[sdiy] coupler module

[Czech Martin]

Good ideas!

The microphone input amplifier with phantom power
is certainly a good thing to have.
For some reason I think it is a module of it's own,
hard to explain.

Same applies to envelope followers etc.

Headphone amp to listen to the line out is really very important.

Balanced out:

-ahhh, I have to look into that. I will build an experimental
 balanced I/O system (very cheap construction) and have
 a look into the noise longer shielded or banana lines will pick up.
 But anyway: digital recording gear tends to bounce up and down
 arround mains ground (because of inductance the internal
 high frequent noise can do this). This is even more true
 if a connection to a computer chassis exists.
 Quiet analog inputs thus look like noisy unless
 balanced wiring is used that suppresses commmon mode
 noise. I experience some -60dB noises that are phase
 modulation products of the DSP clock frequency.
 E.g. if you move the mouse, if interrups come
 it makes some noise pattern change, etc. 

Levels: 
unfortunately there are many different level inside
a synth, and also outside. My examples were in some way
extreme, but not impossible.
This was dicussed already a few years ago.
E.g. a cascade filter will need small signal levels,
like 10mV, this is also true for other structures
wich use "linearised" junctions as variable gain circuits.
Control signals OTOH will have about +-10V levels.
Other modules which do not use "linearised" junctions
will accept 1V to 10V level.
Since you can not decide when something is control
or not control, you end up with 10mV to 10V level (peak).

Forcing your system to -say- 1V level at all patch wires
would mean insane combinations of amplifiers (10x 100x 1000x)
and pads (0.1 0.01 0.001) which would spoil S/N or accuracy.

So some flexibility inside the system is needed to avoid
subsequent amplification and attenuation as much as possible.

So perhaps some pad/regeneration module will be needed
if you want to avoid such circuits in any module input
or output.


EQ:

perhaps the modular concept should be followed.
The I/O system should provide the basic things,
-unbalanced to balanced and vice versa
-level meter (why not mechanical) and overload light with memory
-some level management

the rest , like EQ, mic amp etc. could be managed by additional
modules. these should run with higher levels (1V or so)
so that patching wire noise etc. does not destroy performance.
So some level adapter module will certainly be needed for
signal pathes with lower levels (100mV).
>From that point of view the level management of the I/O
is obsolete in some way.


A modular system may have serval LP, HP, BP VCF,
but usually they have no subtle influence on the signal.
A 6dB fixed (not voltage controlled) 
shelving filter for a  more subtle influence
is therefore not such a bad idea.
And the S/N and distortion without voltage control
is usually also better (except perhaps vactrol).


m.c.


 



> -----Original Message-----
> From: Peachey, Dave [mailto:dave.peachey at rbs.co.uk]
> Sent: Dienstag, 26. August 2003 12:19
> To: Sdiy (E-mail)
> Subject: RE: [sdiy] coupler module
> 
> 
> Martin,
> 
> To add to the (wish)list of facilities:
> a)  You might want to consider adding a microphone input of 
> some description
> (for the all-important treatment of your vocalisations using all the
> exciting wave shaping modules people on the list have been discussing
> recently) - you could give it variable sensitivity for 
> different mike types
> and, go on, add a 48V phantom power supply as well!!
> b)  If you're going down this route, an input envelope 
> follower circuit of
> some description (with some sort of gate/trigger derivation 
> to allow for
> triggering of on-synth envelope generators, sequencers, etc.) 
> would also be
> useful.
> c)  Others thing could be some form of headphone output, a 
> simple stereo
> power amp output to drive speakers, etc . . . .
> 
> On a more practical note, however:
> a) is balanced operation really necessary given the 
> unshielded nature of
> some (particularly those banana-jack-based modular synth) "internal"
> connections?
> b) as you're connecting to the outside world, would it not be 
> easiest to
> scale down to 'normal' line level outputs (+/- 100mV) without having
> multitudinous options?
> c) do you really need to EQ your synth at this point?  Surely 
> EQ can be
> undertaken within the body of your synth (OK, I'm thinking 
> primarily of
> modular synths with a variety of filter options/modules 
> available) or, for
> live playing, at the mixing desk/amplification point?
> d) yes, certainly some form of overload output level 
> detection but can't see
> the need for effects send/return
> 
> Personally, I'd make this unit as simple as possible because 
> I can't really
> see you losing the need for a small dedicated mixer of some 
> sort - do you
> really need to reinvent that particular wheel in this 
> context?  Or am I on
> the wrong track entirely?
> 
> Cheers
> Dave
> 
> > -----Original Message-----
> > From:	Czech Martin [SMTP:Martin.Czech at micronas.com]
> > Sent:	Tuesday, August 26, 2003 9:34 AM
> > To:	Sdiy (E-mail)
> > Subject:	[sdiy] coupler module
> > 
> > *** WARNING : This message originates from the Internet ***
> > 
> > Every synth needs a coupling module to the tape machine or 
> mixing desk.
> > 
> > I plan to build some soon, containing:
> > 
> > -4 balanced inputs, 2 balanced outputs (trafo or electronic)
> > -2 or 4 (several) unbalanced inputs (for other synths)
> > -input or output scaling circuits (the analog synth can 
> have +-13V or
> > +-100mV
> >  as extremes), the usual levels are -10dBu = 0.245 V RMS ~ 
> 0.35V peak
> >                                  or   6dBu = 1.55  V RMS ~ 
> 2.2 V peak 
> > 
> >  assuming that 0 dBu = 0.775V RMS and sine wave form.
> >  So gains of 37,    0.29,  5.9 , 0.045
> >           or 0.027, 3.4,   0.17, 22    (reciprocal)
> >  can be needed, so a range of 37 to 0.027 seems to appear.
> >  This is no problem since resistor networks can be changed
> >  if necessary. Plug in connections of resistors on the PCB
> >  seems to be a good idea.
> > 
> > -A good question is if any EQ is needed. Shelving bass and treble
> >  and perhaps some mid bell shaped EQ.
> > 
> >  I'm not sure if this needed. It could save a mixing desk.
> > 
> > -Another question is if any external effects send/return is needed
> > -Certainly a level meter plus overload indicator with hold/reset
> >  is needed for the line out.
> > 
> > If all features are build, I end up with a little mixing desk.
> > That is certainly too much. 
> > 
> > So what is your practical experience?
> > What is needed?
> > 
> > Martin Czech
> > 
> >  
> 
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