diff --git a/src/pygama/dsp/build_dsp.py b/src/pygama/dsp/build_dsp.py
index 583542409..85a8a708b 100644
--- a/src/pygama/dsp/build_dsp.py
+++ b/src/pygama/dsp/build_dsp.py
@@ -23,10 +23,11 @@
 log = logging.getLogger(__name__)
 
 
-def build_dsp(f_raw: str, f_dsp: str, dsp_config: str | dict, lh5_tables:
-              list[str] = None, database: str = None, outputs: list[str] =
-              None, n_max: int = np.inf, write_mode: str = 'r', buffer_len: int
-              = 3200, block_width: int = 16, chan_config: dict = None) -> None:
+def build_dsp(f_raw: str, f_dsp: str, dsp_config: str | dict = None,
+              lh5_tables: list[str] = None, database: str = None,
+              outputs: list[str] = None, n_max: int = np.inf,
+              write_mode: str = 'r', buffer_len: int = 3200,
+              block_width: int = 16, chan_config: dict = None) -> None:
     """
     Convert raw-tier LH5 data into dsp-tier LH5 data by running a sequence of
     processors via the :class:`~.processing_chain.ProcessingChain`.
@@ -65,6 +66,22 @@ def build_dsp(f_raw: str, f_dsp: str, dsp_config: str | dict, lh5_tables:
         `lh5_tables`
     """
 
+    if chan_config is not None:
+        # clear existing output files
+        if write_mode == 'r':
+            if os.path.isfile(f_dsp):
+                os.remove(f_dsp)
+            write_mode = 'a'
+
+        for tb, dsp_config in chan_config.items():
+            log.debug(f'processing table: {tb} with DSP config file {dsp_config}')
+            try:
+                build_dsp(f_raw, f_dsp, dsp_config, [tb], database,
+                          outputs, n_max, write_mode, buffer_len, block_width)
+            except RuntimeError:
+                log.debug(f'table {tb} not found')
+        return
+
     if isinstance(dsp_config, str):
         with open(dsp_config) as config_file:
             dsp_config = json.load(config_file)
@@ -80,21 +97,15 @@ def build_dsp(f_raw: str, f_dsp: str, dsp_config: str | dict, lh5_tables:
 
     # if no group is specified, assume we want to decode every table in the file
     if lh5_tables is None:
-        lh5_tables = []
-        lh5_keys = lh5.ls(f_raw)
-
-        # sometimes 'raw' is nested, e.g g024/raw
-        for tb in lh5_keys:
-            if "raw" not in tb:
-                tbname = lh5.ls(lh5_file[tb])[0]
-                if "raw" in tbname:
-                    tb = f'{tb}/{tbname}'  # g024 + /raw
-            lh5_tables.append(tb)
-
-    # make sure every group points to waveforms, if not, remove the group
-    for tb in lh5_tables:
-        if 'raw' not in tb:
-            lh5_tables.remove(tb)
+        lh5_tables = lh5.ls(f_raw)
+
+    # check if group points to raw data; sometimes 'raw' is nested, e.g g024/raw
+    for i, tb in enumerate(lh5_tables):
+        if "raw" not in tb and lh5.ls(lh5_file, f"{tb}/raw"):
+            lh5_tables[i] = f'{tb}/raw'
+        elif not lh5.ls(lh5_file, tb):
+            del lh5_tables[i]
+
     if len(lh5_tables) == 0:
         raise RuntimeError(f"could not find any valid LH5 table in {f_raw}")
 
@@ -134,16 +145,6 @@ def build_dsp(f_raw: str, f_dsp: str, dsp_config: str | dict, lh5_tables:
         if n_max and n_max < tot_n_rows:
             tot_n_rows = n_max
 
-        # if we have separate DSP files for each table, read them in here
-        if chan_config is not None:
-            f_config = chan_config[tb]
-            with open(f_config) as config_file:
-                dsp_config = json.load(config_file)
-            log.debug(f'processing table: {tb} with DSP config file {f_config}')
-
-        if not isinstance(dsp_config, dict):
-            raise RuntimeError(f'dsp_config for {tb} must be a dict')
-
         chan_name = tb.split('/')[0]
         db_dict = database.get(chan_name) if database else None
         tb_name = tb.replace('/raw', '/dsp')
@@ -180,12 +181,12 @@ def build_dsp(f_raw: str, f_dsp: str, dsp_config: str | dict, lh5_tables:
                                    write_start=write_offset+start_row)
 
             if log.level <= logging.INFO:
-                progress_bar.update(buffer_len)
+                progress_bar.update(n_rows)
 
