So I got my hands on a Leicozic branded PM10 wireless IEM system recently because price looks attractive for the functionalities & I was genuinely curious how much has product design & manufacturing tech progressed so far in China for such devices, I figured I'll do a bit of a review of the unit here and some rant because there's a function that is missing for me, which I want to add-on later, (I do own a 3000 series IEM system from Audio Technica which i draw comparisons to, its obviously a much better unit with lots more small quality of life features & functionality.)
View attachment 1718359833937.jpg View attachment 1718359833838.jpgView attachment 1718359833877.jpg
The Main PROS: true diversity antenna receiver, IR sync from brush metal bodypack, stereo/mono option on both Tx & Rx, (Alk & Ni-mh) battery type selection & usb-c charging port, L/R pan knob on bodypack. Even got autoscan& squelch control on the receiver pack; rackmont brackets + a somewhat decent IEM (looks like stock OEM under a YJS-820 model, very similar lookswise to a QKZ ZXD)
The Main CONS: seller advertised this as having 32Mhz bandwidth but actual unit has only like 19Mhz bandwidth up to 45 channels, the L/R pan knob is just a simple 3pin pot and is super small (PITA to adjust and for some reason designer put this in parallel to the volume pot and not before stereo/mono stage so I get one side of my earphones attenuated either way). RF Tx output is not so clean (see tinySA scan from about 1meter+ away, I got additional noise about 3Mhz above the channel RF); lets not even talk about the documented manual (its a joke)
Anyway, what I want to do on this thing is to add a mix/focus mode to turn the pan knob into a 2-channel selector so that I can get 2 selectable mono mixes out of the stereo LR inputs. Taking apart the receiver bodypack, here's some pic of the inner PCB:
View attachment 1718359833736.jpg
View attachment 1718359833817.jpg View attachment 1718359833691.jpg (pcb trace of volume & pan)
Hmm, quite a few trim pots there, not sure what biasing parameters do they actually adjust for. Tracing the smaller output holding the pots and stereo jack, I think the signal block looks something like the above. I guess a single gang 3pin pot does a good enough job as a pan pot, but do you guys think that a stereo blend knob could be made with a dual ganged pot? Taking out the black plastic cover also revealed some 3mm spacing between the pcb and edge of housing, which should be just enough space for me to drill a slot on the outer plastic cover & stick a mini 12d18g4 L-shaped switch in there for the mod I'm thinking.
I searched online a bit and figured it should be possible to implement a resistor based stereo summing switch to make the blend knob more usable, but I'm not sure if the implementation is ideal (I thought about doing it on the output stage, but various discussions has suggested that its not good to link 2 amplified outputs together as a sum; which means the summing has to be done pre-amp stage)
View attachment 1718359833668.jpg (Drawing of proposed mod)
I measured 1.5-3k+ Ohms reading with a multimeter between L/R channels at the preamp stage (depending on pots position) I Think the summing 100 Ohm resistor can be placed in between the pan & volume pots by cutting the pcb trace, I'm not sure about having a low value (like <5Ohm) resistor in series with the Stereo/Mono switch if I'm to add it). So the main question is the resistors value & implementation correct? What are some potential effects/consequences I should be aware of doing this kind of summing). Actually, looking at it again I'm not sure if the 100 Ohms are even necessary as I don't think I'll be turning the volume full to 100% most of the time, so there should be some resistance in the path before the summing switch already....
Yea, so anyway I appreciate your valuable insights in advance. Tq!
View attachment 1718359833937.jpg View attachment 1718359833838.jpgView attachment 1718359833877.jpg
The Main PROS: true diversity antenna receiver, IR sync from brush metal bodypack, stereo/mono option on both Tx & Rx, (Alk & Ni-mh) battery type selection & usb-c charging port, L/R pan knob on bodypack. Even got autoscan& squelch control on the receiver pack; rackmont brackets + a somewhat decent IEM (looks like stock OEM under a YJS-820 model, very similar lookswise to a QKZ ZXD)
The Main CONS: seller advertised this as having 32Mhz bandwidth but actual unit has only like 19Mhz bandwidth up to 45 channels, the L/R pan knob is just a simple 3pin pot and is super small (PITA to adjust and for some reason designer put this in parallel to the volume pot and not before stereo/mono stage so I get one side of my earphones attenuated either way). RF Tx output is not so clean (see tinySA scan from about 1meter+ away, I got additional noise about 3Mhz above the channel RF); lets not even talk about the documented manual (its a joke)
Anyway, what I want to do on this thing is to add a mix/focus mode to turn the pan knob into a 2-channel selector so that I can get 2 selectable mono mixes out of the stereo LR inputs. Taking apart the receiver bodypack, here's some pic of the inner PCB:
View attachment 1718359833736.jpgView attachment 1718359833817.jpg View attachment 1718359833691.jpg (pcb trace of volume & pan)
Hmm, quite a few trim pots there, not sure what biasing parameters do they actually adjust for. Tracing the smaller output holding the pots and stereo jack, I think the signal block looks something like the above. I guess a single gang 3pin pot does a good enough job as a pan pot, but do you guys think that a stereo blend knob could be made with a dual ganged pot? Taking out the black plastic cover also revealed some 3mm spacing between the pcb and edge of housing, which should be just enough space for me to drill a slot on the outer plastic cover & stick a mini 12d18g4 L-shaped switch in there for the mod I'm thinking.
I searched online a bit and figured it should be possible to implement a resistor based stereo summing switch to make the blend knob more usable, but I'm not sure if the implementation is ideal (I thought about doing it on the output stage, but various discussions has suggested that its not good to link 2 amplified outputs together as a sum; which means the summing has to be done pre-amp stage)
View attachment 1718359833668.jpg (Drawing of proposed mod)
I measured 1.5-3k+ Ohms reading with a multimeter between L/R channels at the preamp stage (depending on pots position) I Think the summing 100 Ohm resistor can be placed in between the pan & volume pots by cutting the pcb trace, I'm not sure about having a low value (like <5Ohm) resistor in series with the Stereo/Mono switch if I'm to add it). So the main question is the resistors value & implementation correct? What are some potential effects/consequences I should be aware of doing this kind of summing). Actually, looking at it again I'm not sure if the 100 Ohms are even necessary as I don't think I'll be turning the volume full to 100% most of the time, so there should be some resistance in the path before the summing switch already....
Yea, so anyway I appreciate your valuable insights in advance. Tq!
