|JIG FOR TRANSFORMER A-B TESTING|
|MINIATURE 4PDT SWITCH, SELECTS BYPASS OR TEST POSITION|
|MINIATURE 4PDT SWITCH, SELECTS TRANSFORMER A OR B TO TEST|
|L TO R, CRIMSON ISOLATER, 620X, EDCOR 600:600|
|EDCOR 600:600 AUDIO TRANSFORMER|
For reference my studio is aligned to 0 VU = +4 dBu signal level, all of the listening levels were adjusted to be passing 0 VU as an average level through the transformer under test.
These are audio transformers so part of the testing consisted of listening to music and part consisted of measuring performance with an audio oscillator and a NTI Minalyzer to measure the signal levels.
For testing purposes each transformer-secondary was loaded with the line input impedance of my Souncraft mixing console, the manual says the input impedance is 10K ohms so we'll assume that is the load across the secondary of the transformer under test.
I set the Meyer HD-1 monitor speakers to mono since we would be only listening to a single audio channel at one time. I chose "Talking Blues" by Bob Marley as my test piece of music, this tune has a nice deep bass line and snappy percussive tones from the drummer. I looped it over and over so I could listen very carefully and critically to different parts of the song to hear how each transformer affected the sound.
My test jig allowed me to completely bypass the transformers instantly or switch to either of the two transformers under test.
All three of the transformers tested passed the listening test with virtually no audible difference detected between them. To my old engineer ears, all three sounded excellent, deep full bass response and crystal clear high frequency response.
I was surprised to not hear more of a difference. I expected to hear bass roll off or insertion loss or something but all three transformers sounded excellent.
I used the Minalyzer to calibrate the output of the oscillator which feeds the transformer test jig, then moved the input of the Minalyzer over to the output of the transformer so I could see the affect of changing the frequency.
I focused my frequency tests in the bass region since low frequencies below 50 hz are very challenging for transformers to reproduce. Each transformer was fed 100 hz at zero-dBu for lineup and then the frequency was dropped to 20 hz and the level was measured. This showed the low frequency loss in level by the drop in frequency.
Here is the results of the oscillator 100 hz bass frequency tests:
620X = (-.18) dBu @ 20 hz
Crimson Isolater = (-.16) dBu @ 20 hz
Edcor 600:600 (iron laminations) = (-.28) dBu @20 hz
The loss in signal level was almost imperceptible in the listening tests and the frequency tests showed why, all three transformers had great low frequency level at 20 hz. Before moving on I dialed the oscillator down to 10 hz and each part quickly showed more roll off. I did not measure the level difference since I'm not interested in frequencies I can't hear.
Modern audio transformer production is at a pretty highly evolved state with many options to choose from. The Crimson parts had the best audio performance and are smaller and lighter in weight than the Edcor component. Sonically speaking I'd be happy with any of these in my audio signal path.
Good music to all!
SCHEMATIC FOR TEST JIG
|TEST JIG SCHEMATIC FOR REFERENCE|