Caiman Output Noise

[chrism]

Oh no!

I appear to have bodged my Caiman since swapping an input cap out and inserting a 10uf tant (I have done quite a bit of trial and error bodging to it so it is my fault as it worked fine a few weeks ago).

Got a slight high pitched whine from my speakers when the Caiman has a signal connected. Tried Spdif from Squeezebox and also USB from PC both the same. As soon as a music source is detected the whine ramps up. It is not volume dependant just there all the time and particularly anoying when the vol is turned down and the signal still connected.

Wondering if it could be some sort of signal break through?

Any ideas greatfully accepted.

Regards

[Reid Malenfant]

Sounds like it could be RF (radio), have you got the lid on it?

[chrism]

Yes have the lid on it although the scews are a little worn!

The reason for the 10uf tant on the input line was to address potential RF(just swapped for a 10uf Silmic as I wondered if the tant was duff). I had on of these big yellow polyesters in before and wondered about putting it back. I have also made a new PSU interconnect recently with a bit of shelded twin core and I ought to swap the old one back just to be sure.

Regards

[chrism]

Mark,

I had built a twin PSU for the Caiman one set at 12v and the other at 5v. I tried to swap out the Murata's and feed the supplies straight in. Had to reverse engineer it though as just could not get it to work.

The 5v supply drops to 4.3v under load (connected in at the same place as the Murata output pin) and I was too scared to up the voltage back to 5v.

The whine was there before I did all this though.

Regards

[Reid Malenfant]

So it's probably nothing to do with the modified PSU ;) If it was dropping to 4.3V then obviously it was having a little difficulty supplying the required current, either that or there was a voltage drop due to resistance in the lead supplying it :rolleyes:

12V will be low unless you bypassed the internal regulator, i'm assuming you did this or you'd end up with about 9V to the audio output section which certainly won't help things...

I'm at a loss tbh, i do have a Caiman but i haven't played about with it yet.

What i'd suggest is you take the thing back to as near standard as possible & find out through experimentation which change introduced the noise/whine ;)

[leo]

I'm always weary of strange noises , could be a number of things including instability (going by the whining noise)
You got any pics? usually helps spot possible problems

[chrism]

Ok,

Swapped the PSU and cable out and the whine dissapeared. Unfortunately it then returned a few minutes later after being left on with a signal being fed with zero vol.

I have gone over the Caiman 10 times looking for solder bridges etc - clean as a -------(not using that word!).

May have to take it over to Les next week so that he can tell me what's up with it and also show me how to install the 5v supply properly. I suspect it is an issue with the grounding somewhere.

Regards

Chris

[chrism]

Any one know if when shutting the signal off does the Wolfson chip or something close to it give 3 very tiny pip sounds off (lid off and ear very close to it stuff)? If this is not normal this may be a clue to what's wrong.

Regards

Chris

[Reid Malenfant]

Hi Chris, that'd be the two output muting relays opening ;)

[chrism]

Hi Chris, that'd be the two output muting relays opening ;)

Thanks Mark but the pips are audiable when the signal is switched off not on, they do not make any sound when activated. I don't remember hearing them at all until I bodged it!

Interestingly, the whine reduces when the opamp board is swapped back in.

I thnk that two Caimans are a must when modding - you can always check the standard one out when stuck!

Regards

[Reid Malenfant]

Ah, but you were listening carefully to this whining sound so you might have only just noticed them clicking off? :scratch:

All you should get is a quiet click or as they are only small reed relays..

As you say, it's probably for the best if you aren't 100% sure of what you are doing to keep a standard one handy ;)

You have a multimeter don't you, have you tried measuring the voltage into the Caiman to see if there is any AC content? It occured to me yesterday but i forgot to mention it :rolleyes:

[chrism]

Hi Mark,

Think that I will wait and ask someone with some depth of knowledge on the subject aka Les W over at Avondale when he is back at work.

Thanks for your own thoughts though (yes I do know which end to hold the multimeter).

Regards

[andreime]

Post a pic, it might help more!

did you remove anything else than the cap?

[chrism]

Sorted it!

I swapped the Slimic out and put the big yellow polyester 10 microfarad back in and the whine has reduced to almost nothing. Could be RF not sure.

I am feeding 15.8v (without load) into the Caiman through my new Linear PS and checked the voltages under load at the Murata's. I measured 12.76v at the 12v Murata with 11.97v out. The voltage at the input cap is around 14.7v. Any one else checked this as I suspect that the 12v Murata may not see enough voltage drop through it.

Back to my main project which is to feed dedicated 12v and 5v supplies in and take out the Murata's without tears!

Mark, you made a comment about measuring AC but I really cannot get my head around what you have asked as all DC supplies will give an AC reading.

Regards

[MartinT]

Chris - are you really measuring 12.76V at the Murata's input? That's far too low for a 12V reg and it will have trouble doing any regulation at all. Where is the voltage being dropped? Is your PSU generating enough voltage under load?

[Reid Malenfant]

Mark, you made a comment about measuring AC but I really cannot get my head around what you have asked as all DC supplies will give an AC reading.

Regards
If a DC supply had infinite current supply, or if you like an output impedance of zero then there should be no AC voltage at the output terminals of the supply ;)

Introduce any kind of resistance though & a varying load & you'll see AC voltage superimposed on the DC supply line. What i was interested in was how much AC voltage you are seeing superimposed on the DC supply at the Caiman input. In all honesty it shouldn't be a lot, but if it was then we might be getting closer to the problem ;)

Multiple choices, measure different things & narrow it down is all i was trying to help with :)

[chrism]

Hi Martin,

Could you please check your Caiman and measure the 12v Murata voltage as I think you may have mentioned that you have set your PSU to 16v. I am interested in what you find.

Mark, could you please measure a DC supply for AC and tell me what you find. PS I think that you may be addicted to smilies!

Regards

[MartinT]

Chris - my power supply is set to exactly 16V and the voltage at the regulator input is about 15.4V due to the protection diode drop. The output is about 11.9V, perfect. I don't use a Murata, I use a Dexa but the principle remains - my regulator drops about 3.5V which is fine.

[Reid Malenfant]

Mark, could you please measure a DC supply for AC and tell me what you find. PS I think that you may be addicted to smilies!

Regards
Hi Chris, i'd love to but my Caiman is sat in a box :rolleyes:

As for the smilies at least you get the point rather than misunderstanding the intended tone...

I'd expect your voltage readings to be similar to Martins -1V due to his 16V DC feed, they aren't so something is going on somewhere if you are feeding it 15V DC.

[chrism]

Thanks Martin, my PSU is set to 15.8v without load and I read a 0.7v reduction through the diode. I will have a look at the tracks in that area as I have noticed that the DC jack is a little wobbly. I also needed to replace the wiring between boards as it eventually got fed up of being twisted about. I will have another look here to see if a connection is poor.

Mark, all DC supplies will read AC also and I just wanted to make my point. I am really grateful for "useful" discussion about what could be wrong or worth looking at and glad to hear that you don't intend any put downs with smilies added to infuriate.

Regards

[chrism]

Thanks everyone.

Now fully sorted and also got my 5v and 12v linear supplies working - Murata's now redundant! Not even a tiny whimper now from my speakers.

I will do a write up with some pics soon.

Regards

[MartinT]

Excellent Chris, we look forward to the pictures and a full description of your power supplies.