diff --git a/klippy/extras/probe_eddy_current.py b/klippy/extras/probe_eddy_current.py
index f2831fbf1..99dddad44 100644
--- a/klippy/extras/probe_eddy_current.py
+++ b/klippy/extras/probe_eddy_current.py
@@ -515,8 +515,8 @@ class EddyTap:
         sps = self._sensor_helper.get_samples_per_second()
         design = trigger_analog.DigitalFilter(sps, cfg_error)
         design.add_lowpass(25.0, 4)
-        # Create the derivative (sample to sample difference) post filter
-        self._filter_design = trigger_analog.DerivativeFilter(design)
+        design.add_derivative()
+        self._filter_design = design
         # Create SOS filter
         cmd_queue = self._trigger_analog.get_dispatch().get_command_queue()
         mcu = self._sensor_helper.get_mcu()
diff --git a/klippy/extras/trigger_analog.py b/klippy/extras/trigger_analog.py
index 71af1ea65..04ae6cf8a 100644
--- a/klippy/extras/trigger_analog.py
+++ b/klippy/extras/trigger_analog.py
@@ -51,6 +51,9 @@ class DigitalFilter:
                                fs=self.sample_frequency)
         f = signal.tf2sos(b, a)[0]
         self.filter_sections.append(f)
+    def add_derivative(self):
+        # Sample to sample difference (derivative) as stage in SOS filter
+        self.filter_sections.append((1., -1., 0., 1., 0., 0.))
     def setup_initial_state(self):
         if not self.filter_sections:
             return
@@ -66,22 +69,6 @@ class DigitalFilter:
             return [[0., 0.]] * len(self.filter_sections)
         return self.initial_state
 
-# Produce sample to sample difference (derivative) of a DigitalFilter
-class DerivativeFilter:
-    def __init__(self, main_filter):
-        self._main_filter = main_filter
-
-    def get_main_filter(self):
-        return self._main_filter
-
-    def get_filter_sections(self):
-        s = list(self._main_filter.get_filter_sections())
-        return s + [(1., -1., 0., 1., 0., 0.)]
-
-    def get_initial_state(self):
-        s = list(self._main_filter.get_initial_state())
-        return s + [(-1., 0.)]
-
 # Control an `sos_filter` object on the MCU
 class MCU_SosFilter:
     # max_sections should be the largest number of sections you expect