Doepfer

> hello dirk,
>
> well, i'm not sure, but after reading your answer
> i think some of this could be normal behaviour.
> the dry/wet control is a linear crossfade and not
> an "equal power" crossfade, so you have a level drop
> at the center position, this is normal. the bbd output
> is not of the same loudness than the input signal
> (or dry signal), but that is also normal. almost all
> modules alter the loudness in some ways.
> thats why i suggested that you compare the level of
> your bbd module with the output of a filter (which
> usually alters the signal loudness too).
>
> strange is that the lowest level on your bbd
> is not when the mix knob is in center position,
> and that the output is inverted.
>
> dieter, maybe you can chime in and help us?

OK, here is my comment.

1. The output levels of the six different BBD circuits (128...4096
stages/MN3xxx) are a bit different. Consequently the A-188-1 modules with
different stages and circuits behave a bit different. Even BBD circuits with
the same number of stages but different circuit types (e.g. 256 stage BBD
circuits MN3009 and MN3209) are a bit different.

2. The output impedance of the A-188-1 is about 5k. It's because the mix
between the original and BBD signal is made with a linear 10k potentiometer
with the original signal on one terminal and the BBD signal on the other
terminal. The center terminal is the module output. Consequently in the
leftmost or rightmost position the signals (original or pure BBD) appear
without additional serial resistance as the potentiometer is at one of it's
end positions. In the center position the two signals are mixed via 5kOhm
each (10k/2 = 5k). This is why the level becomes a bit lower in the center
position. It depends upon the ouputload how much the level decreases. As
most A-100 modules have a 50k potentiometer at the audio input the level
drop will be about 10% (5k/50k). If the A-188-2 output is connected to a
load less than 50k the level drop may be more. We think about an additional
circuit on the board that compensates the level changes. But as the is no
more space on the pc board a complete redesign would be necessary.

3. The original signal appears indeed inverted at the output. But as the
module has a polarity switch for the BBD signal an additonal polarity switch
for the original signal would not add new features. It would have been
possible to plan a polarity switch for the original signal instead for the
BBD signal but the audible effect would be the same. I can't see any
application where the non-inverted original signal would be necessary.

Best wishes
Dieter Doepfer