Yet another quite detailed description of some more of my audio equipment
It DOES have a couple of minor issues which the new owner will need to sort out ...
If you are looking for something that will work "straight out of the box" ... move along please
If you enjoy servicing and restoration of classic audio gear, this could be of interest to you (brew a cup of coffee before reading the details below!)
TECHNICAL ABILITY REQUIRED: Minimum "average" technician skills but those with more advanced skills could also gain more insight into this amplifier, if such things interest them.
In preparation for this advertisement I read around a few forums about experiences that folks have had with the AU-101 and one thing was obvious (besides many being "knob heads", if you don't know the difference between the Volts and Amps range on your multimeter and you are trying to set your amplifier bias, then you shouldn't have the top off the amplifier!
If you are unaware of the dangers inside an amplifier with the case open - stay well away and save yourself from harm or even death by electric shock!
EQUIPMENT HISTORY:
Everything I am describing below is IMPORTANT, read it please!
This amplifier is part of my "vintage collection" of all things audio, both professional and consumer gear. I like to listen to both consumer and professional audio equipment, take a look around inside, view the build quality and just appreciate the engineering skills (or lack of) in the early days of audio equipment manufacture.
This amplifier, which I refer to as the "baby", must considered as an entry level amplifier for introduction to the well known vintage Sansui "sound". Many started their Sansui collection with one of these AU-101's and then moved on to the 555a or like we did, upwards onwards into audio heaven with the likes of our AU-7700 before we moved on to NAD and others.
Since the early 1980's this AU-101 amplifier was no longer in regular use and was transferred to my personal "storeroom" where it has been sitting ever since! While it was a "sweet girl" back in those early days, it has suffered a little while being kept unused for so long and the FULL details of my observations and assessements are below so that anyone who is contemplating this amplifier has an idea of what they are "up for" ... I call the issues this amplifier has MINOR, probably I should have sorted them out myself but I have so much gear and so little time, I would rather this amplifier went into the hands of someone who has some technical abilities and appreciates what this AU-101 represents in the world of vintage audio equipment.
Preliminary tests made today do indicate some minor electronic "issues" and I have detailed these below ... I also give a lot of detail about the case, this can be just as important with respect to vintage equipment (if not more so) than the electronics because electronic spare parts can usually be obtained but damaged hardware such as cases etc are a different story!
Quite frankly, I don't have the time or the inclination for service work these days (I am worn out after working in the electronics field for 50+ years and I am completely 'over' the servicing side of things) so to be frank, the task of bringing this equipment back to full operational condition is for a new owner to take on. The basic testing information below is just that - basic, but it should give a knowledgeable, experienced technician all the information that is needed to bring the AU-101 back to "just left the factory" condition.
So, enough introductions ... here is the detailed description of what I have to offer
SANSUI - Stereo Power Amplifier
Model: AU-101
Left the factory 1973 ~ 1974 period
Australian market model
Power output 15W RMS per channel
Frequency response 20Hz ~ 60KHz
Maximum THD 0.8%
S/N ratio 65dB ~ 75dB (depending upon the input)
Drives 8 ~ 16 Ohm loudspeaker load
Four inputs: Phono (MM), Microphone, DIN, Line
COSMETIC CONDITION:
UPPER CASE
Constructed of a top steel sheeting, 1.5mm thick and the entire rear folded "lip" has ventilation slots for cooling. This top is extremely strong and it would take a very severe knock to bend it out of shape! It is straight and true of course.
The finish to the top is a matt Black paint with something that looks like a stiple effect.
While this finish is in "reasonable" condition, it does have a slight discolouration to it, particularly in the four corners where other equipment was obviously placed above the amplifier. No severe scratching, dents! or markings. There is a metallic stick on label (a bit worn) that warns about connecting the correct speaker impedance load to the amplifier.
I also noticed that on the rear lip, left hand corner, has been etched some ID information - this could be "in-filled" if it bothered the new owner.
