BYOC Flanger - with modified mix circuits (3 total):
1. Moved R23 flanger feedback to input of IC1a pin 2
2. Changed BBDa/b mix circuit for equal balance and volume (as shown above)
3. Moved wet/dry mix to input of IC5b pin 2 (no separate R27)
First, a reference article for the last post explaining the difference between the
passive and active mixing circuits and why I changed the mixing point to be directly
at the op amp IC5b input pin 3 instead of first passing through R27.
http://sound.westhost.com/articles/audio-mixing.htmAfter multiple tests and configurations I could not hear any difference between
the BYOC Normal/Differential modes. With the change to the BBDb cap to 0.2uF the
tone in the Differential mode is slightly warmer but not really significant. TODO:
There were some suggestions from Mark Hammer that a useful improvement for increased
feedback would be from changing the cap after the feedback pot from 0.1uF (as on
BYOC) to something smaller. Both the MXR (15nF) and EM (4.7nF) use smaller caps in
this position so this should be changed. This may improve the deep flanging
typically used with the MXR. NOTE: The MXR uses the neg input (mix point) of the op
amp where the clean and feedback sum. The EM uses the pos input of the op amp where
the signal then feeds/passes the dry signal to be mixed later. The BYOC is really
like neither but could be made to be more like the MXR (as was done previously).
For me, the original goal of building the BYOC Flanger was to get a combination of
both the MXR Flanger and the EH Electric Mistress.
The MXR Flanger was always obtainable but was vastly improved by two things:
1. The movement of the feedback to the input of the Opamp at IC1a pin 2 (I used the 10k resistor R8 as my connection point).
2. The movement of the wet/dry mix point to a “proper” active mix circuit at the
input of the Opamp at IC5b pin 2.
The Electric Mistress was more elusive. While it was certainly close in the original
configuration. The differential mode really did nothing to enhance or replicate the
EM tone. After testing it appears that the most significant difference created by
the EM circuit is that the feedback path enters the circuit BEFORE the dry signal is
separated. This means that when feedback is used even a little there is some delayed
signal injected into the “dry” signal and then mixed with the delayed (and feedback
enhanced delayed) signal with likely more than just a normal dry and delayed signal.
When the BYOC had the differential mode using two different delays (1024 and 2048)
the tone was very much like the EM in clean settings with much feedback. However,
with distortion it is less controllable.
I was not successful in moving the feedback signal before the dry signal (using
either the + or - input of IC1b did not appear to have any effect or properly mix the
feedback). When I tried to move the dry signal to the output of IC1a it was clear
that this “worked” but actually created “pos” feedback (nasal tone) which is not
desired because the feedback needs to be at the “-” input of IC1a.
However, using a properly mixed BBDa and BBDb with two different delays and an
improved wet/dry mix circuit I was able to achieve a very good EM-like flanger while
maintaining a very good MXR style standard flanger.
I posted a YouTube video at the following so you could hear the improvement in the
Differential mode replicating the EM.
http://www.youtube.com/watch?v=MV-7wzD3XOg