Pocketable headphone transformers
Seems I got a bit carried away with listening to my heavily modded XuanZu amp in the last-to-one blog post. I even considered it was superior to my current headphones - that would mean shelling out on some new ones. Before I went shopping though I did try it into my DT880s, which are 600ohms (hence I usually only use them for special occasions) - they sounded cleaner, although considerably quieter. This amp doesn't have enough voltage swing available to deliver the SPLs into such a high impedance. So was the cleanliness of these phones due to their being higher quality (they're at least 4* the cost of the others)? Or just because of listening at a lower level?
When my over-enthuasiasm for the amp had subsided a bit I decided to consider a way to answer these questions. If the amp was indeed not producing the artifacts which I was hearing on piano into the low-Z cans, then putting a 2:1 step-down transformer on its output would make no difference at all. The amp has plenty of voltage headroom available so it can produce the same SPLs, it just needs the volume up higher.
In order to do the experiment I had to build the trafos - I have recently acquired some small PQ20/20 cores so I wanted to try those out as OPTs. I decided 2:1 step down should be sufficient - after all with speakers on chipamps I first noticed a substantial improvement with only 1.5:1.
Rather than partition the winding window equally between primary and secondary as I'd done in the past, this time I went for a 40:60 split. That's because turns on the outside need more copper as they are longer. To optimize a trafo design the losses in primary and secondary should be equal - but the inner winding gets considerable advantage if the split's 50:50. Being too lazy to do the calculation for the precise ratio, I have adopted 40:60 inner-outer split to see what happens.
These trafos have a 6 layer secondary, wound on first with 0.21mm magnet wire, the DCR is about 5ohms. The primary's wound with 0.17mm and measures about 20ohms. Thus the total impedance seen from the 'phones is 10ohms. Thus its looking like 40:60 was indeed the right choice - each winding is contributing equal loss.
So how about the result of listening? It has proven my original enthusiasm mis-placed. With the trafos in-line the artifacts are considerably reduced. Not totally absent but noticeably lower and hence they must be coming from the amp, not the phones. I took these trafos to try out on my colleagues - driven direct from their smartphones they were all fairly well impressed at the SQ improvement. 'More 3D sound' was a common description.
Now I'm wondering what ratio transformer is sufficient for the artifacts to disappear entirely. I have built a 3.2:1 on a bigger core to listen to next, but for that I do really need more voltage swing than comes from the little XuanZu. So I'm revisiting my desktop Taobao amp (another Lehmann variant) to try out these trafos.....
Update - added pic of second prototype with PQ20/20s. This time I wound the secondary with three two-layer 0.23mm windings so as to give a rudimentary volume control. The switch allows me to compare only one winding vs all three in series.
When my over-enthuasiasm for the amp had subsided a bit I decided to consider a way to answer these questions. If the amp was indeed not producing the artifacts which I was hearing on piano into the low-Z cans, then putting a 2:1 step-down transformer on its output would make no difference at all. The amp has plenty of voltage headroom available so it can produce the same SPLs, it just needs the volume up higher.
In order to do the experiment I had to build the trafos - I have recently acquired some small PQ20/20 cores so I wanted to try those out as OPTs. I decided 2:1 step down should be sufficient - after all with speakers on chipamps I first noticed a substantial improvement with only 1.5:1.
Rather than partition the winding window equally between primary and secondary as I'd done in the past, this time I went for a 40:60 split. That's because turns on the outside need more copper as they are longer. To optimize a trafo design the losses in primary and secondary should be equal - but the inner winding gets considerable advantage if the split's 50:50. Being too lazy to do the calculation for the precise ratio, I have adopted 40:60 inner-outer split to see what happens.
These trafos have a 6 layer secondary, wound on first with 0.21mm magnet wire, the DCR is about 5ohms. The primary's wound with 0.17mm and measures about 20ohms. Thus the total impedance seen from the 'phones is 10ohms. Thus its looking like 40:60 was indeed the right choice - each winding is contributing equal loss.
So how about the result of listening? It has proven my original enthusiasm mis-placed. With the trafos in-line the artifacts are considerably reduced. Not totally absent but noticeably lower and hence they must be coming from the amp, not the phones. I took these trafos to try out on my colleagues - driven direct from their smartphones they were all fairly well impressed at the SQ improvement. 'More 3D sound' was a common description.
Now I'm wondering what ratio transformer is sufficient for the artifacts to disappear entirely. I have built a 3.2:1 on a bigger core to listen to next, but for that I do really need more voltage swing than comes from the little XuanZu. So I'm revisiting my desktop Taobao amp (another Lehmann variant) to try out these trafos.....
Update - added pic of second prototype with PQ20/20s. This time I wound the secondary with three two-layer 0.23mm windings so as to give a rudimentary volume control. The switch allows me to compare only one winding vs all three in series.
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