Pioneer A-8 hot transformer and humming.
QSilver
Super Member
Well, I'm not having much luck with the transformer repair/replacement. One company quoted me but said it would cost too much to realisticly suggest doing it, and another told me that transformers can often run hot and that it could be normal 
. If it is, I don't want it to be getting so hot next to the amp myself... we'll see what they come up with but I'm starting to wonder what to do next. Either get a custom torroid transformer made and house it externally, or have a new EI core transformer made overseas.... any other options?
. If it is, I don't want it to be getting so hot next to the amp myself... we'll see what they come up with but I'm starting to wonder what to do next. Either get a custom torroid transformer made and house it externally, or have a new EI core transformer made overseas.... any other options?
Are you in the UK?
If your voltage is running constantly on the high side, you could have problems with the transformer and power supply from just a high input voltage. You might have to consider a variac to decrease the voltage to manageable levels. Have you done any troubleshooting to see if the amp section is running properly, ie DC offset and bias?
From this pic, you have a single standard type EI laminated transformer? Do you have a picture of the transformer and its Bando number and wire colors?
There is a Pioneer SX-7 receiver power transformer on Ebay, Bando ATT-856 available from the US at $20 plus about $66 international shipping, item number 161859546388. Given that the SX and Ax series of receivers and integrated amplifiers all had international voltage selectors on them, this transformer can probably run on US and UK 220/240 volts. It would probably get you in the ballpark but with somewhat reduced total output power. That could be compensated somewhat by running the primary on the 240V at 250, or even trying the 220 from the 250, current capability would be less though.
Still, its a costly option and not a surefire solution by any means. If you are strongly motivated to keep and use this unit, I'd suggest getting a good tech to check it out and make sure the power supply is operating correctly, so many things can be going wrong with it after this much time, then check the amp boards to see that they are working properly.
Otherwise, you'd be much better off either importing another A8 or A9, or moving up to the A77X or A88X with their dual mono supplies and newer builds.
Still, its a costly option and not a surefire solution by any means. If you are strongly motivated to keep and use this unit, I'd suggest getting a good tech to check it out and make sure the power supply is operating correctly, so many things can be going wrong with it after this much time, then check the amp boards to see that they are working properly.
Otherwise, you'd be much better off either importing another A8 or A9, or moving up to the A77X or A88X with their dual mono supplies and newer builds.
http://www.cieri.net/Documenti/Altri marchi/Pioneer - Tuning Fork No.3 (~1980).pdf
Nice article from Pioneer on Transformer basics.
Nice article from Pioneer on Transformer basics.
6taafondo
Pablo
Well, I'm not having much luck with the transformer repair/replacement. One company quoted me but said it would cost too much to realisticly suggest doing it, and another told me that transformers can often run hot and that it could be normal
It's unbelievable how knowledge is falling down in nosedive fashion... Only someone used to work on the low quality end of the scale can say a heating up transformer could be just fine and normal LMAO ...
What I'd do in your shoes is find a manufacturer in China through ebay that would accept to make custom transformers. Many of them do. Just search ebay for audio diy transformer, even toroid sellers, and ask the one of your preference about your needs.
You'll be very surprised, as they usually are friendly and cooperative. I'd order a EI core transformer similar to what you have there.
Provide them with the following data:
Mains voltage
Secondary voltages required, and windings arrangement (all details, center tapped if needed, etc; Remember your low voltage secondary winding requires not more than 2.5A
Weight of your actual transformer
Size.
Send pictures
Ask for a quote, and expect it to be a fraction of what would cost to make it locally.
QSilver
Super Member
Thanks for all your posts mech986, yes, im in the UK and my voltage is usually on the high side. Its 230 to 250V and I'm at 250V where I live. The transformer is rated at 240V though, so my understanding was that it should cope with this. I recently moved and at my old house the voltage was nearer to 240 and this problem was still present. I have checked the amplifier over and DC offset and Idle currents are all fine - the amp sounds very good with the exception of the hot humming transformer - I believe the hum is being induced into the speakers somewhere down the line as the hum is present ever so slightly on the speakers when you turn the volume up to about 3.
