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Old 2nd May 2007, 04:10 PM   #1
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Default Help Choosing A Sowter Trans For My DAC?

As my very first foray into tubes I thought I'd try the Lampizator Tube Buffer as a compliment to my DAC. After reviewing the schematic I don't see anything beyond my skillset with the exception of choosing the correct Sowter transformer. The schematic uses a TDA1541 DAC and I use a TDA1543. Could somone please give me a brief explaination of these transformers and how it would apply to my circumstances?

Regards,
Dan
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Old 2nd May 2007, 05:50 PM   #2
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I believe that the 9762 and 9545 both require dac chips with no offset which rules out their use with the 1543. The 8347 and 9055 can both take some offset, but you should check the power output of the 1543. It is a higher current output that other chips (which is why it is used as it is), so it may be too much for the transformer. Perhaps you could use a resistor and a cap to do the I/V conversion, then put in the transformer and use one of the voltage out types? I'd send an email to Sowter to see what they say.

http://www.sowter.co.uk/dacs.htm
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Old 3rd May 2007, 06:44 AM   #3
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Heya. The Sowter 8347 will work. However, it was really
designed for the Burr Brown PCM63. The suggested value of
25ohm load has much to do with the minimum THD of the output
stage of the PCM63 in particular...

Can I suggest a cheaper but equally cool first tube project?

Buy a couple of these:

http://www.edcorusa.com/products/tra...sm15k-600.html

These are line-out transformers, 5:1 stepdown. Now, you
need a voltage gain stage. Lots of options here. I'd start
out with low Ra stuff like ECC86/6GM7/5687/ECC88 or even
reuse some 6SN7 or 12AU7 (higher Rp). You'll have a PP pair
of triodes driving the Edcor. You can use a common cathode Rk
on the triodes. Building a CCS will work too and give you the
added advantage of significantly improved power supply noise
rejection.

You can then experiment with various I/V resistor values....

If you start out with the 6GM8/ECC86, you can conceivably
get going with B+ as low as 45V or so, which means an easier
initial power supply.

Unlike the Sowter tx, you can repurpose the ckt into a line stage
or preamp too! Just add a Radio Shack stereo volume pot!

-- Jim
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Old 3rd May 2007, 07:19 AM   #4
oshifis is offline oshifis  Hungary
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Join Date: Mar 2004
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Check out my transformer/tube circuit:

Laszlo's Valve Output Stage with Lundahl transformer

I designed it for TDA1541A, but I believe it can be applied to the TDA1543. The center tap of the primary should be connected to Vref of the TDA1543. The output voltage will be between 1.2 ... 1.5 V.
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Old 3rd May 2007, 12:11 PM   #5
oshifis is offline oshifis  Hungary
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Location: Budapest, Hungary
I calculated the gain with a Sowter 9545 transformer. It will give somewhat large audio output voltage (around 4V RMS). If this is too much, you can put smaller resistors in the cathodes. My circuit has 1.5k; for the Sowter 1+1:5+5 transformer I recommend 0.33k (or look for an 1:10+10 transformer).
All this is true with dual differential DAC drive, see the APPLICATION and FEATURES notes at the Sowter site. I was also considering the Sowter 9545, but for my purpose the Lundahl LL1678 with 1+1:16+16 ratio suited better.
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