| jimbo1968 |
I want to build a pre-amp box that will contain passive attenuator, a simple buffer and an active crossover. It will also let me switch sources between CD and AVamp, thus letting me remove the AV amp for music.
Opinion seems to be that stepped attenuator beats potentiometer, so does anyone know where I can get a kit of parts? Or can recommend where to buy the dual 12way switch (does it need to be a quality item?).
Maybe someone has a built attenuator for sale? |
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| Vikash |
I built a 12 step attenuator with parts from Farnell. Full details at Decibel Dungeon ;)
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| jimbo1968 |
| thanks for those replies. I'm getting a shipping price for the built one. I have read most of decibel dungeon, but I hadn't spotted the pre-amp/crossover, exactly what I want. |
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| hermanv |
Quality is a relative term.
I built my passive pre using Shallco switches (coin silver contacts, high wipe, high pressure) bought at Michael Percy.
He also carries several brands of audiophile resistors priced from oh dear to oh my god.
12 steps seems minimal, if I were to do mine again I would choose steps of 1.5 dB in the nominal listening volume range. Outside that range I would expand to 3 dB steps and then maybe 6 or 10 dB.
A good design would probably run from -40 to +6 dB total range. So 3 steps of 6dB gets you from -40 to -28, then maybe 4 steps of 3dB gets you to -16. Now 7 steps of 1.5dB each gets you to -6.5 followed by 4 steps of 3 dB to get to +5.5. That's 18 steps, a lot of resistors.
My passive stacks up against the very best pre-amp sound quality I have ever heard. For all the work you are about to do, I would consider buying very good parts in order to make it the last one you'll ever build. |
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| jimbo1968 |
Thanks for the comments, I think I'll start with a mid-range unit though as I've only just added pre-amp to my list of things to build and I'm not ready for $300 attenuators yet.
Besides, if I started with a $300 shalco I wouldn't have anything to reference it against. |
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| hermanv |
| The Shallco is only $94 it's the damn vishay resistors that run $300. |
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| dnsey |
| Look out for Winkler stud switches. Expensive new, but available as military surplus sometimes. They come with silver- or gold-plated contacts, and are excellent in this application. |
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