Pot > B1 > step up transformer > B1?

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Fair comment re. cost. There are cheaper ways to add gain. i have the parts though so this doesn't stand in my way.

Would there be a resonance issue with a transformer sitting between two coupling caps? I know it would be best to revise the design to omit the coupling caps between the two buffers, but wasn't sure how much of an issue resonance would be if these were left in place.

The split rail PSU proposed by others on this forum would certainly allow for the removal of all coupling caps. It would be interesting to know if there was a way of removing the caps with the single rail PSU.
 
Fres = 1 / ( 2 * pi * (L*C)^.5 )

Calculate and see what the resonance would be.

Then decide if it an issue.

ticktock:

"...But why coupling caps? The transformer is blocking
any DC...."

The caps are to keep the DC out of the primary (and, separately, possibly the secondary) winding(s), not to keep the DC from getting through to the next stage...yes the transformer does that.
 
Step up transformer > pot > b1 exposes the source to the reflected impedance of the pot, which plummets rapidly as the step up ratio of the transformer increases.

With the standard 25k pot and 1:4 ratio transformer, I believe the source would see a 1563ohm load (plus transformer primary and secondary series R - I think, could be wrong). This should be fine for direct connection to some of the popular Vout dacs (AK4396 etc.) but not ok with all line level sources.

Trapping the transformer between two B1 stages keeps the preamp unit input and output impedances at desirable levels (but throws up challenges re. ac coupling).
 
Step up transformer > pot > b1 exposes the source to the reflected impedance of the pot, which plummets rapidly as the step up ratio of the transformer increases.

With the standard 25k pot and 1:4 ratio transformer, I believe the source would see a 1563ohm load (plus transformer primary and secondary series R - I think, could be wrong). This should be fine for direct connection to some of the popular Vout dacs (AK4396 etc.) but not ok with all line level sources.

Trapping the transformer between two B1 stages keeps the preamp unit input and output impedances at desirable levels (but throws up challenges re. ac coupling).

The B1 article say there is no issue with using a higher impedance pot, what would the source see if a 100k pot was used with a 1:4 transformer in the "Step up transformer > pot > b1" configuration ?
 
From the Lundahl FAQ:
Can I use any of your transformers for converting consumer level -10dB unbalanced signals to professional +4dB balanced signals?
In order to lift signal level from -10 to +4 you need a stepup transformer with turns ratio 1:5, such as LL1935 used 1:5 The consumer equipment output impedance should be reasonable low, and pro audio input impedance must be high, as the transformed output impedance will be 25 times higher than the original source impedance. The transformer should be placed close to the balanced input. If the source impedance is much higher than 600 ohms, the band width will be limited.​

This means a 100k pot would appear roughly like a 6K input impedance if placed after the 1:4 transformer. This is in the range of 10x of a 600ohm source impedance. Am I understanding this correctly?
 
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