Buzzing Amp and speakers

[VanArn]

 Primare  Knob, 

You  may have  pointed out a likely problem which is often found with imported equipment and not just the grey candidates. The fitting of  power transformers with ratings to suit the Australian mains supply is  often overlooked as we are still a miniscule market for high end equipment. Often, despite labelling to the contrary, 220 Volt ac transformers are fitted and consequently filter capacitors are run at higher voltages and this can lead to a reduced service life if the components do not have a sufficient rating to cope with the added stress. Basically the capacitors will operate at a higher temperature  and cause higher peak currents  to be drawn ( the rectification process causes a spikey current to be drawn through the transformer, not a half sinewave ) and this is ,in part, the cause of the transformer buzz. There is also a problem that toroidal transformers run the cores at higher flux levels for reasons of efficiency vs cost.

Edited April 2, 2019 by VanArn
typo

[Primare Knob]

 Primare  Knob, 
You have may have  pointed out a likely problem which is often found with imported equipment and not just the grey candidates. The fitting of  power transformers with ratings to suit the Australian mains supply is  often overlooked as we are still a miniscule market for high end equipment. Often, despite labelling to the contrary, 220 Volt ac transformers are fitted and consequently filter capacitors are run at higher voltages and this. can lead to a reduced service life if the components do not have a sufficient rating to cope with the added stress. Basically the capacitors will operate at a higher temperature  and cause higher peak currents  to be drawn ( the rectification process causes a spikey current to be drawn through the transformer, not a half sinewave ) and this is ,in part, the cause of the transformer buzz. There is also a problem that toroidal transformers run the cores at higher flux levels for reasons of efficiency vs cost.

Is this something that can be fixed, and are the capacitors the only things that are starting to fail?

When proceeding with the repair path, is there any merit in upgrade parts? Trying to figure out what cost I might be to get it fixed.

I can only find Nichicon capacitors at $20USD each that show the same values as the Rubycon, or Mundorf for $45 each.

[Addicted to music]

4 hours ago, Primare Knob said:

Nothing else is connected to the amplifier, and the speakers are AudioPhysics Tempo, no active components.

I can only hear it with my ear at the speakers. I am getting a bit paranoid.
 

To really know whether your Pima Luma integrated is suspect, I would take it to the point of sale and compare it the same model on the shelf, preferable with your speakers.

Even though you pay and arm and a leg for it not all High  end gear is built to certain standards and Definately not valve gear.  Just remember that valves are no where near the SS variety in noise performance due to many factors already mentioned.

 

4 hours ago, Primare Knob said:

I have been told that the filter capacitors on the Parasound could be failing and leaking voltage, which causes the transformer and speakers to hum, due to Parasound not always adjusting the design for the Australian market.

A bit of research shows that this could be a likely scenario. The amp has 4 Rubycon 10.000uF 80V capacitors 85C degree rated. It's a bit sad to see that failing after 5 years.

Don't know how high a voltage could lead to such a short lifespan. I assume that a higher grid voltage is generating a higher output voltage at the transformer.

I’ve started threads and responded to hum and noise issues B4 and also responded to worn psu capacitors.  

A lot of economics and accounting get in the way on production and most products including High End Audio are all effected.  

 

I’ve posted here on a well known power amp where the owner discovered that most of his supply caps were leaking but the amp was fully operational.   Lucky for this owner he was able to obtain all new amplifier pcb and a set of brand new caps (8 in total) that was sent to him free of charge.

upon investigation the Voltage rails were 99.6-99.9VDC on a 240VAC supply,  yet the supply caps were 100VDC 10,000uf.    So you can see here if the Mains were to increase then the voltage rail will increase and go beyond the 100VDC that the caps are limited to.    When questioned the owner of the company, he was adamant that the Capacitor manufacturer told him that they are able to exceed the 100VDC limit and obvious this was not the case.  He now supplied the owner of this amp 120VDC 8200uf.     As you can see, if a manufacturer can get away with cheaper components than they will and risk it!  Not all do this but in general most will.

 

 

 

[VanArn]

11 hours ago, Primare Knob said:

Is this something that can be fixed, and are the capacitors the only things that are starting to fail?

When proceeding with the repair path, is there any merit in upgrade parts? Trying to figure out what cost I might be to get it fixed.

I can only find Nichicon capacitors at $20USD each that show the same values as the Rubycon, or Mundorf for $45 each.

Nichicon, Panasonic and Rubycon are all acceptable brands that I would expect to be used by a technician as replacement filter capacitors. Upgrading as such, would be by way of a higher operating temperature ( 105 d ), low ESR and higher  voltage  and surge current ratings. I would leave the choice to the person that services the amplifier if it is found that they need replacing. The toroidal transformer is the costly part and if it is of  the wrong rating , then you have a problem.

[Guest Muon N']

Just check the mains level, then measure the heater voltage after the amp settles to see if the transformer is a a suitable rated voltage., best a techie person do this.

[Primare Knob]

I went to Garrey Cawsey who did a quick checkup of the amps.

Luckily the amps are well designed within proper specifications, and suprisingly didn't hum or buzz.

Garrey is using some sort of step down transformer, down to 230V. When unplugged and straight from the mains, 250V according to Garrey, the humming and buzzing was back again.