Each of the amplifier top section sides is 3 ply wood 12mm thick (not particle board) with a tacky wood grain plastic veneer. I always found this disappointing but so common with these early amps, nice electronics but the Japanese forget about dressing up the case nicely. I know SONY wen to the effort of using real veneer in some of their amps but alas, Sansui did not. These two sides are secured to the top plate with 4x heavy duty screws on each side - the resulting U shape is very rigid and secure (nice!)
I must say that BOTH side panels are in great shape, barely any marks or scratching at all!
DETACHABLE FRONT PANEL
The front panel that the user sees is completely removeable, no need to undo all those pots and switches to get at this!
It is one panel of Aluminium finished with a Satin Black and two side trims of metallic Gold have been added to each side of this panel. The labelling is all screen printed, although I must say that the print is small and quite difficult to read (in my opinion).
The Black satin finish has some light "dullness" areas, I think this is due to be stored in an environment where there was no airconditioning and humid conditions may well have caused this. This patchy dullness is noticeable but not terrible (a bit subjective I guess!) The metallic Gold trims are in great shape and clean.
I do see a couple of SMALL, short scratches but in my opinion these are not dramatic.
I do observe that around the SELECTOR switch hole has been screen printed a number sequence 546700602 I do not understand why this is there! It has definitely been printed at the time of manufacture (not added later) and is in a position that would normally be covered by the control knob. The number sequence has no relation to the amplifier serial number either. If its a part number, this would normally be on the rear, not the front. I give up and have no clue about this ...
ALL of the screen printed labelling is present and NOT worn away partially or completely - very nice although I just wish Sansui had made the printing just a bit heavier so that there was greater contrast with the Black satin finish.
MAIN CHASSIS
All steel, thick and tough sheet metal. Absolutely no bent or damaged framework at all.
Efforts have been made by Sansui to make life easier for the service technician with a nice underside removeable access cover plate - this gives easy access to the main driver/power output board from the underside.
The sub front panel is on a limited movement pivot so this whole panel can be more easily accessed although I must say that this movement is limited - it is more workable to just remove the two side screws and then have much easier access to the sub-PCB that looks after the input signals, tone control etc
Layout of the amplifier is sensible and logical, it is easy to immediately recognise where the sections of interest are located and wiring is generally tidily run around inside the case with some lacing. All low level signal paths use coaxial cable.
FRONT & REAR PANELS
NO damage to any control switch e.g paddle switches, potentiometers (fluted shafts), rotary switches (Source select & Power ON)
NO damage to the headphone socket, microphone socket, DIN socket (Tape Recorder connection) rear RCA phono sockets, speaker screw down terminals, AC multi-voltage switch or the auxiliary AC output sockets (two pin - not earthed)
NOW FOR THE INTERESTING PART .... Some observations and basic testing
Actually I went through the audio listening test twice, no thrice times ... the first conclusion was BEFORE I had done anything to the amplifier, the second "Power ON" was after I did a quick cleanup inside and solved one significant issue and finally my listening to the amplifier with both channels running.
INITIAL AUDIO TEST (Straight out of the box in the storeroom)
Test loudspeakers were the pair of LEAK I currently have available, sort of suits the amplifier age!
Test signal source was the line out from a very nice SONY analog tuner I am currently testing
Power ON
Orange front panel lamp indicates
Signal source was line level (so I only checked through the AUX inputs) from a very nice SONY tuner I am preparing to put on this website.
Right Channel audio was weak, intermittent and even at times "motorboating" - not good Joe!
Left Channel was even worse, zilch nada zero audio output at all!
When I lifted off the lid I did notice a LOT of accumulated dust inside, so I gave the old girl a good cleanup and focused on the SOURCE rotary switch as this is an open type and known to cause issues if it has dirty contacts. I also gave MOST of the pots a good spray clean although two of the pots are orientated so it is very difficult to give them a spray without completely diassembling the front panel assembly - so I left them. The paddle switches also had a good clean up.
