diff --git a/firmware/common/hackrf_core.c b/firmware/common/hackrf_core.c
index 80841c65..5fe5d5ee 100644
--- a/firmware/common/hackrf_core.c
+++ b/firmware/common/hackrf_core.c
@@ -490,60 +490,36 @@ void cpu_clock_init(void)
 	si5351c_configure_pll_sources(&clock_gen);
 	si5351c_configure_pll_multisynth(&clock_gen);
 
-#if (defined JAWBREAKER || defined HACKRF_ONE)
 	/*
-	 * Jawbreaker clocks:
+	 * Clocks:
 	 *   CLK0 -> MAX5864/CPLD
 	 *   CLK1 -> CPLD
 	 *   CLK2 -> SGPIO
-	 *   CLK3 -> external clock output
-	 *   CLK4 -> RFFC5072
-	 *   CLK5 -> MAX2837
+	 *   CLK3 -> External Clock Output
+	 *   CLK4 -> RFFC5072 (MAX2837 on rad1o)
+	 *   CLK5 -> MAX2837 (MAX2871 on rad1o)
 	 *   CLK6 -> none
-	 *   CLK7 -> LPC4330 (but LPC4330 starts up on its own crystal)
+	 *   CLK7 -> LPC43xx (uses a 12MHz crystal by default)
 	 */
 
 	/* MS3/CLK3 is the source for the external clock output. */
 	si5351c_configure_multisynth(&clock_gen, 3, 80*128-512, 0, 1, 0); /* 800/80 = 10MHz */
 
+#if (defined JAWBREAKER || defined HACKRF_ONE)
 	/* MS4/CLK4 is the source for the RFFC5071 mixer. */
 	si5351c_configure_multisynth(&clock_gen, 4, 16*128-512, 0, 1, 0); /* 800/16 = 50MHz */
- 
  	/* MS5/CLK5 is the source for the MAX2837 clock input. */
 	si5351c_configure_multisynth(&clock_gen, 5, 20*128-512, 0, 1, 0); /* 800/20 = 40MHz */
-
-	/* MS6/CLK6 is unused. */
-	/* MS7/CLK7 is the source for the LPC43xx microcontroller. */
-	uint8_t ms7data[] = { 90, 255, 20, 0 };
-	si5351c_write(&clock_gen, ms7data, sizeof(ms7data));
 #endif
-
 #ifdef RAD1O
-	/* rad1o clocks:
-	 *   CLK0 -> MAX5864/CPLD
-	 *   CLK1 -> CPLD
-	 *   CLK2 -> SGPIO
-	 *   CLK3 -> External Clock Output
-	 *   CLK4 -> MAX2837
-	 *   CLK5 -> MAX2871
-	 *   CLK6 -> none
-	 *   CLK7 -> LPC4330 (but LPC4330 starts up on its own crystal) */
-
-	/* MS3/CLK3 is the source for the external clock output. */
-	si5351c_configure_multisynth(&clock_gen, 3, 80*128-512, 0, 1, 0); /* 800/80 = 10MHz */
-
 	/* MS4/CLK4 is the source for the MAX2837 clock input. */
 	si5351c_configure_multisynth(&clock_gen, 4, 20*128-512, 0, 1, 0); /* 800/20 = 40MHz */
-
 	/* MS5/CLK5 is the source for the RFFC5071 mixer. */
 	si5351c_configure_multisynth(&clock_gen, 5, 20*128-512, 0, 1, 0); /* 800/20 = 40MHz */
+#endif
 
 	/* MS6/CLK6 is unused. */
-
-	/* MS7/CLK7 is the source for the LPC43xx microcontroller. */
-	uint8_t ms7data[] = { 90, 255, 20, 0 };
-	si5351c_write(&clock_gen, ms7data, sizeof(ms7data));
-#endif
+	/* MS7/CLK7 is unused. */
 
 	/* Set to 10 MHz, the common rate between Jawbreaker and HackRF One. */
 	sample_rate_set(10000000);
diff --git a/firmware/common/si5351c.c b/firmware/common/si5351c.c
index 465b2370..18e4a091 100644
--- a/firmware/common/si5351c.c
+++ b/firmware/common/si5351c.c
@@ -184,7 +184,7 @@ void si5351c_configure_clock_control(si5351c_driver_t* const drv, const enum pll
 	,SI5351C_CLK_INT_MODE | SI5351C_CLK_PLL_SRC(pll) | SI5351C_CLK_SRC(SI5351C_CLK_SRC_MULTISYNTH_SELF) | SI5351C_CLK_IDRV(SI5351C_CLK_IDRV_6MA)
 	,SI5351C_CLK_INT_MODE | SI5351C_CLK_PLL_SRC(pll) | SI5351C_CLK_SRC(SI5351C_CLK_SRC_MULTISYNTH_SELF) | SI5351C_CLK_IDRV(SI5351C_CLK_IDRV_4MA)
 	,SI5351C_CLK_POWERDOWN | SI5351C_CLK_INT_MODE /*not connected, but: plla int mode*/
-	,SI5351C_CLK_INT_MODE | SI5351C_CLK_PLL_SRC(pll) | SI5351C_CLK_SRC(SI5351C_CLK_SRC_MULTISYNTH_SELF) | SI5351C_CLK_IDRV(SI5351C_CLK_IDRV_8MA)
+	,SI5351C_CLK_POWERDOWN | SI5351C_CLK_INT_MODE /*not connected, but: plla int mode*/
 	 };
 	si5351c_write(drv, data, sizeof(data));
 }
@@ -223,8 +223,9 @@ void si5351c_configure_clock_control(si5351c_driver_t* const drv, const enum pll
 	/* 3: External clock output is deactivated as it is not used and creates noise */
 	uint8_t data[] = { 3, ~((1 << 0) | (1 << 1) | (1 << 2) | (1 << 4) | (1 << 5))};
 #else
-	/* Enable CLK outputs 0, 1, 2, 3, 4, 5, 7 only. */
-	uint8_t data[] = { 3, 0x40 };
+	/* Enable CLK outputs 0, 1, 2, 3, 4, 5. */
+	/* 7: Clock to CPU is deactivated as it is not used and creates noise */
+	uint8_t data[] = { 3, ~((1 << 0) | (1 << 1) | (1 << 2) | (1 << 3) | (1 << 4) | (1 << 5))};
 #endif
  	si5351c_write(drv, data, sizeof(data));
  }