Hello all,

I'm in the company today as we have to take inventory during we are closed
and found some messages from the group. Here are my comments to some of the
messages:

Erwik filter:

Try to contact Jesper Erwik Johansson ( jesper.johansson@... )
concerning the required current. We were in contact during the development
of the A-107 as this module is based on his filter. The A-107 uses the same
filter circuit as the Erwik and Oberheim filter. Doug Curtis of CES told me
that the filter section of the CEM3372 is exactly the same as of the
CEM3379. Only the additional VCAs are different (2 VCAs at the input for the
CEM3372, 2 output panning VCAs for the CEM3379). The basic principle of the
Oberheim, Erwik and A-107 is the same: the 4 outputs of the filter stages
(i.e. the 6/12/18/24 dB outputs of the low pass) are mixed toghether with
different amplitudes and signs to obtain the different filter types. For the
Oberheim and Erwik filter 15 fixed amplitude/sign relations are realized
with fixed resistors and electronic switches. Instead of this the A-107 uses
4 VCAs to be able to obtain any relation of the 4 filter stages and to add
the morphing feature (i.e. smooth transitions between the different filter
combinations). The control voltages for the 4 VCAs are generated by 4 DACs
(digital to analog converters) that are controlled by a microcontroller
(uC). The parameters for each filter type (36 for the A-107 instead of 15)
are stored in the uC memory. To obtain morphing each VCA control voltage is
processed by a voltage controlled slew limiter. So a lot of hardware is
required to obtain all the A-107 functions (24 dB filter low pass + 4 VCAs +
4 DACs + 4 VC slew limiters + uC).


Modification of guitar stomp boxes (and similar) for external control:

One solution (as described by Florian) is to use an external clock. All BBDs
I know require a dual phase clock with opposite polarity. Normally a
flip-flop (e.g. CD4013) or a special circuit (e.g. MN3102) is used to
generate the dual phase clock from a normal (single phase) clock by
frequency division (1:2). One has to find out the type of power supply used
in the box in question (e.g. single like +9V or +12V, or dual like +/-5V,
+/-9V) to find the right solution for the level of the external clock signal
and the insert point of the circuit. Normally a npn-transistor with a
pull-up resistor to the positive terminal of the internal power supply will
do the job. But that's nothing for electronic beginners.

Another solution is the usage of the announced universal vactrol module
A-101-9. Normally a variable resistor (potentiometer) is used for the
internal clock circuit. One of the vactrol outputs of the A-101-9 has to be
connected in parallel to this potentiometer and the potentiometer has to be
turned to it's max. setting (i.e. to the longest delay time). Now the clock
rate (and consequently the flange/chorus/delay time) is controlled by the
control voltage fed into the A-101-9.


Battery of A-112 (even valid for MCV24, Regelwerk, Schaltwerk):

We will add a remark to all manual of these devices that the battery
(chargeable version, "accumulator") should be checked about every two years.
The batteries are available as spare parts from us but even most of our
representatives have them in stock. Standard 3.6V chargeable batteries for
memory protection are used. They are even available in electronic shops.


Clock suppression for BBD devices:

The A-188-1 will become a small additional redesign with an additional CV
output that reflects the sum of all CV inputs (i.e. manual control + CV1
without attenuator + CV2 with attenuator). This can be used to control the
CV input of an external VCF (low pass) that follows the BBD setting.


Free pc boards:

We have already changed our production to lead-free soldering and lead-free
parts end of last year. We have a lot of unassembled pc boards left that are
not yet lead-free. As it is not possible to combine both types of pc boards
in the production series (because of pullution of the solder bath) we give
away these pc boards to A-100 DIYs for free (only together with any A-100
order because of the shipment charges). A detailed list will follow soon.
The A-100 service manual is required as you need to know the parts list,
position of the electronic parts and so on. Otherwise we will ask for ~ Euro
5 for the copy of the service manual of the module in question. Attention:
the assembly and adjustment procedures in the service manual are in German
language only.


All the best for the new year

Dieter Doepfer