thomasdf
Well-known member
EDIT : Feeler for a "pumpkin" output transformer repro by Moby : https://groupdiy.com/threads/rouge-un-my-attempt-at-a-red-lundahl-5534-preamp.88241/post-1173542
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Orig post :
Hello
A long time ago I was given a set of spare parts, transformers and such among which was a pair of Lundahl LL1538 and LL1539.
Knowing a famous console brand used the 1538 as mic input in a legendary preamp / channel design I thought I'd give this design a shot, in 51x format.
I pretty much went 1:1 on the schematic but this experience is a lot of first times for me : Kicad (used to be a Eagle user... but it's way too expensive) and 500/51x format.
Here is where I am so far :
I have some questions regarding the design :
- what's the deal with R113 / R114 and the trimmer there ? On some schematics the value is "L5240" ?
- what are the most appropriate values for the 5534 capacitors ?
- output transformer : orig transformer is the infamous "pumpkin" is 1:2+1 so am I right to think my option B wiring is better ? LL1539 is 2:1+1 so option B here is reversing the transformer and using it 1:2 and using 2nd tap of primary as 1:1 output for feedback.
I am curious to try to swap U1 for a TDA1034, if I can source some. Maybe I'll add a parallel footprint.
I am open to any input, advice etc. I plan to share the PCB design / gerber when I am done.
Cheers !
Thomas
Join the party !
-----
Orig post :
Hello
A long time ago I was given a set of spare parts, transformers and such among which was a pair of Lundahl LL1538 and LL1539.
Knowing a famous console brand used the 1538 as mic input in a legendary preamp / channel design I thought I'd give this design a shot, in 51x format.
I pretty much went 1:1 on the schematic but this experience is a lot of first times for me : Kicad (used to be a Eagle user... but it's way too expensive) and 500/51x format.
Here is where I am so far :
I have some questions regarding the design :
- what's the deal with R113 / R114 and the trimmer there ? On some schematics the value is "L5240" ?
- what are the most appropriate values for the 5534 capacitors ?
- output transformer : orig transformer is the infamous "pumpkin" is 1:2+1 so am I right to think my option B wiring is better ? LL1539 is 2:1+1 so option B here is reversing the transformer and using it 1:2 and using 2nd tap of primary as 1:1 output for feedback.
I am curious to try to swap U1 for a TDA1034, if I can source some. Maybe I'll add a parallel footprint.
I am open to any input, advice etc. I plan to share the PCB design / gerber when I am done.
Cheers !
Thomas
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