Sansui AU-505 Oddities

T

teletype68

Music Listener
Hi,

I have been long reading and watching this Sansui thread as I love these pieces of equipment. But I decided to write only now.

I am in the process of restoring a nice Sansui AU-505 amplifier that is in very good condition (however some fine scratches present). I have began by cleaning the mechanical parts, front face and knobs, and the chasis. I enjoy working on this machine but, I have discovered some oddities which I want to share with you. I also want to learn from your experience in order to restore this amplifier to its best shape.

Number 1:

The mains transformer is buzzing slightly. Is this normal? I know Sansui's reputation is based on quality transformers. How come this transformer is buzzing in idle, no signal applied to the inputs?

Is there anything I can do to remove this buzzing sound? It is a very faint buzzing sound but as I am a perfectionist, I would like to address this issue.

Number 2:

I have began the recapping operation. I have decided to replace every capacitor in the amplifier, besides the main filtering one and the two output capacitors. For the moment I have no means of obtaining nice replacement parts for these capacitors. For all the other capacitors I have been using Rubycon parts, not new, but "new old stock".

However, while replacing capacitors, I have observed big differences between the schematic and the actual parts installed.

For instance:
- on the amplifier board, there were some 47uF / 16V capacitors where the schematics shows 220uF / 16V.
- on the same board there is a big capacitor rated 100uF / 80V. In the schematic it is rated 220uF / 63V.
- on the same board, there are some weird transistors, standard capsule, black plastic, instead of those that were originally mounted, the metal can types with gold pins. I was not paying close attention on the marking of those transistors to compare against the schematic. I will do it tonight when I will spend some more time with the amplifier.

I am confused.
The main issue is that the amplifier was not modified by some other technician. It had all original parts, ELNA capacitors, and those weird transistors. I have closely inspected the soldering joints and there is no evidence that anyone else besides the factory, worked on this amplifier.

All other transistors appear to be original.

PS: I will come back with the pictures when I will have some time to download from the digital camera.

Thank you!
 
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NOS electrolytic caps are not a great idea IMO, all the caps required are available from somewhere like parts connection or hificollective.
If the part in there are original (this needs to be confirmed) replace with same as what is in there, for caps that are 10v or 16v you can do well to use 25v as they will last longer. This is only with the low volt rated ones, and never use something that is rated at lower voltage.

I did one of these but it was a few years ago now.
 
Thank you for the reply.

I am perfectly aware that NOS parts especially capacitors are not good. The real problem is that I live in Romania where it is very hard to obtain new quality capacitors. So I used what best I had.

I am planning on ordering them (Nichicon or ELNA) from the Europe or the States at some point.

I indeed swapped the existing parts with the same values as were originally found on the boards. I read somewhere that Sansui documentation was not always accurate.
 
For the buzzing, how is the actual voltage in Romania? In Holland we did have 220 volts in the past, and it is supposed to go up to slowly over the years. If you have a voltage selector on the unit and the voltage is over 220 while the selector is still 220, you could put it to 240 volts which makes the operating voltage lower, it can affect the hum a little bit.

Just curious, I did look in the service manual you can download from hifiengine (it is free after registration) and I did see some 47 uF caps in the amps section as well as capacitor c822 rated as 100uF 75V. Do you have the good schematic?
 
Hi gslikker,

Officially, the mains voltage in Romania is set to 230V, as far as I know. I haven't measured to see the real value, yet. I can do this when I reach home later on today. I hope I can upload the pictures also. I need to check whether the AU-505 has a voltage selector also rated for 240V. I would be more than happy to set it to 240V if I can.

Regarding the schematics, I need to take a closer look when I get back home. I haven't downloaded from HI-FI engine, although I have a valid account for some time. Maybe I was looking at the wrong documents. A friend supplied the repair manual for references.

As a general rule of thumb, while recapping various vintage components I have in my collection, I always replace the part with what was on the board before.

If it worked good for close to 40 years, it will also do it after parts swapping.

Later edit:

I have found a picture on the Internet that depicts the AU-505 with the same transistors that I have. Here it is:

100501092635491760.jpg


We can see that standard for the era metal can transistors are replaced (almost sure at the factory) with equivalent plastic package transistors. And the one between the two output capacitors is a BD class transistor looking part. I find this a little weird because almost all AU-505 that I saw were built with metal can transistors. Or maybe this one is a different board revision?

I will come back with pictures.
 
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I did some quick photos of my unit. The quality is not so great as I did them in the hurry.

