How to wire Lundahl 1544A tranny

GeneJazz

Member
2010-10-11 10:50 pm
NYC
I am going to use 2 x Lundahl 1544A transformers to convert a 650ohm balanced output on my preamp to a 100k ohm unbalanced input on the power amp.

What is the best way to wire it?

Here is the data sheet for this transformer:
http://www.lundahl.se/pdfs/datash/1544a.pdf

I am looking at R4B:L1 connection right now. This is a 4:1 turn ratio and should attenuate by 12dbs which the unbalanced input is looking for.

But I have heard 1:1 is okay as well. And on R4B connection, where does pin 11, 13, and 14 go? I won't be sticking these transformers in a chassis.
 
And on R4B connection, where does pin 11, 13, and 14 go?

Assuming you are using the transformers to convert bal to se 11,13,14 apparently go to ground as shown in the schematic. Or maybe i don't get your question.

Btw 1544A is probably too small for line level voltages and would suffer increased LF distortion if you drive your amp anywhere close to full power.
 

GeneJazz

Member
2010-10-11 10:50 pm
NYC
Assuming you are using the transformers to convert bal to se 11,13,14 apparently go to ground as shown in the schematic. Or maybe i don't get your question.

Btw 1544A is probably too small for line level voltages and would suffer increased LF distortion if you drive your amp anywhere close to full power.

I was wondering whether 11,13,14 should be grounded or I can leave it floating.

I have heard conflicting info on whether to tie the shield on the balanced cable to the center tap.

Anyway, I've answered my own question as I wired it up and there is no sound difference at all. It actually sounds quite good and the noise is completely gone now. I guess the LS25MKII has a SE output as a second thought and it does not sound that great. The balanced output sounds much better musically along with no noise.

I was over at a tech's shop and he showed me a Jeff Rowland amp using Lundahl transformers to convert between balanced and se.
 
I guess the LS25MKII has a SE output as a second thought and it does not sound that great.



This is nonsense. The circuit is completely symmetrical and the SE output is just one half. Any reduction in noise you experience is due to the gain reduction and in that respect a resistive attenuator is just as effective. As for the improved sound quality, filtering of out of band noise and introducing of second harmonics seem the only possible reasons. Have you tried passing the SE output through the transformer as a comparison?
 
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GeneJazz

Member
2010-10-11 10:50 pm
NYC
I had an opportunity to try with an VT50 that has both SE and balanced inputs. The LS25 is quiet with balanced and using the SE outputs, the noise is there. After measuring the noise, ARC tells me it is normal and within spec.

I am getting a lot of different answers from all the different techs. Including some here at DIY, ARC, and the local guy here in NYC.

Anyway, I might try some different trannies for fun. The tech here in NYC loves the AudioNote ones so I might try that. Also, Lundahl has a more beefier one.

I am going to do a critical listening session to see if the ones I just made change the sound at all.
 

GeneJazz

Member
2010-10-11 10:50 pm
NYC
Doing a little more studying, I see that this Lundahl 1544a is rated to have 1% distortion at 50hz with +20 dBu. That is close to 8v.

Doing some tests with my oscillosocope, unless the volume on the preamp is cranked to about 5 o'clock for 63hz and 3 o'clock for 20hz, I don't see any distortion on the waveform.

Anyway, I think I am good with the 1544a as I don't ever turn the volume up more that 12 o'clock which already is very very loud.

But just for fun, I am going to pick up a pair of Jensens to do a listening test.

I can't discern the difference in the sound with music with the Lundahls installed or not. Which is a good thing, I would think.