SANSUI AU-5500 repair - 10


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.


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.


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.


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


SANSUI AU-5500 repair - 9


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.


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.


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.


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.


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.


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.


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.


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.


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.


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


SANSUI AU-5500 repair - 8


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.


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.



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.


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


SANSUI AU-5500 repair - 7


The block capacitor in the main power supply was replaced.

The original block capacitor was ELNA 4700uF 50V (size: 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.


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.



The block capacitor replaced this time is "Super Through" 4700 uF 63 V (size: 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.


# NICHICON KG "Super Through" 4700F 63V
- Rated voltage: 63 V
- Rated capacitance: 4700 F (tolerance } 20%)
- Case size: 35 × 50 mm
- Loss angle tangent (tan ): 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 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


SANSUI AU-5500 repair - 6

On Sansui AU-5500 restoration work, the level of the playback sound fluctuated or broke off as a result of the running test. For this reason, it was judged that contact failure of the main volume and toggle switch, and parts cleaning was done.



Since smoke of cigarette penetrated into the inside of the toggle switch, ultrasonic cleaning was carried out with diluted kitchen detergent. I was surprised by the severity of the wastewater after washing.




After rinsing the detergent with purified water, ultrasonic cleaning was performed with IPA (isopropyl alcohol).

After this, take out the toggle switch and let it dry and finish. I believe it is safe to wash with IPA, because the possibility of water remaining is low.


Before washing, when the contact resistance when the toggle switch was turned on was measured, the worst state switch showed contact resistance of up to 800 .

After this washing, almost complete conduction (down to near 0.0-0.1 ) was done, so the effect was tremendous.


As with the toggle switch, the main volume (quadruple volume with left and right balance) is degraded considerably as well. There was noise at various points during rotation, and the resistance value was also discontinuous. Therefore, I carried out infiltration washing with IPA for this part.


When immersing the main volume in IPA and leaving it for 12 hours, considerable dirt leaked out. It seems that there was enough effect of alcohol washing.

I measured the resistance value with a tester, but I could confirm that the resistance value changes smoothly.

Again, after reassembling these electrical components, I turned on the AU - 5500 and confirmed that it works without problems.

The sound was interrupted, the level did not fluctuate, I did not care about the volume noise.


The sound of the AU - 5500 is very clear.

Since the analog amplifier handled very small signals directly, it was realized again that the contact resistance (dirt) of the signal path leads to very great sound quality degradation.
posted by toons at 04:00 | Sound


SANSUI AU-5500 repair - 5


For Tone control, Phono equalizer and sub power supply, I identified some parts that require replacement, and exchanged mainly electrolytic capacitors.

# Tone control section repair

The tone control section is made up of a single board and is attached to the upper side of the front panel. As a result, there was a lot of dirt and the cleaning was hard.

This tone control circuit is divided into 3 bands of low, mid and high band so that it can be controlled.

The electrolytic capacitor used was partially expanded, but overall the condition was better.

Standard products of Nichicon and Elna were mixed, but I replaced it with Nichicon's audio grade products (MUSE-FW, MUSU-ES).



# Phono equalizer repair

In the phono equalizer section, the RCA input terminal and input changeover switch are also arranged on the same board.

There was hardly any component deterioration, but only the electrolytic capacitor was replaced. In the same way as the tone control circuit, I replaced it with Nichicon's audio grade products (MUSE-FW, MUSE-ES).



# Repair sub power supply of phono equalizer part

As well as the power amplifier part, the electrolytic capacitor bulged and it was considerably deteriorated, so I replaced all electrolytic capacitors. I replaced it with Nichicon's audio grade (MUSE-FW) and high voltage standard (VR).



Main circuit board repair is completed.

After checking each board individually, I turned on the main power and made sound. I confirmed that stable operation is in particular without problems.

The sound of the AU - 5500 became considerably clear, it became a sound quality which I can not think as an amplifier 43 years ago.

