EMS filter construction

[Paul Maddox]

Harry,

  I built this one, its in modulus issue somewhere..
It sounds awefull.. I used a TL074 for all opamps, and a CA3046
for the transistors.
  Yes the Resonance mess's around with the volume something
chronic..

  To be honest, its not worth the parts cost... it sounds awefull.
But, some may like it.

  Paul

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-----Original Message-----
From:	Harry Bissell [SMTP:harrybissell at prodigy.net]
Sent:	Thursday, September 09, 1999 4:57 AM
To:	Blandon Ray
Cc:	Synth DIY
Subject:	Re: EMS filter construction

The first 2 opamps could be 741 with no problem at all. The 741 is not a
'bad' opamp.
It has several benefits...
It is well protected... the current limit capabilities save it from
anything other than a short to a higher voltage (beyond the supply
rails... like 120VAC for instance).
It is slow and usually won't oscillate... its good for control voltages
It doesn't have "phase reversal" problem, where if you overdrive (exceed
common mode input range) the opamp will run to the opposite rail (positive
overrange = negative output) and will not latch there... This is a very
real problem...
Its cheap...

The third opamp could be a TL074... but it is much faster and could
oscillate.. add a few picofarads capacitor from the output to the
inverting input and it should behave...

The transistors could be a CA3046 array... use the differential pair for
TR2 and TR3 (pins 1-5 of 3046) and use pin 13 for the emitter of TR4 (the
substrate must be most negative point)  The matching will improve
performance.

C2-C5 should be well matched, use 1% polystyrene if you can...

All the diodes should be matched in pairs (D3-D10, D4-D11...)

ATTN LIST: It looks like the resonance and the volume controls interact. I
haven't built this one... Do they ???

Best of luck... let us know how it works (or doesn't)

:^) Harry

Blandon Ray wrote:

> I originally sent this to AH, but at the suggestion of a listmember
> I'm forwarding it here as well...
>
> greetings all,
>
> Now that I have been able to build several Paia kits with reasonable
> success (most recently a Fatman, with which I am very pleased), I
> want to increase my skills and tackle a true DIY project. For
> starters I thought I would try to build this EMS filter, just as an
> exercise:
>
> The schematics can be found at music machines:
> http://machines.hyperreal.org/manufacturers/EMS/schematics/emsfilt.gif
>
> This specifies 741 opamps, but knowing the conventional wisdom on
> that part I thought I'd try to use something better. I did check the
> archives, but I found a wide variety of opinions on what to use as a
> replacement, so I thought I'd seek some feedback on this particular
> application. If I read the schematic right, IC1 and IC2 are buffers,
> and IC3 is in the signal path as part of the Resonance circuit (I
> don't know enough to look at these things and exactly tell their
> function; that's partly why I want to try building this). Also there
> are these BC109C transistors, which from what I've read seem to be
> obsolete as well.
>
> So if anyone has any recommendations on these issues (or in
> general), I'd appreciate it.
>
> blandon