PCB. He has the same fault repeatedly in almost all his PCB layouts. Single current flows not associated (near) the return current flow in many of the circuits on the PCB.
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Take a dayglow pen and trace out the +ve current flow of a pulse to the speaker. Trace out the complete route from the OUTPUT device out of the PCB via SPKR OUT to the Speaker and then back through the Power Ground, via the MAG, to the device that originated the pulse.
Repeat the trace on fresh paper for a negative pulse to the speaker and remember that pulse MUST COME BACK to source device.
Repeat the trace on fresh paper for a negative pulse to the speaker and remember that pulse MUST COME BACK to source device.
I think the reality will be that the effect is negligable. The two crucial points are that "the two points of reference for the amplifier", the feedback take off and the feedback return are correct. I don't see any practical problem with the routing of the power lines and ground in all honesty.
Hi,
I'll side with Andrew regarding the layout. Most commercial amp designs usually have minimized current loops, PCB and wires, because it simply pays back in greater performance.
One diy example could be symasym by Mike Bittner. Here: SymAsym5 - Project (under Miscellaneous) he testifies that a shorter power GND reduces distortion. More care along these lines cannot be wrong I think.
I'll side with Andrew regarding the layout. Most commercial amp designs usually have minimized current loops, PCB and wires, because it simply pays back in greater performance.
One diy example could be symasym by Mike Bittner. Here: SymAsym5 - Project (under Miscellaneous) he testifies that a shorter power GND reduces distortion. More care along these lines cannot be wrong I think.
Where's C4
I've just done a first pad to pad check and it all looks good although I can't find C4
A 47uf cap across R4. This can be a miniature 16 volt electro as it never sees more than a couple of volts across it. I think there's room but if not then worst case and it can be piggybacked across the 22K, something many big manufacturers do often.
I've just done a first pad to pad check and it all looks good although I can't find C4
A 47uf cap across R4. This can be a miniature 16 volt electro as it never sees more than a couple of volts across it. I think there's room but if not then worst case and it can be piggybacked across the 22K, something many big manufacturers do often.
No Sir, this is not the way.
By staying, all of us will be learning, day by day, a bit more.
After all, everybody knows that even a capacitor orientation over the PCB, or a circular track down under, play an intriguing role.
Please reconsider.
Alex, I think you do a great job, and I am appreciative becasue without seeing the work you did before, ... I would never have made the proposal to buy the pcbs, which got this pcb project started a few days ago. I appreciate the work you did, and hope you can reconsider to stay to the end, because without some like you, I do not believe there will be anyone else stepping up to the plate to do the design.
I wish I knew how to do this pcb planning, but all I can do as a relative beginnier is stuff the boards and construct the amps.
thanks again, John
I wish I knew how to do this pcb planning, but all I can do as a relative beginnier is stuff the boards and construct the amps.
thanks again, John
Alex,
Any one creating something good will always attract attention.
Some will be trying to criticise in jealousy, some with ego, and a few who are trying to make it 'perfect', adding their input.
I have designed pcbs for more years I can admit and you have a supernatural aptitude. You have done wonderful help for many DIYaudio people, and you seem to be very, very quick. If you walk away you will be badly missed here, think about it carefully. Most people will praise your work, and now and again that might even tell you..... that's a nice feeling!
Ciao,
Hugh
Any one creating something good will always attract attention.
Some will be trying to criticise in jealousy, some with ego, and a few who are trying to make it 'perfect', adding their input.
I have designed pcbs for more years I can admit and you have a supernatural aptitude. You have done wonderful help for many DIYaudio people, and you seem to be very, very quick. If you walk away you will be badly missed here, think about it carefully. Most people will praise your work, and now and again that might even tell you..... that's a nice feeling!
Ciao,
Hugh
It seems that these guys from Romania always use to do an awesome job!
Timotei Jinar | Wedding and Commercial films
Timotei Jinar | Wedding and Commercial films
Firstly, I too would like to extend my thanks to Alex for his excellent PCB work. Like Hugh (AKSA), I have been making PCB's for many years although my big problem that I am a relative newcomer to the world of computer software to help with the job. To see the speed that Alex can produce something like this amazes me too.
I hope on reflection that you'll reconsider Alex
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I think it would also be a good idea for us all to take a step back and just make sure that everyone knows what this project entails...
One thing that no one has asked about or mentioned is a switch on delay (speaker relay). This is mentioned in the thread and is mandatory to avoid switch on thumps. There's no way round that, its a function of the single ended design and biasing. So that is something that is needed whether it is a kit or diy. To diy it is very simple and I can put a circuit together for that if anyone needs it. It's little more than a relay, a HEXFET and a C/R network on the gate.
I hope on reflection that you'll reconsider Alex
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I think it would also be a good idea for us all to take a step back and just make sure that everyone knows what this project entails...
One thing that no one has asked about or mentioned is a switch on delay (speaker relay). This is mentioned in the thread and is mandatory to avoid switch on thumps. There's no way round that, its a function of the single ended design and biasing. So that is something that is needed whether it is a kit or diy. To diy it is very simple and I can put a circuit together for that if anyone needs it. It's little more than a relay, a HEXFET and a C/R network on the gate.