A couple weeks ago, I posted something about a tiny, stereo, preamp that could possibly be used an interface between the laptop computer's earphone out and the PSR-3000's auxiliary input, something to boost the inadequate power of the keyboard's input. The preamp I found was very compact, about half the size of a package of cigarrettes and in kit form sells for $12.99 U.S.--dirt cheap. According to the specifications, it provided a 50X signal boost to tiny signals so they could be sent to a power amp.

After spending 3 hours with a soldering iron assembling the preamp on its tiny printed circuit board, something I have not done in more than 40 years, the completed project was hooked up to a power supply and plugged into the appropriate systems.

The bottom line is it is too powerful. I had to turn everything down to it's lowest level to prevent distortion, and even then it was still too much. It works just fine for amplifying a phonograph turn-table pickup, or even the tiny signal emmited from a tape recorder's playing heads, but from the laptop it's just too much. And, there were no adjustments to lower the amplitude. Oh well, back to the drawing board.

BTW: I'll happily sell it to anyone that wants it for $20. Keep in mind, it's a raw printed circuit system that is not in any type of case.

Cheers,

Gary

Gar:
I sorta get what you're trying to do. Sounds like you almost made it except too much boost. Not to swift on these things myself, but maybe on the output of the little amp a pot to lower the output? or on the input side to lower the signal to amplify???
Sounds like you had fun though.....Pose

Yes, a poti between line-out and ground. So the poti's slider represents the new output (I recommend to buy a stereo-poti)...
This is the more comfortable solution.

You can also solder a little resistor to each of the stereo line-out channels (100 ohm might be enough if not, try higher values) to damp the signal just a little bit (like it was done with older headphone outputs). This is the cheaper solution.

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Greetings from Frankfurt (Germany),
Sheriff ;-)

I have a few stereo trim pots around the workshop, and that's the next logical step. Just have to find time to do it, which is more difficult than performing the actual task. Too many irons in the fire I guess.

Cheers,

Gary

Gar:

What the hey, solder one of them Iron's on the end might be just the right amount of R or steal the Pot out of the wife's Iron. Let us know how it turns out?
Pose

If it is an "op-amp" pre-amp circuit then you ought to be able to reduce the gain by lowering the value of the feedback resistors.

If however it is an RIAA equalised pre-amp (for bringing a phono cartridge up to mixer level) then this may no be feasible.

Have you got a circuit diagram, and do you have any idea how much gain you really need?

There is no op-amp--it's totally transistorized. Very simple circuit, just too much power, which is something unusual in this industry.

I rigged it with a stereo pot on the input side, and I did solve some of the problems, however, it was obviously not designed for the application for which I had hoped it would apply. Consequently, I had a good offer from Bill Grosse in Alabama, and I packed it up to be shipped to him in the morning. Bill has a lot more time, expertise and patience than I, and maybe he can come up with something.

Thanks for the response everyone,

Gary

Aren't there plenty of preamps that would work?
I have Sansamps, A mizpad 9, fishman pre-amps, etc. I use most for preamps for instruments, like uprights, or acoustic guitars with a pieso and no pre-amp. DOD makes one the size of a guitar pedal with controls that let you vary the signal.

The Mixpad 9 has stereo ins and outs, with pots.

Just a suggestion..

Russ

Russ,

If you can, post a link to the preamps you were talking about.

Gary

http://www.musiciansfriend.com/srs7/g=home/search/detail/base_pid/180616/ Is that what your talking about?

Phil

Phil,

Those devices you posted the link to are available locally and do not do the job. They're intended for turntables that do not have a built-in preamp and do not have the correct impedience or any volume controls. They can be purchased for $29 at a nearby electronics store.

Gary

Gary...you'd want to look at these things, and any full-line music store would probably have the DOD, Fishman and Sansamps. Haven't seen the Mixpad 9 for a while, and it may be a little overkill, but I think Berringer has a small unit with impedence pads, one LXR and one stero input for under $50.00.

Russ