I have a few metallized polyester, film stacked, but no ceramic ones. As they are poor performers, I'll leave the AUX without them for now.
An externally hosted image should be here but it was not working when we last tested it.
Do you have saparated amp and preamp with a transformer for each? I'm trying this with a small integrated (55W/8Ω) that has one transformer.
Other than CD and Tuner inputs, there's a USB powered DAC from PC into the AUX...
Just be careful not to remove the RF decoupling caps at the input.
Regarding the ground loop isolator, I'm using a Stinger SGN20 right in between my Sansui preamp output and the amplifier input. Pretty inexpensive stuff with absolutely audiophile level performance.
I can get a few Polypropylene 630V 1% or even Mica. I still want to make a couple of tests.
Has no one else noticed that the "100pF" caps removed are NOT series caps (value far to small!) but parallel RF/noise filters to ground.
That is verified by the picture with the caps removed. It is clear that the two caps share a common connection (holes very close together) which is probably ground.
So if you prefer the sound with those filter caps removed you are either imagining a difference or like having RF pollution in your pre-amp.
That is verified by the picture with the caps removed. It is clear that the two caps share a common connection (holes very close together) which is probably ground.
So if you prefer the sound with those filter caps removed you are either imagining a difference or like having RF pollution in your pre-amp.
Polyester/mylar caps are fine for coupling, provided they are not setting the LF rolloff and so have appropriate values. No significant signal voltage across the cap means no significant distortion is possible.rayma said:
I suspected this. I suppose a particularly bad ceramic cap fed from a particularly high source impedance might create a little HF distortion. I am not familiar with the unit so I can't comment further.cliffforrest said:
I'll go with the second choice. Audiophiles sometimes prefer a little background noise as it seems to add dynamics and sparkle.
I seem to remember tests, maybe by R. Marsh, that found an order of magnitude more distortion in polyester types. They certainly sound like it.
Thank you so much for the observations, folks!
These "input" 100pF ceramic caps are not in the list of components in the amp's schematics/SM and aren't even marked in the preamp board.
I had to draw and mark them in red them as you can see here below (2nd pic for detail):
It's a Denon PMA-737 integrated. My main goal was to change these ceramic caps to others of better quality as someone advised for any recap work. Also for the 100pF value.
To be fair, after trying the previous 470pF cap, with which lacked (to my ears) full bass sound and had harsh mids, I found it much better without these unmarked ceramic caps.
They might indeed have a good reason to be there, even if they were not marked in the board. And I still want to do other tests with other caps/values. 🙂
..
These "input" 100pF ceramic caps are not in the list of components in the amp's schematics/SM and aren't even marked in the preamp board.
I had to draw and mark them in red them as you can see here below (2nd pic for detail):
An externally hosted image should be here but it was not working when we last tested it.
An externally hosted image should be here but it was not working when we last tested it.
It's a Denon PMA-737 integrated. My main goal was to change these ceramic caps to others of better quality as someone advised for any recap work. Also for the 100pF value.
To be fair, after trying the previous 470pF cap, with which lacked (to my ears) full bass sound and had harsh mids, I found it much better without these unmarked ceramic caps.
They might indeed have a good reason to be there, even if they were not marked in the board. And I still want to do other tests with other caps/values. 🙂
..
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I disagree.
Ceramics are made in many different types for many different duties.
For some duties, the correctly selected ceramic, cannot be improved upon.
LOL so in the end it was not the input caps that you were removing...
The topic has gone off now, discusing whether or not some cap type is better or more suitable for this or that..
From what you shared with us above I presume you have the 737 service manual. May you post the input section squematics? (instead of the circuit board layout)
We need to know if there are input caps to be bypassed to begin with. I couldn't find the 737 squematics online to check this out.
I already warned you to check out you were not removing the RF decouplers on post #63. That's a bad decision and removing them should only affect sound towards the bad side.
Check the value of the RF attenuation capacitors.
Check the impedance fitted on board before the RF cap.
Check the impedance in the cable and Source that will add to the RF attenuation.
Most Members fit RF attenuation with RC time constant from 300ps to 1.5us.
It could be that the caps fitted fell outside this normal range.
Check the impedance fitted on board before the RF cap.
Check the impedance in the cable and Source that will add to the RF attenuation.
Most Members fit RF attenuation with RC time constant from 300ps to 1.5us.
It could be that the caps fitted fell outside this normal range.
It was (is?) quite common in commercial electronics for all audio inputs to have a small (eg 100pF disc ceramic 😀 ) between input and "ground" - often direct to chassis if there is one.
This has nothing to do with audio magic dielectrics and similar nonsense, but a sledge-hammer attempt to bypass all hf input.
Since these (as marked in red) are on the pcb but not the drawings they are obviously a later revision - put there to kill rf! So I suggest you put them back in move on to something else - preferably study some electronics theory! 🙂
Karl may also like to revisit comments made in #56 in the light of updated information, but probably will not ....
This has nothing to do with audio magic dielectrics and similar nonsense, but a sledge-hammer attempt to bypass all hf input.
Since these (as marked in red) are on the pcb but not the drawings they are obviously a later revision - put there to kill rf! So I suggest you put them back in move on to something else - preferably study some electronics theory! 🙂
Karl may also like to revisit comments made in #56 in the light of updated information, but probably will not ....
My bad. Here they are.
An externally hosted image should be here but it was not working when we last tested it.
An externally hosted image should be here but it was not working when we last tested it.
So, at least I can replace them with Polypropylene 630V 1% of the same value, 100pF...
Calculate the impedance at audio frequencies. Compare to the input impedance. That scaling should clue you in as to the criticality/noncriticality of that cap for sound.
I will retain them because frankly I think the sound is still good, although might be quite polluted, lol.
Thanks, folks. My goal was/is see if there is further sound improvement by replacing these "input capacitors" with better ones. 🙂
But you still haven't GOT the fact that these are not input capacitors!
Input capacitors are in series with the inputs to block DC. This function may have some audible effect depending upon the circuit details. If an input cap is removed, NO signal gets through and there is only blissful silence.
We are talking about (your caps in red) input parallel caps to remove or at least reduce Rf pollution.
I feel I am wasting my time here ..
Input capacitors are in series with the inputs to block DC. This function may have some audible effect depending upon the circuit details. If an input cap is removed, NO signal gets through and there is only blissful silence.
We are talking about (your caps in red) input parallel caps to remove or at least reduce Rf pollution.
I feel I am wasting my time here ..
Cliffforrest said it; those caps even being at the input terminals -generalizing- are not what this thread is about.
Those caps marked in red WILL affect sound in one way ore another, and I say this without making any calculations, just from experience.
It's important that you do not remove the RF bypass caps from input negative to ground (like C302 in the diagram)
I suggest you test those specific circuit points searching for RF with an oscilloscope, with all interconnects there and all the devices ON. If you'd try this remember to lower the amp volume potentiometer to zero.
BTW, please post a big picture of the whole amp board circuit diagram so we can check it out.
Those caps marked in red WILL affect sound in one way ore another, and I say this without making any calculations, just from experience.
It's important that you do not remove the RF bypass caps from input negative to ground (like C302 in the diagram)
I suggest you test those specific circuit points searching for RF with an oscilloscope, with all interconnects there and all the devices ON. If you'd try this remember to lower the amp volume potentiometer to zero.
BTW, please post a big picture of the whole amp board circuit diagram so we can check it out.
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