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Author Topic: HiFi Amp question  (Read 2051 times)

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tigers_gonads

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HiFi Amp question
« on: 23 February 2018, 11:36:44 »

I'm running a Cyrus 2 / PSX power supply.
Absolutely love the sound it makes but recently its seems flat as a fart when first used so yesterday, I had a little play  :)

Play any source straight after its powered up and it sounds flat at any volume.
Power it up and leave it for 20 mins or so before sticking a source though it and it sounds punchy as hell  :y

A bit of research tells me that there are 2 whopping big capacitors in there which are the old 80's waxed paper variety which deterate over the years.

Apparently, there is a upgrade with a more modern cap which will make the amp bounce again.

Question is .............. are these caps in the amp section OR the power supply section ?
Also, where is the best place to source these ?

Don't want to have to send it off to a specialist who will rape my wallet because i'm skint anyway  :(

TIA  :)
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Bigron

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Re: HiFi Amp question
« Reply #1 on: 23 February 2018, 11:44:24 »

Happy to try to help, but I do need more details regarding those capacitors, please, and do you have a circuit diagram?

Ron.
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Kevin Wood

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Re: HiFi Amp question
« Reply #2 on: 23 February 2018, 12:21:46 »

Here's the place to go for manuals and schematics, etc. :

https://www.hifiengine.com/manual_library/cyrus/2.shtml

They symptoms sound odd to me. Sometimes you'll find electrolytic capacitors in equipment of this sort of age that are past their best but not sure they'd contain any paper caps being a late 80's design.

It can be good to squirt a bit of cleaner in any switches / pots / relays in case there's a poor connection. Checking the PCBs for any dry or cracked solder joints can be a good idea, too, especially under heavy components like the reservoir caps and output stage transistors.
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tigers_gonads

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Re: HiFi Amp question
« Reply #3 on: 23 February 2018, 12:24:37 »

Happy to try to help, but I do need more details regarding those capacitors, please, and do you have a circuit diagram?

Ron.



Thinking about it, i'd say the caps will be in the amp box and if iirc you can't miss them  ::) :-\

I'm on my way out of the door now but will have a look for a drawing of maybe take a picture with the cover off  :y
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tigers_gonads

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Re: HiFi Amp question
« Reply #4 on: 23 February 2018, 12:29:05 »

Here's the place to go for manuals and schematics, etc. :

https://www.hifiengine.com/manual_library/cyrus/2.shtml

They symptoms sound odd to me. Sometimes you'll find electrolytic capacitors in equipment of this sort of age that are past their best but not sure they'd contain any paper caps being a late 80's design.

It can be good to squirt a bit of cleaner in any switches / pots / relays in case there's a poor connection. Checking the PCBs for any dry or cracked solder joints can be a good idea, too, especially under heavy components like the reservoir caps and output stage transistors.


There is talk about these caps on the AV forums Kev.
Apparently there is a known good upgrade for them when they start to fail.
Burr Brown are mentioned (whatever they are)  ;D

All the switches and pots are absolutely smooth and silent unlike my old Cyrus 2 which had a few issues on that front.
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Kevin Wood

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Re: HiFi Amp question
« Reply #5 on: 23 February 2018, 12:42:06 »

OK, I'll have a dig when I get a minute. The capacitors you can't miss are probably the reservoir capacitors for the power supply. They'll be large electrolytics and might well be getting a bit tired now depending on how hot it runs. Sometimes, you can see that their cans have bulged slightly, or there is a sign of leakage from the valve near their connecting pins. A photo might be handy. :y
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Kevin Wood

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Re: HiFi Amp question
« Reply #6 on: 23 February 2018, 12:45:01 »

.. and the reference to Burr Brown is likely to be the Op-Amps in the preamp section. Standard ones look to be NE5532 / NE5534s which, despite being cheap and old as the hills, actually aren't that bad.

Put it this way: your music will have gone through many of these in a mixing desk before it made it onto a CD, so a couple more in the amp won't hurt!
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deviator

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Re: HiFi Amp question
« Reply #7 on: 23 February 2018, 12:52:08 »

I do miss my Cyrus amp, I regret selling it. The NAD that replaced it was good, but broke and the Technics I have now isn't a patch on either - although it is still good.
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Re: HiFi Amp question
« Reply #8 on: 23 February 2018, 13:04:50 »

There is talk about these caps on the AV forums Kev.
Apparently there is a known good upgrade for them when they start to fail.
Burr Brown are mentioned (whatever they are)  ;D

Burr Brown are a niche silicon chip designer who have recently been bought up by Texas Instruments. Their products are usually very (very!) good. Unlikely they are responsible for your fault IMV.

