Hiss

[dsm]

Hello All,

I have a new tube amp with  La Scala speakers and have noticed a hum, which may have been there previously , but is now much more pronounced with this new setup.

With the amp volume all the way to 10 and the NOS1 switched off and connected by the  RCA jacks, there is very little noise. The same is true if I use something other than the NOS1 to play music through the RCA jacks. Everything seems to work pretty quietly except for the NOS1.

If I turn on the NOS1 but leave switch 4 off, it is silent. If I play music with switch 4 off, the static hiss returns and is quite noticeable.

If the NOS1 is powered on and switch 4 is on, there is quite a bit of hiss without even playing music.

I have an older house and the electric outlets are only two wire, so no earth ground. I have plugged in only the amp and the NOS1 and tried a couple of different outlets but unfortunately, I always have the same hiss.

My plan is to re-run grounded outlets with a dedicated circuit but before that, does anyone have any suggestions for how to remove this hiss? I've ended up just turning the amp volume to about 2 o'clock to reduce the noise but I know that is not ideal in the long run.

Best,

David

[PeterSt]

Hi David,

After reading this a couple of times, I only now see the relation with the battery. So what if you detach the battery ? in this case Switch #4 can't do anything.

I take it (though wild guess) that something is amiss with the internal wiring related to the meters inside. The two wires running to the meters from of the middle section of the DAC connect via single pins (detachable on purpose). Maybe they are not joint thoroughly any more ?

The NOS1 should be completely silent, like my own and 30W into the 118dB sensitive speaker (no volume control).

I never heard of what you describe ...
Best regards,
Peter

[dsm]

Hi Peter,

Dumb mistake. Instead of switch 4 it should be 2. There was some other thread I read about the noise level with number 2 switched off and music still playing. I just did not double check the numbering yesterday.

David

[PeterSt]

Hmm ...

If I turn on the NOS1 but leave switch 4 off, it is silent. If I play music with switch 4 off, the static hiss returns and is quite noticeable.

David, then I'm afraid this can not be correct (or something is plain wrong with that).
Switch #2 Off means the DAC board is without power. So it shouldn't be able to play/show music.
Do you hear a relay clicking when you flip switch #2 (either direction) ?

Peter

[dsm]

Hi Peter,

No you can't hear any music but the hiss returns. So with switch 2 off, there is no hiss but if I play music from the computer, there is no sound but the hiss returns. Just like there is hiss all the time when switch 2 is on.

 Here is where I saw the idea- I did not find out what it signified though...

I've got a 1KHz track recorded at 0dB FS. With the Sauermann monos I can still hear this track over the amp's (white) noise with XX set to -120dB! OK, that's with my ears right next to the 115dB horn.

Haha. I didn't try any lower with the Sauermanns, but with the quiet channel of the BD amp, I can hear the tone with XX's vol set to -144dB!!!

Weirdly, as the attenuation gets very high, the tone starts coming and going. At > -132dB attenuation, it seems to be riding on a 1-2Hz modulation.

Now, I have no idea if XX's vol control is at fault here. Or maybe there's some sort of 'Nick effect' going on - the house is 130 years old, so ghosts can't be ruled out.

Mani.

Mani hi,

That is the breakthrough suspected I2S de modulation noise I get as well. I can hear it with music playing at -144db vol particularly music with a strong beat. I also use a 0db 1khz tone teach for testing. I don't get the modulation that is interesting.

Do you know what the gain is of you Sauremann amps are my bridged gainclones are about 36db IIRC. I wonder if amp gain it important.

Regards,

Nick.

Ps hears another test try playing the music / test signal into the NOS with the NOS turned ON but with switch 2 turned OFF ( eg the DAC board not powered on). Can you hear anything ?

[dsm]

It seems like the issue could  be with my amp. If I unplug the RCA from the DAC,  leaving only one end of the RCA connected to the amp, I have hiss.
If it is pugged back into the DAC and the DAC is off, no hiss.  Once power is back on he DAC, the hiss returns.

I'll take another look at all the soldering and grounding in the amp and see if I can find the problem.

[PeterSt]

David,

I have just been reading in that topic you quoted from and stopped halfway page 2 . If you ignore what you quoted (about Nick's -144dB which was a totally different subject as I recall it turned out), it should be something like what's being dealt with in that topic. It is quite complicated.

So instead of trying to repeat what's all in there, I think it could be a good idea to at least read the first two pages in there. Btw, very clever that you found that topic !

Best regards,
Peter

[PeterSt]

Btw, assumed that you don't have isolator transformers (like Mani), key should be the ground reference which for the NOS1 is 0V (it is set up differentially). For that amp it is most probably no 0V at all because derived from the mains. The difference in voltage could be the noise you perceive.

[manisandher]

David, probably a dumb question on my part...

Are you sure your DC offset is at its minimum? If not, that could be creating noise.

Keep switching #2 off and on until the meters read ~10mV. (One of my NOS1s reads ~15mV, the other ~3mV.)

HTH.

Mani.

[PeterSt]

Mani, Thank you.

David, in your case I think it should be (about-ish) :

The DC Offset of your NOS1 is ~ –04.4mV/+00.6mV.

(from April 5, 2015 - unless you have a NOS1a by now - at quick look I could not find that)

Peter

[dsm]

Thanks Mani and Peter.

I'm reading -05.0, -00.0 and it is the same NOS1, no "a" yet...

I took the amp apart yesterday and resoldered anything that looked like it could be causing an issue but once it was back together, the hiss was still there.

I am wondering if there is a problem with my assumption that if there is no hiss with the NOS1 off, then that should be how quite the amp can possibly get.

If an amp doesn't have an input plugged in, is it realistic to assume that with the volume to maximum, that should be the same amount of noise/hiss that should be strived for when inputs are plugged in? Or is there something invalid or unrealistic with trying to test an amp that way?

Is possible that once I have an outlet which is earth grounded things may change?

David

[manisandher]

If an amp doesn't have an input plugged in, is it realistic to assume that with the volume to maximum, that should be the same amount of noise/hiss that should be strived for when inputs are plugged in?

No, definitely not... in my case, at least.

I think it depends on the amp, but I have a pair of ultra-quiet fully balanced mono amps in my office. With no input connected, there is slight hissing/buzzing sound with my ear right next to the 97dB/W speakers. However, with the outputs of the NOS1 connected to the amps' inputs, they are dead quiet - absolutely no noise, even with ear right at mouth of high horn or next to mid-driver.

I would recommend that you test for noise with everything connected.

Mani.