LA2A - rather poor specs. Any DIYers tried to improve it?

Old thread but: Please don't underestimate the importance of the "rather poor specs" in this unit's popularity - specially the easily overloaded output stage is a signature that many would miss if "updated"..

Jakob E.

Does the physical placement in the build on the NE-2 cause any noise? Should it have shielded leads and located net the AC voltage and the power transformer?

I know ther has been some discussion of replacing the NE-2 with Zener diodes which the writer note worked fine but failed.

The output stage "thumps" before the transformer. Not a "spec", but something that can be improved.
Also surprising in the old units is the quality of the components. But sometimes installing better components in that unit "ruins it" for some customers.

I did this to the LA2 concept.

https://www.facebook.com/ProHarmonic/photos/a.315982861852458.75816.315947311856013/794024257381647/?type=1&theater

RE: LA2A noise.

On original units and replicas this may indeed get troublesome. Let's be honest, bad by todays standard. I'm specifically talking about PSU 50/60hz hum and its rectification related multiples. They were ok for the time with AC heaters and only low-uF electrolytics available.

But we can completely defeat these problems by throwing actual DC at B+ and heaters these days, and not just a close equivalent like back in the day. PSU hum can be completely eradicated.

I'm lazy to post the RMAA images, but in common studio level unity gain use noise will only barely rise over AD/DA loop -110 dBu self noise. At max gain it's still at -90dBu.

But this applies to all gear where PSU is done right and not just the very specific case of LA2A.

Quayhog said:

Does the physical placement in the build on the NE-2 cause any noise? Should it have shielded leads and located net the AC voltage and the power transformer?

I know ther has been some discussion of replacing the NE-2 with Zener diodes which the writer note worked fine but failed.

Click to expand...

Quite simply, bin the NE-2 and forget any discussion related to it. It has no place today anywhere. In LA2A it's used doing the duty of a zener - was it 60-70V maybe - regulating voltage for the gain reduction metering part of the circuit.

I have been thining about this since I built my first LA2A... its rather loud noise figures.

I now ordered some parts to do a upgrade in form of a completely new PSU... toroid power transformer and well filtered DC for the heaters and perhaps even change the 6AQ5 for the 6v6GT (I have a few in store after building some tweed deluxes a few years back)... I also have noticed that the output transformer is very prone to pick up noise from the transformer and such... so a careful placement or even getting rid of it is in my mind.

Regards

/John

Kingston said:

RE: LA2A noise.
I'm lazy to post the RMAA images, but in common studio level unity gain use noise will only barely rise over AD/DA loop -110 dBu self noise. At max gain it's still at -90dBu.

Click to expand...

And there's a ton of gain available in a LA2A!

I generally don't get mine beyond 1/3 of the way up unless, as an effect I'm looking to seriously distort something.

A noise floor of -90dBu at full crank is a non-issue for me.

Mark

I also built the Drip LA2. I used high end caps throughout the build and the end result was remarkable. Clean and quiet with quite a bit more output.....