The main amplifier board was pretty dirty and I gave that a good clean, particularly around the output transistor leads on the heatsink and the bias adjustment trim pots which are of the open frame type (Yuck!)
SECOND AUDIO TEST (After the above clean up)
Power ON
Orange front panel lamp indicates
Right channel is now fine - actually, it produced a really nice sound! Tone control(s) and balance work fine and without any noise or scratching when being rotated. Volume level adjustment is smooth. Paddle switches perform their functions fine and the 3 position source switch operates nicely without horrible "clunks" in the audio as the source is changed. Impressed!
Left channel however still had an issue ... dead as .... no audio at all
So now it's time to look around and undertake some basic measurements to determine what could be wrong with the Left channel ... I always start from basics, even if one channel is "good" I start my tests right at the source ... the power supply.
First up, from everything I can observe, this amplifier is original in every way. I cannot see any signs of component changes or work on the two PCB's
This can be a good thing (if someone else has "been inside" it is always a concern that they may not have known what they are doing!) or a bad thing - after almost 50 years, those electrolytic capacitors (particularly the larger caps around the power supply or providing AC power filtering) do 'fail' - most often the electrolyte just drys up inside. Usually with these vintage amplifiers, the first thing to tackle is the electro's (usually not every single one) even if the amplifier is fully functioning - those caps can be like ticking "time bombs"!
OBSERVATIONS AT THIS POINT:
A nice straightforward, small audio amplifier but the microphone input is a bit quirky! Perhaps Sansui had in mind use as a PA amplifier but then just a single channel would have done the job and 15W RMS will not "fill" much of a listening area if used for PA work.
The thing that struck me immediately when looking around inside, fuses fuses and more fuses! Sansui must have had a job lot of fuses because I have never seen so many in an entry level, low power amplifier before! There are dual fuses on the secondary winding of the AC power transformer, main AC fuse at the input to the amplifier, dual fuses on the channel supply rails and even a fuse on the incandescent Power ON lamp (6.3V)
What is even more strange is that 3 of the fuses are hard wired into circuit, they look like festoon lamps that Wharfdale uses in their speaker crossover networks but they are definitely plain old fuses. It just means that if those hard wired fuses go open, you will need to solder in replacement fuses. Just a bit of quirky design from the Japanese.
BACK TO THE TESTING AND MEASUREMENT
The AC transformer is multi input AC voltage capable, ranging from 100V (Japan) through 117V (USA) and of course 240V for Australia or UK/Europe. The transformer fitted is type 400-4567.
First testing step was to measure the AC output from the secondary (Purple wires) and I have 68.5V raw AC - good. I also measured after the fuses, same result, so the fuses (soldered to tag strips) are also fine.
The other secondary provides just 6.3V for the front panel lamp, again via a soldered fuse. I didn't need to measure this as the front panel Orange coloured lamp illuminates! While this lamp is working fine, it is a very strange looking lamp encased in some sort of Black rubber or plastic material with a "light window" - talk about using custom components for what is otherwise a rather mundane component.
So, the AC transformer is fine.
OVER ACTIVE BRAIN AT WORK HERE ...
Actually I had an after thought about this transformer ... it could also be removed and used in a 12AX7 tube based preamplifier system, although I have not sat down and worked through this thought clearly! With half-wave rectification I would only get just on 100V for the plate supply, so maybe it's not such a great idea! Thinking aloud ...
BACK TO TEST AND MEASUREMENT
Next I took a look after the full wave bridge rectifier block (across the filter capacitor) and measured 45.8V DC - seems pretty close to the schematics which indicate 44V
The electrolytic is an ELNA, in fact all three electro's on the main PCB are from this manufacturer - no signs of stress, leakage etc
So, at this stage we have a good DC supply to the amplifier PCB's and as I had easy access to the main board, I took a quick look around the power output transistors (2x pairs of 2SC1060 NPN Sillicon).
