TDM-1911 Automatic Distortion Meter schematic

[RuudNL]

I recently bought one of those 'cheapo' Chinese distortion meters.

To my surprise they work reasonably well, although there is some room for improvement.
(There is some AC buzz from the power supply in the circuit, causing the most sensitive distortion scale not to be accurate. When I listen to the distortion signal output, I can hear more 50 Hz. than a distortion component.)
Does by any chance somebody have a circuit diagram of this meter? (Otherwise I have to do some reverse engineering myself.  :'( )
I am particularly interested in the functions of the trimpots inside.
Help would be highly appreciated!

 

[RuudNL]

In the meantime I have traced the functions of some trimpots:

Left PCB: Lock range 400Hz/1 KHz.
Main PCB, Left front: DC offset of input amplifier
Main PCB, Left back: Calibration of AC level meter
Right PCB: Output of the 400Hz/1 KHz. filters

2 trimpots remain on the main PCB, who knows more about their functionality???

 

[TopasGracias]

Hi
Did you find the schematics or any other solution?
Regards
From Aus

 

[clintrubber]

Made me think of the (old) Leader LDM-17x  (171, 177 etc) meters from Japan, perhaps schematics for those (if available) can be of help.

Judging by the type-number  (TDM- i.s.o. LDM-) they're based on/copied from those, or in fact have been the previous brandname for these new types.

 

[Murry]

I recently bought one of those 'cheapo' Chinese distortion meters.

To my surprise they work reasonably well, although there is some room for improvement.
(There is some AC buzz from the power supply in the circuit, causing the most sensitive distortion scale not to be accurate. When I listen to the distortion signal output, I can hear more 50 Hz. than a distortion component.)
Does by any chance somebody have a circuit diagram of this meter? (Otherwise I have to do some reverse engineering myself. :'( )
I am particularly interested in the functions of the trimpots inside.
Help would be highly appreciated!

Would you have a user’s manual