LA-2A input and output transformer DIY winding

[Spencerleehorton]

Hi,

Everyone, this has probably been covered but I haven't found where yet.
I have two LA-2A and I'm using the OEP 262A7 as input txf and output txf.
Needless to say the bottom end is awful!!!
These where only termporary until I either bought one or now as I have the facility to wind my own I wanted to try this.
I'm not that fussed about getting an exact replica just want to be able to plonk a mic or be able to use it in line for summing out f the DAW, so may not need somethings?
Would anyone be able to chip in with some ideas?

Regards

Spence.

 

[Spencerleehorton]

I wanted to start with my basic requirements then go on from there.

LA-2A

Input txf - ratio = 1:9.1
Pri - 600 ohm sec - 50000k

Output txf - ratio = 4:1
Pri -  10000ohm sec - 600ohm

 

[Deepdark]

Cinemag has some great candidate for it. Output transformer would be CM-2840 (5:1) and input would be CM-2570 (1/2:18CT) you basically strap it 1:9. It will cost you about 100USD for the pair and you'll have a top quality transformer set. The CM-2570 has much more lamination than the A10, according to David from Cinemag

 

[Spencerleehorton]

I'm not that interested to be honest in buying one, would much rather diy one.
I have the specs for winding the 1176 txf now just need to sort the LA-2A in/output.

Spence.

 

[Spencerleehorton]

I have this information just need to decipher it.
Anyone help please?

what gauge wire? how many turns on each winding?

 

[Nele]

Uhm.. did you do a search? Seems all the info is right here:

http://groupdiy.com/index.php?topic=35743.0

 

[Spencerleehorton]

That awsum!!! I completely missed it, I have started to wind my own and just as a test piece I've got a 1:5 which can also be configured to 1:10 so should get me close.
With having the 1:6.5 OEP in there and the sowter on the input (1:3) I was getting distortion on the bottom end, hopefully once I put these new winds in it should be better, then I attempt a 100X version.

Regards

Spence.

 

[Spencerleehorton]

thanks CJ for this!!!

 

[Spencerleehorton]

Having a few phasing issues, which I am sorting with the first go at getting something better than the OEP output txf.
The original it seems uses a 25.4mm X 25.4mm bobbin, I have a 25mm X 25mm.
Going to try and work out hitting the same inductance with slightly larger wire, this should hopefully end up in a better txf.

Spence.

 

[Spencerleehorton]

With the first two txf I've wound I'm getting great top end but bottom end is very light.
The tone compared to using the OPA txf is much improved and sounds much more real.
Going to do another two txf using #36 AWG, going to try and get 900,9000 turns on there for the 10:1.
I wonder whether the bottom end is light due to set the input txf is set to 5:1 rather than 10:1, will swap it to 10:1 to see but I think it's the fact that I haven't put enough winds on there.
Getting good results so far, it's looking promising .

Spence.

 

[mitsos]

I have the specs for winding the 1176 txf now

Spence.

In or out? Can you post it? Thanks

 

[Spencerleehorton]

1176

Output txf Ratio 1:1

Core ei42
Primary 500 turns
Secondary 500 turns
If you wound for an example
p1=166 turns
s1=250 turns
p2=166 turns
s2=250 turns
p3=166 turns
you will get good results and frq response.
Of course you need to connect p1,p2,p3 in series and s1,s2 in series.....it is also possible to wound it on some other core but must be very similar in dimensions.
I don't know exactly how thick was a package of laminations but I think some 15mm.
I can check if you want......
Secondary 600 winds to allow for output loss.

 

[Spencerleehorton]

Got some nice AWG 38 now so going to try and wind another input and output txf.

Spence.

 

[Spencerleehorton]

Have started to wind at 10:1 txf  444 on each Pri winding and 4440 on each secondary.
Will test tomorrow.
Using 0.1mm wire, on 25mm X 25mm bobbin.

Spence.

 

[Spencerleehorton]

on first initial test top end very good and clear but lack of bottom end, i need to check phase as it seems i have it out of phase.

Spence.

 

[Spencerleehorton]

Wow!!!! very pleased!!

Had a terminal wrong way round and consulted wrong info for order of txf, sounds amazing now!!
if anyone needs a LA-2A output or input txf i'm prety sure i've cracked it, mid forward,  lovely bottom end and top end!!
just swapping over other txf on 2nd LA-2A to 10:1 and 5:1 so i've got stereo LA-2A.
i'll put up some sound samples to see what people think.

regards

Spence.

 

[Spencerleehorton]

Holy smokes!!!! replacing the C4 from ARCO to mica has opened up the sound amazingly!!!
I used a mica on the other unit by mistake but it sounded better than this other unit with arco caps.
Have 2 great units now.

regards

Spence.

 

[JessJackson]

well done spenc, upload some pics bro!

 

[Spencerleehorton]

Yes Jess I'll put up some photos, we still need to the LA-2A shoot out!

 

[Spencerleehorton]

Here's a front pic, will do insides when I move all my rack stuff around.