Does anyone have a build/schematic for a 1/2 LA-2A >> 1/2 LA-3A (tube audio, solid state optical)??

[777funk]

I was thinking today this may be a budget way to build the best of both worlds. Does it already exist and if so is there a schematic for this?

Does the 3a use the same T4b?

 

[mrclunk]

Does the 3a use the same T4b?

yes

Output transformer is the same as an 1176 but you also need the interstage transformer so wouldn't be saving any money really.

 

[777funk]

Interesting and good point. I guess interstage transformer on the 3a (just before the T4b) is to increase the voltage to closer to the 130 something that the driver tube in the 2A runs at?

Edit: This guy from this thread:
https://gearspace.com/board/geekzone/328173-transformers-la-3a.htmlseems to maybe have a cheap solution to this problem:

The transformer that drives the EL panel doesn't necessarily have to be an autotransformer (which is really just a tapped inductor). I believe UREI used that part just because they had it laying around. If you look at it, it's actually a speaker matching transformer and they don't use the secondary. Basically, all you need is a 1:10 step-up transformer that can handle a large signal swing (signal goes into the transformer at line level, and comes out 20dB louder). The frequency response of the transformer isn't critical, except that it'll affect the response of the compressor (will it respond more to midrange than it does to bass or treble?). Any distortion in the transformer is a non-issue. The EL panel represents a very light, but completely capacitive, load across the transformer secondary. If you wanted to use a power transformer, I'd suggest one with a 120V primary and a 12V secondary (that's 10:1) and wire it backwards. The wattage of this transformer can be very low - I'm not sure you could even find a power transformer too small for this application. You might consider trying the Amveco torroidal power transformers from Digikey.

 

[Bo Deadly]

yes

Output transformer is the same as an 1176 but you also need the interstage transformer so wouldn't be saving any money really.

The "interstage transformer" is just a cheap line matching transformer. I used this one:

Parts-Express "Quam TBLU" Line Matching Transformer

with my PcbStac PCBs for my "Channel Strip 2" build and it works great.

 

[777funk]

I figured maybe I could get away with building just the inner sections of the LA2A (unbalanced) and patch it in with a true bypass in/out switch (like a guitar FX pedal) into the middle of my Neve build. I did this with an 1176 (Gyraf's) and it's working nicely without transformers between it and the Neve gain stages.

A similar approach with the LA2/3A (solid state sidechain) would be pretty cheap to build since there would be no i/o transformers. I've patched my unbalanced (capacitor coupled) tube preamp between the Neve's gain stages (I have one Neve channel with a TRS insert jack) and it sounds better with the two 12ax7 stages than without (to my ears). I like tubes in the signal path. This is what got me thinking on the LA2/3A idea. Might be a good cheap way to get a little bit of the LA2A flavor without spending several hundred to a thousand.

 

[777funk]

On other thought I just had... the Klark Teknik Pultek copy I'll bet could have the LA2A compression features (not dead on of course but the idea) added in without too many added parts. I'm not looking for a perfect LA2A or even a meter. I may try to build enough of the 2a (or 3a) inside of this. If I need another tube or two, the Pultek clone already has the heater voltage and B+ (and probably low voltage as well) in the box. There's a little space in the chassis to work with.

 

[pucho812]

I figured maybe I could get away with building just the inner sections of the LA2A (unbalanced) and patch it in with a true bypass in/out switch (like a guitar FX pedal) into the middle of my Neve build. I did this with an 1176 (Gyraf's) and it's working nicely without transformers between it and the Neve gain stages.

A similar approach with the LA2/3A (solid state sidechain) would be pretty cheap to build since there would be no i/o transformers. I've patched my unbalanced (capacitor coupled) tube preamp between the Neve's gain stages (I have one Neve channel with a TRS insert jack) and it sounds better with the two 12ax7 stages than without (to my ears). I like tubes in the signal path. This is what got me thinking on the LA2/3A idea. Might be a good cheap way to get a little bit of the LA2A flavor without spending several hundred to a thousand.

We have an LA2A at the studio that was once owned by les paul. He added guitar jacks in the front. the guitar jacks bypass the I/O transformers. He used it in his guitar chain after his preamp.

 

[nielsk]

You wrote "tube audio" so I take that to mean SS side-chain, basically what the TT CL1B does (and very nicely, too).
It is shown in the technical documents section

 

[CJ]

Pucho does that thing have the original T4b?