I attached a picture of the transformer - weighs around 4.6Kg. Yes, I think its an EI core.
I'm glad its not just me! When he was telling me this I was quite suprised - I told him that I had a number of amplifiers and NONE of them got remotely this hot when in operation but he seemed to shrug it off. I have since then been in contact with someone else in the same company so we'll see what they think about it all..... failing that, I'll probably try what you suggest, though I might recheck those voltage readings - maybe underload too if I can manage it...
I attached a picture of the transformer - weighs around 4.6Kg. Yes, I think its an EI core.
I'm glad its not just me! When he was telling me this I was quite suprised - I told him that I had a number of amplifiers and NONE of them got remotely this hot when in operation but he seemed to shrug it off. I have since then been in contact with someone else in the same company so we'll see what they think about it all..... failing that, I'll probably try what you suggest, though I might recheck those voltage readings - maybe underload too if I can manage it...
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Thanks for the reply. Wonder if you could borrow a variac to decrease your input AC and see if the humming improves at all. Would also check to see if you have proper grounds in the gear and in the home. Have you tried it at any other circuit in this house, or at another place, perhaps even a technician's bench?
QSilver
Super Member
I have a variac although It'd not encased yet so I'm not so keen on using it just yet! I did try the amp at my old home around 3 months ago and it did the same thing. I think the grounds in my property now are good. We have breakers and the hosue was rewired not too many years ago.
When I use the transformer through a DBT the 60W bulb glows orange and there is no humming but as I increase the size of bulb, the humming starts to grow. It seems if you throttle the power its allowed, the humming dies away.. not sure if thats relevent.
When I use the transformer through a DBT the 60W bulb glows orange and there is no humming but as I increase the size of bulb, the humming starts to grow. It seems if you throttle the power its allowed, the humming dies away.. not sure if thats relevent.
Freds.Bands
Live Music Listener
Just a thought here: high voltage can saturate a transformer core, causing it to heat excessively. I don't know if yours is into saturation, as that depends on the core's magnetic characteristics and how close to core saturation it was designed for. Maybe you can try it on a supply with lower voltage; maybe you have a friend living farther away from the distribution substation, where voltages are typically lower. Just check the voltage there first.
About speaker hum at 3 o'clock position, just wondering about how effective your power supply filtering is, assuming this is at light load. chances are you can't hear it if your instantaneous load is high. It's not the volume control position, it is the actual load. so if you can hear hum then, that confuses me. Try a different input, not a phono one.
About speaker hum at 3 o'clock position, just wondering about how effective your power supply filtering is, assuming this is at light load. chances are you can't hear it if your instantaneous load is high. It's not the volume control position, it is the actual load. so if you can hear hum then, that confuses me. Try a different input, not a phono one.
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allanmatters
Active Member
Nice thread . I have a pioneer a-7 which I have been breaking my head on in the last 3 years . I saw the pic of your transformer. It's so neat compared to mine.
Mine gives out 60hz buzz . Very annoying.
I am coming to the stage of I give up . As i tried many and many solutions . I have a thread here on audiokarma on the same issue.
So what did you do finally ?
Mine gives out 60hz buzz . Very annoying.
I am coming to the stage of I give up . As i tried many and many solutions . I have a thread here on audiokarma on the same issue.
So what did you do finally ?
QSilver
Super Member
I've put it to the side for now, but I have now built up the Variac to work safely and with good read outs (voltmeter and ammeter) so I can try running it on a lower voltage and see how it performs. However, I have been considering replacing the transformer with a new one or a NOS if I can find one but that's unlikely. A new one would likely be a torroid but then there is the problem of increased inrush and maybe the implementation of a soft start circuit. The other alternative is to have a new EI-core transformer made likely in China by a good transformer company. 6taafondo was helping me with the new EI core transformer line but that broke down when I had to shelve the amp and tackle more pressing matters.
