Meixing Mingda MC-7R Preamp

In this blog post I test and review the Meixing Mingda MC-7R Preamp. I purchased this preamp from a reputable seller on Canuckaudiomart. 

The unit arrived from shipping and it was carefully packaged. I was pleased to find that the preamp was in "like new" condition. However I was unsure what tubes were installed, however they certainly were not stock. The seller is an avid tube gear enthusiast, so I suspect that it has good tubes installed. 

Harmonic Distortion 

I tested the distortion at the following output voltages:

  • 0.06V
  • 0.25V
  • 1.00V
  • 4.00V

The 0.06V output is predominately noise floor which rises with frequency. The preamp is -2.5dB at 50Hz and only down -0.50dB at 50kHz. Distortion measures 0.16% for H2 at 10kHz. 

The 0.25V output below we see the preamp rise out of the noise floor with improved distortion. H2 is now only 0.044% for the 10kHz region. The bass region sees H2 remain at around 0.09% with H3 and H4 very low at 0.01%.


The 1.00v output below sees distortion improve even further with H2 only 0.013% for the 10kHz region. H2 for the bass remains below 0.10%. However we see bass output at 50Hz is now -5dB down and 50kHz is now -1dB down.  We see three similar and unusual peaks emerge in the upper treble for H2,H3, and H4. 

The 4.00V output sees bass performance suffer being -6dB down. However H2 still remains low at only 0.10%  H2 starts to rise above the other harmonics through the midrange but this is still very low in value. 

Intermodulation Distortion 

I tested intermodulation distortion at the same output voltages for harmonic. 

IMD is at -62dB across the spectrum. 

The 0.25V reveals a moderate improvement to -64dB for the 10kHz region. However we see some grass showing a little higher through the midrange. 

The 1.00V shows a moderate improvement to -64dB at 10kHz. 

The 4.00V output sees IMD reduced to -50dB across the spectrum. 

Gedles Metric (Gm) Distortion 

Below is the Gm distortion for the four voltage levels. The lower the number the better. 


Tube Rolling 

 Since I purchased this tube preamp used, I was not certain what tubes were installed. They were not the stock tubes however. For this blog post I purchased all new Electroharmonix tubes. The preamp uses 12AU7 for the primary stage and 12AX7 for the secondary stage. I also purchased a new rectifier tube. I decided to replace each tube and conduct the same set of measurements as above with each tube replacement, starting with the first tube in the signal chain, the 12AX7. I won't bore you with every single measurement again. Suffice it to say, the distortion measurements did not change at all with the replacement of the 12AX7. When I changed the next tube in the signal path, which is the 12AU7, I did not see any change in the distortion there either. I then replaced the rectifier tube, and again, I did not see any change in my distortion measurements for any of the output voltages. Despite all this, I am still going to publish my distortion results as there may be some subtle changes in the results that you may find interesting. 

Replace Primary Stage Tube (12AX7) with New Electroharmonix 

4.00V output 

Replace Secondary Stage Tube (12AU7) with New Electroharmonix 

Replace 5AR4 Rectifier Tube "Noble Voice" 

Comparison to Don Sachs Preamp 

I decided to see how my measurements compared against the Don Sachs Audio Preamp. 

Below is the harmonic distortion for the same test voltages conducted earlier. 


The Meixing Mingda MC-7R preamp exhibits the following characteristics. 

  • Generally the overall distortion performance changes very little with preamp output levels 
    • Harmonic distortion remains at around 0.01% for all output levels 
    • IMD remains at around -65dB for all output levels except for the 4.00V output where we see it drop to -50dB. 
    • Gedlee Distortion (Gm) is generally unchanged for the various output levels 
  • Provides high gain output 
    • Harmonic and Gm distortion changes little even at the 4.00V
  • Replacing the tubes did not alter the distortion performance 
    • I sometimes see distortion change when rolling tubes, but not here.
  • There is no dominant harmonic such as H2 like we saw with the Don Sachs Preamp (this is neither a good or bad thing since H2 is benign, with some listeners preferring the subjective sound character of some H2 infusion)
    • The Don Sachs Preamp exhibited elevated levels of H2 for the 1.00V and 4.00V output compared to the MC-7R preamp
  • The Don Sachs Preamp exhibited altering distortion profiles for the various output levels. 

MC-7R Subjective Listening 

  • Good bass authority 
  • Sounds similar at various volume levels 
  • Treble lacking some smoothness compared to the Don Sachs Preamp
  • Soundstage lacking some depth compared to the Don Sachs Preamp 
  • Quiet noise floor 
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