Hiss from scm40a’s

[lazyscott]

Hi all, i use a pair of 40a’s with which i am very happy with. However, today i noticed hissing from the tweeter, now you have to get very close to hear it and it was still there (but at a lower level) when i disconnected the the xlr cable. Is this normal? and anyone have any ideas how to reduce it or eliminate it.
Regards
Leo.

[jophill]

A small amount of noise with your ear close to the tweeter of an active loudspeaker is normal and is actually almost inevitable.

Genelec explains it here. If you can't hear any hiss at the listening position then it's usually nothing to worry about. Since the noise reduced when you disconnected the cable then some of it came from your source electronics and what remained came from the SCM40A electronics.

Reducing this noise is sometimes possible but you can't entirely eliminate it [1]. If it's something you cannot ignore then some detailed investigation may be needed.

[1] Something called Johnson-Nyquist Noise is unavoidable in electronic systems. That's electronic noise and IME is the usual source of audible noise in audio systems.

[lazyscott]

Hi, Jophill thanks for the reply and info. (i thought i replied but it doesn’t seem to have been sent). It’s good to know that the small amount of hiss is normal, i’ll try another preamp and see if that makes a difference.

[jophill]

I assume you think the SCM40As are quiet enough when nothing is connected. For reference I can hear just a very faint hiss from my SCM50As, but only when I put my ear within a few centimetres of the tweeter. If the SCM40As are not similarly quiet with no source connected then that may suggest a 'phone call to ATC. I assume this is not the case.

A long time ago (on a completely different system) I had to deal with excessive noise generated by a pre-amp. I did that by making a small tweak to its internal circuit. That's probably not appropriate here but does confirm that different designs of pre-amp may generate more or less audible noise. However without knowing some quite technical details of the existing pre-amp and the one(s) you are able to try out it may be impossible to predict the potential result, thus requiring experiment.

Regards

John

[lazyscott]

Hi John yes with the 40a’s I have to get very close to the tweeter to hear any hiss, so not to bothered. I was just wondering if this was normal.
Thanks for the responses.
Leo