I'm from italy and I've just finished a point-to-point version of La2a (based on cayocosta layout).
This is my first experience with point-to-point (and I think the last one!!).
I've a problem of motorboating (I think is this the name): I've read in this thread several cases of my problem.
I've done some tests that I'm going to post, to help me and other like me that find this problem to fix it.
Before posting, I've checked all previous post about this problem and I've done this tests:
- my neon (NE2) works correctly
- la2a clone startup correctly, and all tubes works.
- I've tried to move the wires in the backs of sockets, but motorboating change his velocity, but remain.
- I've tried moving OUTPUT CAPACITOR, but nothing changed. The only thing I noticed is that moving wire that connect Pin 6 with C2 on the board, motorboating change in frequency.
I put as attachment a pic of my clone, to understand if I done a mistake in placing tubes and PSU in the rack.
1. I've done a test with all tubes and no T4b. Moving clockwise gain pot, increase motorboating and full clockwise noise disappear, leaving this sort of white noise.
2. Test with V1 and V2 no T4b, no input: motorboating is still there, without changing nothing.
3. Test with V1 and V2 no t4b, SM57 mic input: when I startup the unit, the sound pass without motorboating, but when tubes warm up motorboating starts. As you can listen in my tests mp3 in link, sound pass and unit preamp correcly. I've put my mobile in front of SM57 only to try if it works. The lack in frequency is obiouvsly due to mobile speaker.
After few seconds, problem of motorboating change and depends directly on the source with input: no input, only white noise - no motorboating. With input, motorboating starts!
You can listen my tests here:http://soundcloud.com/aleguitarpro/sets/la2a-tests
How can I solve this problem??
It depends on the messy wiring inside my la2a rack or in the position of tubes?
I think that I could change positions of tubes, putting them toward the back of the rack. In this way I could reduce the lenght of wires, but anyone that have found this problem on his clone, could share his experience in order to fix definitively this problem??
Thanks very much!!!!!!!