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Tweakers' Asylum Tweaks for systems, rooms and Do It Yourself (DIY) help. FAQ. |
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Tweakers' Asylum Tweaks for systems, rooms and Do It Yourself (DIY) help. FAQ. |
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In Reply to: Sowter I/V transformers - anyone tried them? posted by Spartacus on February 26, 2002 at 09:14:45:
I have not tried the Sowters, but am using Altec Lansing microphone step up transformers which have very similar characteristics. Works very well except you lose a lot of gain. Since most folk's systems have too much gain (mine included) it shouldn't be a problem. Some things to keep in mind:1. You will need an I/V resistor across the DAC, and it makes a huge impact on the sound quality. Once you find a value that sounds good (I'd recommend 25 to 33 ohms) then get a Caddock or Vishay of the smallest wattage available. You can try a resistor across the secondary (40K to 50K) but it doesn't sound very good.
2. My xformers are 1:18.25 step up, with a 150:50,000 spec'd ratio. The primary is center tapped (38 ohms) and that's where I'm attaching the resistor. The impedance step up is the square of 18.25, or approx. 333. Thus a 30 ohm I/V resistor will yield a 10K output impedance load. Your preamp needs at least a 50K input impedance or you'll lose bass response.
3. You may need a small (100-500 pF) cap across the primary or secondary to cut RF from the DAC chip.
4. Use shielded coax for all your wiring to reduce RF pickup. Keep the xformers away from the power supply and esp. the xformer as they're very suseptible to hum pickup.
5. Ground the xformer can, and negative secondary output to the chassis to avoid the worst hum you'll ever experience in your life...;-)
Have fun,
Pete Fowler, Austin TX
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Follow Ups
- Re: Sowter I/V transformers - anyone tried them? - petef 08:09:27 03/01/02 (0)
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