Modded Caimen - nice, shame about the hiss

[Ashmore]

Ok so Jimmy over at Tirna just returned my Caimen having blinged it to within an inch of its life. He even improvised a new foot pad for one I pulled off as a consequence of over enthusiastic application of blu-tac. What follows is not a criticism of his handiwork.

My mods included the Elnas, Muratas and Rubycons and the 826s. The sound is definitely improved. All those subtle improvements others have observed; improved bass, clarity and soundstage. No doubt, if some who visit here are to be believed, it will continue to get better until it reaches optimum burn-in some time around my 85th birthday in 45 years' time.

However...

There is a hiss. It's subtle. But it's there. It's like static through my speakers. It's not dependent on volume. I have a biamp system. I first noticed it on turning on the A85, which runs the tweeters. The P80 didn't hiss. Swapped wires, no change. Took out the A85 to try it as single amp system and get this, the bloody hiss was now in the P80, albeit slightly less obtrusively.

Now, I have not observed this in my system before, so logic tells me it's the Caimen and I'm wondering whether it's something to do with the 826s - maybe increasing the gain?

I admit I don't understand all this stuff. Suggestions for a cure, and offers to do soldering for me gratefully accepted!

Simon

[AlanS]

Have you tested by simply removing the dac from the amps input and seeing if the hiss goes?

[Ashmore]

Thanks Alan.

I neglected to mention that I've been using the Caimen as a preamp. This, I feel, is at the root of the issue.

Yes... having played around with wires and sticking my head right next to the speakers for most of the evening these are my observations:

There is always a slight hiss, regardless of how I've set up the DAC or indeed if the DAC is omitted, but it's barely noticeable.

However, when I use the Caimen now as preamp, on top of that very slight hiss there is a more prominent hiss when the Caimen is feeding a signal. If I pause the music the 'Caimen preamp' hiss remains for maybe half a second until the DAC disengages the signal and then I'm left with the background hiss.

I have never used the word 'hiss' so frequently as today.

Simon

[The Vinyl Adventure]

Haven't we had this issue before? Infact, wasn't it you? Am I just have déjà vu (check out my phone adding the accents on déjà)

[Ashmore]

I don't know if we've had this issue, but if we have, I assure it wasn't me! I am neither that drunk nor that stupid (though some might argue the second point).

[The Vinyl Adventure]

Hmmm, i might be going mad... Hannah has got it in her head I have been acting oddly lately, she has mentioned it so many times now, I'm starting to belive her... Which might in it's self be making me act oddly.... ..... ...........
Hang on il have a look see if I can find what I'm talking about ....

[The Vinyl Adventure]

Cant find it...
Sorry, ignor me!
Does it happen when you use just one amp?
Did you have that resistor 12k mod done?

[trailer]

Have you some other op-amps you can try in the Caiman? Failing that just take them out and try naked (the Caiman I mean).

[The Vinyl Adventure]

Maybe you could try the cb radio power supply ... That might help (purely a guess, I don't really know what I'm talking about really)

[Ashmore]

Yes I had the 12 k resistor one done.

I know this will come as a shock to some here, but I have never opened my Caimen and there are no guarantees I'd recognise an opamp even if it leapt up and kissed me.

Trailer: I have not tried nakedness yet, but it's something I've always been tempted to do... ;)

Yes Hamish it still hisses if I reduce to a one amp system.

The hiss is not there when I use it as a DAC and not preamp.

Simon

[Ali Tait]

That would suggest a problem with the variable output but not the fixed.Noisy pot perhaps?

[StanleyB]

I was thinking the same. I haven't heard of such a problem before, but I can have a look at it for you.

[Ashmore]

Thank you Stan

I very much appreciate that.

I would not have started the thread had it not been instantly noticeable in my system and led me to revert almost immediately to using the A85 as preamp.

In your experience is it possible that the 'pot' might settle? If so should I perhaps give it a few days before sending it over to you?

Simon

[StanleyB]

I have no idea why it should even be possible to be noisier. Is this when the music is playing or when there is no music going through the DAC? I don't want to be looking for a needle in a haystack over several weeks...

[Ali Tait]

Try turning the pot up and down loads of times and try it then.

[Ashmore]

Thanks. I will try that. The wife will admire me.

Stan, I understand; I'm sensitive to not wanting to waste your time.

The behaviour I observed last night was that there was an increased hiss when the DAC was sending a signal. It was very noticeable right at the start of tracks but continued through the track, as it was discernable in quiet sections.

If I paused the track, the hiss would continue for a fraction of a second until the DAC stopped sending the signal. I conclude from this that (contrary to my initial speculation) it is not an amplification of recorded detail, as the track was stopped.

I will fiddle with it some more, let it settle and then get in touch if needs be.

Thanks again

Simon

[StanleyB]

I think that what you now need is a linear power supply. The mods have lowered the noise floor on your DAC, causing you to pick up the noise from the Switch Mode power supply. See the linear power supply discussion for some ideas.

[DSJR]

I may be way off, but if the output of the DAC buffers is slightly too high for the power amps, you may notice a touch more thermal noise from the DAC.. I have very old gear, but on headphones I have to slightly back off the power amp gain, otherwise the slight noises from the Quad 33 are audible and the Quad's volume control is set very low. Reducing the power amp gain gets rid of any noise from the 33 and I just advance the 33's volume a bit more - there's still loads in reserve..

Forgive me if this is thread cr@p.

[StanleyB]

I may be way off, but if the output of the DAC buffers is slightly too high for the power amps, you may notice a touch more thermal noise from the DAC..
I think you just solved the case.

[Ashmore]

Thanks for these thoughts.

I don't think I can change the gain on either the A85 or P80 as can be done on some of their other amps. But I may pop a query into Arcam, just in case I've overlooked something or there's a workaround.

In the meantime the blinged Caimen is on DAC-only duties and performing its task very admirably.

Simon

[Ashmore]

Ok so I've been in touch with Acram and they've confirmed I can't change the gain on my amps. (Very responsive, the Arcam people). Helpfully, the chap suggested I could use inline attenuators to suppress the signal from the Caimen.

I've seen various ones online for about 40 quid each.

I don't want to spend money on stuff if it isn't going to work, moreover my system isn't exacly bad when I use the A85 as preamp so the quality gain from Caimen as preamp might not justify additional cost. Lastly I have a niggling feeling that if there's an issue I should address it at source. All subjective questions, I know.

What would you do?

[DSJR]

If you have any soldering skills, you can do it yourself with a handful of 1/4W resistors of the right value (perhaps the engineers here can suggest suitable values for your setup). With the right resistor values I can assure you their insertion should be inaudible - IMO, it's if the wrong values are used that real audible problems arise.

[Ashmore]

Update

I picked up a couple of -10Db RCA attenuators from ebay (£6.50 can't go far wrong), but regret to report they make no difference to this hiss when the Caiman is used as preamp within my system.

The attenuators are working, as there is a clear volume difference when they are in place.

Right now I'm not really that bothered; whilst the hiss is clearly audible to me, and will prevent me from using it as preamp, I am enjoying the modified Caiman as a DAC (it is clearly better than before modification).

I even wonder to what extent I have become fixated on this subtle little hiss - I am listening for it - and whether others might ignore or simply not hear it.

Simon