Noise from caps and tubes

johnheath · Aug 16, 2014

Hi again

After having a "comeback" in diy building amps and other stuff I recently have built me a p2p clone of the LA2A and it is just a fantastic machine for my singing voice and my acoustic guitar playing.

But... after solving some hum and ground loops I am very satisfied with the overall low noise... when connected to my mixer for live use. But when I run the signal via mic preamp - LA2A - to active speaker the LA2A has a rather annoying hiss like a summer breeze through a tree crown (you know the sound). It is not very loud but rather "breezy" =)

My question is if there is a way to get rid of this (without having to connect it via the mixer)? I am thinking replacing tubes and caps or filter caps?

Any idea is welcome to me =)

Thanks in advance

/John

ruffrecords · Aug 17, 2014

This is probably the active speaker being too sensitive. Most of them have a sensitivity control you can adjust and this may be all you need to do. If you do not want to disturb the active speakers' controls then what you need is a level control on the output of the LA2A. You can do this quite easily with a dual log 1K pot to make a simple balanced level control.

Cheers

Ian

johnheath · Aug 17, 2014

Hi Ian

Well the active speaker itself has a similar sound and is mostly due to a on board fan.

The thing is that when I connect the la2a to a mixer which is then connected to the speaker there is no "summer breeze". And then, when I connect the la2a to the speaker the breeze becomes stronger. I was hoping that maybe there are a way to reduce this breeze…. some sort of trick from somewhere.

I do not run the la2a very hard just letting the mic pre do the job and lightly turn up the gain on the la2a.

/John

ruffrecords · Aug 18, 2014

When you connect the LA2A to the mixer, do you plug it into a mic or line input?

Cheers

Ian

johnheath · Aug 18, 2014

That will be to a mic input… the speaker itself is connected to the mixer as well.

For live performance that would be just fine but the plan is to use the la2a for recording and then the mixer won't be present and therefore I want to reduce the windy noise as much as possible.

ruffrecords · Aug 18, 2014

johnheath said:
That will be to a mic input… the speaker itself is connected to the mixer as well.

For live performance that would be just fine but the plan is to use the la2a for recording and then the mixer won't be present and therefore I want to reduce the windy noise as much as possible.

OK, that may be a factor. The impedance of the mic input is relatively low, about 1 to 2K ohms, and so provides a load to the LA2A output transformer. The powered monitor will have a 10K bridging input load. This difference may be enough to change the character of the noise from the LA2A. I suggest you try loading the output of the LA2A with a 1K resistor and then plug it into the powered monitor to see if that changes things

Cheers

Ian