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Inexpensive IC based phono preamp for LOMC
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Author:  gofar99 [ 04 Nov 2014, 08:29 ]
Post subject:  Re: Inexpensive IC based phono preamp for LOMC

Hi, What Mark is showing will work, but I have one running very happily on just 2 nine volt batteries. The IC will run fine down to about + and - 5 volts. Not much headroom there though so +/- 9 is better.

Good listening
Bruce

Author:  Dr.Turner [ 04 Nov 2014, 09:11 ]
Post subject:  Re: Inexpensive IC based phono preamp for LOMC

Great Bruce!
From the spec sheet I read a minimum Operating Voltage Range of +/-2.5V and now your "on the field" confirmation gives me peace of heart. I will use two 8.4V rechargeable batteries.

Since I've already ordered the Meanwell converter I will give the (WW + DC-DC) a try also.

Kind regards

Author:  mwhouston [ 04 Nov 2014, 16:52 ]
Post subject:  Re: Inexpensive IC based phono preamp for LOMC

Dr.Turner wrote:
Will this work?
I'm using rechargeable 9V batteries that are actually 8.4Vr

Perfect.

Author:  Dr.Turner [ 16 Nov 2014, 03:20 ]
Post subject:  Re: Inexpensive IC based phono preamp for LOMC

BTW, since I don't see any volume pot in the project, how are you setting the volume with this preamp?

Do you feed the output into an integrated amplifier via the AUX input.
Do you have a power amplifier with volume pot?

Please share your experience/setup.

Later,
Dr.Turner

Author:  mwhouston [ 16 Nov 2014, 06:14 ]
Post subject:  Re: Inexpensive IC based phono preamp for LOMC

Dr.Turner wrote:
BTW, since I don't see any volume pot in the project, how are you setting the volume with this preamp?

Do you feed the output into an integrated amplifier via the AUX input.
Do you have a power amplifier with volume pot?

Please share your experience/setup.

Later,
Dr.Turner

Pots do not belong in phono preamps. Nor do they belong in pure power amps. True integrated amps with a proper pre-amp section, maybe.

Author:  Dr.Turner [ 16 Nov 2014, 07:01 ]
Post subject:  Re: Inexpensive IC based phono preamp for LOMC

I had a feeling the question wasn't top rated smartwise :)
Anyway, what's your setup (when you eventually need to turn the volume down)?

I may connect our phono preamp to the Main Input in a Sansui AU-555 and AU-777A or Power Amp Direct of a Denon PMA-1500AE.

But for a true integrated amplifier (without pre-main separation, like the Sansui AU-222 or the AU-101) which is my best bet?
And if I would like to listen to my couple of Rotel RB-980BX brifged mono power amplifiers, what's your suggestion to set the volume?

Later,
Dr.Turner

Author:  Dr.Turner [ 16 Nov 2014, 07:09 ]
Post subject:  Re: Inexpensive IC based phono preamp for LOMC

Last question and I will be quiet for a while...

I run out of 0,1uF axial poly cap but I have plenty of Panasonic X2 radial poly cap.

May I use two of them to replace the following:
  1. the one between the AC-DC wall wart and the Meanwell DC-DC converter
  2. the one on the +12V after the Meanwell

Later,
Dr.Turner

Author:  gofar99 [ 16 Nov 2014, 08:56 ]
Post subject:  Re: Inexpensive IC based phono preamp for LOMC

Hi, In those locations they are used to bypass electrolytics and polys will do fine. Often better. In my projects where I specify a particular type of capacitor, like the X2 ones connected to the AC mains other types should not be used. Same for coupling capacitors if a "poly" is shown then that is the best type for the application. In other locations it is pretty much users choice. I prefer and generally only use polys when I build things, the exception is for values over 5uf then electrolytics are pretty much mandatory and as I mentioned the X2 ones.


Good listening
Bruce

Author:  Dr.Turner [ 16 Nov 2014, 09:32 ]
Post subject:  Re: Inexpensive IC based phono preamp for LOMC

Thanks Bruce,
I've noticed that, in your August 8th 2014 update, you replaced the 470uF (on the +12V) with a 100uF.
I'm curious about the reason.

Later,
Dr.Turner

Author:  gofar99 [ 16 Nov 2014, 14:26 ]
Post subject:  Re: Inexpensive IC based phono preamp for LOMC

Hi, I don't see that particular version (I'll look in my other files). The value for that capacitor can range widely. I used 470s and 1000s. So if I bunged up and listed one at 100.....it really should have been 1000uf. I prefer to over filter rather than under filter. The converters ....particularly the second one really clean up the DC and since the current is small and essentially constant filtering is easy. Sorry for the confusion

EDIT: I found the error and indeed in one version of the schematic a 100 did show up in the place of the 470. OOPS. It should be 470uf.
EDIT: A revised schematic is attached.
Good catch

Good listening
Bruce
Attachment:
LOMC IC Phono NAB Preamp November 17 2014.jpg

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