I've recently taken a VP312 preamp and outfitted it with four different transformers:
Cinemag CMMI-8pca input
Ed Anderson 2622 input
Profile 4804 output
Ed Anderson 2503 output
For swapping the input transformers, the zobel capacitors were swapped, 220pf for EA2622, and 22pf for Cinemag.
I ran frequency sweeps for the following four combinations:
1. Cinemag in / Profile out
2. EA2622 in / Profile out
3. Cinemag in / EA2503 out
4. EA2622 in / EA2503 out
For the most part these all measured the same. All of the combinations tilted upwards to about 4k, leveled off to about 8k, then started a gradual slope down. The one standout was the EA2622/EA2503 combination. Where all other combinations hit 4k and leveled off, the all EA setup continued to rise up to a peak at about 16k.
What has me a little puzzled is this:
Combo 1, pretty flat and extended response.
Combo 2, slightly less bottom and top rolls off sooner/faster.
Combo 3, pretty much identical to Combo 1.
Combo 4, slight boost in HF.
I'm having a hard time wrapping my head around why the EA2622/EA2503 combination produces the most HF. The EA2622/Profile combination rolled off earlier than the Cinemag/Profile combination (note EA2622 less HF). So if the EA2622/Profile combo rolls off early, and the EA2622/EA2503 has extended HF, then the Cinemag/EA2503 combination should have the most HF. In reality though, that combination showed no difference compared to the Cinemag/Profile combination.
Granted, this is mainly academic and I would be perfectly happy using any of these combinations. We're not talking major differences...At most a 0.5db spread, but it did surprise me somewhat. Any thoughts on why I'm seeing what I'm seeing?
Cinemag CMMI-8pca input
Ed Anderson 2622 input
Profile 4804 output
Ed Anderson 2503 output
For swapping the input transformers, the zobel capacitors were swapped, 220pf for EA2622, and 22pf for Cinemag.
I ran frequency sweeps for the following four combinations:
1. Cinemag in / Profile out
2. EA2622 in / Profile out
3. Cinemag in / EA2503 out
4. EA2622 in / EA2503 out
For the most part these all measured the same. All of the combinations tilted upwards to about 4k, leveled off to about 8k, then started a gradual slope down. The one standout was the EA2622/EA2503 combination. Where all other combinations hit 4k and leveled off, the all EA setup continued to rise up to a peak at about 16k.
What has me a little puzzled is this:
Combo 1, pretty flat and extended response.
Combo 2, slightly less bottom and top rolls off sooner/faster.
Combo 3, pretty much identical to Combo 1.
Combo 4, slight boost in HF.
I'm having a hard time wrapping my head around why the EA2622/EA2503 combination produces the most HF. The EA2622/Profile combination rolled off earlier than the Cinemag/Profile combination (note EA2622 less HF). So if the EA2622/Profile combo rolls off early, and the EA2622/EA2503 has extended HF, then the Cinemag/EA2503 combination should have the most HF. In reality though, that combination showed no difference compared to the Cinemag/Profile combination.
Granted, this is mainly academic and I would be perfectly happy using any of these combinations. We're not talking major differences...At most a 0.5db spread, but it did surprise me somewhat. Any thoughts on why I'm seeing what I'm seeing?
