Pioneer A-8 hot transformer and humming.

[allanmatters]

Yes I have seen this recommendation on many threads about changing the filter capacitors . I have a question though. Which filter capacitors are you referring to ? The ones on the power supply board or the two main biggest capacitors between the heat sinks ?

 

[allanmatters]

So I used the system for about 2 hours . Played it at low volumes in the beginning, moderate volumes and later at high volume towards the end . The PT was super silent for about 45 mins then slowly it picked up buzz. But not noticeable at all even while I was listening to music at low levels . I could not hear it’s buzz at all. The only time you will hear the buzz is if u actually concentrate enough or put your ear to the top back of the amp.

Here’s a video of how it used to buzz at unbearable levels ( before I did the varnish submerge process)

And here’s a video I took today after 2 hours of play back time ( after the varnish submerge process )

It seems the buzz reaches to a certain peak and can’t go any higher . IL have to run the system for more than 2 hours to know for sure . At least 4 hours

Note - both the videos have been recorded through the same mobile

I am going to invest in new caps I will look for 10000uf 63v main filter caps . Was thinking of Cornell-dubilier . Can any one tell me is this is ideal for the amp because the lead seems to measure only 10mm and I require 18mm of lead length

 

[QSilver]

I have an A-7 too, I can check but I think the capacitor connections are the same on both the A-7 and the A-8 (Between the heatsinks on a PCB) If they are then I know that KEMET make a perfect drop in replacement for the originals which have 5 pins on the bottom. 1 for +, 1 for - and 3 for anchoring.... actualyl the moden one only has 2 for anchoring but they are the same orientation.

I have changed the filter caps on my A-8 and although its made it less hot and buzzy, the transformer still gets hotter than the amplifier and hums to the point it pushes the hum into the audio circuitry... unless I have a bad bridge rectifier??? The hum is only slight...

I just envisage the transformer one day overheating and blowing the internal thermal fuse...

 

[allanmatters]

Sheesh it’s starting to buzz through the audio circuit???? These non switching amps really need patience and time .

I am actually not hearing the buzz on my PT as even after an hour of listening to soft classical music on low volumes ,I cannot notice the buzz since the last varnish is effective .A good 80% to 90% reduction in buzz and the remaining 10% buzz starts to make its self known after about 53 minutes (again it’s barely noticeable) so I am wondering how long this will go on since it’s not really bothering me now

Also I noticed something interesting . So after about 50 minutes of using the system and then when that 10% buzz occurs just like in my second video . I then switch off the system and let it be for 3 mins and then I turn it on again . As soon as I turn the system back on The PT is super quite and it takes 5 mins for that 10% buzz to return . It’s interesting because usually it’s suppose to be Instant ( the 10% buzz) because the PT is hardly cooled down in 3 mins.
Mine is also getting hot but don’t know how hot .

 

[QSilver]

Yes, its strange, the hum seems to be coupling into all the circuits. I have a few amps of similar design, at the moment im using an A-77X which is a next generation Non switching amp. There is no hum with the volume turned up to 12 o'clock. The A-8 gives me noticeable hum at around 10 o'clock so I'm sure something is not right...

Perhaps I could wire it into a different transformer and see if it goes away? I have a transformer with a 30-0-30 tap... might that work for the main input for a test? I'd have to find another transformer for the 16V supply but I might have something somewhere.....

 

[allanmatters]

I do not have any hardcore experience on this to comment . Trying a different transformer is a risky process . I have worked on my a-7 before in the past and as far as I can say we need to be really really careful on these units as they are not very easy to work with.

 

[allanmatters]

Interestingly though it dint buzz today . I did a random test today (after a more than a day break on the system ). I powered it up and just kept the a-7 running on idle mode. For two whole hours no buzz . It’s was super silent like a it was new system , I had then realised that my speaker A and B switches where in the OFF position .

So after 2 hours I switched on the speaker B set ( as my speakers are connected to that ) and waited for another 45 mins . There was Hardly any difference . I also checked my house voltage from a socket it displayed 240 to 242 v and even went to 243v at times .
The system ran for 2 hours and 55 mins and therrr was no buzz at all . Maybe after 2 and half hours there was a very very slight low buzz but nothing like before and it’s sounded like a 2% increase. So basically for 2 and a half hours my power transformer for the first time was 100% silent and after 2 and a half hours after I switched on the speaker B relays , half and hour after that it was 98% silent . It seemed very quite this time . Got to do more tests .

Note I’ve kept my voltage selector on the back of my amp at 240 now . It had been on 240 the day before as well but the power transformer was slightly more buzzy at that time as compared to today

 

[allanmatters]

Latest update . I used it may be 3 to 4 times since January 13th 2019 after I did the submerged varnish process on the PT . The transformer has become very quiet . NO buzz or sound from the transformer at all, even when it is run for 4-5 hours continuously . The system was tested 4-5 times . And it’s become silent as ever like it’s a new transformer. Got to wait another 6 months to know for sure

 

[QSilver]

That sounds very promising. I got a chance to listen to the buzzing in your video. Its much much worse than mine. Mine just has a gentle hum. But I wanted to ask what temperature your transformer runs at? Besides the humming, I'm worried that my transformer is running hot...

I've actually just recently managed to get hold of another A-8 and an A-9! Both need a little work. The A-9 wasn't working very well but I've fixed all the problems now. (Lots of power supply issues and past "repairs"). I've yet to try the new A-8 for a long period of time but so far, it has been silent during operation.

 

[allanmatters]

My power transformer has actually become dead silent . I am pretty happy with the results . I guess I did a proper varnish this time and also because I actually managed to dip the PT (while it was super hot) in hot boiled varnish on each side until I could see all the bubbles come out slowly .

Congratulations on finding another a-8 and a-9. My a-9 too has just been fixed of some minor problems .

Regarding temperature of the PT , I will have to check and let you know

 

[QSilver]

Let me know if you can, I might try re-varnishing my own transformer but it depends on the fault....

 

[allanmatters]

That sounds very promising. I got a chance to listen to the buzzing in your video. Its much much worse than mine. Mine just has a gentle hum. But I wanted to ask what temperature your transformer runs at? Besides the humming, I'm worried that my transformer is running hot...

I've actually just recently managed to get hold of another A-8 and an A-9! Both need a little work. The A-9 wasn't working very well but I've fixed all the problems now. (Lots of power supply issues and past "repairs"). I've yet to try the new A-8 for a long period of time but so far, it has been silent during operation.

Hi there @QSilver . Sorry I have not really looked seriously into checking the temperature of the power transformer.. But I have been using the amplifier almost every week for a minimum 4 hours ,and I am very happy with it. No buzz not even the slightest. You can smell a bit of the varnish if you look above the unit but thats normal.

Did you manage to do anything to your A-8?

 

[Kecap Manis]

If you are in US, Antek is a good choice, Plitron if you want something premium. If you are in Europe, Nuvotem is a good choice, or Toroidy of Poland.

Antek and Toroidy always respond rather promptly to questions. I hope this might help.

 

[allanmatters]

Any luck with you transformer @QSilver ?