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Old 8th February 2013, 03:29 AM   #3091
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Hi guys, new to DIY. I ordered the kit from headn'hifi, I know how to solder and have all the right tools. BUT I can't work out how to sort and label all the parts I got and match them with the reference numbers on the BOM.

main problems is the tiny resistors. Do I really have to look at each color code and slowly decipher them? Only problem there is the resistors seem to have 5 stripes and i'm not sure how you tell which end to start at.

Sorry for the novice questions
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Old 8th February 2013, 04:05 AM   #3092
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Default A question about bypass cap.

I finished building my 1st O2 successfully.During the build process a ques. popped into my mind ( Pls don't misunderstand me, I'm not doubting RS's design capability)-

In all audio system/sound cards employing opamps, I've seen a pair of small bypass cap. (typ. 0.1uF) located close to +V pin & gnd and -V pin & gnd of each opamp. Instead O2 has 0.22uF (6 of them- 2 for reg., 2 between +V/-V to gnd., 2 between +V & -V)but they are located far from both +/- pin of opamp(except C17,18 but still not in pairs for each JRC4556 ) & also not in pairs(1 for each rails). IMHO their should be 6 more bypass cap. in the existing design.I thought of adding bypass cap. underneath the PCB myself, but feared it might upset carefully designed ground plane layout by RS.

Any comments or thoughts are welcome
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Last edited by availlyrics; 8th February 2013 at 04:11 AM.
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Old 8th February 2013, 04:15 AM   #3093
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Quote:
Originally Posted by Bassd View Post
Hi guys, new to DIY. I ordered the kit from headn'hifi, I know how to solder and have all the right tools. BUT I can't work out how to sort and label all the parts I got and match them with the reference numbers on the BOM.

main problems is the tiny resistors. Do I really have to look at each color code and slowly decipher them? Only problem there is the resistors seem to have 5 stripes and i'm not sure how you tell which end to start at.

Sorry for the novice questions
Use/Buy a multimeter(even the El Cheapos will do) for measuring resistors & capacitors it will help a lot
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Old 8th February 2013, 05:46 AM   #3094
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Quote:
IMHO their should be 6 more bypass cap.
There's nothing that says 1 cap can't work for more than 1 op amp. The O2 obviously doesn't need the extra bypass caps.
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Old 8th February 2013, 06:04 AM   #3095
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Quote:
Originally Posted by sofaspud View Post
There's nothing that says 1 cap can't work for more than 1 op amp.
Ok but what about the distance from +/- V pins of opamps & the cap. (C17,18 & U1)?.Though I admit the use/location of bypass cap. depends between the PCB designer's implementation & opamp datasheet recommendation. I think I've read this on tangentsoft "Use SMD cap. for bypass or use shortest lead for connecting to +/- pins of opamp & the remaining (longer) lead of the through hole cap. to gnd. to avoid lead inductance",
BTW I've not heard anybody's O2 going into HF oscillation though
How I wished RS was here to answer this Q.!
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Last edited by availlyrics; 8th February 2013 at 06:12 AM.
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Old 8th February 2013, 06:33 AM   #3096
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tangentsoft is, IMHO, referring to the ideal. Surely in many many situations SMD is not a must, but in many many situations it would be the ideal implementation. Working in 3 dimensions on the circuit board necessitates some compromise. My recollection from RS's blog is that the circuit board layout was perhaps his greatest challenge with the O2.
My knowledge here is admittedly sketchy at best, unfortunately. I'm just a perpetual student of this stuff. My understanding of bypass theory though is that capacitance can be used to swamp inductance and vice versa. It's the negation of reactive parasitics that is one of the main goals in the selection of components and layout to achieve suitable bypassing.
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Old 8th February 2013, 08:21 AM   #3097
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With strict criteria like - using only thru holes comp.,AC/DC op, min. foot print, real world h/p drive capability backed by solid specs.... even RS admitted having difficulty in sharing real estate of PCB with 3-PCB mounting holes!
Still hats off to RS & special thanks to "jtktam" for providing PCBs & "swalter" for the critical components, without which I'd still be listening to CMOYs.
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Old 8th February 2013, 09:24 AM   #3098
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Quote:
Originally Posted by sofaspud View Post
...Surely in many many situations SMD is not a must, but in many many situations it would be the ideal implementation...
Yeah, especially when using opamps with slew rate in excess of 2,000V/usec. designed for non-audio applications to drive headphones!
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Old 8th February 2013, 06:38 PM   #3099
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No doubt in my mind that if the O2 used fast op amps like that the circuit would look different.
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Old 8th February 2013, 08:57 PM   #3100
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Everybody probably knows all of this already. But I'm happy that someone is even thinking about it at all. I do also think that it's a lot more important than many people believe.

There's bypassing and there's decoupling. People use those two words in different ways, often interchangeably. But in this post, by bypassing I mean using a capacitor to short-circuit high frequencies, which is needed because of the hidden positive feedback loop, through the power rail, that exists in many/most transistor amplifier topologies, at high frequencies.

For bypassing high frequencies, a capacitor that is more than two millimeters from an IC's power pins is probably too far away, in many cases, mainly because of the inductance of the conductors. You wouldn't hear the oscillations or ringing, because it would be at RF frequencies. But it could degrade the system's performance, possibly only subtly. It could also contribute to significanty hotter device temperatures.

For bypassing, the best practice is usually to use the capacitor with the smallest case size, since the capacitors don't usually have much intrinsic inductance, except for the equivalent of the self-inductance of a conductor with a length equal to the case length (or the lead spacing plus lead length, for a through-hole cap). So, usually, the largest capacitance value available in the smallest case size that will work is what would be used. Sometimes improvements can be had by mounting them in unusual ways, such as on their side (for surface mount).

Decoupling is when a capacitor is used as a local supply of current transients. Bypass capacitors will also provide as much decoupling as they can. But typically more capacitance is needed.

Decoupling caps could supply the transient current demands of more than one IC or active load. But their value and their distance from each load will determine at up to what amplitude and at up to and down to what frequencies they can be effective-enough.

It is relatively easy to calculate the worst case minimum capacitance required and the maximum distance or inductance that can be tolerated, given the load's current requirements and the acceptable maximum rail-voltage disturbance per unit of current for the worst-case shortest and longest time intervals.

But to get it right you usually do have to actually calculate them, because they can easily surprise you (although that's probably more common in decoupling for power amp output stages). It is also fairly common for there to be NO good-enough solution that can be physically implemented, especially when using DIY through-hole construction, without either using multiple smaller parallel caps, or, using real ground and power planes and many paralleled caps plus very-low-inductance connections to the planes.

But ALWAYS, it's a tradeoff, because you can always make the system's response more accurate if you spend more time or money or both on improving the decoupling capacitors' configuration.
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