Ah Ha ... the Left channel fuse was open circuit! I measured the current being drawn here and it is only 30mA idle so it looks as though the fuse just went "bad". Unfortunately I do not have a spare 1.5A 3AG fuse easily at hand so I just did my testing by moving the remaining good fuse from one channel to the other. While I say it is ONLY 30mA, this is a bit high for the quiescent current from the supply rail. I checked the other (working) channel and it sits at 12mA
SPECIAL NOTE: Although not detailed in the service manual, this is one method to set and measure the bias/idling current of each channel. Pull out the fuse, connect your meter across the fuse holder and make sure your meter is set to read mA (FSD around 1A is fine, you are actually looking for current flow in the region of 10 ~ 30mA)
So, at this point I had an idling current of 12mA in one channel and 30mA this faulty channel. But that's just the bias and it is the fuse being open circuit that killed the Left channel.
Ideally the bias setting on each channel should be very close to each other, in region of 20mA is comfortable for the amplifier. So, to set things "right" the new owner needs to adjust the two trim pots (VR801, VR802 200 Ohm value) to set the "correct" bias. Just a basic multimeter is needed for this BUT if you really want to take a closer look at the amplifier behaviour, a scope could be connected to the output(s) along with a known good sine wave source signal and look at the output on a scope - you want the best linearity possible on both channels.
I did not touch either of these trimpots, other than to give them a good spray clean. I have seen (and it makes sense) others who have changed these trimmers for nice sealed multi-turn types - it sort of future proofs the bias adjustments.
Remember, ALWAYS allow the amplifier "settling time" and make any bias adjustments over a period of say 10 minutes. You will encounter some setting drifting until the amplifier "settles down"
LET'S LOOK AROUND FURTHER ...
I took a look at the collectors of the 2SC1060's (the mounting screw(s) is a good point to access the collectors) and the measured voltages are very close to those indicated on the schematic (45V & 21.4V) for BOTH channels.
Again, I powered up the amplifier one last time but using my meter in place of the non-working fuse (seems stupid but I just don't have 1.5A 3AG fuses lying around and I am not about to buy one for this amp, my meter will do for my tests!)
Now we are in business! Beautiful sound comes forth from the Left channel as well now. No detectable distortion, nice loud levels and clean sound.
Acutally, just one comment here about the sound ... the tone controls are VERY impressive, especially the Bass control. As it is turned clockwise, the low end really "grows" and sounds so sweet - I love this.
Here I decided to cease and desist with further investigations and adjustments!
If I keep going then I am practically going to end up restoring the amplifier myself, and I just don't wish to do that.
As I was working on the SONY Analog tuner (coming up soon) I left this AU-101 running ALL DAY long playing my favourite "off air" music via the tuner and this amplifier did not miss a beat. Nothing strange happened to the "idling" current being drawn by each channel, which of course increases as the audio level is increased but nothing of any concern to the amplifier.
So what I am offering (in the end, after all the waffle above) is a nice AU-101 with BOTH channels running fine BUT the new owner needs to put in a 3AG 1.5A Fast blo fuse into the socket on the main board.
Then to just "polish it off", set up the idle/bias current using a meter across the fuse holder (no fuse fitted of course) and adjust those trimpots to achieve a stable current at idle (no signal input, Volume at 0 and it really doesn't matter if loudspeakers are connected or not with this design for idle current purposes) in the range 10 ~ 20mA
Advanced users may wish to take a peek at the output with their scope too! I would have LOVED to do this but my test equipment has mostly found new workshops to live in so my testing abilities are now very limited.
I have now reassembled the amplifier to original condition, no screws or bolts left out! Don't you hate it when someone goes inside a piece of gear and leaves screws missing, my pet hate!
Keep in mind that shipping of this equipment ANYWHERE around Australia (only) is FREE, fully insured and tracked.
I have a policy 'site wide' that orders which total more than A$75, I will ship for free within Australia - this option will show automatically in the 'checkout' area
