another [silent:arts] LA-2a

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inputoutput

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Jan 23, 2008
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very happy now!  ho hey, this was a fun build!! Big thanks to the always generous [Silent:arts].

Input iron switch between 1:1 (sowter 3575) for normal compression, and 1:9.1 (sowter 1009) for harder compression and pre-amp use. Output iron Sowter 1010 (similar to UTC A24)  -  Three-step switch on the (totally unnecessary) limiter/compression option. Added an 6K resistor there. Can hear some difference in the sound when I crunch the input level. Maybe later I´ll try to add some side-chaining features on this switch instead or something. donno yet.

Will continue to experiment with different kinds of ecc83 tubes. They do certainly play a big part in the sound and how much unwanted noise that comes out of this thing.  At the moment I´m using Golden-dragon tubes, They gave the best noise-floor result -75dBu.

most of the knobs and lamps are bought on auctions throughout the years. The meter is from ebay, but a chopped up a new VU meter and squeezed it in there with a new homemadepaper-front.  Other than that, nothing new here.

wrongroom-la2a-back.jpg

wrongroom-la2a-front.jpg

wrongroom-la2a-inside.jpg


The output-level is too loud. Has anybody clamped the output-pins with a resistor....  ?

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LATE EDIT :   CJs tips on how to adjust the boards for 12AY7 is a HIGHLY recommended mod.  Now I use it all the time, and the 1:10 input transformer actually makes sense

Good shielded cables are also important, as always
 

Kingston

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inputoutput said:
The output-level is too loud. Has anybody clamped the output-pins with a resistor.... will I create some impedance issues by doing this ?

There's an easier fix. Change the 100K output volume pot to 25K.

As you've probably already noticed, you only really need the first quarter of the 100K in any modern studio I/O situation.
 

inputoutput

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Jan 23, 2008
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You mean the gain pot? (the silent:arts mod)+ a 75K.  yes, I have already done that, but I would like to lower the volume even more.

 

Kingston

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inputoutput said:
You mean the gain pot? (the silent:arts mod)+ a 75K.  yes, I have already done that, but I would like to lower the volume even more.

You could use a balanced T-pad directly on the XLR output, after the transformer.
 

rob_gould

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Jul 8, 2007
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Netherlands
Great build!

Just need to design a case for mine now, and this is great inspiration.

Did you put the power transformer outside the box for noise reasons, or purely because it wouldn't fit inside?

 

bernbrue

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Mar 13, 2006
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Wolfenbüttel - Germany
Very nice built. Volkers board is so straight forward. I really enjoyed building this excellent compressor. It has such a unique sound and vocals are somehow "warmly embraced" by this compressor. Lovely. Congratulations !!
regards
Bernd
 

Bluzzi

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Jun 6, 2004
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Montreal
Replace V1 with 12AY7 for slightly lower gain and smoother sound. Replace R9 and R13 with 100k. I have these on my 2 LA2As and although I haven't changed the gain pot down to 25k yet it helped tame the volume enough. I imagine using the 25k pot would complete bringing the gain down to a more practical level.

On my first LA2A I had original values and tubes but I liked it more after the mod.

Jim
 

desol

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Jun 20, 2005
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Nice. The case looks awesome.

I'm doing eight 1290's in a case...and was thinking about doing the same with the toroid.
 

kato

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Aug 16, 2004
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Indianapolis, USA
Nice knobs!

Never heard of the 1:9 input option. But I like the idea of mic --> LA2  --> record.

Is there info on this mod? or something you came up with. Any other component changes required on the input?
 

inputoutput

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Jan 23, 2008
Messages
112
Location
Norway
kato said:
Nice knobs!

Never heard of the 1:9 input option. But I like the idea of mic --> LA2  --> record.

Is there info on this mod? or something you came up with. Any other component changes required on the input?

nah, depends on how much level you want coming out of the inputtranny. No extra components here. Just  a relay based switch - going to two relays for left-right.  To test out different input transformers is really interesting on tube-equipment. With the input transformer switch -the unit acts as two different compressors. I thought that I would probably never use the "Krunsj" mode except maybe on drums and bass etc. But it actually does terrific things to vocals and all kinds of instruments.  I haven´t seen it done on any other DIY project, but I am certainly gonna include an "iron switch" on upcoming projects too. It is easy to make, you just have to figure out the wiring to and from the transformers.
 

plabass

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Nov 19, 2008
Messages
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Well I hate to pick out such a small detail in that awesome build but... where'd you get the knobs? Very cool look!
 

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