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Lundahl LL1540 for SY's heretical?
Lundahl LL1540 for SY's heretical?
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Old 24th May 2006, 08:00 AM   #1
Andypairo is offline Andypairo  Italy
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Default Lundahl LL1540 for SY's heretical?

Hi,
I was wondering is the Lundahl LL1540 can be a good choice for SY's Heretical line stage.

http://www.lundahl.se/pdfs/datash/1540.pdf

It can be configured as 1:1 or 1:2 to give some boost (if needed), what do you think about it (electrically and soundwise)?

Cheers

Andrea
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Old 25th May 2006, 07:30 AM   #2
Andypairo is offline Andypairo  Italy
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Another thing,
how does it compare to the Jensen and the Cinemag trafos suggested for this amp?

Cheers

Andrea
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Old 25th May 2006, 11:57 AM   #3
SY is offline SY  United States
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Lundahl LL1540 for SY's heretical?
I haven't personally used it (I've only tried Jensen, Cinemag, and Ampex), but I would have no hesitation using the Lundahl. Their transformers are superb up and down the line.
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Old 25th May 2006, 09:13 PM   #4
Andypairo is offline Andypairo  Italy
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Hi,
thanks for the reply.
I have another question: in case I need to use them as step-up (1:2) the source would see 1/4 of the input impedance (roughly equivalent to the potmeter paralleled to the 15K resistor in your schematics.
Do I need to adapt these values to keep the impedance at about 10k?

Is there a particular reason to use a 100K pot with a paralleled resistor instead of a lower value pot?

I ask because I have on hand a motorized 50k blue velvet and a 20k black velvet...

Cheers

Andrea
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Old 25th May 2006, 09:17 PM   #5
SY is offline SY  United States
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Lundahl LL1540 for SY's heretical?
Lundahl does spec a higher load than Jensen, so if you use their network and a 50k pot, you should be fine.
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Old 6th October 2006, 01:20 PM   #6
mark_titano is offline mark_titano  Italy
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Another lundahl transformer for the heretical...

http://www.lundahl.se/pdfs/datash/1545a.pdf

Can I use it without any changes in the schematic if I'd choose R4B / R4U : L4B / L4U connection?

Thaks SY

Mark
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Old 6th October 2006, 01:43 PM   #7
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Lundahl LL1540 for SY's heretical?
That connection is (according to the sheet) optimized for 10k:10k, so should work fine with no changes with no gain at stepup. Check square wave resonse to see if you have to load the secondary with a Zobel to get rid of any ringing.
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Old 6th October 2006, 04:01 PM   #8
Eusebius is offline Eusebius  United Kingdom
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I've used the LL1540 as an output to a balanced 12b4 line stage, and it sounds fine in parafeed - doesn't overload to my ears. I don't think it likes many volts of signal through it, though, so a low mu valve might be required. A friend put it on the scope with a 3A5 driving it (higher mu) and found that it was overloading.
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Old 6th October 2006, 08:33 PM   #9
mark_titano is offline mark_titano  Italy
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Thanks Stuart.

I'll try to assemble it as soon as possible.

Just another question ( a bit OT, sorry): I've read the DiyAudioMag article about the heretical line stage and, in the last schematics, I can't see how you feed the opamp. I suppose using the +/-12V supply...I'm right?

Mark
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Old 6th October 2006, 08:45 PM   #10
SY is offline SY  United States
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Lundahl LL1540 for SY's heretical?
You're right.
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