You can see the transistors I've been talking about.
I also downloaded the service manual from HI-FI engine but take a look at the picture I did on my tablet. It says values that are not on the boards.

C815 / C816 on service manual is 220uF / 6.3V, on the board they were 47uF / 6.3V.
C822 on service manual is 220uF / 75V, on the board it is 100uF / 80V.

I'm not sure where's the mistake.

PS: I swapped the voltage selector to 240V and the buzzing slightly reduced in intensity and frequency. Not much of an improvement but still.

I am doing a list of transistors on the power amplifier board and the originals as we speak. I will post it in a few moments. You can see I am interested in the original metallic can transistors. I have seen many AKers that swapped those metallic can transistor to modern ones. If any of you can part with them replaced parts, I would be happy to pay shipping costs to Romania.

167v6s0.jpg


25p34vm.jpg


21nh6z8.jpg


9kwe43.jpg


11kcv83.jpg


3359kxc.jpg


neykb7.jpg


2qd0i8w.jpg


Thank you,
 
Part No. - Schematic - Board

T801/802 : 2SA640 - NEC A640
T803/804 : 2SC875 - 2SC875
T805/806 : 2SC281 - can't find, probably temperature controller
T807/808 : 2SC875 - C1211
T809/810 : 2SA532 - A697
T815 : 2SC959 - SONY C1124

As you can see in the left column there are original transistors and the right column ... still originals but other markings (equivalents?).

Is my amplifier unit a newer revision of the AU-505?
 
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I did see your parts list.

So I checked these schematics again. Now look at hifiengine they have TWO operation/service manuals posted by two different people.

They are NOT the same!

In there you will find the transistor differences as well as the capacitor differences.

But Sansui really messes up documentation versus what you get, my AU666 did have a protection board which did not look like the schematic, and accidentally I found this board being documented in an AU999 schematic.
So I downloaded all these AU??? schematics and manual I could find.
 
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Oh, I see now!
I just downloaded the first schematic, and apparently is the same as the one I had originally.

I need to get the second schematic this evening and compare against my amplifier. I also see some unusual stuff on the back of the amplifier PCB, factory mounted also.

There are two small ceramic disc capacitors in series with appropriate resistor, all in a silicon tube, soldered on certain positions on the board. I am perplexed.
I need to check both schematics and figure out what the differences are, and why, and if the PCB is the same between the two revisions, maybe I could choose the original parts-list of the 1973 (or so) release.

I also did some quick research on the Internet, looking through pictures of other AU-505 units and I found some that resemble mine. But most of them, resemble the original release.
This leads me into thinking there were two different revisions of the same amplifier.

Another "oddity" is that on my unit, the microphone socket is black plastic, while the headphone socket is all metal. On most pictures I saw, both sockets are black plastic. Interesting.
 
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Transformer hum

transformer hum usually occurs in an excessive/overload condition which is presumably not the case here.

I have had this noise problem which was caused by the transformer frame bolt tension relaxing. These are the bolts which hold the core laminations together; it may be worth checking they are still tight...
 
Hi DougBrewster,

Indeed there is no case of overloading in this application. The humming is also present while the unit is idling.

To access these bolts that hold the iron core laminations, I need to first remove the black Faraday shield case, correct? This also has 4 bolts running through, securing the metal enclosure.

Thank you,
 
I have tightened the transformer and the buzzing slightly diminished. It is OK now, bearing in mind that I am having the amplifier by my head, near the bed (in order to facilitate access to it each night).

I have also continued with the recapping of the entire unit using those NOS capacitors. I have used a mixture of Rubycon, Nippon Chemi Con, and Nichicon. I am not very happy with the replacements, but still these capacitors are far more superior than anything else on the market in my town.

I am going to do another recapping when I will find a good source of quality capacitors.

My impression is that the sound is more dynamic and soft now. It sound totally different in the good way. I did some measuring of the old capacitors and their values fall in between the accepted tolerances. ESR values are good to, the old ELNAs being quite "low-esr" with cca. 5 Ohm for a 10uF / 16V capacitor.

However, the sound much improved with the new (er, old) replacement capacitors.
 
congrats with your update.
Maybe, the NOS capacitors took away all the possible problems with the old ones, and maybe you would not have heard any difference between the NOS and 'new' new capacitors anyway.
 
A mechanical buzz from the transformer can be caused by DC on the AC mains, this is more of an issue these days with so many switching appliances, and inverters in use.

If it is the cause, only a DC blocking device or isolation transformer will get rid of it. I have this problem here in AU.

Good that you have it reduced significantly :thmbsp:
 
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