home made phono pre?

[daz]

I still have my turntable and vinyl that hasn't been used in i guess 20-25 years. I got a wild hair the other day and pulled it out and surprised to find rubber belt was not rotted and the turntable worked fine. But i couldn't use it because i no longer have a stereo receiver. Question is, what is different about a phono pre than a typical preamp? Is it a impedance thing or can i just use any mixer or preamp who's inputs match well enough? And lastly, anyone know of a schematic for a simple build that will allow me to use it? I want to simply use my PC's powered speakers for it. (high end speakers, not those little junky numbers)

[52 Bill]

I still have my turntable and vinyl that hasn't been used in i guess 20-25 years. I got a wild hair the other day and pulled it out and surprised to find rubber belt was not rotted and the turntable worked fine. But i couldn't use it because i no longer have a stereo receiver. Question is, what is different about a phono pre than a typical preamp? Is it a impedance thing or can i just use any mixer or preamp who's inputs match well enough? And lastly, anyone know of a schematic for a simple build that will allow me to use it? I want to simply use my PC's powered speakers for it. (high end speakers, not those little junky numbers)

The main difference is the addition of the RIAA equalization network.

[Jazz P Bass]

You may be better off simply purchasing what you want.
Having an adjustable output level is a very nice feature.
Phonopreamps.com TCC TC-750LC Details and Hookup

[Jazz P Bass]

A bit of a primer on the RIAA circuit.

When the master record is 'cut' there is a reverse RIAA curve that is applied to the cutting head.

The lower frequencies are reduced in amplitude & the higher frequencies are boosted.

If this circuit was not applied the cutting head would move too far on the bass notes & not enough on the treble notes.
Therein lies the function of the RIAA circuit as applied to the master record.

Now when the actual record signal is retrieved by the magnetic pickup, it is lacking in bass & has too much treble.
The RIAA input circuit restores order by increasing the bass & reducing the treble.

It's kind of interesting that this did not apply at all to the original pickups.
The element was typically a crystal, Rochelle Salt, and it had a 'built in' abilility to restore the bass & treble signals.

So, the RIAA circuit only came about when magnetic pickups where utilized.

[Chuck H]

And are you sure your table doesn't have a preamp built in so that it can be plugged into any modern amplifier with standardized inputs (usually labeled "1, 2, 3, 4" rather than "phono, tape, receiver. aux") Some later models (as turntables go) are already RIAA'd and you can plug them into almost anything.

[Enzo]

Daz, just plug you turntable into a regular preamp input and listen to how it sounds. Probably rather thin. As they said above, the phono preamp is not only more sensitive than the "regular" inputs, but also has a very special EQ.

[g1]

And there are many available for less money than the one Jazz posted, though not adjustable. You can probably buy one for what you would spend on parts to make one.

[olddawg]

A cheapo phono preamp from Frys or off of Amazon is about $19. You can probably have it mailed to your house with free shipping and no tax..... They work fine.

[Enzo]

Radio Shack used to sell them, if they still do and you have a local store blowing out inventory, they might be a deal.

[daz]

Thanks all. I'll look into frys and radio shack. As to whether mine has a built in pre, i don't think so because it's a 70's turntable, one of those phillips with the touch sensitive "buttons". I doubt they had preamps built in back then, plus as i recall i had it plugged into a receiver's phono input.

[km6xz]

You can build one pretty easily since a single dual amp is more than enough low noise gain. At the low frequencies the peak gain needs to bit just a bit over 18db gain and 2 pole high pass filter with high freq shelving point down 36 db. It is simple to design because there are standardized feedback design values that establish the desired multi-inflection point response slope. There are also a lot of DIY'ers experimenting with optimizing it with standard values. Here are some with close tracking to the RIAA curve:
Just use one of these in the feedback loop of an opamp amplifier. A good slew rate will work best. For quietest operation use a pair of 9 volt batteries, and low current opamps.

[Mark Hammer]

Like many "young folks" these days, my older son recently got into vinyl. He asked me if I had a spare turntable, and I dug one up from the basement. "Does your amplifier have a phono input?", I asked him. "Oh yeah, it has every kind of input and output jack.", he assured me. Given that it was less than 5 years old, I had my suspicions, but thought I should take him at his word.

Well, he clearly knew nothing about vinyl. His integrated amp did have a whole lotta jacks, but not a one of them pertained to vinyl and its tiny signal levels. So, I put together a phono preamp for him, of reasonable quality, and he hooked it up. The cartridge and stylus had seem better centuries (Likely last used in 2001). Then, I get a call from him, and in a sheepish voice he asks "Umm, how do I make the tone arm go down?". I guess he had never seen me actually use the turntable. I had to explain to him all the physics of vinyl and turntables, counterweights, stylus tone-arm-mass requirements, etc.

One can purchase turntables that come with a cartridge, and a built in preamp and USB output for converting your favourite vinyl to digital form. While there is much I still love about vinyl, there is no denying that the archival aspects of digital conversion - especially if you own discs you'd like to play a lot but don't want the hassle of the many obligations to attend to for long disc-life and low noise - can be very handy.

It hasn't been raised, and may well never be raised here, but there are three basic types of turntable cartridges. The first was crystal. I had a really nice Philips crystal cartridge back in the early 70's that yielded surprisingly decent tone, with no EQ-ing required. The second is moving magnet - the most common type - which requires both signal level boosting and EQ-ing. The third type is moving coil. This is much less common but apparently yields superior high-frequency response because of the much lower mass internal to the cartridge. There, the coil is moved around by the stylus, relative to the fixed magnet, instead of the coil fixed and the magnet being moved around. However, the yield a coil of sufficiently low mass to permit that lightning-speed movement, fewer turns of wire are used. So the moving-coil type "head amp" provides additional gain to compensate for what the cartirdge can not put out on its own.

In descending order of output signal level, it's crystal, moving magnet, moving coil.

[daz]

You can build one pretty easily since a single dual amp is more than enough low noise gain. At the low frequencies the peak gain needs to bit just a bit over 18db gain and 2 pole high pass filter with high freq shelving point down 36 db. It is simple to design because there are standardized feedback design values that establish the desired multi-inflection point response slope. There are also a lot of DIY'ers experimenting with optimizing it with standard values. Here are some with close tracking to the RIAA curve: [ATTACH=CONFIG]33910[/ATTACH]
Just use one of these in the feedback loop of an opamp amplifier. A good slew rate will work best. For quietest operation use a pair of 9 volt batteries, and low current opamps.

Thanks, but i only posted this question because i was of the belief phono preamps were rather expensive and didn't even bother to look till somone posted you could get them for $20. When i looked after reading that sure enough they can be had dirt cheap and the ones i read reviews on had great reviews for as little as $17 shipped ! So i wouldn't even bother to build one when they are so cheap.

[Mick Bailey]

I've built a few preamps - mainly because I like to build things to my own liking to go with my DIY tube amps - even if they work out more expensive than a commercial product. I always power off 2x9v batteries and this gives a very long life.

Here's a link to the schematic I use;

http://http://phonoclone.com/diy-pho5.html

[g1]

Mick, that link doesn't work, too many http's.
RJM Audio - The Very Simple Phono Stage