I'm currently ordering the parts for a BrianGT amplifier someone generously gave me the PCBs for.
However, I noticed the lack of an input capacitor. Why is this? Won't this cause problems with DC offset?
(Also, on an unrelated issue...has anyone noticed an increase in sound quality with the CarlosFM style unregulated PSU vs. the Chipamp.com style PSU?)
However, I noticed the lack of an input capacitor. Why is this? Won't this cause problems with DC offset?
(Also, on an unrelated issue...has anyone noticed an increase in sound quality with the CarlosFM style unregulated PSU vs. the Chipamp.com style PSU?)
Look here
http://www.diyaudio.com/forums/showthread.php?s=&threadid=64573&highlight=
or use the search button
http://www.diyaudio.com/forums/showthread.php?s=&threadid=64573&highlight=
or use the search button
The capacitor in question is (or is not, actually) at the input to the amplifier, and not PSU related.
An input capacitor is not required if DC is not present. Neither the BrianGT amp nor the datasheet app note circuit use one. A transformer or output capacitor may be needed at the preamp output though.
An input capacitor is not required if DC is not present. Neither the BrianGT amp nor the datasheet app note circuit use one. A transformer or output capacitor may be needed at the preamp output though.
It is however a most convenient way of setting up lower frequency rolloff.
Just know that if you use it this is the most important cap in your system, and should be of the best quality you can possibly afford.
Not the most expensive thats out there, I think if you look at the most expensive lines of caps at say RS components you get a good feel for "real world" performance otherwise they would stock all those funny caps too.
I changed from 0.5 x 1.5cm input caps yesterday to proper audio caps measuring some 4 x 2 cm, it is not a slight change, its like my amp grew up, the very room feels larger when I close my eyes.
Just know that if you use it this is the most important cap in your system, and should be of the best quality you can possibly afford.
Not the most expensive thats out there, I think if you look at the most expensive lines of caps at say RS components you get a good feel for "real world" performance otherwise they would stock all those funny caps too.
I changed from 0.5 x 1.5cm input caps yesterday to proper audio caps measuring some 4 x 2 cm, it is not a slight change, its like my amp grew up, the very room feels larger when I close my eyes.
Eh, they look okay.Nordic said:Real audio quality caps with 5% tollerance can be had for $10... come on you probably spend more on sweets in a month... don't be a 2 dollah ho, be a 10 dollah ho
Can you reccomend a brand?
Also, ApexJr has quite a few other inexpensive (surplus) capacitors. Because this is going to be external anyway, can you reccomend one?
http://www.apexjr.com/capacitorsR.html
Also, can you reccomend an inexpensive pot?
Attachments
Go with a film and foil polypropylene capacitor versus a metallized capacitor. Theres nothing wrong with the apexjr cap, and its a steal, but this is not a cap to scrimp on. Certainly beats mylar or electrolytic caps.
Metallized capacitors have some advantages over film and foil capacitors in that they can be self healing, but that is utterly irrelevent to this application.
Metallized capacitors have some advantages over film and foil capacitors in that they can be self healing, but that is utterly irrelevent to this application.
lol, yeah the bigger the better, in my book.
In fact, when I chose my new input caps, what made me took the one over the other, with all other specs the same, was that the ampohm cap was half a centimeter thicker.
I can only recommend part no. 365-7479 from RS components, as I have not yet tried other brands (all of which would be more expensive due to audiphile phenomena).
It is a low ESR 630V DC cap with 5% tollerance it would measure about 2 by 1 inch.
The arcotronix one from RS (384-7868), also looks worth wile, but on values larger than 1uF, is a bit more expensive than the ampohm ones.
In fact, when I chose my new input caps, what made me took the one over the other, with all other specs the same, was that the ampohm cap was half a centimeter thicker.
I can only recommend part no. 365-7479 from RS components, as I have not yet tried other brands (all of which would be more expensive due to audiphile phenomena).
It is a low ESR 630V DC cap with 5% tollerance it would measure about 2 by 1 inch.
The arcotronix one from RS (384-7868), also looks worth wile, but on values larger than 1uF, is a bit more expensive than the ampohm ones.
Overture design guide may help you.
Rin and Cin are the relevant fields and set the high pass frequency. With a 2.5uF or bigger cap and 20k ohm+ input impedance I get 3.4hz as the -3dB low frequency roll off. I dont think I'd go bigger than 2.7uF or so. Rather buy a better smaller cap. If there just isnt money for film and foil, go met poly, you can upgrade later with care.
Bigger is not necessarily better, though it can be. It is not the only factor at play. Too big can lead to excessive inductance.
Rin and Cin are the relevant fields and set the high pass frequency. With a 2.5uF or bigger cap and 20k ohm+ input impedance I get 3.4hz as the -3dB low frequency roll off. I dont think I'd go bigger than 2.7uF or so. Rather buy a better smaller cap. If there just isnt money for film and foil, go met poly, you can upgrade later with care.
Bigger is not necessarily better, though it can be. It is not the only factor at play. Too big can lead to excessive inductance.
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