diff --git a/diagnostic/server.js b/diagnostic/server.js
index ffd6b17..c3935a3 100644
--- a/diagnostic/server.js
+++ b/diagnostic/server.js
@@ -1439,19 +1439,14 @@ wss.on("connection", (ws) => {
           xttsVoice: msg.xttsVoice || "",
         };
         if (msg.whisperModel !== undefined) voiceConfig.whisperModel = msg.whisperModel;
-        // F5-TTS Tuning-Felder — leere Strings entfernen damit der Default greift
-        if (msg.f5ttsModel !== undefined) {
-          if (msg.f5ttsModel) voiceConfig.f5ttsModel = msg.f5ttsModel;
-          else delete voiceConfig.f5ttsModel;
-        }
-        if (msg.f5ttsCkptFile !== undefined) {
-          if (msg.f5ttsCkptFile) voiceConfig.f5ttsCkptFile = msg.f5ttsCkptFile;
-          else delete voiceConfig.f5ttsCkptFile;
-        }
-        if (msg.f5ttsVocabFile !== undefined) {
-          if (msg.f5ttsVocabFile) voiceConfig.f5ttsVocabFile = msg.f5ttsVocabFile;
-          else delete voiceConfig.f5ttsVocabFile;
-        }
+        // F5-TTS Tuning-Felder — immer mit dem vom User gesendeten Wert setzen,
+        // auch leeren String. Leer = "reset auf Hard-Default". Sonst merkt die
+        // Bridge nicht dass der User den Wert loeschen wollte (absent key war
+        // vorher 'keep current' semantik → BigVGAN blieb drin obwohl User
+        // leer eingetragen hatte).
+        if (msg.f5ttsModel !== undefined)     voiceConfig.f5ttsModel = msg.f5ttsModel || "";
+        if (msg.f5ttsCkptFile !== undefined)  voiceConfig.f5ttsCkptFile = msg.f5ttsCkptFile || "";
+        if (msg.f5ttsVocabFile !== undefined) voiceConfig.f5ttsVocabFile = msg.f5ttsVocabFile || "";
         if (msg.f5ttsCfgStrength !== undefined && !isNaN(msg.f5ttsCfgStrength)) {
           voiceConfig.f5ttsCfgStrength = msg.f5ttsCfgStrength;
         }
diff --git a/xtts/f5tts/bridge.py b/xtts/f5tts/bridge.py
index 3553e68..f9e1ae1 100644
--- a/xtts/f5tts/bridge.py
+++ b/xtts/f5tts/bridge.py
@@ -175,10 +175,31 @@ class F5Runner:
 
     async def update_config(self, payload: dict) -> None:
         """Liest f5tts*-Felder aus einem config-Broadcast.
-        Bei Modell-relevantem Wechsel wird neu geladen."""
-        new_model = (payload.get("f5ttsModel") or "").strip() or self.model_id
-        new_ckpt = payload.get("f5ttsCkptFile", self.ckpt_file) or ""
-        new_vocab = payload.get("f5ttsVocabFile", self.vocab_file) or ""
+        Bei Modell-relevantem Wechsel wird neu geladen.
+
+        Semantik:
+          - key fehlt in payload     → aktuellen Wert behalten
+          - key da, nicht-leerer str → diesen Wert nehmen
+          - key da, leerer string    → RESET auf Hard-Default (User hat Feld
+                                       in Diagnostic geleert und Apply geklickt)
+        """
+        if "f5ttsModel" in payload:
+            v = (payload.get("f5ttsModel") or "").strip()
+            new_model = v if v else DEFAULT_F5TTS_MODEL
+        else:
+            new_model = self.model_id
+
+        if "f5ttsCkptFile" in payload:
+            v = payload.get("f5ttsCkptFile") or ""
+            new_ckpt = v.strip() if isinstance(v, str) else ""
+        else:
+            new_ckpt = self.ckpt_file
+
+        if "f5ttsVocabFile" in payload:
+            v = payload.get("f5ttsVocabFile") or ""
+            new_vocab = v.strip() if isinstance(v, str) else ""
+        else:
+            new_vocab = self.vocab_file
         try:
             new_cfg = float(payload.get("f5ttsCfgStrength", self.cfg_strength))
         except (TypeError, ValueError):