When I made a running test, I worried about the noise of the main volume and the balance volume and the discontinuity of the sound by switching the switch.

It seems that the deterioration of the signal system is serious so it seems that we have no choice but to do internal cleaning of electric parts.

posted by toons at 16:05 | Sound

SANSUI AU-5500 repair - 4


Sansui AU-5500 integrated amplifier (made in 1975) dismantling and repairing!

As a result of examining the reason why reproduced sound can not be output, it was found that the DC offset voltage of the power amplifier part was supposed to be around 0 V originally, which was near 1000 mV, indicating that the protection circuit is working.

As a defective part, it turned out that the electrolytic capacitor of the driver stage was almost in a puncture state. The electrolytic capacitor was burnt and it was expanding. When it turned on the power, the part itself was vibrating inside. The spark might be flying inside the parts, so it was very heat.


Sometimes the sound comes out when the electrolytic capacitor is charged up over time and the protection circuit is released when the voltage stabilizes.

If this amp was used continuously, the power transistor would have broken.

I exchanged parts of this electrolytic capacitor and turned on the power, the protection circuit was immediately released, and sound began to come out safely!

In this state, I checked transistors, diodes and other parts again, but I was relieved that there is no particular problem.


As it is, as many parts waiting for failure will be left untouched, I decided to exchange all the electrolytic capacitors.

When dissolving the solder and removing the part, there were a lot of electrolytic capacitors where the electrodes easily detached. I was very scared.




It assembled and powered on, the protection circuit was immediately released, and it became possible to output sound properly.

With this, I could dispel the uneasiness of the power amplifier part.


posted by toons at 05:26 | Sound

SANSUI AU-5500 repair - 3


For repair of Sansui AU-5500, I got the service manual from web. It is a very happy to obtain an electronic manual of this vintage amp.

The outline specifications of AU-5500 are as follows:

- Output power: 32 W + 32 W (8 , 1 kHz)
- Total harmonic distortion ratio: 0.15% (at rated output)
- Frequency response: 10 - 35000 Hz (+ 0.5 dB, -1 dB)
- S / N ratio: 85 dB or more
- Channel separation: 55 dB or more (1 kHz at rated output)
- Damping factor: 30 (8 )


Although it is unbelievable spec now, the stereo amplifier of this era was such a thing. From the days after that, the audio industry became competing in the specifications, and the physical characteristics were competed.

The next year 1975, AU-707/607 amplifier which became a big turning point of Sansui was released, so it seems that this 4-digit model number series has been discontinued for a few years.


posted by toons at 04:16 | Sound


New updated - "Vibroscope / Lie" ver 3.0

icon-vs_v300.png icon-vslite_v300.png

"Vibroscope" and "Vibroscope Lite" have been updated to ver 3.0.

"Vibroscope" is a powerful measurement tool for analyzing vibration by using iPhone's acceleration sensor in realtime. It allows you to monitor by visualizing the very low-frequency vibration such as inaudible by ear.

It can be intuitively detected an acceleration amount, that displays the two-axial coordinates in the horizontal direction and the time-axis waveform in the vertical direction.

VS_1_v300.png VS_2_v300.png

It is also equipped with the ability to analyze the frequency components of the very low frequency vibration by FFT analyzer.

It can be measured by determining the horizontal or vertical direction to suit the attitude of the iPhone, so as to be available in a placement of the floor and desk or Handheld.

VS_FFT_1_v300.png VS_FFT_2_v300.png

Please to click the following link to show "Vibroscope" from App StoreTM. It will be open our product page on App StoreTM.


Please to click the following link to show "Vibroscope Lite" from App StoreTM. It will be open our product page on App StoreTM.


posted by toons at 08:50 | News


Information on season's holidays closure

We will be closed from 2018/12/28 to 2019/1/6 for the season's holiday.

Regarding inquiries received during the holidays, we will respond sequentially after the holidays. Thank you for your understanding.

Have a good new year !


posted by toons at 23:55 | News