Power supply capacitors (assuming its an old style linear transformer - bridge rectifier - cap thing) are usually huge cylindrical things - ranging between the size of a cardboard toilet roll centre and the size of a large aerosol can. Values range from about 10,000uF up and often rated at 50V+. There are usually at least two, although they don't often cause much grief.

The problems I've come across have all been with smaller electrolytic capacitors mounted on main PCB's. These 'dry out' and can bulge on their aluminium lids. It is/was a common cause of failure on computer motherboards and was put down to manufacturers using cheap Chineese/Tiawanese components. Genuine Japanese caps are now often used as a selling point - supposedly being more reliable.
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Re: HiFi Amp question
« Reply #9 on: 23 February 2018, 15:12:42 »

Its always difficult to diagnose problems without having the thing in front of you and hearing or seeing whats going on. The fact that it improves with time or warm up would kind of point me in the direction of Voltage / Current or a Thermo issue in the PSU or Amp itself.

For me, first thing I would be doing is measuring the Voltage Output of the PSU against its spec and does that change with  time / warm up, also if possible look at the current feed, if that proves difficult to do, then easiest way would be to look at any Voltage variation under high loads that should give some clue as to stable the PSU Voltage vs Current supply is doing. Faulty or deteriorated Caps could or would upset the Voltage / Current supply.

Assuming the PSU is doing its Job and that fact that the Amp works but changes with warm up I would then be looking at similar issues within the Amp, Firstly correct voltage and current supply to the Amp and within, as said, Connectors, plugs, switches, dry joints etc, and then move on to see if any thermo coupling design within the Amp is a problem, is the Amps Output Heatsink getting too hot or Cold, without knowing the design is there any Thermo Sensing around the Heatsink or Output Stages or has any Components attached to the Heatsink with Silicon Heat Sink compound, has the compound over dried or powdered through age.

Good tools for this, would be Decent Volt Meter, Hair Dryer and a Can of Freezer, and Ideally a good Oscilloscope.
« Last Edit: 23 February 2018, 15:18:26 by zirk »
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Bigron

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Re: HiFi Amp question
« Reply #10 on: 23 February 2018, 15:17:44 »

And also a sweep generator, spectrum analyser, distortion factor meter, chart recorder, coffee and chocolate digestive biscuits..... ;D

Ron.
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zirk

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Re: HiFi Amp question
« Reply #11 on: 23 February 2018, 15:20:18 »

And also a sweep generator, spectrum analyser, distortion factor meter, chart recorder, coffee and chocolate digestive biscuits..... ;D

Ron.
Sounds like He may have to supply His own Soldering Iron then Ron.  ;)
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Bigron

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Re: HiFi Amp question
« Reply #12 on: 23 February 2018, 15:38:39 »

Oh damn, I KNEW I would forget something!

Ron.
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Re: HiFi Amp question
« Reply #13 on: 23 February 2018, 16:33:21 »

Did someone just say Chocolate digestive biscuits? I have everything else on that list. :-*

I have a feeling in the back of my mind that I've heard of a notorious problem with these amps. I think it related to the mounting of the phono / speaker connectors on the rear and the solder joints around there failing. As zirk says, though, it's not easy to diagnose without hearing it (just like when someone says their engine is making an odd noise).

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Bigron

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Re: HiFi Amp question
« Reply #14 on: 23 February 2018, 16:36:36 »

Only the plain choccy ones, Kevin.....

Ron.
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Re: HiFi Amp question
« Reply #15 on: 23 February 2018, 17:06:32 »

A bit of research says they have a couple of 470uF 6V bipolar electrolytic caps in them that tend to go bad. They are in red plastic cans and located under the ribbon cable that runs across the PCB, apparently.
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Re: HiFi Amp question
« Reply #16 on: 24 February 2018, 10:48:56 »

Okay, i'll remove the cover off the amp and power supply and take some pictures later  :y

Thanks lads  :)
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