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Rundmaus 4th March 2012 06:35 PM

OPT choice for PP1C
Hey there,

I am still working on my PP1C, see:

Rundmaus at work - PP1C without sand - diyAudio

Now, here's another question to the diyaudio community, concerning the choice of output transformer:

The schematic suggests a 5k plate-to-plate transformer, and at first sight I thought a Lundahl LL1663 5k:8 Ohms would do. But with the winding ratio of 24:1 given in the Lundahl datasheet, this is merely 4.6k:8 - with the ratio being even worse when impedance variations (usually downwards) of the speakers are taken into account.

What do you think, is 4.6k:8 acceptable with the usual impedance variation 8 Ohm speakers produce?

Alternatively, one could use the LL1620, LL1623 with primary impedances of 5-6k, but the LL1663 is already 130 Euros and the larger ones are close to 200 Euros per piece. This is getting too expensive!

Alternatively, I have a transformer vendor who could custom-wind C-core output transformers - stock values are 6.6k:8 but different ratios are doable on request.

So the choices are:

1) Take the cheaper Lundahls and live with 4.6k:8 or worse.

2) Pay a lot of money for the multi-impedance Lundahls.

3) Get a custom-wound C-core OPT for half the price of the Lundahls, but with no experiences concerning quality. The power transformer bought there was very nice, but OPTs and their winding techniques are a different beast....

What do you think?


Nelson Bass 4th March 2012 06:52 PM

Hi Andreas

Allen recommended the LL1663/PP over other Lundahl OPTs. Allen claimed the Lundahl OPTs to better than Tamura.

I use the LL1663 myself and I'm most satiesfied.

Get'em all tell us your findings... ;-)

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