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-   -   Opus, meet Jensen: how to implement an OPT? (http://www.diyaudio.com/forums/twisted-pear/181483-opus-meet-jensen-how-implement-opt.html)

pjanda1 20th January 2011 05:18 AM

Opus, meet Jensen: how to implement an OPT?
 
I believe I have a pair of these headed my way (link to a Jensen 11ssp-6m datasheet, for those averse to downloading PDFs). I'd like to use them to convert the opus output to SE. I've reviewed the OPUS thread, and looked at the thread re: the Buffalo and opts. I've seen a few ideas, but much of the discussion is a bit over my head. I also don't see a great deal of consensus. I gather that I'll be choosing either 600:600 or 600:150, probably the former. (No worries about output impedance, its feeding a tolerant tube stage). And I'll need some resistors, at least on the secondary. I'd love some specific recommendations from folks that know more than I.

thanks!

Paul
Wild Burro Audio Labs - DIY Full Range Speakers

Skip Pack 20th January 2011 04:44 PM

I have been using Lundahl 1544As on the output of my Opus for
a couple of years now. Work beautifully. I have them configured
at 1:1 with a 4PDT switch between the Opus outs and the transformers
to flip phase.

Skip

pjanda1 20th January 2011 04:47 PM

Why do you flip phase? Are you using any resistors or RC networks?

Paul
Wild Burro Audio Labs - DIY Full Range Speakers

Skip Pack 20th January 2011 04:59 PM

I just wanted to be able to reverse absolute phase without
swapping speaker leads. I have open baffle Altec 605s with
2-way crossovers, and the effects of changing absolute
phase and relative phase (highs versus lows) on the OBs
is interesting. I did not load the outputs of the transformers
beyond that of the amplifier it's driving, which is about 15K
at present.

Skip

pjanda1 27th January 2011 09:54 PM

1 Attachment(s)
Hooked 'em up and they work. I only listened for a couple of minutes, but it sounds good! The guy I bought the trafos from sent a little PCB that had resistors and caps. I added a resistor across the output jack. So, the transformer should be seeing 600 ohms at each end.

Should I be using the G connection somehow from the DAC board? I know I could could connect it to the "center" tap of the primary (have a two primaries wired in series), but is there any reason to? Should I be worried about DC? I'm not using output caps on the OPUS, nor do I want to. In Jensen's most relevant app note, they use a pot to balance it. I'm not in favor of excessive complexity, but I don't want to magnetize the transformer cores either.

Paul
Wild Burro Audio Labs - DIY Full Range Speakers

pjanda1 28th January 2011 05:26 PM

I hooked the G to the center taps and put it back together. Definitely a less "romantic" sound than running it SE through oil filled caps! The output level difference is less pronounced than I expected (based on the position of my volume knob, I didn't measure it). It does sound cleaner and faster, better defined. Probably a worthwhile upgrade for me. Others might be happier with the caps (which, FTR, were some little old motor runs).

Paul
Wild Burro Audio Labs - DIY Full Range Speakers

io 28th January 2011 09:11 PM

1 Attachment(s)
Hi

opus recommended output transformer design LL1527

pjanda1 28th January 2011 09:44 PM

Why use an opamp and an OPT? I'm sure it is technically sophisticated, but it also seems a little like the worst of all worlds: the sound of an opamp and the added distortion of the transformer.

Paul
Wild Burro Audio Labs - DIY Full Range Speakers

io 29th January 2011 01:48 PM

2 Attachment(s)
Hi

I do use it, not OPA
WM8742 DAC 1+1:1,75 a TP PCB
now test hearing


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