From Andrew Horton Sent Fri, Jan 25th 2019, 16:52
Side question with all this talk; has there even been a SEM patch that sounded like anything other than a muffled flugelhorn? On Fri, Jan 25, 2019 at 11:50 AM Royce Lee <xxxxxxxxxx@xxxxx.xxx> wrote: > > SEM filter observations: hopefully these comments will not be off topic. > Perhaps this may be relevant to the conversation about Oberheim filters a= nd component differences. First the disclaimer that the only SEM filter I h= ave is the Dopefer and Studio Electronics SEM filters. But I do like both o= f them. > > Recently I've been using the Nord Modular is a digital oscillator for a E= urorack system, feeding the SEM/doepfer bandpass. I noticed that when sendi= ng the SEM a polyphonic signal, say a duophonic oscillator with arbitrary p= itch spacing (fifth, seventh etc.) the result sounds a bit ring modulated. = It took me a lot of patching into alternate filters and double checking eve= rything to conclude that it is the SEM filter is what was doing this. Perha= ps this is simply the effect of filter saturation. But this filter does it = more than other filters I use. > > Royce > > > On Fri, Jan 25, 2019 at 9:47 AM Sam Mims <xxx@xxxxxxx.xxx> wrote: >> >> The tropical fish caps are made by Mullard - here's one used in the >> Minimoog: >> >> https://syntaur.com/Items.php?Item=3D1285 >> >> Sam Mims >> Syntaur >> >> >> >> On 1/25/2019 1:14 AM, Brian Willoughby wrote: >> > There=E2=80=99s more to a capacitor than its capacitance. There=E2=80= =99s also ESR and leakage, as well as microphonics. Just because the same c= apacitance is reported doesn=E2=80=99t mean it=E2=80=99s the same cap. >> > >> > Many modern surface mount caps are exactly like their through-hole anc= estors. However, a few kinds of capacitor chemistries simply aren=E2=80=99t= available SMD. One example is for Sample and Hold, where super-low-leakage= poly caps simply aren=E2=80=99t available in SMD. Of course, there are oth= er SMD caps that are good enough for S&H, but maybe those tropical fish cap= s were poly? Maybe they were mica? Foil? I=E2=80=99d be curious to know the= manufacturer and model of those caps. >> > >> > Lots of old caps were really bad, and nobody really wants the problems= any more. Again, it=E2=80=99s not that their value changes, it=E2=80=99s t= hat they don=E2=80=99t act exactly like a pure capacitor, but more like a c= omplex combination of capacitor, resistor, and inductor. >> > >> > That said, why hasn=E2=80=99t someone just recreated the flaws of the = old tropical fish caps by adding parallel or series resistors and inductors= ? >> > >> > Brian >> > >> > >> > On Jan 23, 2019, at 8:10 PM, M V <xx_xxxxxx@xxxxxxx.xxx> wrote: >> >> Speaking of the new and old SEMs though, it's pretty well known that = there is a clear difference between the new and old filter (more than TO wo= uld care to admit it seems). The former is brighter and sharper when resona= nce is at max, and not just because of an increased cutoff range. However, = it came to light recently through the work of Oldgearguy over on GS that th= e likely culprit is the tropical fish caps that the old one uses and the ne= w ones do not. OGG pulled the tropical fish cap on his old SEM and replaced= with a modern hi-fi cap and found that the filter pretty much sounded the = same as the new SEM. So this is sort of proof through absence of evidence b= ecause he didn't/couldn't put the through hole trop. fish cap in the new SE= M's SMT PCB, but it does strongly suggest that with some very minor tweakin= g, one could get the new ones to sound identical to the old. >> >>