Sakis,
Imagine all the wires are 10 ohm. Imagine the amp is delivering 1 amp into a 10 ohm load. Work out the volt drops. Even with 10 ohm wires the amps should still behave correctly.
The problem appears when you couple the two input grounds together at some point-- preamp etc.
This is where D Self slipped up big time with his official boards for the Class B amp and this is what I am refering to in the above link.
Imagine all the wires are 10 ohm. Imagine the amp is delivering 1 amp into a 10 ohm load. Work out the volt drops. Even with 10 ohm wires the amps should still behave correctly.
The problem appears when you couple the two input grounds together at some point-- preamp etc.
This is where D Self slipped up big time with his official boards for the Class B amp and this is what I am refering to in the above link.
hei mooly
have you noticed the photo i made for Andrew ????
this the exaact same topology except the zobel that is located on board (s) and its returned to the local star ground ...
this as is is working perfectly ....absolutely noiseless ...also if we add Eva's remarks this pcb( in the photo ) is even worst ....
but i listen to it every day for more than 8 month now ....its absolutelly noiseless
have you noticed the photo i made for Andrew ????
this the exaact same topology except the zobel that is located on board (s) and its returned to the local star ground ...
this as is is working perfectly ....absolutely noiseless ...also if we add Eva's remarks this pcb( in the photo ) is even worst ....
but i listen to it every day for more than 8 month now ....its absolutelly noiseless
Hi,
Yes I looked at it
I am only commenting on the layout in your first post. If you wire two of these PCB's to a common PSU they will cause interaction.
In post #8 you show the speaker return to the PCB itself.
Think of it as a DC problem and try and visualise what happens. Put some numbers in. Different currents etc for each channel as it would be with music. Each amp is at a different potential with respect to the other. That's fine UNTIL the two input grounds are connected together. A loop is then formed.
Under dynamic conditions the large caps on the PCB also add their own currents into the ground.
Only trying to offer some practical advice You did ask
Yes I looked at it
I am only commenting on the layout in your first post. If you wire two of these PCB's to a common PSU they will cause interaction.
In post #8 you show the speaker return to the PCB itself.
Think of it as a DC problem and try and visualise what happens. Put some numbers in. Different currents etc for each channel as it would be with music. Each amp is at a different potential with respect to the other. That's fine UNTIL the two input grounds are connected together. A loop is then formed.
Under dynamic conditions the large caps on the PCB also add their own currents into the ground.
Only trying to offer some practical advice
You did ask groundplane picofarads
Perhaps if you made power traces as large as possible,ie remove least copper as possible,and have groundplane,the board itself is a capacitor.Anyone used multilayered boards as pseudo farads.or wiring direct with high capacitance wire.
regards
max
thinking more,the seperation is far too much to be effective,i,ll get me coat.
Perhaps if you made power traces as large as possible,ie remove least copper as possible,and have groundplane,the board itself is a capacitor.Anyone used multilayered boards as pseudo farads.or wiring direct with high capacitance wire.
regards
max
thinking more,the seperation is far too much to be effective,i,ll get me coat.
now we are going to loose
track of what is going on cause some talk about my pcb and others are talking about the pcb of mjl21193....
no probs though as long as we understand wtf are we talking about .....
ha ha ha ha please state your pcb before yor comments
best regards to everybody this is getting nice
track of what is going on cause some talk about my pcb and others are talking about the pcb of mjl21193....
no probs though as long as we understand wtf are we talking about .....
ha ha ha ha please state your pcb before yor comments
best regards to everybody this is getting nice
sakis said:
Back to your board, the biggest problem is trying to put the filter caps on the pcb, then sharing the supply with multiple channels. If the main filter caps are off-board, sharing the supply becomes easier - the star ground is off board between the caps. Then you put smallish (100uF) bypass caps on the board, find a shorter ground path to connect between them, then run a separate lug back to the star ground. Gets rid of most of the evils that you'll be fighting. Even if you reroute the filter caps and power ground through the center you'll end up fighting ground loops when you hook up the other channel. The only other option is to get everything (supply and all channels) onto one board and use a ground plane.
MJL21193 said:
At least the small signal circuits are not wrapped with a power loop around them this time
And the high current paths are close one to another, but the +V and -V connections are still far apart. Layouts are not in any way required to be symmetrical to the eye.+V, -V, speaker output and power ground connections should be together. Twisting these four wires tends to cancel induction, at least twisting +V and -V since they carry chopped halves of the speaker current waveform that are rich in harmonics. The two decoupling capacitors for V+ and V- should be placed together too, they lose their effectivity if they are far apart and joined by a long and inductive ground track.
