RIAA preamp/headhpone amp combo
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mezzman

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I am planning on building a phono preamp/headphone amp combo for a friend who owns a record shop. He has numerous turntable 'stations' where customers can listen to vinyl before buying. At the moment he's got the little Radio Shack mini-stereo amps hooked up, but the pots on the unit just aren't up to the heavy use and give out rather quickly. The RS amps also have uneeded line level inputs as well as an unsused power amp that just wastes electricity.
I would like to be able to offer him a solution based on the following cirteria:
- Heavy duty construction
- AC powered
- better sound quality than rat shack
- budget oriented

I have found a few circuits for the RIAA preamp side that look pretty good, now I need a good headphone section. I am considering a Cmoy type, the low parts count/simple design looks like it will do the trick so far.
I'd like to know if a decent quality, robust pot exists that will suit this type of project. I'm not looking for an ALPS pot, something a little more economical and tough.
If anyone has a few pearls of wisdom regarding something like this, please let me know, as I am trying to gather as much info as I can (lots of R&D ahead!) to make this box work.
I hope I'm correct in assuming that I can just pass the output of the RIAA pre into the inputs of the Cmoy without incidence. Could it be this easy?
 
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TimSchirmer

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I'm no expert, but i think you might be able to incorporate a Mosfet headphone amp (headwize project) with one of the better diy phono stages out there these days.

Just an idea.
 
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mezzman

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Hmmm, although the MOSFET design looks pretty straightforward (and cheaper), I am worried a little about the heat output. I plan on using a fairly heavy guage metal box, so perhaps I can use the enclosure as a heatsink. I do like the fact that it can run on a single rail power supply, makes it easier to use an external wall-wart type transformer to keep the enclosure size to a minimum.
 
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eric343

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Consider buying some "Fake Alps" stepped attenuators and wiring them up with removable connectors for rapid replacement when/if necessary. Dirt cheap ($6/ea), gives the "Hi-Fi" stepped attenuator feel, and tougher than probably anything else in the pricerange.
 
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mezzman

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I had thought about those, but the price is a little too high for this project. At the moment I'm looking into the Panasonic EVJ series.
 
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eric343

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Good luck; those things are not fun to desolder when you need to replace them (it's not terribly difficult to ruin them by cranking the knob too hard) and I don't believe they use standard spacing that would let you use header strips.
 
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geom_tol

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For the headamp section I would make a cmoy type amp. But use an opamp that can be run from single powersupplies. This is by far the simplest amp you can make, it is also very economical and sounds great if you use a decent opamp and powersupply.

For the phono preamp I don't really have alot of ideas... I know Walt Jung published some nice circuits in his latest opamp applications book. They're high performance though so they will cost alot more than the headamp.
 
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gavinbirss

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Hello mezzman

More about the shop ...

Tell me more about the shop.
Does he also sell records?
What products that he sell ?
Is there perhaps a web site I can visit on his shop ?



It may also be important to know what headphones will be used in conjunction with the record stations.

This will help in designing a well matched headphone amp.

Also are the record players Moving Coil, Moving Magnet or Grado Moving Iron. The loading R/C values for most high end MC and MM cartridges differ quite alot. So if there is more that one cartridge brand and type the loading will change.

Maybe you can try looking at the Analog Addicts El cheapo phonostage

here is two links :


The Vinyl Zone

fortune city

Note that a battery supply is recommended for this design.

Good luck on your design.

Gavin

 
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rickcr42

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Simple rules (KISS-keep it simple stupid) but still gotsta sound good soooooo..................



easy build but great sound , i use this presently for my vinyl.Due to the high gain you MUST put this baby in a shielded box and keep ALL AC away.

Run it straight into



OF course what else


Set the gain at X10 to cover various headphone brands , power the whole thing with a "wall wart" based power supply to get the +12 volt for the preamp and and the +/- 12 volt (artificial ground split supply) for the headphone amp

Simple,effective,low cost,great sounding

rick "missing in action moderator"cr42

Edit=DAMMIT



I had a feeling that link would not work ! (yahoo groups file).What it was MEANT to be is a simple two jfet (per channel) RIAA phono stage,three jfets for mc operation.Very few passive parts.If interersted email me and I can get the schema to ya

Rickamondosuarusrex
 
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