I did exactly that, ended up having lots of "GND"s wires running back to the PSU.
I used the L/R but my speaker wires are only about 2 feet long. Perhaps I should not have bothered.
I removed the R+C because it was attenuating high frequencies by as much as 50%, I remember, at 20 KHz.
no! the PSU should have ONE zero volts wire going to a centrally located STAR/AUDIO Ground. The Audio Ground can be located on the PCB IF the amp is a monoblock. If you intend building a multichannel amplifier then the Audio Ground is best off the PCBs. That will require ~ 3 ground wires from each amplifier PCB and a wire from the speaker return (now 8 for a 2channel amp) and one wire from the PSU. The PSU will also be connected to the Protective Earth (PE or Safety Earth).
Then you chose the wrong Zobel component values.
100nF + 2r7 should have no audible effect if the amplifier is operating correctly.
100nF + 2r7 has F-3dB @ ~600kHz. i.e. an impedance of ~5.7ohms at 600kHz. Now consider what effect adding 5.7ohms in parallel to the speaker for a 600kHz signal. Will you hear that?
What is the difference where the "star" ground is located? Mine is on the PSU PCB, I cannot see why putting it somewhere else and then running a wire to the PSU should make a beneficial change. Actually running a wire to the PSU means generation of voltages across that wire and separation from the transformer centre tap and caps. Why is that better? Actually leaving it on the PSU is quite convenient, everything converges there naturally and the PSU ground forms the absolute ground of my device. It is a very thick track which binds all the ground wires and the centre tranformer tap together. Please explain
Your filter has its pole at the 600KHz, mine was at 800KHz if I remember correctly. And yet it screwed up....
if the main audio ground is located on the single amp PCB and you now connect two channels inside the box, where do you connect the common audio ground. It is impossible.
Where do you take the PSU zero volts? to one or the other.
Where do you take the RCA signal grounds?
The PSU zero volts connection has massive charging current pulses running back to the transformer. This is not a good place for the main audio ground.
Where do you take the PSU zero volts? to one or the other.
Where do you take the RCA signal grounds?
The PSU zero volts connection has massive charging current pulses running back to the transformer. This is not a good place for the main audio ground.
no, it's not an absolute ground.
There is no "main audio ground". Every PCB has individual components and stages and they have their own ground if they are carrying different currents, there are no big planes of "ground" anywhere on any PCB. All those grounds meet up separately at the PSU, everything is referenced at the PSUs (pre-amp PSU and post-amp PSU). There is no other "common" ground.
Forgot to say , on the PSUs speakers and high currents are closer to the tansformer, lower levels are further out - you could conceive this as a start arrangement where the star is 1 inch further than the caps+transformer and connected by one thick wire.
Forgot to say , on the PSUs speakers and high currents are closer to the tansformer, lower levels are further out - you could conceive this as a start arrangement where the star is 1 inch further than the caps+transformer and connected by one thick wire.
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So NOW I´m having problems understanding everything you´re writing here...
However, this is what my PCB now looks like:
However, this is what my PCB now looks like:
An externally hosted image should be here but it was not working when we last tested it.
I can´t find the Edit-Button?! So sorry for double post!
Now with R/L an the two caps on board... what do you think? Is the "GND-Point" ok?
Now with R/L an the two caps on board... what do you think? Is the "GND-Point" ok?
An externally hosted image should be here but it was not working when we last tested it.
Hi,
give pin7 it's own connection to that central PCB GND.
Remove the speaker return from the dirty Power ground, move it to the central PCB GND.
Is there a way to move C2 & -18V to the other end of the PCB?
That will very much shorten the length of Power Ground trace between the two decoupling caps.
It also allows a twisted triplet of power wires from the PSU to the amp PCB thus minimising loop area of the dirty radiation from the power wires.
Consider removing the N/C pins. It allows more flexibility in placing/routing traces/pads from adjacent used pins.
give pin7 it's own connection to that central PCB GND.
Remove the speaker return from the dirty Power ground, move it to the central PCB GND.
Is there a way to move C2 & -18V to the other end of the PCB?
That will very much shorten the length of Power Ground trace between the two decoupling caps.
It also allows a twisted triplet of power wires from the PSU to the amp PCB thus minimising loop area of the dirty radiation from the power wires.
Consider removing the N/C pins. It allows more flexibility in placing/routing traces/pads from adjacent used pins.
You should really use a bigger PCB. All components should have some air around them for several reasons. One is cooling. Another is to avoid mechanical noises that ocurr, when adjacent components vibrate and touch each other. Then there are possible shorts not only from soldering, but also from mechanical movements. Later there is the question, how to service the amplifier. E. g. you need to remove the LM3886 to replace Rm, if you find out that it does not have the right value.
It is always a good thing to run wires of the same function together, and wires of different functions separate. E. g. the power supply wires should run side-by-side and therefore have their connections on the PCB next to each other. But they should be as far away from the signal wires as possible.
