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Old 22nd February 2006, 07:03 PM   #1
VEC7OR is offline VEC7OR  Lithuania
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Default My (semi-)reference preamplifier

Long ago I've been thinking about adding a serious preamp to the system, because I want to have a turntable, casette (for "compartibility") and a tuner.

This project is reference wannabe

Ok, the features:

6 channel relay input selector
6 channel relay tape-return selector (most likely I will have this one separate, to select any source, in case I want to record stuff)
128 step (7bit) logarithmic relay attenuator (0.5dB or 1dB per step)
4 level 2 band(treble/bass) relay switched tone control (most likely -3dB 0 +3dB +6dB settings)
RIAA stage for turntable (I know how the curve looks but dont have any idea how this gonna look like)
Built in 3-way crossover (modules are already built, http://images.bite.lt/banga/files/cl...635138c408.jpg)
Level indicators for all channels ? (maybe?)

It will be controlled by static logic IC's (nothing fancy here, no need for MCU, no noises from MCU clock etc.)

Stainless steel case.

I plan using AD797 for input stages (RIAA corrector maybe) for low noise floor, NE5532 elsewhere (BJT input, low noise, besides I like the sound of it), Wima caps in signal circuits, SMD film resistors (the whole thing will be pretty much SMD), russian RES80 sealed, metal can, small signal, gold contact signal relays.

Pretty much all, details of each block in the following posts.
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File Type: png preamp-block.png (29.8 KB, 3022 views)
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Old 22nd February 2006, 07:12 PM   #2
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Relays.
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Profanity took a very interesting form in Russia where there exists a language of sorts, most of its words based on four basic profane roots - nouns p...is, wh.0.e, c..t and verb f..k. It is possible to sensibly communicate using just these four basic roots.
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Old 22nd February 2006, 07:25 PM   #3
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Random brain noise.

Some ideas how relay switched tone stack will work.
Finite state automata for it.
How preamp will pretty much look.
Some ideas how to make good looking buttons for it.
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File Type: png preamp-ideas.png (91.0 KB, 2447 views)
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Old 22nd February 2006, 09:33 PM   #4
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Basic attenuator block.
Exact resistor values to be found.
I plan using these blocks:
(0.5?) 1 2 4 8 16 32 64dB
Maybe instead of 128dB max I'll use 96dB.
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File Type: png attenuator-block.png (6.6 KB, 2109 views)
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Profanity took a very interesting form in Russia where there exists a language of sorts, most of its words based on four basic profane roots - nouns p...is, wh.0.e, c..t and verb f..k. It is possible to sensibly communicate using just these four basic roots.
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Old 22nd February 2006, 09:37 PM   #5
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Logic based volume controller with preset, basically 2 reversive asynchronous counters + some logic to ensure that counters dont roll over 0000000 and 1111111.
4 (or maybe 5) upper bits will be fed to (several) 4-to-16 decoders and will display volume as a lighted tick.
Quadrature decoder to be added.
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File Type: png vol-controller.png (27.0 KB, 2244 views)
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Old 22nd February 2006, 09:39 PM   #6
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Input selector blocks.
Uses some D-latches. Simple.
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File Type: png input-selector.png (20.8 KB, 2072 views)
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Old 2nd March 2006, 09:26 PM   #7
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Pretty standart PSU.
I still think about using discrete regs for +/- 15V lines.
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File Type: png preamp-psu.png (31.1 KB, 1949 views)
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Profanity took a very interesting form in Russia where there exists a language of sorts, most of its words based on four basic profane roots - nouns p...is, wh.0.e, c..t and verb f..k. It is possible to sensibly communicate using just these four basic roots.
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Old 2nd March 2006, 09:29 PM   #8
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Tone stack controller, uses 3 simple logic ICs to allow simple +/- control, can be extended to more levels, but i think 4 is sufficient to slightly adjust tonal balance.
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File Type: png preamp-tonestackcontrol.png (18.7 KB, 1892 views)
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Profanity took a very interesting form in Russia where there exists a language of sorts, most of its words based on four basic profane roots - nouns p...is, wh.0.e, c..t and verb f..k. It is possible to sensibly communicate using just these four basic roots.
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Old 2nd March 2006, 09:33 PM   #9
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4 led indicator for each tone stack section. Will use 74LS15X (dont remember exactly which one, but the double 2-to-4 decoder)
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File Type: png preamp-tonestackindicator.png (14.0 KB, 1820 views)
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Profanity took a very interesting form in Russia where there exists a language of sorts, most of its words based on four basic profane roots - nouns p...is, wh.0.e, c..t and verb f..k. It is possible to sensibly communicate using just these four basic roots.
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Old 2nd March 2006, 09:37 PM   #10
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32 led "tick" to indicate current volume level, pretty straightforward using 2 4-to-16 decoders + inverter.

Analog parts coming soon.
Probably I will need help on what to use in the RIAA section, I dont even know what preamp is needed for MM/MC, and what is the difference on amplifying those, how much gain, eq ?
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File Type: png preamp-voldisplay.png (39.9 KB, 1873 views)
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Profanity took a very interesting form in Russia where there exists a language of sorts, most of its words based on four basic profane roots - nouns p...is, wh.0.e, c..t and verb f..k. It is possible to sensibly communicate using just these four basic roots.
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