As I have mentioned, linear amplifiers are very forgiving of bad PCB layouts most of the time, they even work on breadboards or point to point with long leads. This is unless very high bandwidth MOSFET or CFP output stages are employed (there are plenty of threads of people complaining of extremely hard to solve oscillations in these cases, and for a good reason
).The guidelines that I'm giving are to create better than usual layouts, more like "RF-grade". Even the worst layouts can produce sound without self-destructing (unlike in class D or switching supplies).
well....
never used a ground plane to any of my amps( even if it works good its nothing i ever tryied in the past )
still i belive that the amp will work just fine but give it few days and lets see ....
also the pcb that is ppresented in the photo works with the exact same logic and is very quiet ....
the only thing that i never tryied before is the return of the zobel directly to main star ground .... this might cause complications
one of the main reasons i work this out like this is that i want to have the option in the feature to make it a dual mono
wg_ski said:
never used a ground plane to any of my amps( even if it works good its nothing i ever tryied in the past )
still i belive that the amp will work just fine but give it few days and lets see ....
also the pcb that is ppresented in the photo works with the exact same logic and is very quiet ....
the only thing that i never tryied before is the return of the zobel directly to main star ground .... this might cause complications
one of the main reasons i work this out like this is that i want to have the option in the feature to make it a dual mono
eva ....
no matter what i always follow your posts and always i find something very usefull to them ....thanks for showing arround i am happy for that ....
the thing is that after your post that comment my pcb and spoting a few things for me i said to my shelf : """" ok i'll have a cup of coffe on them """"
i end up rebuilting my pcb under your point of view
but with someother issues involved also :
my "thingy " about square and symmetric pcb ( ...... this is my ''thingy'' this the way i like to do things ...... )
the rest of audio rulls that apply and so on .....
do yo know with what i come up with ?????
if you design like that then you need costum made heatsinks or find some other way to do all this.....
i will give a try ....i dont think that its easy .... dont know if iam going to make it ....but ill try
will see
no matter what i always follow your posts and always i find something very usefull to them ....thanks for showing arround i am happy for that ....
the thing is that after your post that comment my pcb and spoting a few things for me i said to my shelf : """" ok i'll have a cup of coffe on them """"
i end up rebuilting my pcb under your point of view
but with someother issues involved also :
my "thingy " about square and symmetric pcb ( ...... this is my ''thingy'' this the way i like to do things ...... )
the rest of audio rulls that apply and so on .....
do yo know with what i come up with ?????
if you design like that then you need costum made heatsinks or find some other way to do all this.....
i will give a try ....i dont think that its easy .... dont know if iam going to make it ....but ill try
will see
Eva said:In other words, you have started a thread asking for advice on PCB layout but you are going to use your original layout no matter what advice is given. Then, as usual, there is not much point in giving any advice
This was just a test. I don't use to write in the solid state section
hei there ...i didnt ask for advice .....my pcb is alot better than a lot of others seen arround for simular application ...
i asked for comments ha ha ha of course advice is always welcome
Eva said:
Most amplifiers will *work* with a poor layout. They may even sound ok. But when trying to get singe-digit ppm residual THD+N you can't get careless. Most of the time you'll be stuck in the .05% range regardless of topology, component selection, or bias point. Which may be good enough, but may not be as good as it gets. The rest is in the details.
p3a layout
Hi sakis here is my contribution i have built a few versions of this amp with my own pcb design with no problems.Some of the criticism directed to your layout would also apply to Rod Elliot's pcb-the designer of the circuit! There isn't a lot wrong with it. Are they implying that rods pcb are sub-optmal?!
Hi sakis here is my contribution i have built a few versions of this amp with my own pcb design with no problems.Some of the criticism directed to your layout would also apply to Rod Elliot's pcb-the designer of the circuit! There isn't a lot wrong with it. Are they implying that rods pcb are sub-optmal?!
wg_ski said:
That almost sounds nasty
Where were your helpful comments when I laid this out?The V- and input only appear to be close and the wires that leave the board from these two positions do not / would not run parallel.
The THD figure was a bit higher than the figure you quoted but certainly well below the threshold of audibility. I'll take it.
Eva said:
At least the small signal circuits are not wrapped with a power loop around them this time
Thanks Eva,
I'm learning as I go and I listen to all of the advice I get and put the good stuff to good use. My objective with that layout was to make it compact, single sided with no long traces and keeping the high current section away from the small signal.
I like it to look good, but my goal was not symmetry. I have a lot of components on a relatively small board housing an amp that is capable of more than 150watts output. I thought it was a good idea to make the traces as wide as possible within the space restrictions.
I thought it was fairly well organized for what it is and I know there is always room for improvement. Getting good advice is the key, putting us that don't have the experience or know-how on the correct path is much appreciated.
Eva said:
Thanks for these tips. I'll be keeping them in mind for the next time.
PS: Sorry Sakis, I saw my chance to grab some advice.
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