Mully


The beast is ALIVE!

After a fair bit of fiddling this afternoon/evening, she is up and running and the studio floor is awash with tone juice everywhere..... these are called Drip for a good reason... tone just drips outta this thing.

Had some interesting problems to solve and the process has resulted in a much better understanding of the La2a beasties and their design... cool units and the Opto4 is an excellent interpretation.

Anyway, more updates if anyone is interested and how I got this beast to be noise free (yes!) and running after some tribulations (I was sure I'd installed a 2k and not the 22k found in circuit!!). Got one last mod to do using the filament voltage to light the VU and currently I've hung a temporary and knarly looking rectifier off a T4 (photo prolly up tomorrow) to give it half the volts it wants.

Did a few sample recording tonight with lace sensored Strat and found that once the Opto saw a pre amp (JLM 1290) at her front end, she really bursts into life and the VU starts to dance it's crazy samba and the room fills with lushness. All round pleasing experience it has to be said.

Anyway, time to turn the soldering iron off and think happy thoughts.
Cheers.

Mully


Hey thanks guys, appreciate the interest.

The resistor I found after hunting through the La2a schematic tracing back where the voltage drops to 270 (voltage was low at most test points) and sure enough, I had a 22k instead of the 2k... I am typically beyond fussy about this sort of thing and can only attribute this to one of the late night build sessions when i really should have walked away like other times...  oh well, it still resulted in good things learned about the mighty La2a.

Here's a pre completion piccy... still final VU power to do and last tidy up:



This one is another poor mobile phone piccy of the temp VU power reg strapped to a T4.



This is purely a gratuitous (new) mobile rack shot of the vacant slot begging for the Opto 4 to be bolted into:



Couple of misc things...

1. Have done some 'inventive' cable paths in an effort to reduce induced noise/hum. No real noise issues now I've pathed the earths properly and completely I have to say and some of the weird cabling could be reworked for aesthetics.

2. I mounted the board in reverse to the norm (mentioned previously in the thread) in order to minimize audio cable lengths. Suspect no real advantage.

3. This thing is actually very quiet... very pleased.

4. Case panel earth bonding was the final path to resolve... the front panel was high resistance to earth and was the source of the final hum. Rather than add an ugly fixing hole for another lug, I used a Utilux crimp around a switch and ran it to a common earth tie and voila!

5. Thinking about getting the JLM VU meter mod kit to resolve the VU Light issue the easiest. It will prevent the need to parasite 12VDC from somewhere in the case.. just use the existing heater supply terminations on board.

6. If you can see in the photos, I've mounted all transformers inside the case. No nasty hang outs of the rear and noise floor as mentioned appears to be quite low.... not noticeable and there is also loads of gain available. Will do some level checks soonish for reference.

Last thing... do people typically just put 0db (1.228V, Sine wave approv 1kHz) into these units, set to GR and then adjust the VU to 0? Is that the 'standard' method? Drip info on this is quite vague.

Cheers for now.