My_Ref Fremen Edition - need help on PCB evaluation

[ClaveFremen]

Originally Posted by soongsc

C9 is an electrolytic capacitor, if there is a DC offset across this cap then it's fine. If not, then I was thinking about changing it to an bipolar type electrolytic and add a bypass cap to improve it's linearity. I probably should also try it one one of my chip amps too.

a small dc offset is probable, since LM318 is a bipolar opamp, a bipolar caps works as well, in fact there is people that use a bipolar for C9.

Bipolar caps are bigger though (but the 16mm diameter helps... ).

[soongsc]

The smaller types are called NP, they carry a lower current rating. Actually smaller than the normal electrolytic. I am also thinking about the solidstate caps.

[ferynov]

thanks Dario for starting this thread..for me , your design very nice, no problem to attach input caps on board...or direct attach cpas on input connector(rca).

[madisonears]

If C13 is moved off board, then you don't really need an AC and a DC input pad. With a coupling cap, it's AC. Without, it's DC. Correct? Although two pads would allow connection of both inputs at the same time (with two input jacks) and not take up much space, and let the builder decide. Kind of a cool idea. Perhaps just label both pads DC+ input. Then the jacks (sockets?) on the chassis would be labeled AC and DC. Is that what you mean, Andrew?

I can't think of a cap that's equal to the quality of this amp that will fit onto the space provided, so it's just as well to leave it off. Using a hefty film cap to connect input jack to board is exactly what should be done. I don't know what else that space can be used for, but it would allow relaxation of the somewhat tight spacing of other components that exists now.

Perhaps install a mounting hole on that side of the board so builders can physically attach the coupling cap against edge of the board instead of it floating around inside the chassis. I attach mine to the chassis floor with a cable tie, but then I must cut it or detach the cap in order to lift the board.

Just throwing out crazy ideas here.

Peace,
Tom E

[soongsc]

Has anyone tried snubbers on the power supply of this amp?

[ClaveFremen]

Originally Posted by ferynov

thanks Dario for starting this thread..for me , your design very nice

Thanks

Originally Posted by madisonears

Using a hefty film cap to connect input jack to board is exactly what should be done. I don't know what else that space can be used for, but it would allow relaxation of the somewhat tight spacing of other components that exists now.

At the moment for nothing...

And, probably, the input trace crossing R10 is not a problem at all since since between the trace and the resistor there is the ground plane, which should shield...

And that zone is probably the less congested of all the PCB...

Sincerely, I don't think this or the C13 outboard/onboard are high priority problems, first we shoud:

• find any fault of the PCB layout (if possible)
• design the PS for LM318 (here I need help, I'm not good with transistors)

Originally Posted by madisonears

Perhaps install a mounting hole on that side of the board so builders can physically attach the coupling cap against edge of the board instead of it floating around inside the chassis.

This is a great idea!

Take a look at the attachment, it could be good?

I've also moved a bit the input connector (it was too near to the edge) and used Russ' C13 so the input is a bit farther from the output ground.

Originally Posted by madisonears

Just throwing out crazy ideas here.

It's called brain-storming...

It works, usually.

Originally Posted by soongsc

Has anyone tried snubbers on the power supply of this amp?

Sorry, this is a taboo...also in the original thread they were proposed upsetting Mauro...

BTW who tried them gave different opinions, some heard an improvement, others didn't.

Rudi, which realized an alternate PCB called X-Calibre, initially tried them and heard an improvement but after some days he changed his mind.

[ClaveFremen]

Sorry, I was wrong, Rudi never changed his mind about snubbers what I was referring to, in reality, is this post in Rudi's X-Calibre thread:

Russ White on snubbers

And I do agree with Russ, particularly on the fact that snubbers should be calculated for each different transformer used for optimal performance.

[soongsc]

I hate to comment on what is "not" audible or not mainly because there are so many factors that influence the results. But the concept of the snubber itself is certainly quite widely used and studied. Some people even use it on diodes. My main interest in this type of amplifier is the relationship between current and voltage, and how it actually shows differences when measuring speakers.

[AndrewT]

Hi Madi,
the C13 as you describe works fine. just an extra phono socket on the back of the amplifier. This requires a hot&return two pin connection on the PCB.

The Jens' Leach clone was a bit different. It had a single input socket. The "changeover" was done on the PCB using a shorting plug. This requires a hotAC, hotDC, return, three pin connection on the PCB.

[soongsc]

Originally Posted by ClaveFremen

...
And I do agree with Russ, particularly on the fact that snubbers should be calculated for each different transformer used for optimal performance.

I somehow recall that snubbers are more load transients dependent.