Mitsubishi DA-P20 Preamplifier Measurements

[Bruce Morgen]

i dont get it.. where's the car?

...or the nimble, prop-driven fighter plane?

 

[testp]

...or the nimble, prop-driven fighter plane?

beatiful nonetheless..

 

[Bruce Morgen]

Totally agree!

The problem is, equipment owners are requesting recapping as a service and are willing to pay for it -- and, as a pro technician trying to make a living, the customer is always right whether that's actually true or not. Electrolytic caps by their very nature tend to drift in value over time -- whether that drift and any associated ESR change are measurable, audible, or worth swapping in a few bucks of new parts to remedy is what's questionable, but considering the age of this particular unit it wasn't a bad idea and IMO extremely unlikely to degrade performance if competently done. Moreover, long-term electrolytic capacitor quality from the dependable brands has improved markedly over the past 40+ years due to technical advances, so wholesale recapping exercises can conceivably improve overall equipment longevity.

 

[EJ3]

From Quirk Audio's Blog (a different Mitsubishi Amp but similar {no measurements but great pictures}):
Mitsubishi DA-30 an underrated gem​

By QuirkAudio February 10, 2019Restorations and upgrades
No Comments
In the 1980’s Mitsubishi made a series of amplifiers that are somewhat unknown, however they are really standouts in the their class. The DA 30 is a plain looking 105w RMS per channel power amp. It is not till you open the case does the design reveal itself.
The amp is basically a dual mono design, with two transformers and separate power supply for each channel, and unlike others of this vintage (NAD, APT etc) this unit can only be operated in Stereo. The power supplies are completely independent, with 2 10kuf caps per channel. The input/voltage amp and bias sections have their own independent regulated power supply which is tapped off each transformer separately form the output stage power supply.
The front end of the amp uses a dual FET for the input stage (2SK109) which then feeds the voltage amp stage. There are two inputs marked AC and DC. The AC input has a cap (non polar) across the input whilst the DC input does not. There is a volume control on the back panel- though generally this is set and full open.
There are no capacitors in the audio path through out the whole amp. The main outputs are the well respected Sanken 2SC2837/2SA1186. There is an over power detection circuit and a protection circuit with independent relays for reach channel. The two front panel leds indicate power and protection status.
The other unique feature is the heatsinks which use a copper “heat pipe” coupled to a set of fins, which appears to do a very fine job of handling the thermal energy from the amp.
So having examined the amp, of course this looked like a great amp to upgrade! So all the electrolytic caps have been replaced with low impedance types, Nichicon PW and HE, as the are all associated with some form of power delivery. Where appropriate some values were increased, though the original design provided adequate capacity.
The outcome is a very good sounding amplifier, neutral and quiet and transparent- in fact so much so that I use one as my “reference” in the lab- connected to a modded APT pre amp and B&W speakers. The sound is simply whatever the music is delivering, the bass is tight the mids and highs neutral, with plenty of power for transients and excellent dynamics.
This amplifier is certainly underrated and deserves its place with the other stand outs form that period , the NAD 2200 and APT 1.

After the upgrade ready to have the cover put back on- note the dual power supplies and symmetrical nature of the PCB layout

on the bench fully restored

There is support for 2 sets of speakers, which can be switched on the rear or remotely via a separate meter bridge which is connected via the 8 pin socket seen here. note the “bumps” which are where the heat pipes are situated.

 

[Bruce Morgen]

From Quirk Audio's Blog (a different Mitsubishi Amp but similar {no measurements but great pictures})

Not even really all that "similar" AFAICT -- very different physical layout and different output transistors (two rather than four per channel perhaps?) delivering considerably less power. I suspect the front end circuitry along with the two combination protection and speaker switching relays are somewhat "similar," but I'm too lazy to download manuals and compare schematics to confirm that.

 

[PristineSound]

UV meters. . .me like.

 

[Hipocrates]

The problem is, equipment owners are requesting recapping as a service and are willing to pay for it -- and, as a pro technician trying to make a living, the customer is always right whether that's actually true or not. Electrolytic caps by their very nature tend to drift in value over time -- whether that drift and any associated ESR change are measurable, audible, or worth swapping in a few bucks of new parts to remedy is what's questionable, but considering the age of this particular unit it wasn't a bad idea and IMO extremely unlikely to degrade performance if competently done. Moreover, long-term electrolytic capacitor quality from the dependable brands has improved markedly over the past 40+ years due to technical advances, so wholesale recapping exercises can conceivably improve overall equipment longevity.

I'll add that some of those Japanese old caps fails all the time and create havoc, Sanyo light blue ones, CDE orange ones, matsushita CE Purple ones (I forgot the models but they have pretty colors) just like some signal transistors like 2SA726, 2SC1313 etc etc. Yes one can spend time testing and measuring or spend a couple of bucks just replacing those well know troublemakers and do some preventive maintenance.
Do I recap a Sansui from late 90's for japanese market? No way!.. but a Mitsubishi, Technics, Pioneer or Marantz from the 70's with a lot of those mentioned caps? Most probably.

Yes shootgunning boards is not a good practice, and recapping things have a bad reputation because enthusiast mainly see it as a silver bullet that fix everything, but experience shows some caps are shoot in sight, saves time, avoid the unit coming back and improve reliability, it doesn't have to do with the usual "recap vs not recap" silliness that internet people fight all the time.

That's why Tony replace caps (plus as you said usually the client demands it)

 

[EJ3]

Not even really all that "similar" AFAICT -- very different physical layout and different output transistors (two rather than four per channel perhaps?) delivering considerably less power. I suspect the front end circuitry along with the two combination protection and speaker switching relays are somewhat "similar," but I'm too lazy to download manuals and compare schematics to confirm that.

Dual Monaural & Dual Monaural The idea is the same.
If I meant to say that they were twins in circuit design, I would have.
But I did not.
Because what you say is correct.
But I was not diving that deep into it.
So, I guess that I must say that the INTENT of the design was also Dual Monaural but it was different in design. Jeez!
Actually the intent was just to show some nice pictures of the inside of a Dual Monaural Mitsubishi AMP.
Just to show some eye candy. Or AMP PORN.

 

[Bruce Morgen]

Dual Monaural & Dual Monaural The idea is the same.
If I meant to say that they were twins in circuit design, I would have.
But I did not.
Because what you say is correct.
But I was not diving that deep into it.
So, I guess that I must say that the INTENT of the design was also Dual Monaural but it was different in design. Jeez!

Fair enough -- and they're obviously part of the same product line, which is why I suspect the unusual front end circuit and the two dual-function (protection and speaker switching) relays are probably identical or close to it.

 

[EJ3]

Fair enough -- and they're obviously part of the same product line, which is why I suspect the unusual front end circuit and the two dual-function (protection and speaker switching) relays are probably identical or close to it.

So we technically agree that we are both correct! Thank you!
I think (but not sure) that the Harman Kardon "Twin Powered" were more consistent in their circuit designs.

 

[Count Arthur]

The green light may not be original, but that looks great.

 

[jdg78]

That massive cassette deck on the bottom is amazing. Looks like it belongs in an airplane cockpit.

I grew up in that brief period of the 80's when cassette tapes were the dominant format and I used to have boxes and boxes of them.

Can't say I miss them though.

 

[tomtoo]

Great times for Japanese electronics.

 

[Nango]

So beautiful all that old stuff

 

[Salt]

Mitsubishi was noted for automotive in my book until now .
Thanks for widening my range of knowledge.

 

[Hart]

View attachment 449659

That massive cassette deck on the bottom is amazing. Looks like it belongs in an airplane cockpit.

I grew up in that brief period of the 80's when cassette tapes were the dominant format and I used to have boxes and boxes of them.

Can't say I miss them though.

Funny, cassette decks were okay for cars and Walkmen, but they really were a pretty flawed delivery system for home audio. I was suprised that even the Nakamichi Dragon did not perform very well as tested here. That was the pinnacle of cassette technology.

 

[AnalogSteph]

View attachment 449542

The green light may not be original, but that looks great.

I dunno, the emerald green seems a bit overwhelming and is clashing with the deep red of the frequency display. This is not an easy one, and the stock choice of moderately bright warm white may be hard to beat, but what about, say, a nice amber?

('Shop for illustration purposes.)

BTW, this is another analog tuner with a grid-locked oscillator, like some Pioneers of the time. The high selectivity and low phase noise of a mechanically-tuned frontend (and I imagine nice weighted flywheel tuning at that) with the frequency stability of a PLL synthesizer.

Great times for Japanese electronics.

Indeed. Yamaha, Technics and Sansui akso had very nice gear at the time, as did Kenwood (even if their "Age of Plastic" designs were a bit eccentric). Same for their music, actually. (Japanese instrument makers became as good as they were for a reason.)

 

[Hipster Doofus]

Awesome stuff…..thanks for the info.

 

[Settembrini]

I have an old Mitsubishi DA-P20 preamplifier. It was part of a modular lineup of separate components.
View attachment 449314

The preamp could be bolted onto a couple models of matching amplifier:
View attachment 449316

The resulting Franken-Receiver is slightly unwieldy.
View attachment 449315

Fortunately Mitsubishi had a pair of VU meters you could bolt onto the amps.
View attachment 449318

The matching DA-F20 FM tuner is remarkable and I still use to this day:
View attachment 449319

My preamp has had a bumpy life though.
View attachment 449321
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.
View attachment 449323
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:
View attachment 449328
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:
View attachment 449330

Sweeping input voltage at unity gain results in the following output THD and THD+N:
View attachment 449332

I think that is outstanding. I cranked it all the way up to see if it can really deliver 18V :
View attachment 449334
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:
View attachment 449336
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:
View attachment 449338

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:
View attachment 449346

View attachment 449345

The tone filters roughly conform to the spec, have 2 dB increments.

The subsonic filter is different than spec:
View attachment 449348

Mitsubishi claims -6dB at 18Hz, but slowly rolls over an hits -6dB just below 10Hz.

Here is the performance of the volume control:
View attachment 449355

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:
View attachment 449354

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:
View attachment 449356

What a beautiful rack!

 

[ruinevil]

Think I have a Mitsubishi P20 in closet with one of the channels broken.