He still advised to replace the caps though.

So it seems that my place, and most of Melbourne and surroundings has to high a voltage.

[andyr]

1 hour ago, Primare Knob said:

I went to Garrey Cawsey who did a quick checkup of the amps.

Luckily the amps are well designed within proper specifications, and suprisingly didn't hum or buzz.

Garrey is using some sort of step down transformer, down to 230V. When unplugged and straight from the mains, 250V according to Garrey, the humming and buzzing was back again.

He still advised to replace the caps though.

So it seems that my place, and most of Melbourne and surroundings has to high a voltage.

 

Glad that you were able to identify the culprit, with Garry. 

 

Re. the caps - yes, that's probably a worthwhile thing to do but you might like to get Garry to look at the power transformer, when he's replacing the caps.

 

The problem with having 250v at the mains is that if your power transformer is, say:

• 240v primary, with
• 40v secondaries

... then by feeding the primary with 250v ... the secondaries will produce 42v.  So the DC rails in the amp will be at +/-58v ... instead of +/-56v.

 

That's no biggie but if the tranny has a 230v primary then the secondaries will be delivering 43.5v - which means +/-61v DC rails.  That's 10% over the rated voltage.

 

So if the power transformer is one with a 230v primary ... you might like to get him to swap it for a transformer which has a 240v primary winding.  If there are none readily available, Harbuch will be able to supply one with 240v primary and whatever the secondaries are supposed to be - at whatever VA rating you need.

 

Andy

 

[Addicted to music]

What you need to ask Gary is what the  voltage rails are measured @230VAC mains.  He is right, I still measure everywhere in Melb 240VAC.  I rarely measure exactly 230VAC.    Then ask him what the supplied caps are rated at.   If you are convinced to replaced the caps then definitely go to the next voltage up and definitely go with brands that have spec sheets available on the net.  After the new caps are in, then get him to test it to 250-270VaC and see whether the buzz and hum still exist! 

 

Edited April 6, 2019 by Addicted to music

[VanArn]

  A high wattage Variac is the usual method  of  testing an amplifiers performance  at its rated mains voltage. A 'quick check up ' implies that the amplifier was not left with Garry so that a full internal assessment could be carried out. Possibly the  covers were not removed so that the  filter capacitors could actually  be read for  values and the rail voltages measured. If you  need to check mains voltages and care is needed, a true RMS voltmeter is required and in some circumstances the waveform  of the mains supply should be examined on an oscilloscope. In my area the mains is always close to the 240 v specification.

 When obtaining a replacement transformer , the physical size needs to be checked to make sure it will  fit into the available space.

 What specification,  concerning the mains supply and VA ratings are given on the compliance plate of the Parasound amplifier?  

[Primare Knob]

Thanks all for your comments.

The voltage on the rails I believe has been tested as it roughly measured 1.5-2 Volts more with 250 volts.

I think the the voltage measured was less than 50Volts and the caps are rated for 80Volt, but showed some signs of bulging.

Whether or not it is really necessary, it can't hurt to have them replaced for not to much money, and the amps are still in his care.

The humming definitely wasn't there with his stepdown transformer in place. I am thinking about hooking the whole home cinema up to a step down transformer or something like a regenerator, as they can usually function as a small step down transformer as well I believe.

Carrey showed me something he made himself, that you put inbetween, and that drops the voltage by 12Volts without a transformer.

Looking into something that can handle the whole cinema setup, preferably something up to 15amps as I haven't been able to trigger the circuit fuse switch.

[andyr]

4 minutes ago, Primare Knob said:

The humming definitely wasn't there with his stepdown transformer in place. I am thinking about hooking the whole home cinema up to a step down transformer or something like a regenerator, as they can usually function as a small step down transformer as well I believe.

Carrey showed me something he made himself, that you put inbetween, and that drops the voltage by 12Volts without a transformer.

Looking into something that can handle the whole cinema setup, preferably something up to 15amps as I haven't been able to trigger the circuit fuse switch.

 

We still heard hum using my "non-stepdown" (isolating) transformer, Maarten - so it seems that over-voltage is the problem.

 

I saw there was a Thor PS10 in the classifieds here - maybe this is what you need?

 

Andy

 

[Primare Knob]

Ok, I have checked the mains voltage with a multimeter, and it measured close to what the plug in power meter is reading.

Which would suggest that it is reliable, which would mean that I don't have an over voltage problem at home.

The big question would than be;
What the heck is going on then? Hooked up to the step down of Carrey, it definitely did not hum.

[andyr]

2 hours ago, Primare Knob said:

Ok, I have checked the mains voltage with a multimeter, and it measured close to what the plug in power meter is reading.

Which would suggest that it is reliable, which would mean that I don't have an over voltage problem at home.

The big question would than be;
What the heck is going on then? Hooked up to the step down of Carrey, it definitely did not hum.

 

So what is the transformer primary rating, Maarten?

 

If you don't have an 'over-voltage' problem in your house ... does that mean you have 230v (the so-called Oz standard) - or 240v?

 

If you have 240v - then is your amp power transformer specced for 220v?  (A US amp which is originally designed for 110v could well have dual 110v primaries: connect them in parallel for the US ... and connect them in series (giving 220v) for the rest of the world.  So not suitable for 240v?)

 

Andy