Interestingly though, this has been on my mind again in recent weeks....
Interestingly though, this has been on my mind again in recent weeks....
allanmatters
Active Member
I submerged my pioneer a-7’s transformer in hot varnish . Well I submerged just half of it as I did not want to disconnect it from the main power supply board . Since I was able to submerge just about quarter of it . I did it for all sides one at a time , submerged it in the hot varnish . Again boiled more varnish and submerged it again on all sides possible . Could see bubbles come out slowly everytime I submerged a different side of the PT.
Will post results day after. Let it dry out thoroughly. I did this before but at that time I did not submerge it in varnish , I only poured the varnish on the top of the PT , the sound disappeared but came back 5 months later . I wonder if the submerged process will make a difference .
Will post results day after. Let it dry out thoroughly. I did this before but at that time I did not submerge it in varnish , I only poured the varnish on the top of the PT , the sound disappeared but came back 5 months later . I wonder if the submerged process will make a difference .
QSilver
Super Member
Keep me updated on this as I've recently been using the A-8 again. Mine is drawing excessive current and humming. Perhaps re varnishing would help. Otherwise I'll need a rewind or new....
As far as I know, when transformers are coated in varnish at factory completion, they are put into a tank of hot varnish under vacuum which pulls the air out. Submersion will probably be better than pouring but the extra addition of any vacuum would be an added bonus.
As an added piece of information about my transformer. I do now have a variac and also made a bucking transformer to cut down my line voltage from 253V, to approximately 240V. While this helped a little, the transformer still draws excessive current and gets hot and hums so its not only just saturation from over voltage.
As far as I know, when transformers are coated in varnish at factory completion, they are put into a tank of hot varnish under vacuum which pulls the air out. Submersion will probably be better than pouring but the extra addition of any vacuum would be an added bonus.
As an added piece of information about my transformer. I do now have a variac and also made a bucking transformer to cut down my line voltage from 253V, to approximately 240V. While this helped a little, the transformer still draws excessive current and gets hot and hums so its not only just saturation from over voltage.
I was thinking there should be parts units around for this amp, it was not that uncommon. I assume you watched ebay? You can put an auto search so it will email you when keywords pop up.
QSilver
Super Member
I had thought about that. I've seen one or two A-8's listed but not or parts or spares and if I was going to get another unit, I'd just repair or keep that one instead. I don't like breaking things up for parts. I always try to fix them... and call it a challenge!
I know. Unfortunately other people DO part them out, or they sell/give away broken ones. In fact if you subscribed to AK you might find something on Bartertown. I did search A-8 for you and found nothing currently but folks have a lot of equipment in closets and basements.
I remember an AKer around KC area who had a whole stack of that series, including the amp. Can't remember if the amp worked or not. I almost grabbed it at an AK fest in KC.
I remember an AKer around KC area who had a whole stack of that series, including the amp. Can't remember if the amp worked or not. I almost grabbed it at an AK fest in KC.
allanmatters
Active Member
Yes . You are right . I am aware though that the vacuum process is definitely a must . However I am quite afraid of disconnecting the wires from the power supply board unless I label them really well to identify them later. And then I would send the entire transformer for varnish and impregnatation vacuum
My pioneer A-7 Power transformer runs hot , after about an hour on idle mode. I can touch the naked laminations for about 4-5 seconds. That’s how hot it gets.
I will update u in a day or two on results as the climate turned pretty cold hence I was a little skeletal on the drying time , but real results will have to wait for several months to come.
My transformer seems to be identical to yours except that the aluminium housing has been stripped off for the varnishing process .so the laminations are visible + I broke off the plastic housing on one side of the PT where the wires goes through.
I hope yours can be recovered similarly.. probably I am in the same boat where the transformers time is up
My pioneer A-7 Power transformer runs hot , after about an hour on idle mode. I can touch the naked laminations for about 4-5 seconds. That’s how hot it gets.
