[Coco] WTB Orchestra 90 cartridge

[Jayeson Lee-Steere]

Sure is an interesting topic.

One point in the link shared earlier is that for decoupling caps, the
distortion is scaled down according to the relative voltage drop across the
cap. Using an oversized cap value will reduce the voltage drop and
therefore the distortion. For this particular usage, I wouldn't be overly
concerned about distortion from ceramic decoupling caps.

However, the piezo effects are potentially huge. I just soldered a 10k
resistor across a 1uF 1206 MLCC cap. Tapping that arrangement with tweezer
points easily generated spikes approaching +-10v.  I'm interested in how
NPO/low K cap types would go, but it seems easier to just use polyester and
be done with it.

I guess one other note is that the circuit has some low value caps to
ground. They look to me to be for RF suppression and so I think should be
ceramic. I'm pretty sure there are plenty of low K options available in
those small values.

Jayeson

On Tue, Aug 2, 2016 at 6:30 AM, Zippster <zippster278 at gmail.com> wrote:

> This is a pretty interesting topic, and I’ve learned quite a bit
> researching it.
> It would seem that while ceramics are on the bad end of the scale (in
> general)
> when it comes to harmonic distortion of audio, they are commonly used in
> the
> audio path, especially where size is a factor.
>
> Not all ceramics are equal, and it’s pretty clear a lot of the bad
> reputation comes
> from larger, through hole components, especially using the less stable
> dielectrics.
>
> I saw some information in manufacturer application notes indicating SMT
> packages
> using X7R dielectric to be similar to tantalum SMT packages in THD of
> audio, around .1%
> in their comparison.  Which doesn’t sound too bad, but didn’t compare to
> polyester
> at .001% or less.  Electrolytic came in ~.05% or so.
>
> Some ceramics seem to be more suitable for the audio path, Class I-C0G-NPO
> type,
> with their more stable capacitance.  I would guess closer to electrolytic
> in distortion.
>
> So relatively speaking, film is best, then electrolytic, then tantalum and
> ceramic.
> Another interesting question though is, how much THD is too much?  One
> manufacturer page
> added some perspective by noting that the worst ceramic in their test, a
> through-hole using X5R
> dielectric with THD of .2% at -3dB, still paled in comparison to the THD
> caused by audio DACs
> and codecs.
>
> Though a lot is made of capacitor induced distortion in audio, I’m
> guessing it’s somewhat
> overstated.  At least in a lot of situations.
>
> Anyway, since we aren’t especially space constrained on this board, I’ve
> picked out some non-polar
> SMT electrolytic caps for the final PCB version, since there’s certainly
> no reason not to go that
> route.  It’ll make an interesting comparison when I have boards built both
> ways in hand later too.
>
> Learning is fun…  :)
>
> - Ed
>
>
>
> > On Aug 1, 2016, at 4:13 PM, Simon Jonassen <simon at roust-it.dk> wrote:
> >
> > You *can* use a nonpolar mylar cap with good results... (I know from
> playing with various audio preamp circuits over the years (mostly riaa))
> >
> > /Simon :-)
> >
> >
> > -----Oprindelig meddelelse-----
> > Fra: Coco [mailto:coco-bounces at maltedmedia.com] På vegne af Zippster
> > Sendt: 1. august 2016 20:05
> > Til: CoCoList for Color Computer Enthusiasts
> > Emne: Re: [Coco] WTB Orchestra 90 cartridge
> >
> > It’s certainly standard operating procedure.  Not a big deal to change
> it.
> >
> > - Ed
> >
> >> On Aug 1, 2016, at 12:59 PM, Simon Jonassen <simon at roust-it.dk> wrote:
> >>
> >> I would tend to agree that any audio OUTPUT that needs to be AC coupled
> (eg dc filtered out) should use an electrolytic cap
> >>
> >> just my 2c
> >>
> >> /Simon :-)
> >>
> >>
> >> -----Oprindelig meddelelse-----
> >> Fra: Coco [mailto:coco-bounces at maltedmedia.com] På vegne af Zippster
> >> Sendt: 1. august 2016 15:02
> >> Til: CoCoList for Color Computer Enthusiasts
> >> Emne: Re: [Coco] WTB Orchestra 90 cartridge
> >>
> >> Things can get a little weird when you get into audio land with
> opinions on capacitors, but…
> >>
> >> I think ceramic will be fine here considering the value (.1uF), and use
> (ac coupling).
> >> If we were using a much larger value, I’d probably agree and go
> electrolytic or film.
> >>
> >> In any case, I’ll put a scope on it and take a look at the signals.
> >> As well as the highly subjective test of human ears.   :)
> >>
> >> - Ed
> >>
> >>
> >>> On Aug 1, 2016, at 2:44 AM, Jayeson Lee-Steere <
> cocolistemail at titaniumstudios.com> wrote:
> >>>
> >>> On audio, there are a lot of options about which caps are appropriate
> for
> >>> audio, but all references I have seen say that ceramics are not an
> >>> appropriate choice in the audio path. Given their strong piezoelectric
> >>> properties, it is not clear to me what are appropriate uses for the
> >>> recently available, high value MLCC ceramic caps. Too bad, because
> they are
> >>> smaller and less costly than tantalum.
> >>>
> >>> This reference on audio caps seems fairly balanced:
> >>> http://sound.westhost.com/articles/capacitors.htm
> >>>
> >>> Film capacitors are the thing to use where practical. It would seem
> some
> >>> film types are better than others, but for this use, polyester would be
> >>> more than sufficient. That is probably what the small value caps are
> in the
> >>> original Orch 90. Next down the line are electrolytics, which are
> >>> apparently fine for audio coupling if an appropriately large value is
> used.
> >>>
> >>> Jayeson
> >>>
> >>
> >>
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