When you use big copper areas, you should use thermals. Without them soldering can become very tedious, because all the heat is drawn away from the place, where you want to solder. That means, you need more power and more soldering time, both of which is bad and can even lead to component destruction.
The coil and resistor are there to protect the amplifier, when the load is capacitive. A highly capacitive load will have a very low impedance at high frequencies and can appear like a short-circuit. The resistor provides a higher impedance there and the coil shorts the resistor at lower frequencies, so that it does not affect the signal in the audio range.
It is always a good thing to run wires of the same function together, and wires of different functions separate. E. g. the power supply wires should run side-by-side and therefore have their connections on the PCB next to each other. But they should be as far away from the signal wires as possible.
When you use big copper areas, you should use thermals. Without them soldering can become very tedious, because all the heat is drawn away from the place, where you want to solder. That means, you need more power and more soldering time, both of which is bad and can even lead to component destruction.
The coil and resistor are there to protect the amplifier, when the load is capacitive. A highly capacitive load will have a very low impedance at high frequencies and can appear like a short-circuit. The resistor provides a higher impedance there and the coil shorts the resistor at lower frequencies, so that it does not affect the signal in the audio range.
The L//C does both jobs.
It acts as a high frequency load
and
it acts as an attenuator to high frequency signals being injected back into the speaker terminals.
A completely different one now... is it ok to connect all the seperate grounds to the powerground on that way?
An externally hosted image should be here but it was not working when we last tested it.
turn C3 & C4 around so that the traces to pins 1, 4 & 5 are VERY short.
The location of C2 wastes a lot of PCB area. Move it up next to it's partner, or even above C1. But keep a gap to the heatsink, you don't want it running hot.
Could you bend pin4 back and allow more clearance to the adjacent traces.
Move Signal Ground back up to next to Signal In. Connect R2 to the same signal Ground. Run one trace back to the Central Ground. Insert a pair of pads in to this trace to allow a 10r resistor to be fitted if the need arises.
Move R5 and C5 to the right to allow room to fit the Rz & Cz into the gap next to Rz1.
The location of C2 wastes a lot of PCB area. Move it up next to it's partner, or even above C1. But keep a gap to the heatsink, you don't want it running hot.
Could you bend pin4 back and allow more clearance to the adjacent traces.
Move Signal Ground back up to next to Signal In. Connect R2 to the same signal Ground. Run one trace back to the Central Ground. Insert a pair of pads in to this trace to allow a 10r resistor to be fitted if the need arises.
Move R5 and C5 to the right to allow room to fit the Rz & Cz into the gap next to Rz1.
I think I know how you want me to turn and place C3 - but I´ve got no idea how that schould work with C4?!
You mean, i shall place C2 beside C1?
No, i don´t think so - but I´ll try to solve this Problem!
10R in series with R2?? Why?
The +/- 18 Volts (why so little?) and that resistor are too close to the heatsink. Assuming there is a terminal post there it could even touch the heatsink and make it hard to connect/disconnect.
post37 is looking good.
Connect the NFB cap to Signal Ground and delete the redundant ground trace.
The new resistor 10r can be linked across or inserted.
If two PCBs are put in one chassis then the power ground will connect to an off board star ground.
The 10r /link is omitted and the empty pad is used to connect signal ground to the star ground.
The speaker return is left empty and the actual speaker return goes to the star ground.
The power ground to PCB central ground link is omitted and the spare pad is used to connect the Zobel and pin7 to the star ground.
This gives you a dual purpose PCB for monoblock and for dual channel.
I see what you mean about C4 and not rotating it. C3 & C4 may perform better if they are 5mm (=0.2inch) pitch.
Connect the NFB cap to Signal Ground and delete the redundant ground trace.
The new resistor 10r can be linked across or inserted.
If two PCBs are put in one chassis then the power ground will connect to an off board star ground.
The 10r /link is omitted and the empty pad is used to connect signal ground to the star ground.
The speaker return is left empty and the actual speaker return goes to the star ground.
The power ground to PCB central ground link is omitted and the spare pad is used to connect the Zobel and pin7 to the star ground.
This gives you a dual purpose PCB for monoblock and for dual channel.
I see what you mean about C4 and not rotating it. C3 & C4 may perform better if they are 5mm (=0.2inch) pitch.
The 10r lifts the signal ground away from the high current grounds.
In some situations it removes hum from multichannel amplifiers.
It can be linked across with a copper lead cut-off on the underside of the PCB if the resistor proves to not help or is not needed.
If you decide to ground the input RCAs to a star ground (main Audio Ground in a multi-channel amplifier) then the 10r resistor must be fitted to break the hum loop that would otherwise be created.
In some situations it removes hum from multichannel amplifiers.
It can be linked across with a copper lead cut-off on the underside of the PCB if the resistor proves to not help or is not needed.
If you decide to ground the input RCAs to a star ground (main Audio Ground in a multi-channel amplifier) then the 10r resistor must be fitted to break the hum loop that would otherwise be created.
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