[Coco] WTB Orchestra 90 cartridge

Bill Pierce ooogalapasooo at aol.com
Tue Aug 2 18:38:57 EDT 2016

<Applause> Good job!



Bill Pierce
"Charlie stole the handle, and the train it won't stop going, no way to slow down!" - Ian Anderson - Jethro Tull


My Music from the Tandy/Radio Shack Color Computer 2 & 3
Co-Contributor, Co-Editor for CocoPedia
Global Moderator for TRS-80/Tandy Color Computer Forums

E-Mail: ooogalapasooo at aol.com



-----Original Message-----
From: Zippster <zippster278 at gmail.com>
To: CoCoList for Color Computer Enthusiasts <coco at maltedmedia.com>
Sent: Tue, Aug 2, 2016 2:40 pm
Subject: Re: [Coco] WTB Orchestra 90 cartridge

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>>>>> >>>> >>>> >>>> -->>>> Coco mailing list>>>> Coco at maltedmedia.com>>>> https://pairlist5.pair.net/mailman/listinfo/coco>>>> >>>> >>>> -->>>> Coco mailing list>>>> Coco at maltedmedia.com>>>> https://pairlist5.pair.net/mailman/listinfo/coco>>> >>> >>> -->>> Coco mailing list>>> Coco at maltedmedia.com>>> https://pairlist5.pair.net/mailman/listinfo/coco>>> >>> >>> -->>> Coco mailing list>>> Coco at maltedmedia.com>>> https://pairlist5.pair.net/mailman/listinfo/coco>> >> >> -->> Coco mailing list>> Coco at maltedmedia.com>> https://pairlist5.pair.net/mailman/listinfo/coco>> > > -- > Coco mailing list> Coco at maltedmedia.com> https://pairlist5.pair.net/mailman/listinfo/coco-- Coco mailing listCoco at maltedmedia.comhttps://pairlist5.pair.net/mailman/listinfo/coco

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