Treble and Bass cap replacement question

rg12

Member
2010-08-10 3:52 am
It's about the Pioneer SA-7300 amp again...

Here is a nice pic of the amp with the treble and bass caps
marked in red: http://www.milkbands.co.il/caps.jpg

The disc caps are for the treble and the green ones (NP1) are for
the bass.

What do you recommend doing to improve the sound? to replace them
to which type? Also, i always place the bass pot very low (3 out of 10
in the marks of the face panel) because the bass is very "closed",
very "smudgy", so what can i do to make it more accurate and punchy?

About the treble...i don't like those disc caps...

Also, the right red circle shows the same cap pattern but for the balance
pot. If i mod the bass and treble, would i benefit from replacing the balance caps too?

BTW, Why don't they write the capacitance value on disc caps and NP1 caps? i found them by the copper tracks and not by the values (because
they only have numbers that aren't related to capacitance value as far
as i can see).

What do you guys think?
 

bob91343

Member
2010-03-11 10:43 pm
I have no idea what your terms closed, smudgy, accurate, and punchy mean. How does the response look with an oscillator and oscilloscope? That is the proper way to measure.

Disc capacitors are fine. They do have a slight voltage coefficient and a little piezoelectric effect, both of which are probably inconsequential. If the idea bothers you, replace with film capacitors.

Most capacitors are marked with value but it's sometimes coded. What markings are on these units?

The life expectancy of ceramic capacitors is very long. Usually the film and, of course, electrolytic capacitors fail far sooner.
 

rg12

Member
2010-08-10 3:52 am
I have no idea what your terms closed, smudgy, accurate, and punchy mean. How does the response look with an oscillator and oscilloscope? That is the proper way to measure.

Disc capacitors are fine. They do have a slight voltage coefficient and a little piezoelectric effect, both of which are probably inconsequential. If the idea bothers you, replace with film capacitors.

Most capacitors are marked with value but it's sometimes coded. What markings are on these units?

The life expectancy of ceramic capacitors is very long. Usually the film and, of course, electrolytic capacitors fail far sooner.

Well, i don't have an oscillator nor oscilloscope.

Will i benefit anything if i change the ceramics to metalized polypropylene?
will it work without problems?
 

bob91343

Member
2010-03-11 10:43 pm
Yes it will work with almost any kind of capacitor.

If you plan on doing this sort of stuff I strongly recommend you get an oscilloscope and audio generator. They will pay for themselves in education and to keep you from barking up the wrong tree. The latter is very common; people will glean a snippet of information here and there and come up with some of the most fantastic mythology. When someone uses terms that aren't defined scientifically, I immediately see a red flag. Expressions like 'sonically' and 'sound stage' make me ill.

If you don't understand the theory behind this stuff, there are literally thousands of ways to remedy that. You won't have to get a degree in engineering, although you may at times with you had one.
 
I don't care for the sound of "disc" caps, or electrolytics, in the signal path (imho), but they are less offensive between the signal path to ground. In most tone stacks with cut, no true boost (0 to 10 instead of -5 to +5), treble caps are in the signal path, bass and midrange caps are not. A schematic of the tone circuits would have been helpful. I'd replace the "disc" caps, and leave the "green" caps. Just one man's opinion.

Dave
 

rg12

Member
2010-08-10 3:52 am
The bass is actually the thing that bothers me the most.

About learning more about electronics, im doing so everyday since i
started with the whole amp modding, but it's nothing close to really
understanding it.

I would of put more time to this matter if i was to do anything besides the recapping of this specific amp, but this is the only time i need this info,
otherwise i would go and get a degree in electronics.

Link to the schematic:
http://www.milkbands.co.il/Pioneer-SA-7300-int-sch.pdf
 
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If you have listened to your speakers with another receiver and liked the sound of the bass (accurate, punchy), then I would look at the POWER SUPPLY CAPS, not the tone stack caps. The PS caps are the tall cylindrical caps by the bridge rectifier and power transformer. I would use the largest value caps that will fit in the physical space allotted to them. I believe your power supply caps are 8000ufd/50v. I would replace these with 10000ufd/50v or 63v. Replacing the PS caps will stiffen the power supply, increase its reserves, so it has enough juice for punchy accurate bass. If you haven't heard your speakers with another receiver, and been happy with the bass, I would start there.

Dave
 
BTW, Why don't they write the capacitance value on disc caps and NP1 caps? i found them by the copper tracks and not by the values (because
they only have numbers that aren't related to capacitance value as far
as i can see).
They should be marked with 3 digits something like:
104 or
333 or
685

104 = 10e4 or (10 * 104) pF = 100000 pF = 100 nF = 0.1 uF
333 = 33e3 or (33 * 103) pF = 33 nF = 0.033 uF
685 = 6.8 uF