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Inexpensive IC based phono preamp for LOMC
http://diyaudioprojects.com/Forum/viewtopic.php?f=10&t=4441
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Author:  gofar99 [ 16 Mar 2014, 08:52 ]
Post subject:  Re: Inexpensive IC based phono preamp for LOMC

I certainly agree. I opened up a few that were already bad and decided it was above my skill and equipment. A stereo microscope and really great soldering gear would be needed.

Good listening
Bruce

Edit: What OM are you using?

Author:  mwhouston [ 16 Mar 2014, 15:48 ]
Post subject:  Re: Inexpensive IC based phono preamp for LOMC

Still a little off thread: it reminds me at one time back in the 60s and 70s guitarist were purchasing expensive acoustic guitars then using a razor blades, shaved the lacquer off. They claimed the guitar sounded better this way. I say find a cartridge or guitar which sounds the way you want and leave it mainly alone. Different stings or a different platter mat are one thing but denuding and lacquer shaving are another.

Author:  Dr.Turner [ 02 Nov 2014, 12:45 ]
Post subject:  Re: Inexpensive IC based phono preamp for LOMC

Hi Bruce, hello everybody,
first of all my compliments for your excellent projects and for this forum, cosy, familiar and very pleasant to read.

I'm would like to build your phono preamp for a Grado Gold mounted in a SME 3009 tonearm on a Technics SL151 MkII using standard MM values of 330R and 47K and OPA2134.
I'm going to build it Manhattan Style i.e. cutting islands on a bare single side copper clad and soldering components directly on the board.
The enclosure will also be DIY and made of double sided copper clad.

I understand that power circuit should be fisically separated from inputs and main circuit.
What about using the bottom of the enclosure as the power circuit board? The ground will be the whole case itself, connected to the circuit only thru' the 150 ohm and 0.1 uF type X2 capacitor.
The main circuit will be raised above the bottom plate by four 1" nylon spacers and placed next to the input/output jacks (isolated from the case) just like your example.

Do you think it will work or, being quite a noob, I neglected something fundamental?

Kind regards,
Dr.T

Author:  gofar99 [ 02 Nov 2014, 14:53 ]
Post subject:  Re: Inexpensive IC based phono preamp for LOMC

Hi, Should work OK. In all mine (4 so far for various uses) I have the DC to DC converter on the same board as the active circuit. In one case within about 3 inches. It is fine. The source for the DC for the converter is external in all but one of the cases. Some are just plain 12VDC wall warts. They do fine. The one exception uses another Meanwell AC (100-240 VAC) to DC (12 V) converter. It is about 6 inches away from the active circuitry. It too is fine. My sense is that if you use a conventional transformer and power supply to power the preamp some additional shielding could be required. That is part of the reason I used DC to DC and AC to DC converters. They operate well above the audio band and any crud they produce is easy to filter out.
BTW you can power it with a pair of 9 V batteries. With a current drain in the 5-7 ma range they ought to last about 20-40 hours (perhaps a lot more).

Good listening
Bruce

Author:  Dr.Turner [ 02 Nov 2014, 15:11 ]
Post subject:  Re: Inexpensive IC based phono preamp for LOMC

Dear Bruce,
I'm going to use a couple of 600mA Li-Ion 9V batteries to power the phono preamp.
I should use the UF 4005 rectifier in the updated circuit just the same?

I will post the progress of my work as soon as teh BOM order will hit my door.

Thanks,
Dr.T

Author:  gofar99 [ 03 Nov 2014, 09:01 ]
Post subject:  Re: Inexpensive IC based phono preamp for LOMC

Hi, The two nine volt batteries would replace the second DC-DC converter and everything in front of it. There is no need for the 12 DC to +/-12 DC converter then. Alternatively you could supply 10-18 VDC to that converter (12V gel cell perhaps) and eliminate the wall wart or if you used one like I did the first AC-DC converter. In that case I would keep the rectifier to prevent accidental reverse polarity connections to the DC-DC converter. The end requirement for the circuit is a clean +/- 9-15 volts DC. I used the Meanwell converters as they seemed to do what I wanted inexpensively and well. No chance of hum from the PS and easy to use. I wanted to hit that magic range of -100 dbv for both MM and LOMC. With a conventional supply the power side would cost considerably more than the pair of converters and the rather few parts that I added to be sure the DC was clean. Batteries would of course be even cheaper and I considered a batch of rechargeable ones with a charger that disconnected when the preamp was in use. Since I always forget to charge stuff....this didn't seem to be a great idea. As shown in the schematic it is quiet and I don't need to do anything special to make it work (replace or recharge batteries).

Good listening
Bruce

Author:  Dr.Turner [ 04 Nov 2014, 03:24 ]
Post subject:  Re: Inexpensive IC based phono preamp for LOMC

Dear Bruce,
so you mean that if I decide to power it with 9V batteries I can feed the OPAMP directly?
No need for:
  1. the Meanwell DC-DC converter
  2. five capacitors and the 150R after the converter itself

Of course two 9V batteries in series will only give +9V...ground...-9V :confused:

But I'm reading mwhouston in this very thread:
Quote:
Go for at least 12V +/-. I achieved this with 3 X 9V batteries, two resistors and a couple of 220uf 16V low ESR caps

What circuit I'm looking for?
I'm not asking for a crash course in electronics (which I should attend, after all...), only a hint and I will do my Google-job.

Thanks.

Author:  mwhouston [ 04 Nov 2014, 05:36 ]
Post subject:  Re: Inexpensive IC based phono preamp for LOMC

Dr.Turner wrote:
Dear Bruce,
so you mean that if I decide to power it with 9V batteries I can feed the OPAMP directly?
No need for:
  1. the Meanwell DC-DC converter
  2. five capacitors and the 150R after the converter itself

Of course two 9V batteries in series will only give +9V...ground...-9V :confused:

But I'm reading mwhouston in this very thread:
Quote:
Go for at least 12V +/-. I achieved this with 3 X 9V batteries, two resistors and a couple of 220uf 16V low ESR caps

What circuit I'm looking for?
I'm not asking for a crash course in electronics (which I should attend, after all...), only a hint and I will do my Google-job.

Thanks.

You need a differential PS.

Author:  Dr.Turner [ 04 Nov 2014, 05:45 ]
Post subject:  Re: Inexpensive IC based phono preamp for LOMC

Thanks mwhouston,
I will report for duty very soon :)

later

Author:  Dr.Turner [ 04 Nov 2014, 07:20 ]
Post subject:  Re: Inexpensive IC based phono preamp for LOMC

Will this work?
I'm using rechargeable 9V batteries that are actually 8.4V

Attachment:
eq12.png


Later

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