[Coco] WTB Orchestra 90 cartridge

[Zippster]

The DACs seem to be working ok.

<https://drive.google.com/open?id=0B1sgl615FlGnY2dEMVpvWHFoZ3M <https://drive.google.com/open?id=0B1sgl615FlGnY2dEMVpvWHFoZ3M>>

- Ed



> On Aug 1, 2016, at 10:39 PM, Jayeson Lee-Steere <cocolistemail at titaniumstudios.com> wrote:
> 
> 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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