Re: [AH] Behringer announces OB-Xa clone project

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.
>> >>