-            if start_row+n_rows > tot_n_rows:
+            if start_row+n_rows >= tot_n_rows:
                 break
 
         if log.level <= logging.INFO:
             progress_bar.close()
 
-    raw_store.write_object(dsp_info, 'dsp_info', f_dsp)
+    raw_store.write_object(dsp_info, 'dsp_info', f_dsp, wo_mode='o')
diff --git a/src/pygama/dsp/processing_chain.py b/src/pygama/dsp/processing_chain.py
index e19b115f8..ed69117a2 100644
--- a/src/pygama/dsp/processing_chain.py
+++ b/src/pygama/dsp/processing_chain.py
@@ -1082,8 +1082,8 @@ def write(self, start: int, end: int) -> None:
                   self.raw_var[0:end-start, ...], 'unsafe')
 
     def __str__(self) -> str:
-        return (f"{self.var} linked to numpy.array({self.io_buf.shape}, "
-                f"{self.io_buf.dtype})@{self.io_buf.data})")
+        return (f"{self.var} linked to numpy.array(shape={self.io_buf.shape}, "
+                f"dtype={self.io_buf.dtype})")
 
 
 class LGDOArrayIOManager(IOManager):
@@ -1130,7 +1130,7 @@ def write(self, start: int, end: int) -> None:
                   self.raw_var[0:end-start, ...], 'unsafe')
 
     def __str__(self) -> str:
-        return f'{self.var} linked to {self.io_array}'
+        return f'{self.var} linked to lgdo.Array(shape={self.io_array.nda.shape}, dtype={self.io_array.nda.dtype}, attrs={self.io_array.attrs})'
 
 class LGDOArrayOfEqualSizedArraysIOManager(IOManager):
     """IO Manager for buffers that are numpy ArrayOfEqualSizedArrays"""
@@ -1176,7 +1176,7 @@ def write(self, start: int, end: int) -> None:
                   self.raw_var[0:end-start, ...], 'unsafe')
 
     def __str__(self) -> str:
-        return f'{self.var} linked to {self.io_array}'
+        return f'{self.var} linked to lgdo.ArrayOfEqualSizedArrays(shape={self.io_array.nda.shape}, dtype={self.io_array.nda.dtype}, attrs={self.io_array.attrs})'
 
 
 class LGDOWaveformIOManager(IOManager):
@@ -1243,9 +1243,10 @@ def write(self, start: int, end: int) -> None:
             self.t0_buf[start:end, ...] = self.t0_var[0:end-start, ...]
 
     def __str__(self) -> str:
-        return (f"{self.var} linked to <pygama.lgdo.WaveformTable: values: "
-                f"{self.wf_table.values}, dt: {self.wf_table.dt}, t0: "
-                f"{self.wf_table.t0}>")
+        return (f"{self.var} linked to pygama.lgdo.WaveformTable("
+                f"values(shape={self.wf_table.values.nda.shape}, dtype={self.wf_table.values.nda.dtype}, attrs={self.wf_table.values.attrs}), "
+                f"dt(shape={self.wf_table.dt.nda.shape}, dtype={self.wf_table.dt.nda.dtype}, attrs={self.wf_table.dt.attrs}), "
+                f"t0(shape={self.wf_table.t0.nda.shape}, dtype={self.wf_table.t0.nda.dtype}, attrs={self.wf_table.t0.attrs}))")
 
 
 def build_processing_chain(lh5_in: lgdo.Table, dsp_config: dict | str, db_dict: dict = None,
diff --git a/src/pygama/lgdo/lh5_store.py b/src/pygama/lgdo/lh5_store.py
index c8f8096af..a2ff6d8cb 100644
--- a/src/pygama/lgdo/lh5_store.py
+++ b/src/pygama/lgdo/lh5_store.py
@@ -623,7 +623,11 @@ def write_object(self,
         # scalars
         elif isinstance(obj, Scalar):
             if name in group:
-                log.debug(f"overwriting '{name}' in '{group}'")
+                if wo_mode in ['o', 'a']:
+                    log.debug(f'overwriting {name} in {group}')
+                    del group[name]
+                else:
+                    raise RuntimeError(f"tried to overwrite {name} in {group} for wo_mode {wo_mode}")
             ds = group.create_dataset(name, shape=(), data=obj.value)
             ds.attrs.update(obj.attrs)
             return