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This part seems fine to me - I used it in the MMM and plan to use it in the PPA. Is there any point to using an overpriced boutique part here?

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Do you have a 4-wire meter? If not, forget matching such low-value resistors. With my Fluke 189, I don't bother with anything from 10 ohms on down.

well, on the other hand, my buffers use 1/4W smd 4R7 resistors in that place and I've sold lots of them and haven't heard of anyone with them fried or anything.. I'm plugging and unplugging headphones with music playing, even aloud, and there's absolutely no problem..

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Doesn't making voltage dividers and recording the midpoints work? I'd borrow a 9V trickle charge circuit for source. On the other hand, if there's no advantage...

Edit: measure current using a constant voltage source, or voltage using a constant current source, either is better than 5% even on my sketchy meters?

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OK, I'll bite. I believe that a 4-wire meter would be necessary to measure the precise value of a given resistor, but why is it necessary for comparing several resistors, if the meter and cables are unchanged between comparisons? We don't care about the exact value of the measurement, only how it varies between resistors.

Tangent wrote in his Part Selection Guide:

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On the other hand, he gives parts numbers for all equal values, 10mm lead spacing.

So here's a portion of my parts spreadsheet that I'm now thinking through:



Am I ok going to the particular staggered caps shown in alt B? This introduces the MKP 418 line, any differences to concern me from the MKP 417 line?

Am I ok going up to the smallest values that buys me a longer cap, i.e. just making the size breaks for 10mm and 15mm as shown in alt C?

(The board has multiple C2 holes, so both 10mm and 15mm lead spacings fit cleanly, but 5mm would be a stretch, so to speak.)

These caps are all on Digi-Key catalog p950. Balancing cap sizes, lead length, ratio of capacitances for best performance, what is the optimal "even, odd" cap selection for C2, restricting to this catalog page?

Speaking of C2, does anyone know what type caps are in the picture on the PPAv2 web page? (Tangent would know obviously )

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Yeah, a lot of work, though. If you really wanted to be clever, you could build a Wheatstone bridge instead.

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Depends on how 'constant' your sources are. It isn't uncommon for a quick-and-dirty CCS to have a 1% error, or more. If you're going to match resistors to 0.1%, that's not going to be good enough.

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For one thing, down at such low values the varible contact resistance between the probes and the resistor leads is a big source of error.

This is also illuminating.

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Vishay-Somethingorother MKT 1813s. They're actually labelled ERO, but they were definitely sold under the Vishay name, from Mouser.

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So I found myself revisiting Digi-Key page 950 for C5, and came up with these choices:

C2 odd BC MKP 419 400V 10mm 0.022uF 2222 419 42203 BC2194-ND Digi-Key 0.50
C2 even BC MKP 417 160V 10mm 0.22uF 2222 417 42204 BC2099-ND Digi-Key 0.65
C5 BC MKP 416 63V 10mm 0.27uF 2222 416 42704 BC2064-ND Digi-Key 0.65

This gives exactly the C2 values that tested best for Tangent, in pin spacings that cleanly fit the board holes, but at the expense of going to unnecessarily high voltages. C5 is the largest value cap that fits.

On the other hand, Tangent made a recommendation with an unnecessarily high voltage, in choosing from the MKP 417 series rather than from the MKP 416 series for his uniform 0.1uF recommendation for C2. He usually has a good reason for these things; what am I missing? If MKP 416 is to be avoided, then I should change my C5 selection.

In trading off

1. poor fit
2. changing values from tested
3. increasing voltage rating

I went with increasing voltage rating, to get a good fit with tested values. For other cap applications, I've read that wasted voltage rating can be undesireable, but in the absence of feedback from anyone who knows, I'm guessing that here this is the correct optimization.

You know C2 and C5 don't have to be polypropylenes, polyesters work equally fine (negligible audible difference) with a larger selection of parts..

Wima MKS2 63V/1uF fit C5 wonderfully... though I don't know about US availability. BC have equivalent caps (but oh my god, they're not red).

As for C2 the Vishay MKT1813 are also available from RS (for the europeans) as well as mouser.

185-3990: 63V/0·22uF - L:11mm, Dia:5mm
185-4123: 250V/0·022uF - L:11mm, Dia:5mm

I am a bit skeptical regarding this complex bypass capacitor arrangement. Clearly it won't hurt, but will it make a real world difference? Pretend I'm from Missouri and show me.

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I have no doubt Tangent measured something, maybe a person can't pick out one 2% difference blind, but pile on twenty of them? Amb tweaks till he gets a perfect square wave on his scope. I don't want to ever hear a perfect square wave, with my Ety 4s phones I'd think one would make my ears bleed. However, I believe that there's merit to this design approach, simulators will never be able to "wire the last mile" here.

I want to understand what I'm doing, but for me it always takes me much longer to pick parts than to build a working amp, so the cost here is that the question hung me up. If there had been an optimum parts selection posted for this tweak, I would have breezed by this question. Future builders won't see this as a big deal either way.

I plan to post my parts list, not that I have any special knowledge, but I wish that everyone who posted a build pic would also post their parts list for others to use at their own risk. I'd start by loading in their work, then thinking critically. Also more interesting to look at their parts choices than the colors of their caps.

So what hung me up in my most recent parts selection session were the C7 bass boost caps.

In bass boost, Tangent writes:

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The datasheet for

C7 Bass boost film cap Panasonic ECGP 50V 0.12 µF ECQ-P1H124GZ P3124-ND Digi-Key 1.06

lists maximum dimensions 17mm x 8.5mm. The following picture shows this outline; the smaller squares are 0.1":



Morsel's bass boost calculator was the only one I could get working, and then only on a Windows box. My Mac is as fully loaded as possible, I believe that it can be used to cross-develop Java in Swahili for Windows 98, yet both bass boost calculators balked. For comparison, I have no difficulties using any other calculators on Tangent's site.

(I have Mathematica and know how to use it, so I really have no excuse here, the original bass boost threads are still around...)

Morsel's calculator implies a bigger effect from my changing R4 to a 5.4x gain that Tangent's notes suggest will be the case. I've always avoided tone controls, I have no idea if a jacuzzi temperature should be 150F, so I just threw in the towel here and went with Tangent's part. I can always desolder after I hear it.

My bass boost calculator uses the correct equations, and so does amb's. Tangent still uses my 3 year old numerical approximation, which is not as accurate. If you are having problems on a Mac, make sure you are running a good up to date browser like Firefox or Mozilla.

As for my comments about the PPA v2 odd/even cap scheme, I am suggesting there may be no real world difference even with a scope and RMAA.

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http://www.pa.msu.edu/hep/d0/ftp/run...pling_caps.pdf
http://www.avxcorp.com/docs/catalogs/caparray.pdf
http://www.analog.com/library/analog...5-02/avoiding/
http://www.latticesemi.com/lit/docs/...TOKEN=87373138
http://www.eetasia.com/ARTICLES/2004..._AMD_TAC01.pdf
http://www.xilinx.com/bvdocs/userguides/ug072.pdf