Ancient phono preamp

[walkad]

Instead of buying a readymade phono preamp for transferring vinyl records to computer for burning to CD, I want to use a stereo preamp kit I bought many years ago. Unfortunately I have misplaced the circuit diagram, parts list and instructions.

The kit was originally published in Electronics Today International (July 1976) as kit ETI 445 using dual opamp LM382N.

I have the PCB and most of the components but the board overlay does not have any markings re components.

Does anyone know how I might obtain a copy of the circuit diagram?

Otherwise I'll start again with a much more uptodate version of a phono preamp.

Thanks.

 

[stevez]

Something I recall, but know very little about is RIAA (I think) equalization or compensation. I think that this had to do with the fact that a record did not capture sound uniformly across the audio spectrum and that some compensation was made in the electronics and possibly by the recording industry, (Recording Industry ...., RIAA). You may want to be sure your system accounts for that.

 

[Chippie]

Have a look here:

https://www.electro-tech-online.com/custompdfs/2009/10/LM382PDF.pdf

and here:
https://www.angelfire.com/sd/paulkemble/sound4.html about half way down the page

 

[chemelec]

Hopefully this will help?

**broken link removed**

This is the LM381, which is the Single Op-Amp Version of the LM382.
So use the proper pins accordingly.

 

[audioguru]

Something I recall, but know very little about is RIAA (I think) equalization or compensation. I think that this had to do with the fact that a record did not capture sound uniformly across the audio spectrum and that some compensation was made in the electronics and possibly by the recording industry, (Recording Industry ...., RIAA). You may want to be sure your system accounts for that.

RIAA equalization reduces recording of low frequencies because they take up a lot of space on a vinyl record and the recording cutter cannot move much. The low frequencies are boosted back to normal during playback.
The high frequencies are boosted during recording then they are cut (and the hiss is also cut) during playback.

 

[walkad]

Many thanks, Chippie and chemelec for the info on LM382. The Paul Kemble link was particularly helpful - not only the history of preamps but also the details of LM382 circuits and the later improved LM833 which I used in a preamp some years ago.
I enjoyed your website, chemelec, and as I am also retired I have time now to try out some of your devices. Audioguru and Stevez, your discussion of RIAA equalization was concise and enlightening -thanks.
Regards
Walkad

 

[tblo163]

Don't know if this will help!I have been transfering old video cassetts to dvd,with success.I have been using AVS4YOU programs for all my burning projects,you only need to pay for one,and you get the other 30 applications free,I simply connect my old VCR to my computer and capture the contents,then convert them to the format required.

 

[walkad]

The end of the story

I ended up building a magnetic cartridge pre-amp using LM833 dual op amps.
But there was an unacceptably high level of white noise.
I contacted Chemelec who suggested 0.01µF caps between the power pins and earth.
With the caps in place there was a noticeable drop in white noise. The gain control on the preamp means that the signal level can be reduced so that the white noise is insignificant.
Thanks again to all for your help.

 

[bountyhunter]

I ended up building a magnetic cartridge pre-amp using LM833 dual op amps.
But there was an unacceptably high level of white noise.
I contacted Chemelec who suggested 0.01µF caps between the power pins and earth.
With the caps in place there was a noticeable drop in white noise. The gain control on the preamp means that the signal level can be reduced so that the white noise is insignificant.
Thanks again to all for your help.

This isn't really a good home project. magnetic phonos have such a low voltage level that noise is a real problem. The aftermarket ones usually come in a shielded box.

On side note: I wonder ifthere is some software out there that could take the "flat" output from a mag cartridge amplified and let you apply the RIAA equalization in the software. The PYRO audio processing software I have can do all kinds of amazing things for equalization and noise elimination.