All things LA2a related

[Bluzzi]

[quote author="cannikin"]Hey Jim,

did you replace both 12AX7 with AY7? or just one?[/quote]

No just on V1. A little less gain but smoother sounding. I had both to experiment. But if you use Jensen XFRs you may not need.

jim

 

[cannikin]

I'm using sowter so I'm going to give ay7 a try

 

[Bluzzi]

I think Sowter is also a lower gain ration on input. But why not try anyways and compare for yourself.

I know for some a stock LA2A is fine. I just found it touchy on the Gain knob. The 12AY7 gave me a bit more spread and I'm hoping 100K for R9 and R13 will give me even more.

From the sounds of what some are saying I would use Sowter or Jensen on any of my future LA2A builds.

jim

 

[cannikin]

yeah I want to check out the sound of it...

and likewise give a bigger spread, glad you posted the 100K R9 R13 substitution too... I'm gonna give that a try, what drives me a little crazy is turning R1 to 12 o'clock slams the unit with gain....... don't like it.

 

[Bluzzi]

David

I can't get my R1 past 9 oclock without starting to distort (not in a nice way).

If I bring it down its OK but I'm loosing gain and have to makeup on my desk.

People using Sowter and Jensen never seem to complain of this.

I wanted to build my first one stock to get a perspective on how original sounded. But this 2008 and impedances and output levels have changed and I guess that is why I'm having problems.

I was going to use an A24 reversed but I was never sure of how to wire it to input so I went back to A10. The second one is finished and I did a burn-in test but haven't patche it into my board so no audio test yet.

I should be doing that this weekend and I'll post my findings with the R9 and R13 changes.

Don't get wrong though its a great sounding unit without all these mods its just that Gain knob bugs me when I can't get it past 9 oclock and it has hardly any gain under 8!

jim

 

[cannikin]

[quote author="Bluzzi"]
People using Sowter and Jensen never seem to complain of this.
[/quote]

Really? in the past 3 sowter La2a I have built... the gain is painful...
I hate it... you can't use 75% of R1, I think your right.. gain staging has changed a lot since the creation of the La2a.... in the olde dayz, Source material wasn't as loud and you needed something like the la2a to help out.

Keep me posted on your developments

 

[SSLtech]

the actual gain control position shouldn't really be an issue, other than where noise is concerned...

The real test is how much OUTPUT can it drive.

What's the VU meter doing on "+4" position? -if it's "reading the maker's name" pinned hard against he endstop then there's no INPUT transformer problem...

-But I'm not entirely sure that I'm correctly understanding the nature of your dissatisfaction though, so I may have the wrong end of the stick.

Keith

 

[emrr]

[quote author="Bluzzi"]

I see no reason why a SS (regulated) PS shouldn't work.

jim[/quote]

Well, sure it will work. That wasn't my question. I'm looking for sonic impressions from anyone who's tried PSU variations with the stock circuit; tube, regulated SS, DC filaments, etc. See my post above, again.

The question of audio circuit mods is another never ending tale, which I'm largely trying to stay away from. You could use a billion different things for audio output amp, and it's kind of interesting we haven't seen a plethora of variations there. There's a ton of existing large footprint tube program amps that could have a T4 and sidechain hacked into'em.

 

[Bluzzi]

I guess it was just an impression I got then.

But surely using a 1:1 instead of 1:10 has to tame things a lot more no?

You get to 12 oclock, I only get to 9. Now maybe your 12 is same as my 9 but you have a smoother or more detailed gain range ( 0 to 12 is more than 0 to 9). So already that is some improvement in my mind.

I don't need the LA2A to have a flatter or cleaner sound (when properly set) as I find the UTC XFRs good enough and whatever they are doing I like. Not to say I won't like the Sowters or Jensens. I'd love to try them in the future to see.

jim

 

[emrr]

[quote author="Bluzzi"]

But surely using a 1:1 instead of 1:10 has to tame things a lot more no?

jim[/quote]

about 20 db less gain with 1:1, off the top of my head.

[quote author="cannikin"][quote author="Bluzzi"]
People using Sowter and Jensen never seem to complain of this.
[/quote]

Really? in the past 3 sowter La2a I have built... the gain is painful...
I hate it... you can't use 75% of R1 [/quote]

The Sowter is still adding 12-13 db of gain, and you don't really need any transformer gain in most applications.

 

[khstudio]

[quote author="Bluzzi"]I guess it was just an impression I got then.

But surely using a 1:1 instead of 1:10 has to tame things a lot more no?

You get to 12 oclock, I only get to 9. Now maybe your 12 is same as my 9 but you have a smoother or more detailed gain range ( 0 to 12 is more than 0 to 9). So already that is some improvement in my mind.

