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Inexpensive IC based phono preamp for LOMC
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Author:  mwhouston [ 07 Dec 2013, 05:20 ]
Post subject:  Re: Inexpensive IC based phono preamp for LOMC

Just finished another chip based phono preamp. Not as flash as the other. Switch on the back for MM\MC operation but I found enough gain to use it in MM mode with my MC cart. But due to wrong loading the sound was squeaky. Flipping to MC mode gained an instant boost in level and brought the bass back. This one is quieter than the first. Loading for MC is 100ohms which from what I understand suites most MC carts. I usually run mine on the Jean Hiraga biploar MC stage on 45ohms. 100 though is fine. At the front power switch, LED and battery test point on the rear MM\MC switch Input and output RCAs. When in either mode the correct loading is switch in also.

This from scratch took about a day that included drilling etc. I had one fault which was fixed in a few minutes. Sounds OK but need a bigger test when the wife is out playing.
Attachment:
Finished1.jpg
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Finished1.jpg
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Finished2.jpg
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Inside.jpg

Author:  mwhouston [ 08 Dec 2013, 18:03 ]
Post subject:  Re: Inexpensive IC based phono preamp for LOMC

What did help make this build easy (and the earlier one) is a four pole double throw, 4PDT, switch. In one switch you can change the gain (via the FB resistor) and the load. So as I switch from one gain to the other I switch the 100ohm load which I just sit over the 47K MM loading.

With a lesser switch I would need two. One for FB selection and one for loading. So far I am enjoying the preamp. I have a chance for a big listen today.

Author:  gofar99 [ 08 Dec 2013, 22:16 ]
Post subject:  Re: Inexpensive IC based phono preamp for LOMC

Hi Mark, I did the same in one of them. The newest has an array of dip switches to change gain and loading for several cartridges. Not all my LOMC like the same load. I am experimenting with it as a tape head amp. The gain is right and it seems that the tape heads like about a 47k load. I have an internal switch to change from RIAA to NAB. It is promissing.

Good listening
Bruce

Author:  mwhouston [ 09 Dec 2013, 07:23 ]
Post subject:  Re: Inexpensive IC based phono preamp for LOMC

After spending a long afternoon with the second preamp I have to say it is well worth the build. This is from a purely sonic point of view. Simply put, it sound excellent. But it is also well worth the build from a simple project point of view. It is a project which can be assembled in an afternoon and costs little for the components. Even if you have a good phono section, as I have, build yourself one.

The enclosure maybe the greatest cost. Take the cheats way out as I did and run it on batteries. Go for at least 12V +/-. I achieved this with 3 X 9V batteries, two resistors and a couple of 220uf 16V low ESR caps. The PS section can be built on the same piece of cct. brd. as the preamp. It really sounds excellent with my Ortofon Rondo Blue MC cart. Good one Bruce.

Now the bad news. I have a name for the second one.

Author:  gofar99 [ 09 Dec 2013, 08:29 ]
Post subject:  Re: Inexpensive IC based phono preamp for LOMC

....and the name is? I was asked for a name on that one and on the simple tube headphone amp. Suggestions are always welcome.

Good listening
Bruce

Author:  mwhouston [ 09 Dec 2013, 15:33 ]
Post subject:  Re: Inexpensive IC based phono preamp for LOMC

gofar99 wrote:
....and the name is? I was asked for a name on that one and on the simple tube headphone amp. Suggestions are always welcome.

Good listening
Bruce

I'm having the name plate engraved today. I was going to wait until then. But seeing I'm being pressed: "MIMIC". Let's face it that what this that is what this device does. It MIMICs electrically what is encoded in a static grove.

Author:  gofar99 [ 09 Dec 2013, 17:46 ]
Post subject:  Re: Inexpensive IC based phono preamp for LOMC

That's suitable, perhaps Gio could add that to the project title. Since I gave out an Oddwatt T shirt for the last successful name I should send you one.

BTW, I took apart my recently acquired Akai reel to reel recorder. It now has a switchable direct conenction to the play back heads. I feed it into the IC preamp (with NAB equalization selected and high gain / 47K input) and the sound is really nice. The S/N on play back is at least 6 db better than with the original circuitry. LPs recorded directly to it (via the Groove preamp) now play back as quietly as the LP was to start with and the sound is virtually identical to the source.

Good listening
Bruce

Author:  mwhouston [ 09 Dec 2013, 19:48 ]
Post subject:  Re: Inexpensive IC based phono preamp for LOMC

gofar99 wrote:
That's suitable, perhaps Gio could add that to the project title. Since I gave out an Oddwatt T shirt for the last successful name I should send you one.

BTW, I took apart my recently acquired Akai reel to reel recorder. It now has a switchable direct conenction to the play back heads. I feed it into the IC preamp (with NAB equalization selected and high gain / 47K input) and the sound is really nice. The S/N on play back is at least 6 db better than with the original circuitry. LPs recorded directly to it (via the Groove preamp) now play back as quietly as the LP was to start with and the sound is virtually identical to the source.

Good listening
Bruce

By all means use the name. I'm about to pick-up the name plate. I'll put up an image.

Author:  mwhouston [ 09 Dec 2013, 21:53 ]
Post subject:  Re: Inexpensive IC based phono preamp for LOMC

Just in case you missed it first time around here it is again. With "Mimic" name plate.
Attachment:
Mimic.jpg
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MimicII.jpg

Author:  mwhouston [ 06 Jan 2014, 19:11 ]
Post subject:  Re: Inexpensive IC based phono preamp for LOMC

A friend and I compared my second and cheaper build of Mimic to a Cambridge 640P ($200-$300) and we agreed Mimic actually sounded better. Better in the bass and strings sounded clearer. Bruce 'tended to agree that this simple phono stage performs in the league of a $200-$300 commercial unit. Hope you don't mind me quoting you Bruce?

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