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

From Jason Proctor
Sent Fri, Jan 25th 2019, 18:43

seems like someone has yet to discover the filter cutoff knob?

i loved the Doepfer SEM filter but somehow could never find two that
sounded anywhere near alike. i know #analogue but they weren't even
comparable. i thought one i had was a Wasp filter behind an SEM panel,
even...


On Fri, Jan 25, 2019 at 10:41 AM skkatter <xxxxxxxx@xxxxx.xxx> wrote:
>
> SEM filters sound great. I tried sticking two SEM oscillators into five S=
EM filters and mixed all the bandpass outputs together to get this: https:/=
/www.instagram.com/p/Biu7s0UgekB/
>
> -Stephen
>
> On Fri, 25 Jan 2019 at 16:50, 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 =
and component differences. First the disclaimer that the only SEM filter I =
have is the Dopefer and Studio Electronics SEM filters. But I do like both =
of them.
>>
>> Recently I've been using the Nord Modular is a digital oscillator for a =
Eurorack system, feeding the SEM/doepfer bandpass. I noticed that when send=
ing the SEM a polyphonic signal, say a duophonic oscillator with arbitrary =
pitch spacing (fifth, seventh etc.) the result sounds a bit ring modulated.=
 It took me a lot of patching into alternate filters and double checking ev=
erything to conclude that it is the SEM filter is what was doing this. Perh=
aps 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 an=
cestors. However, a few kinds of capacitor chemistries simply aren=E2=80=99=
t available SMD. One example is for Sample and Hold, where super-low-leakag=
e poly caps simply aren=E2=80=99t available in SMD. Of course, there are ot=
her SMD caps that are good enough for S&H, but maybe those tropical fish ca=
ps were poly? Maybe they were mica? Foil? I=E2=80=99d be curious to know th=
e manufacturer and model of those caps.
>>> >
>>> > Lots of old caps were really bad, and nobody really wants the problem=
s any more. Again, it=E2=80=99s not that their value changes, it=E2=80=99s =
that they don=E2=80=99t act exactly like a pure capacitor, but more like a =
complex 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 inductor=
s?
>>> >
>>> > 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 w=
ould care to admit it seems). The former is brighter and sharper when reson=
ance 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 t=
he likely culprit is the tropical fish caps that the old one uses and the n=
ew ones do not. OGG pulled the tropical fish cap on his old SEM and replace=
d 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 =
because he didn't/couldn't put the through hole trop. fish cap in the new S=
EM's SMT PCB, but it does strongly suggest that with some very minor tweaki=
ng, one could get the new ones to sound identical to the old.
>>> >>