I don't need the LA2A to have a flatter or cleaner sound (when properly set) as I find the UTC XFRs good enough and whatever they are doing I like. Not to say I won't like the Sowters or Jensens. I'd love to try them in the future to see.

jim[/quote]

I've NEVER got past 10 O'Clock on mine & they work & sound great... don't worry about that. People have been using these for years & that is not an issue nor does it effect sound or quality at ALL!

With the 1:1 on the input... I also have no problems... it may just hit the T4 a little less but so what... that's what the Peak Reduction control is for.

Changes to the input (tranny or tube) don't seem to have too much effect on the output gain control, at least not that much.
I found that the 12ay7 changes the character & feel more than gain & I also find that my Gain & Peak Red. controls end up in about the same spots.

 

[Bluzzi]

Kevin have you made any with UTC A10?

jim

 

[cannikin]

Here's a couple of pix of mine, went with a strip in the back and will make pigtails.. neutrik connectors are too expensive for the unemployed, daven 600/600 on the output to act as a pad

 

[khstudio]

[quote author="Bluzzi"]Kevin have you made any with UTC A10?

jim[/quote]

No.
I'm no expert, just wanted to share what I've experienced after 3 builds.

Also, I've NEVER loved a piece of gear as much as my LA2A's... My Neve 1272 Pre's & FATSO are a close runner up. :grin:

 

[emrr]

[quote author="khstudio"]
Changes to the input (tranny or tube) don't seem to have too much effect on the output gain control, at least not that much.
I found that the 12ay7 changes the character & feel more than gain & I also find that my Gain & Peak Red. controls end up in about the same spots.[/quote]

My assumption is that the lower gain from a 12AY7 is, for all intents and purposes, mostly subtracted from the feedback loops negative gain, and you arrive at a very similar place. The negative feedback amount is lower, as is the positive gain. And that's really secondary to the fact that actual db gain difference between 12AY7 (40) and 12AX7 (100) is fairly small in practice. But, the changes I think exist in total feedback are going to most significantly alter the character of the sound, without altering the actual gain quantity by very much.

Transformer gain, or lack thereof, is the whole game with knob position and stock tube circuit. And even without transformer gain, you have tube gain to compete with if feeding in high level signals. Hot +12 recording in a +18 system will require a knob setting that chucks out almost all of the system gain, so more gain in the input transformer means more to chuck out with the knob. Thus, the sub-9 o'clock settings.

10K:10K Jensen etc = -1 db or less transformer insertion loss
600:10K Sowter = +/- 13 db more gain
600:50K UTC = +/- 21 db more gain

 

[khstudio]

600:50K UTC = +/- 21 db more gain

WOW :shock: I didn't realize how much of a step up the UTC had.

It's been a long time since I looked at the specs of the "REAL" LA2A trannys...+ I've been so satisfied with the Jensen's I never looked back.

Is that really the original UTC tranny ration???

 

[emrr]

Yes. Preamps with 200:50K inputs usually get 24-25 db gain from the input trans. You put modern mic signals into vintage iron like this and you frequently overload vintage headroom concepts. The iron can take it, but frequently the amps cannot, since they were usually designed with input of -30 dbm or lower in mind.

You can see comparing the Sowter to UTC that db gain is not a linear relationship to ratio. That's why the backwards A-24 (600:15K) wasn't a huge difference from the A-10 (600:50K).

 

[Bluzzi]

Yeah, thats what I thought too. I'm no expert either but I figured 1:10 has to have more gain then 1:1 or else I'm crazy.

I never tried the backwards A-24. Had it wired but unsoldered it and put in the A10.

With an A10, I figure I could probably hook up a microphone into it and I would probably get enough gain to get a decent signal through the LA2A.
Never felt the need to try it yet.

jim

 

[khstudio]

[quote author="Bluzzi"]

With an A10, I figure I could probably hook up a microphone into it and I would probably get enough gain to get a decent signal through the LA2A.
Never felt the need to try it yet.

jim[/quote]

Yes... but maybe not enough to hit the T4.

 

[emrr]

[quote author="khstudio"][quote author="Bluzzi"]

With an A10, I figure I could probably hook up a microphone into it and I would probably get enough gain to get a decent signal through the LA2A.
Never felt the need to try it yet.

jim[/quote]

Yes... but maybe not enough to hit the T4.[/quote]

People seem to do it. Never heard specifics of possible compression amounts, but I don't see a problem. Mics frequently overload 40 db preamps with max input of -22db. There's probably 50ish db of gain for driving T4 with UTC input and sidechain amp combined. Somebody measure the sidechain gain!

Here's this from 30 pages back:

[quote author="drpat"]
You can use the LA2A as a mic preamp without any mods. I do it all of the time with my vintage rev1 units. It won't compress as hard as it normally will, but that's probably a good thing while you're tracking anyways...[/quote]