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Old 20th October 2013, 10:13 PM   #11
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Thanks for the help, Alex. Your timing was great.
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Old 13th December 2013, 09:17 PM   #12
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Checked the amp and there was a loose connection of the ground wire to the chassis, all ok now.

But before checking that we used another Creek amp of a friend the 4040, and the strange thing is that his amplifier popped my speakers during power on and power off.
We tried with another set of speakers and the same again, speakers pop out for a sec no matter the volume setting is.

Is that dangerous for the speakers?
Is the amp faulty?

It's the Creek 4040 s2

Any ideas?
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Old 13th December 2013, 11:29 PM   #13
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The speakers may give a brief pop or thump on powering up or down without issues since most small amplifiers were like this until speaker relays were generally fitted (e.g. CAS model 4140 s2 onwards according to X-pro) but 1 second is too long for any amplifier.

I understand that the 4040S2 version still had a capacitor output, (3,300 uF?) so it should not be possible to have more than a brief pulse or thump pass to the speakers. It suggests the capacitors have shorted in both channels (unlikely) if that really is true.

In any case, check the output terminal voltage without speakers or inputs fitted. An old analog meter or 'scope is best since DMMs are hopeless at brief events. If the DC voltage holds at more than than a volt or so upon power-up there is quite a problem.
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Old 13th January 2014, 08:01 PM   #14
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Actually i cant find something wrong.

Trying to check the bias current according to the manual but there is nothing written on the board itself and i don't have a layout of the amp to see components topology.

Aarghh
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Old 14th January 2014, 07:04 AM   #15
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Still the hum? If so, have you replaced the large caps at least?
Can you post a link to the service manual as that is critical to giving accurate advice.

You can identify the bias test points on most amplifiers by finding the 2 large, low value (probably 0.22 or 0.33ohms or 0R22, 0R33 in modern parlance - red,red,silver or orange,orange,silver bands) located either side of the bias adjust pot, near each channel's pair of output transistors. The bias is calculated by ohms law from the small DC voltage (actually millivolts - mV) measured across these - either will do. There may be special pins for this but I can't see any. Service adjustments in the manual are usually just specified in mV. I used a good pic on the net for this but it is not official advice.

Please post readings before adjusting as the specified voltage possibly may not refer to this. Take care not to slip with meter probes in there - it can be curtains for your output stage.
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Last edited by Ian Finch; 14th January 2014 at 07:22 AM.
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Old 14th January 2014, 06:51 PM   #16
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I guess the hum is normal.

Problem now is the switch off thumb from the speakers.

Trying to check the current according to this schematic :

http://www.diyaudio.com/forums/attac...c-4040s2pa.pdf

"6mV drop across R19 or R20" but i can't find them since there is nothing written on the board
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Old 14th January 2014, 09:26 PM   #17
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Thanks for linking schematic. It's quite a basic design without any output capacitor or relay so it should give little trouble provided it's not overdriven or abused with low impedance loads.

I've already described the large resistors R19, 20 and their approximate location above, in the 2nd paragraph. If, as in later versions, the resistors are not colour coded red-red-silver + gold tolerance band, the substitutes' body colour will be a dull oxide colour and the value printed. If in doubt, just measure the resistance. These are 1W wire-wound resistors - not hard to distinguish by size and value from anything else in there.

BTW, remove inputs and speakers if you're setting bias or you'll get nonsense.
Google " CAS 4040S2 pics" and you'll see the differences between S2 and S3 PCBs and examples of those resistors.
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Old 14th January 2014, 10:47 PM   #18
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Got it, thanks

I noticed when i connect the speakers and source and by adjusting the volume the mV change, is that normal?

I set the bias at 6mV with no speakers and source connected and volume at zero.

The mV were lower than recommended, is there some sort of "derating" by the time?
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Old 15th January 2014, 01:11 AM   #19
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The voltage "6 mV" is analagous to the DC current I = V/R (.006/.22) or 27mA flowing through the output transistors, from +rail to -rail power supplies. There is also a temperature compensated regulator to ensure the pot. setting is fairly stable but it will still vary within limits since thermal regulation designs are usually far from ideal.

You should also measure DC "offset" or rather, just the DC voltage across the output terminals. This will help understand what's happening with the amp that affects the speakers and maybe the thump as well. You should find a voltage less than 50mV on either channel but the actual voltage or difference between channels is not important at this low level.
If something is wrong and the voltage is higher, that could well cause problems with the speakers, even when there is no signal. A clue to this lies in whether both channels are much the same or quite different, which in turn points to a fault condition.

To make sensible DC measurements, the capacitors need to be in good condition, They are a wet cell like a battery and dry out/deteriorate over time, which is why others have raised this point too. There will be changes over time with all DC settings but a 10% difference may arise from many causes, even your mains voltage fluctuation. However, we still may discover something more critical. Please post the DC measurement at the outputs.

It's not normal to see much variation in bias by adjusting volume unless there is a load. That's why we disconnect it and any input that could affect bias too. It suggests DC is present in the signal path at the volume control and C1 may be leaky. Is this the same for both channels?

Think carefully about proceeding here - if there are problems with amplifier components and following the schematic, we shall be at an impasse if you can't deduce what and where they are. You will need a service person to get you out of that problem. Still, we will assist where we can if you decide to continue. Also, I'm just hoping V2 is not greatly different to your version, whatever that may be. It's incredible that the manufacturer needed to apply 3 levels of coding to specify the model and official details of them no longer exist. Lessee...it's maybe a CAS 4040/S2/V2 or would that just be lucky coincidence?
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Old 15th January 2014, 07:42 AM   #20
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Addition to above:
Settling time for bias greatly affects measurements. I mentioned bias setting is thermally controlled so as the amplifier heats up, bias will remain within limits rather than skyrocket to massive current and burn your amp by thermal runaway.

What that means is the idling amplifier has to warm up to the temp. level dictated by the new current setting before you get steady or correct readings. That's quick if the sense transistor Q8 is attached direct to an output transistor or the heatsink but interminably slow if, like so many little black box amps, the sensor is some 25 mm away in ambient air like many Creek models. So, if you were to touch, heat up or cool the transistor, you would see bias current going crazy.

That demonstrates bias current is controlled by the temperature of Q8 but the air space and time lag between adjusting and Q8 also compensating, may confuse your setting process and will need the cover on and wait and see what it ultimately settles to. Annoying, but it's just par for the course, unfortunately.
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