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Old 14th September 2012, 03:03 PM   #911
dadod is offline dadod  Croatia
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Quote:
Originally Posted by HarryDymond View Post
That looks a good place for the ceramic decoupling capacitors* but only if you place the emitter traces of the output transistors on top of (or underneath) the collector traces and bring the zobel ground to the ceramics' ground connection.
Harry,
I changed the zobel ground, but how to place the emitter traces of the output transistors on top of (or underneath) the collector traces I am out of ideas. Is that so impotant as emitter currents are low distortion music signals???
Damir
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Old 14th September 2012, 03:35 PM   #912
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Harry,
I changed the zobel ground
We're talking C99 and R99, correct? The ground connection needs to be made at the same point as the ground of the ceramics; currently it is not.

Quote:
Originally Posted by dadod View Post
but how to place the emitter traces of the output transistors on top of (or underneath) the collector traces I am out of ideas
That would require a somewhat more fundamental change to your layout. Also for maximum fun, you could make the +ve and -ve pathways perpendicular to one another (try orienting the output devices at 45 degrees, to make an inverted "v" shape: the NPN devices forming one edge of the "v", and the PNP devices the other edge)

Quote:
Originally Posted by dadod View Post
is that so impotant as emitter currents are low distortion music signals???
Damir
The emitter traces only carry low-distortion music signals once they have mixed. Before the join, the +ve and -ve pathways are rich in high-order harmonics. Placing collector paths on top of emitter paths minimises inductance and possibility of radiation.

Last edited by HarryDymond; 14th September 2012 at 03:38 PM.
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Old 14th September 2012, 04:03 PM   #913
dadod is offline dadod  Croatia
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Quote:
Originally Posted by HarryDymond View Post
We're talking C99 and R99, correct? The ground connection needs to be made at the same point as the ground of the ceramics; currently it is not.
Sorry, there is additional wiring from the back side. Showed are the wires to the PSU and the loudspeaker too. I think that you suggested this way to connect the loudspeaker.
I prefare to use aluminium L bracket to mount output transistor and that requires the transistors in a line arrengement. In that way I can finish whole amp board and test it outside the box. Additional, it is much easier to service as whole amp board together with output transistors by fixing it to the temporary heat sink. Some thinks that this configuration could provoke the output transistors over heating as a consequence of not so good heat transfer, but I never had any problem with it.
dado
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Old 14th September 2012, 04:16 PM   #914
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Quote:
Originally Posted by dadod View Post
Harry,
...........
but how to place the emitter traces of the output transistors on top of (or underneath) the collector traces I am out of ideas.
...........
Damir
Damir,

Indeed, it's impossible do that, that is, all the the way from begin to end. But you can neutralize the loop area, see my post about the lemniscate trick #876.

Cheers,
E.
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Old 14th September 2012, 04:36 PM   #915
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I have measured resonance as ell. I had 3 470nF MKT films, beteen rails and ground, and the third beteen the rails. These caps ere separated in trace length by only a fe inches but the resulting resonance alloed my output stage to oscillate. My problem as that the main lytic reservoirs ere several inches of tisted alligator clips aay. I had to add 120uF caps directly to the prototype hich as air-ired. Lo-impedance lytics can oscillate as ell. It is alays best to simply check your rails ith a sept sine generator, and/or model the trace inductances and capacitors in SPICE. A 1uF RC can be used but a lytic ill take up less space, although ho knos ho it's ESR might vary ith time.

I have a problem. My keyboard is missing a button and my mouse doubleclicks itself every time (has been for several months). Maybe I have too much patience ith these things...
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Old 14th September 2012, 04:53 PM   #916
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Originally Posted by Edmond Stuart View Post
Damir,

Indeed, it's impossible do that, that is, all the the way from begin to end. But you can neutralize the loop area, see my post about the lemniscate trick #876.

Cheers,
E.
Thanks Edmond,
It is not easy to make good layout. I've got Cherry's article, I think you mentioned this one.
Damir
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Old 14th September 2012, 04:57 PM   #917
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Hi Damir,

Exactly, that one.

Cheers,
E.
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Old 14th September 2012, 04:59 PM   #918
AndrewT is offline AndrewT  Scotland
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look at the PCB layout.
The two traces for speaker output have all their connections away to the right hand side.
I can see no advantage to bringing the speaker output to the left alongside the input traces. Take the speaker out from the middle of the PCB and delete the unnecessary traces.
The 10r signal gnd to power gnd link could be moved to tap in to the right hand side of the hatched area. Then all of the output traces are to that same right hand side.

Does the power input need to be fed from the left?
Or would it be better to feed power into the right hand side? Then bring the low current power traces to the left hand side.

I note that Cherry is using the Chassis as the Main Audio Ground. Is this the best way? Or should there be a separated Main Audio Ground with a tapping to the Chassis to gain the screening effect of the enclosing case?
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Last edited by AndrewT; 14th September 2012 at 05:05 PM.
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Old 14th September 2012, 05:03 PM   #919
dadod is offline dadod  Croatia
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Hi Edmond,
But I think that something is wrong with this approach, the current though the cap is not even close to the current trough the emitter resistor. Were is power line current??
Damir
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Old 14th September 2012, 05:07 PM   #920
dadod is offline dadod  Croatia
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Quote:
Originally Posted by AndrewT View Post
look at the PCB layout.
The two traces for speaker output have all their connections away to the right hand side.
I can see no advantage to bringing the speaker output to the left alongside the input traces. Take the speaker out from the middle of the PCB and delete the unnecessary traces.
The 10r signal gnd to power gnd link could be moved to tap in to the right hand side of the hatched area. Then all of the output traces are to that same right hand side.

Does the power input need to be fed from the left?
Or would it be better to feed power into the right hand side? Then bring the low current power traces to the left hand side.
Sorry Andrew I am not sure what PCB layout you are talking about, there is double side one and single side one.
Damir
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