Hi!
danielwritesbac, you suggested to add a 1M resistor to the input. Doesn't it raise the input impedance, or am I not understanding something?
And some questions about designing the PCB:
1. Should I make two separate boards for the chips or one common?
2. How wide traces should I use for the signals, grounds etc.?
danielwritesbac, you suggested to add a 1M resistor to the input. Doesn't it raise the input impedance, or am I not understanding something?
And some questions about designing the PCB:
1. Should I make two separate boards for the chips or one common?
2. How wide traces should I use for the signals, grounds etc.?
Hi,
the 1M0 goes from RCA input to RCA barrel.
It is in parallel to Zin and very slightly lowers the effective Zin.
The purpose of the 1M0 is to short out the DC leakage that can occur through the DC blocking cap inserted into the input line.
Similarly the output of the source can also benefit from a high value resistor to ground fitted after the DC blocking cap.
the 1M0 goes from RCA input to RCA barrel.
It is in parallel to Zin and very slightly lowers the effective Zin.
The purpose of the 1M0 is to short out the DC leakage that can occur through the DC blocking cap inserted into the input line.
Similarly the output of the source can also benefit from a high value resistor to ground fitted after the DC blocking cap.
Nenola said:
Its to preserve the load, pass, load, pass, load, etc. . . layout of the input circuit. The 1M is just enough load to prevent noises, but not enough to become a voltage divider (in this application).
Let's say you have an in-series resistor (Rb), and you also have an input filter cap (Cin). Ut oh! That's two "pass" components in a row, and the potential for a noise (although unlikely). Okay, so just make a 1M load in-between these two.
Special treatment of 1M resistors: The + side needs to be as short as possible; however, the ground side can be as long as necessary. If a short + lead isn't possible, then either omit or use a firmer load.
That's all that I know about 1M resistors. Before this, I wondered why use they could be. As it turns out, the guesses were pretty close. The 1M resistors do something useful while simultaneously doing absolutely nothing.
ratza said:
The definition of bigger depends on the load of the input circuit. In this case, it looks like the example is 47k.
So, 1uF is about maximum size for a film cap. Even 0.1uF is a workable figure and it is -3db at 16hz, meaning that 0.1uF has no effect at 32hz, except possibly an efficiency boost that could result in more of the lowest bass notes. So, film caps would be somewhere in-between 1uF and 0.1uF, depending on whatever is most pleasant with your speakers.
That would all be true of film caps, yet it would be quite different with electrolytic caps. Electrolytics would need to be larger values, and the exact amount would vary by sample.
I'm using metallized polyester film for input caps when the amp is finalized. For testing I use electrolytics as I always have some around, but 10 times the polyester value, i.e. if the polyester is 1u, for electrolytic would be definitely 10u.
The cap used in reaction is always electrolytic as I haven't heard any sound modifications between different types of caps. Maybe my hearing is not so sharp, who knows...
The cap used in reaction is always electrolytic as I haven't heard any sound modifications between different types of caps. Maybe my hearing is not so sharp, who knows...
Nenola said:
You can use polyester caps. At that size, Wima brand is a nice choice. You can also use ceramic mono caps, which can be less expensive. You can use ordinary ceramic disc caps with are very inexpensive, yet remarkably good.
For C10, its electrolytic. For this, some good options are Nichicon KZ, Elna Tonerex, Elna Cerefine, or really anything with a decent reputation for carrying an audio signal.
For C13 and C9, polyester is a nice choice and so is polypropylene.
If only one brand is available, or for the purposes of getting some variety from just one vendor (one shipping bill), then note that different voltage ratings on capacitors (different physical size) does make a big difference in the sound. Whichever is most helpful, well, that's up to you.
Hi!
Thanks for the information! The caps that I found are the following:
C1, C3, C13: 0.1UF 63V ±5% (polyester)
C2, C4: 220UF 50V ±20% (aluminium electrolytic)
C9: 1UF 63V ±5% (polyester)
C10: 68UF 50V ±20% (aluminium electrolytic)
C15: 0.22NF 100V ±10% (polyester)
The voltage ratings and capacitance tolerances vary because I tried to find the ones which can be ordered in smaller amounts. I didn't want to order 50 or 100 caps which I'll only use 4
So, what does the list look like?
Oh, and I'm thinking of using 1/2W metal film resistors with a 5% tolerance. Are they suitable for this use?
Thanks for the information! The caps that I found are the following:
C1, C3, C13: 0.1UF 63V ±5% (polyester)
C2, C4: 220UF 50V ±20% (aluminium electrolytic)
C9: 1UF 63V ±5% (polyester)
C10: 68UF 50V ±20% (aluminium electrolytic)
C15: 0.22NF 100V ±10% (polyester)
The voltage ratings and capacitance tolerances vary because I tried to find the ones which can be ordered in smaller amounts. I didn't want to order 50 or 100 caps which I'll only use 4
So, what does the list look like?
Oh, and I'm thinking of using 1/2W metal film resistors with a 5% tolerance. Are they suitable for this use?
Today I seeked up some resistors and found what I needed. They're all 1% and power rating is 500mw or 750mw.
What about the caps I listed here before? Are the voltage ratings and tolerances ok? I found some similar caps from my school today, but they were like 25 volts or so. Could I use those?
What about the caps I listed here before? Are the voltage ratings and tolerances ok? I found some similar caps from my school today, but they were like 25 volts or so. Could I use those?
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