MAB
Major Contributor
I have an old Mitsubishi DA-P20 preamplifier. It was part of a modular lineup of separate components.
The preamp could be bolted onto a couple models of matching amplifier:
The resulting Franken-Receiver is slightly unwieldy.
Fortunately Mitsubishi had a pair of VU meters you could bolt onto the amps.
The matching DA-F20 FM tuner is remarkable and I still use to this day:
My preamp has had a bumpy life though.
I've loaned it out a few times. It was used for a business for a couple years. It's never been serviced. It has no obvious faults, and even the stepped volume attenuator, tone controls and switches have only the faintest noise. It has dual tape loops, MM and MC cartridge inputs, and boasts a 'dual mono' design with separate left and right input attenuators, plus separate tone controls for each channel. It boasts some killer specs.
18 Volt output, 10 Hz - 100 kHz frequency response, 0.002% THD for line-level devices, 290 mV phono overload for MM. I'm going to test as much of this as I can, compare to Mitsubishi's published spec. I'll also provide a similar dashboard of test conditions that Amir provides. I measured the unit with a QuantAsylum QA403. I measured, cleaned and adjusted Left and Right rail voltages to spec. There is a slight channel imbalance, more on that below. I was able to compensate for the imbalance with the handy input attenuators.
Feeding 2.5 V 1 kHz, gain set to provide 2 V output similar to Amir's dashboard:
This is great performance. The above is with the tone controls defeated.
With the tone control switch enabled and response in flat position there is a small 2dB degradation in performance:
Sweeping input voltage at unity gain results in the following output THD and THD+N:
I think that is outstanding. I cranked it all the way up to see if it can really deliver 18V
:
It does put out 18V, even into 1 kOhm! You need a hot source, but it will do it if fed enough input voltage! I think you can spot weld with this.
Mitsubishi claim wide bandwidth:
I measure -0.2 dB at 10Hz, -1dB at 80 kHz; so slightly below spec but still great. Green trace is with tone controls defeated, the yellow is with the tone on and the controls flat:
I don't know if this is overpromising or due to age. The FR degrades when tone is on, but still impressive.
The tone controls have the following response for the +-2 dB, 6 dB, and 10 dB settings on bass and treble:
The tone filters roughly conform to the spec, have 2 dB increments.
The subsonic filter is different than spec:
Mitsubishi claims -6dB at 18Hz, but slowly rolls over an hits -6dB just below 10Hz.
Here is the performance of the volume control:
Maximum gain on the left of the chart is 16 dB. The largest left / right imbalance is at moderate listening volumes, in the range commonly used.
The stepped attenuator staircases in this region:
I cleaned the volume control, it didn't help with the channel mismatch or the staircasing. I measured the resistance of the ladder at each volume position, it tracks exactly the L and R gain. The L/R imbalance is due to the attenuator. I don't know if the resistive properties have changed over time, or if this is the same performance as new. It's still good performance, and the small amount of scratchiness that had developed is now gone. I am able to level the channels with the input attenuators for the measurements, but that isn't practical in real world since the imbalance changes with each attenuator position. It's not bad, but the nonlinearities in the volume control may be the most audible artifacts of this preamp since the rest of the line level performance is so good.
I'll test the MM and MC sections next. For instance, I want to see if it meets the 290mV overload spec:
The preamp could be bolted onto a couple models of matching amplifier:
The resulting Franken-Receiver is slightly unwieldy.
Fortunately Mitsubishi had a pair of VU meters you could bolt onto the amps.
The matching DA-F20 FM tuner is remarkable and I still use to this day:
My preamp has had a bumpy life though.
I've loaned it out a few times. It was used for a business for a couple years. It's never been serviced. It has no obvious faults, and even the stepped volume attenuator, tone controls and switches have only the faintest noise. It has dual tape loops, MM and MC cartridge inputs, and boasts a 'dual mono' design with separate left and right input attenuators, plus separate tone controls for each channel. It boasts some killer specs.
18 Volt output, 10 Hz - 100 kHz frequency response, 0.002% THD for line-level devices, 290 mV phono overload for MM. I'm going to test as much of this as I can, compare to Mitsubishi's published spec. I'll also provide a similar dashboard of test conditions that Amir provides. I measured the unit with a QuantAsylum QA403. I measured, cleaned and adjusted Left and Right rail voltages to spec. There is a slight channel imbalance, more on that below. I was able to compensate for the imbalance with the handy input attenuators.
Feeding 2.5 V 1 kHz, gain set to provide 2 V output similar to Amir's dashboard:
This is great performance. The above is with the tone controls defeated.
With the tone control switch enabled and response in flat position there is a small 2dB degradation in performance:
Sweeping input voltage at unity gain results in the following output THD and THD+N:
I think that is outstanding. I cranked it all the way up to see if it can really deliver 18V
:It does put out 18V, even into 1 kOhm! You need a hot source, but it will do it if fed enough input voltage! I think you can spot weld with this.
Mitsubishi claim wide bandwidth:
I measure -0.2 dB at 10Hz, -1dB at 80 kHz; so slightly below spec but still great. Green trace is with tone controls defeated, the yellow is with the tone on and the controls flat:
I don't know if this is overpromising or due to age. The FR degrades when tone is on, but still impressive.
The tone controls have the following response for the +-2 dB, 6 dB, and 10 dB settings on bass and treble:
The tone filters roughly conform to the spec, have 2 dB increments.
The subsonic filter is different than spec:
Mitsubishi claims -6dB at 18Hz, but slowly rolls over an hits -6dB just below 10Hz.
Here is the performance of the volume control:
Maximum gain on the left of the chart is 16 dB. The largest left / right imbalance is at moderate listening volumes, in the range commonly used.
The stepped attenuator staircases in this region:
I cleaned the volume control, it didn't help with the channel mismatch or the staircasing. I measured the resistance of the ladder at each volume position, it tracks exactly the L and R gain. The L/R imbalance is due to the attenuator. I don't know if the resistive properties have changed over time, or if this is the same performance as new. It's still good performance, and the small amount of scratchiness that had developed is now gone. I am able to level the channels with the input attenuators for the measurements, but that isn't practical in real world since the imbalance changes with each attenuator position. It's not bad, but the nonlinearities in the volume control may be the most audible artifacts of this preamp since the rest of the line level performance is so good.
I'll test the MM and MC sections next. For instance, I want to see if it meets the 290mV overload spec
:
