2019/06/22

MOGAMI 3082 Speaker Cable

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MOGAMI 3082 SuperFlexible Studio Speaker Cable

It is currently used as a main system speaker cable.

MOGAMI 3082 is a very flexible and easy-to-use speaker cable for professional audio, with an unusual coaxial structure as a speaker cable.

It has a very high resolution, well balanced frequency response and natural sound. Also it has excellent cost performance for professional use.

Having found this cable, I was able to stop using the expensive high-end cable. After all, I think it's better to gain the emphasis on tuning the audio system and the listening room.

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MOGAMI 3082 uses a coaxial structure to maximize the conductor cross-section within a limited outer diameter. This standard speaker cable is designed to meet XLR audio connector cable clamp.
Mogami's cable designer said that this cable structure is the best speaker cable.

In fact, while the cable diameter is 6.5mm and very easy to use, both the center conductor and the shield conductor realize a cross section of 2.03mm2 (equivalent to 14AWG).
 
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Because the MOGAMI 3082 has a coaxial structure, its wire processing takes a little more time.

It just peels off the jacket, bundles long ground wires, and insulates with heat-shrinkable tubes. Because the jacket is soft, it can be easily peeled off with a cutter knife.

#MOGAMI 3082 Spec.
 Conductor
  - Details:80/0.18 OFC (80×33AWG)
  - Size:2.03mm2 (Approx. #14AWG)
 Insulation
  - Ov. Dia.(mm):4.6Ø (0.181")
  - Material:PVC
  - Colors:White
 Served Shield
  - Details:80/0.18 OFC (80×33AWG)
  - Size:2.03mm2 (Approx. #14AWG)
 Jacket
  - Ov. Dia.(mm):6.5±0.5Ø (0.256±0.0197"Ø)
  - Material:Flexible PVC
  - Color:Black

#ELECTRICAL & MECHANICAL CHARACTERISTICS
 DC Resistance:0.009Ω/m(0.0027Ω/Ft) at 20°C
(Same value for both internal and outernal/shield conductor))
 Capacitance:253pF/m(77pF/Ft) at 1kHz, 20°C 
 Inductance:0.4μH/m(0.12μH/Ft)
 Electrostatic Noise:0.2mV Max.
 Electromagnetic Noise at 10kHz:0.2mV Max.
 Voltage Breakdown:Must withstand at DC 500V/15sec.
 nsulation Resistance:100000 MΩ × m Min. at DC 500V, 20°C
 Flex Life:15,000 cycles
 Tensile Strength: More than 980N
 Emigration:Non-emigrant to ABS resin
 Applicable Temperature:-20°C 〜+70°C(-4°F 〜 +158°F)
 Standard:UL13 CL2 75°C
posted by toons at 17:53 | Sound

2019/06/12

Nakamichi CA-5 pre amplifier Repair - 1

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Repairing the pre amplifier "Nakamichi CA-5" now!

I could easily obtain Nakamichi CA-5 Service Manual from the web.

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When I looked at the electrical schematic in service manual, it seems to be a simple discrete circuit configuration.
Since it was a product of the mid-1980s, no surface mount components were used, and it was not a lead-free solder with a high melting point, so I seemed easy to replace components.

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First of all, I checked the flat amplifier section of the main board, so I was relieved that it was working properly. This was probably due to the small number of parts, and the fact that heat stress was hardly added to the electronic parts by the proper component placement design.

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Then, I examined the cause of the interruption of the left channel sound. The main variable resistor (NOBLE) was normal, but the balance variable resistor(ALPS) was found to be very unstable, causing contact failure even at the center position.

Once the balance variable resistor was bypassed and the input signal was sent directly to the main variable resistor, it became possible to reproduce without any problems. As I also cleaned the contacts of the signal connector, the sound freshness also increased.

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The failured parts was ALPS Mini-dent resistor (RK27 series, MN type). It was easily obtained because of the audio parts currently being manufactured, but it did not the exist same resistance value parts.

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When I replaced the balance variable resistor to new one, there was no break or noise in the playback sound, and it was played with a good sound.

Probably because the sound was made in the flat amplifier section, I felt that the low frequency range was very rich and dense, and the resolution was very high. It is a little different from the realistic monitor sound that can be heard on the Nakamichi's high-end tape deck.

Because I used a pure class A amplifier (Accuphase) as the power amplifier, it might have become a warm dense sound image that is the opposite of the cool realistic sound of my reference full digital amplifier (FOB SD05 - Feedback less power DAC).

The contact cleaning of the main variable resistor and switches need to be disassembled, so I will use it in my sub audio system for a while under this condition.

After a while, I will try to tune the sound while checking the details of this amplifier.

posted by toons at 23:59 | Sound

2019/05/24

Nakamichi CA-5

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I just got the Nakamichi CA-5 pre amplifier !

The Nakamichi CA-5 was a legendary product when Nakamichi entered the high-end amplifier markets in 1985.

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This pre amp was released under the product names CA-5 for North America, CA-5E for Europe, and CA-50 for Japan. In addition, there were the top model CA-7 and the power amplifier PA-7/PA-5 products.

These amplifiers were commercialized in a technical partnership with Threshold Electronics. The PA-7/PA-5 power amp was developed with STASIS technology. And the CA-5 pre amp was also designed by Mr. Nelson Pass at Threshold.

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This amp seems to have been treated very carefully and the front panel is almost flawless.

Well the problem is inside the amp, so I tried to open it before turning on the power.

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There is no dust inside because of the sealed structure. There seems to be no swelling of electrolytic capacitors. This condition is unbelievable as it was over 30 years ago.

I looked closely at the circuit and found that in fully discrete components configuration no OP amps or ICs were used. It is a very simple circuit configuration of the MC phono preamplifier, the MM phono preamplifier, the RIAA phono equalizer and the line-level amplifier. Left and right channel circuits have been completely isolated in pure copper bus bar, so it was “dual mono” circuit board design. The phono stage seems to be a very sophisticated circuit. In addition, six giant film capacitors has mounted as coupling capacitors.

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I turned on the power in this state and looked at the state of the internal parts for a while, but there are no parts that generate heat. I tried measuring the voltage of the line output with a tester, but there seems to be no DC leakage.

Then I connected the CD player and the power amplifier and tried to play music.

The playback sound was output with noise mixed in the left channel. I think that it is a high possibility of poor signal contact, so I will try to repair it carefully.
posted by toons at 03:31 | Sound

2019/04/12

Test measurement of the remade SP using Fostex & Olasonic units.

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I fine-tuned my remade SP with using a tweeter of Fostex 2-way and Olasonic fullrange unit.

The picture below is the original SP previously crafted using Fostex 2-way units.

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In the remade SP, the front baffle was doubled and two full ranges were installed there.

I measured frequency characteristics with the RTA app "Audio Frequency Analyzer ". (Measured at 1 m position on the axis, pink noise)

@ Characteristics of Olasonic full range only (8 Ω parallel → 4 Ω)
Bass reflex tuning is almost as calculated around 120Hz. The high frequency is cut by the air core coil (0.18mH), but it has a 10k-12kHz peak unique to the unit.

Tw-non.PNG

@ Total characteristics by Fostex tweeter's Low-cutoff frequency with each capacitor(1.0/1.5/2.2/3.3uF)
It can be seen that the 4k-8kHz dip disappears as the capacitance of the capacitor is increased. The characteristics of 3.3μF seem to be good, but on hearing the sound is still high and it still feels awkward. It may be interfering by the peak of the fullrange unit. So, I will try for a while with 2.2 μF as a temporary condition.

# C=1.0uF
Tw-1.0.PNG

# C=1.5 uF
Tw-1.5.PNG

# C=2.2uF
Tw-2.2.PNG

# C=3.3uF
Tw-3.3.PNG
posted by toons at 03:34 | Sound

2019/04/11

Remade SP using Fostex 2-way & Olasonic fullrange

FostexTw+OlasonicFR.jpg

I was wondering what to do as a woofer unit of Fostex 2-way SP in the appendix of STEREO magazine (August 2014) had damaged.

So I tried combining Fostex 2-way with Olasonic fullrange in the appendix of DigiFi No.19 magazine.

The crossover network is set to -6 dB/oct, the crossover frequencies are 4 kHz LPF on the full range side and 6 kHz HPF on the tweeter side.

The tweeter side is adjustable, so I will do fine tuning from now on.
posted by toons at 23:57 | Sound

2019/02/07

TRIO KA-8100 returns

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I have taken out the vintage amp, TRIO "KA-8100" integrated amplifier that had been sleeping for a long time in the storeroom. TRIO "KA-8100" was internationally exported from Japan as the product name of KENWOOD "KA-601".

Last year I restored SANSUI "AU-5500" and I got confidence a little, so I will try it with this amp.

TRIO "KA-8100" is a product released in 1978.
It was called high-speed DC integrated amplifier, it was a product at the time when importance was attached to physical characteristics such as high frequency response, wide band frequency characteristics. There were other KA-9900, KA-8700, KA-8300 in the product series, and this amp was a low end model.

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It is undamaged and beautiful on the front panel. In addition, the rear panel is clean and rust is not floating. However, one speaker terminal of SP-A channel had been damaged. The power supply cable was also replaced, it was shortened to about 50 cm.

For the time being, when I tried to energize this amp there was no smoke, and the protection circuit was canceled, and the amplifired sound was safely.
However, since the operation is unstable, the sound of one channel is distorted. If I was electrified for a while, I got stereo sound normaly. Although it seems not to be fatal, there seems to be contact failure somewhere.

As a tendency of sound, it is quite different from the thick sound of Sansui "AU-5500", it is a refreshing sound with high frequency extended.

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I removed the top cover and checked the interior top surface, but it is hardly dusty or dirty as it was contained in the original box.

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It seems that "KA-8100" was used for about 3 years, but it was stored for the following 38 years.

Furthermore, I removed the bottom cover, I was surprised that there was some electrical remodeling. Film capacitors had paralleled to the block capacitor of the main power supply, and the output signal wiring had shortened out minimum.

Not remembered why I did this, but probably I could not be satisfied with the original sound.

Once restored to its original state, I would try to repair.

Also, I checked DC leakage of output signal, but both channels were excellent, less than 0.1 mV. "KA-8100" is certainly a DC amplifier.

Anyway, I think that it will take quite a while to repair "KA-8100" amp.
posted by toons at 03:24 | Sound

2019/01/10

SANSUI AU-5500 repair - 10

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Repair of the Sansui AU-5500 Integrated Amplifier has been completed.

The sound reproduced from the AU-5500 has become a sound quality that I can not believe to be an amplifier manufactured 43 years ago.

As a result of sound tuning, while keeping sufficient resolution and playback frequency range, it sounds a pretty dark sound. It is a very realistic sound such as jazz of 1950 - 60's.

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The front panel became beautiful, but the rust is floating on the rear panel, and it makes me feel old indeed as expected.

Also, as I was checking the sound after final assembly, I heard it as cloudy as the sound quality during muting (-20 dB) operation changed, so I replaced parts for metal film resistance from carbon resistance. Even at low volume it became pretty clear.

The replacement parts in this repair are as shown in the following picture. The total number of parts has now reached 64 pieces. Many parts deteriorated in nearly half a century, it was a timing just before a fatal failure occurred.

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I wanted to replace all the switches and the volume. But there is no compatible parts, so it became only life prolonging measures such as ultrasonic cleaning and contact revival.

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I hope that AU-5500 plays good music sound for a long time under the owner again.
posted by toons at 02:12 | Sound

2019/01/09

SANSUI AU-5500 repair - 9

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I'm running test running, but it is stable now.

It was clearer and more prospective sound than before it was repaired. Sound tuning to raise the resolution a little more and repair of the anxious place was done.

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Part 1: Change coupling capacitor
The coupling capacitor of the input signal of the power driver section was originally a standard electrolytic capacitor (ELNA 2.2 uF 50 V) was used.

I tried replacing it with an electrolytic capacitor for audio (TOSHIN UTSJ 2.2 uF 50 V) at this repair, but it was not feeling fit to this amp. For this reason, the coupling capacitor was replaced with a metallized polyester film capacitor (WIMA MKS 2 2.2 uF 50 V). I think that the resolution improved with this change and the sound quality was also improved considerably.

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Part 2: Capacitor change of high impedance compensation circuit
The Mylar capacitor (0.068 uF 50 V) that was connected to the final output stage was replaced with a film capacitor (WIMA MKS 2 0.068 uF 100 V).

Since all capacitors of the power driver section are supposed to be replaced, I think that it will lead to higher reliability of the amplifier.

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Part 3: Change of time constant of low cut filter
It has a function to cut low frequency with Low Filter switch. Original is a cutoff frequency of 70 Hz (-3 dB) which is a considerably higher frequency and is used to prevent low frequency resonance of analog records. Since it is not practical in modern times, I changed the filter time constant and set the cutoff frequency below 10 Hz.

Just at hand, there was a film capacitor (ROEDERSTEIN MKT 1818 0.33 uF 63 V) that sounds pretty good, so I adopted it.
If pop noise is mixed in from an external connection device, I think that it will be a countermeasure against it.

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Part 4: Replace the power cable
The original power cable was torn and the copper wire was exposed.
I decided to replace it with the 125V 15A cabtire cable on hand, but I had a hard time implementing it because it is a fairly thick cable. After all, it was able to attach to the cable gland part and pulled out to the tight.

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Part 5: Partial disabling of service outlet
The internal wiring of the service outlet was poor and I was concerned. Leaving only one outlet, we removed the wiring of the other two lines. Factors of power noise incorporation will also be reduced, and electrical security risks will also be reduced.

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Part 6: Change insulators
The original parts had hard plastic legs, but they were considerably deteriorated. I replaced it with an insulator with a metal cover. I had a solid foot around and it felt very good from a design point of view.

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Part 7: Nameplate of back panel
The nameplate of the back panel was in a beautiful state without miraculous scratches because the protective vinyl was affixed to the surface. Peel off old protective plastic and paste the liquid crystal protective film.

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In addition, I performed electrical checks at once and readjusted the offset voltage and bias current as the final adjustment of the power driver section.

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For this time, the bias current was set to 30 mA slightly deeper (setting standard: 25 mA ± 10 mA). The distortion factor in the high range at the time of the small signal should be lower than the previous setting.

I will do continuous operation for a while, and will make the final assembly.

posted by toons at 06:28 | Sound

2019/01/07

SANSUI AU-5500 repair - 8

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In the power amplifier section, I adjusted the DC offset voltage and the bias current.

It seems that the original semi-fixed resistance seems to be considerably deteriorated, and it turned out that it shifts slightly every time it adjusts each time.

It is a carbon-coated type semi-fixed resistor that was used frequently in the past, but now it is a discontinuous component. As it is still an electrical part with moving parts, the resistance value seems to fluctuate considerably due to contamination of the internal electrode.

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I decided to replace it with a cermet type sealed semi-fixed resistor. It is some parts of Marine Blue which is very conspicuous on the board of the main amplifier part. Cermet has advantages such as good temperature characteristics and less noise generation due to sliding.

DC offset adjustment is like this, it was set to almost 0V. The recommended value is 0 V ± 10 mV.

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In addition, I adjusted bias current and was adjustment while checking the sound quality with some current values.

The recommended value of the bias current is 25 mA ± 10 mA, but I tried it with a slightly deeper 28 mA. In truth, I want to pass more bias current, but this is a balance with reliability.

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I tried to raise the bias current to 100 mA and listened to the playback sound in class A operation area, and it was confirmed that it reproduced with very good sound quality.

However, it is not likely to withstand practical use in this heat dissipation structure of this amplifier because the calorific value is too much. So it should set the bias current near the recommended value.
posted by toons at 08:34 | Sound

2019/01/06

SANSUI AU-5500 repair - 7

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The block capacitor in the main power supply was replaced.

The original block capacitor was ELNA 4700uF 50V (size: φ 35 x 70 mm).

Because the layout of the main power supply part of this amplifier was good, the temperature rise of the block capacitor was suppressed to the minimum and it seemed that it was not exposed to the thermal stress so much.

Apparently there is no abnormality such as expansion and leakage of electrolyte in particular, but electrolytic capacitor is an electronic part which easily deteriorates over time, so decided to replace it.

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The original two block capacitors slightly differed in feeling in hand. So, I measured each weight.

Then, it had a weight difference of about 10%. It seems that the internal electrolyte is getting dry up in 43 years. There is a high possibility that the electrostatic capacity is also decreasing. I think that I tried to replace it just in case.

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The block capacitor replaced this time is "Super Through" 4700 uF 63 V (size: φ 35 x 50 mm) of Nichicon's audio electrolytic capacitor KG series. It is a gold and black sleeve and a fearless appearance.

Electrolytic capacitors are now extremely miniaturized, and the size is not suitable for mounting in this amp, so it was very difficult to select parts.

au5500-blockcon-KG-4700uF.jpg

# NICHICON KG "Super Through" 4700μF 63V
- Rated voltage: 63 V
- Rated capacitance: 4700 μF (tolerance ± 20%)
- Case size: φ35 × 50 mm
- Loss angle tangent (tan δ): 0.22
- Rated ripple current: 4.5 Arms
- Category temperature range: -40 ° C to + 85 ° C
- High temperature no-load characteristic: 85 ° C. 1000 hours

Even though it may be much bigger, the problem of rush current and the possibility of collapsing the sound balance are also high, so I kept it the same capacity.

This block capacitor adopts low resistance electrode foil for audio, and it can be expected quite a bit because tan δ is very small even at large capacity.

As soon as I switched on the power and tried to make a sound, I thought that the frequency range was narrow and I failed with a dull sound, but it gradually became clear in about 3 hours, the low frequency also steadily emerged It was.

Since new electrolytic capacitors also have thermal stress due to soldering, it is necessary to conduct electricity for several tens of hours until the internal anodized film self-recovers.

I think this capacitor is the most expensive among the parts that I exchanged, so I'd like it to work for improving sound quality.

posted by toons at 23:57 | Sound