I will update u in a day or two on results as the climate turned pretty cold hence I was a little skeletal on the drying time , but real results will have to wait for several months to come.
My transformer seems to be identical to yours except that the aluminium housing has been stripped off for the varnishing process .so the laminations are visible + I broke off the plastic housing on one side of the PT where the wires goes through.
I hope yours can be recovered similarly.. probably I am in the same boat where the transformers time is up
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allanmatters
Active Member
ok so RESULTS : I fired up the A-7 today and waited. listened to some soft music. No noticeable sound from the PT. Compared to before. Before I did the submerge process I observed how noisy the PT would get. It used to get noisy within 15 mins an after and hour it would be unbearable.
So after about an hour it started to BUZZ. but its picking up buzz very slowly gradually(though still its not noticeable when listening to music on very low volumes), I only tested it for about an hour. I am pretty sure the buzz will return to noisy after about a month or so, You see this happened before as well.
(1)The first time I tried fixing the PT, I poured hot varnish over it while the PT was quite hot. Let it sit for a day or two and then fired it up, it was silent maybe for just a month. then it got noisy again.
(2)The second time i shoved a half inch piece of wood between the PT base and the amp's chassis and tightened the screws until the sound was minimal. However the noise returned again after a month or so.
(3)The third time (which I just did) I submerged the PT in hot varnish while the PT was hot as well. The buzz disappeared, you can listen to soft music for about and hour or so with no noticeable buzz noise. But I have not further tested it out for a longer duration.(however still feel the buzz is trying to make itself known very gradually)
I am pretty confident the buzz will return after a month or maybe even 3 weeks depending on usage. I feel the buzz tries to find a way to come back at some point of time.
@toxcrusadr is right. It is better to sell the amp and get another one . In my case I cant rely on ebay because I dont know/or I am not sure how expensive shipping will be to India, hence I am refusing to part with it.
I guess I am in the same boat as you are. the PT is mostly finished. What did you understand on those three points I mentioned ??
So after about an hour it started to BUZZ. but its picking up buzz very slowly gradually(though still its not noticeable when listening to music on very low volumes), I only tested it for about an hour. I am pretty sure the buzz will return to noisy after about a month or so, You see this happened before as well.
(1)The first time I tried fixing the PT, I poured hot varnish over it while the PT was quite hot. Let it sit for a day or two and then fired it up, it was silent maybe for just a month. then it got noisy again.
(2)The second time i shoved a half inch piece of wood between the PT base and the amp's chassis and tightened the screws until the sound was minimal. However the noise returned again after a month or so.
(3)The third time (which I just did) I submerged the PT in hot varnish while the PT was hot as well. The buzz disappeared, you can listen to soft music for about and hour or so with no noticeable buzz noise. But I have not further tested it out for a longer duration.(however still feel the buzz is trying to make itself known very gradually)
I am pretty confident the buzz will return after a month or maybe even 3 weeks depending on usage. I feel the buzz tries to find a way to come back at some point of time.
@toxcrusadr is right. It is better to sell the amp and get another one . In my case I cant rely on ebay because I dont know/or I am not sure how expensive shipping will be to India, hence I am refusing to part with it.
I guess I am in the same boat as you are. the PT is mostly finished. What did you understand on those three points I mentioned ??
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I wonder why it is buzzing after a period of time. The only explanation I can think of is that it's something that doesn't buzz until it heats up.
I'm no technician but is it possible that other components, when they heat up themselves, are drawing more current and overloading the transformer? Such as, failing filter caps. I bet this was already discussed in the other thread you mentioned.
Squirrely problems to deal with, for sure.
Oops, I didn't even notice your location!
I'm no technician but is it possible that other components, when they heat up themselves, are drawing more current and overloading the transformer? Such as, failing filter caps. I bet this was already discussed in the other thread you mentioned.
Squirrely problems to deal with, for sure.
Oops, I didn't even notice your location!