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Old 25th August 2003, 01:06 AM   #1
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Question Any phono pre-amp recommendations?

Hi,
I've acquired for free the parts to make a power-supply putting out 24-0-24 DC (max 200mA), which I can add some regulators to. I thought it might be suitable for a phono pre-amp. Does anyone have some recommended circuits that would suit such a power supply. I'm after something preferrably with discrete componenets (though not essential), decent sounding, and cheap/easily available components.

I realise that some of the Pass Labs stuff would be excellent, if I had a better power supply - I'm going to make an Aleph Ono some day soon.

Cheers
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Old 25th August 2003, 10:49 AM   #2
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If you want a discrete amplifier for moving-magnet cartridges with very low noise and you are not in a hurry, there will be one published in Electronics World for October 2003. It needs well-regulated +/-14V or +/-15V supplies, so with a couple of 15V regulators, it can work on your supply.

In general, I think there are many published RIAA amplifier designs working at +/-15V, so with a 7815 and 7915 added to your supply, you should have plenty of choice.
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Old 25th August 2003, 12:34 PM   #3
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Could you develop this a little bit more (without telling too much if you're allowed)?
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Old 26th August 2003, 06:40 AM   #4
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Peranders, I guess there is no harm in telling you things that were already published in a letter to the Editor I wrote some time ago. Anyway, I wrote an article about noise optimisation of RIAA amplifiers for moving-magnet cartridges. A simple way to account for all the frequency dependencies in the source impedance, transfer of the amplifier and transfer of the ears of the listener is derived in the article. Besides, it contains an example of a discrete RIAA amplifier which, with a practical cartridge as the signal source, adds less noise than any RIAA amplifier with a 47kohm resistor shunted across its input. To obtain this low noise, its 47kohm input resistance is realised by combining different types of feedback, which is a common technique in RF electronics but which is rarely used in audio equipment.
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Old 26th August 2003, 11:24 AM   #5
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I'll guess you already have seen the very good application note from National which turns this subject up side down? The conclusion is that a MM cartridge generates around 1.3 uV noise. My personal reflexion on this is that it's not that hard to design sufficiently low low RIAA amp these days.

http://www.national.com/an/AN/AN-104.pdf
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Old 26th August 2003, 12:14 PM   #6
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It's a little irritating that you can't edit your post after 30 minutes. I forget words sometimes or write them twice (also in swedish!)

I ment low noise...not low low...

Quote:
Could you develop this a little bit more (without telling too much if you're allowed)?
I ment _not_ allowed.
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Old 26th August 2003, 01:38 PM   #7
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I just browsed through the application note. It seems to me that that 1.337uV is the total noise, cartridge and amplifier, of their example RIAA amplifier. Only 343.8770129nV comes from the cartridge itself. With my approximations, assuming a frequency independent effective series resistance of 1350 ohm (which is not correct for a practical cartridge by the way), I'd find a RIAA and A-weighted cartridge thermal noise of 265.2431129nV. The difference is probably due to the fact that they assume a treble boost in their example.

I agree that it's an interesting application note and I hadn't read it before, as far as I remember. Thanks for the link.

Anyway, there are many extremely suboptimal moving-magnet RIAA amplifiers around, so apparently it is not that easy. The most common error is designing an amplifier with a way too large input noise current.
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Old 26th August 2003, 03:36 PM   #8
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Default Re: Any phono pre-amp recommendations?

Konnichiwa,

Quote:
Originally posted by bm_mode
Does anyone have some recommended circuits that would suit such a power supply. I'm after something preferrably with discrete componenets (though not essential), decent sounding, and cheap/easily available components.
While I would not start building a Phonostage from the angle you apply, there where some recent threads that discuss a variety of circuits (including some of mine) that would be suited.

I PERSONALLY will have to recommend the "El Cheapo" as a good starting point. Fitted with Burr Brown OPA637 and with a suitable supply it is EXTREMELY good for a solid state design based on Op-Amp structures (discrete r monolithic makes virtually NO difference other than political/demagogical).

El Cheapo Thread from way back when....

For cheapness the OPA604 is suitable and does not sound too horrible, but it is jolly noisy for my taste, but then again, not ecessively so in view of the source noise which is only slightly lower than the Op-Amp noise.

Another thread covering simple discrete circuits is here:

Simple MM only RIAA preamp

These should get you started....

Sayonara
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Old 26th August 2003, 04:04 PM   #9
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Default Discrete opamp

If you want to maximize the difficulties but have the satidfaction of pulling off something tough try the following:

A check out and built a couple of discrete opamps, (example: http://www.dself.dsl.pipex.com/ampin...te/discrop.htm). you can find a number of these by "googling" or just check out sound.au.com (Project 07).

B- wrap circuitry around it from a source like the TL1115 data sheet or any opamp based design.

Sounds dumb, but in AudioXpress a few issues back someone did that principly to set a baseline for evaluating so opamp based RIAA preamps. The discrete opamp was a Pass design.

WARNING: This is easy for me to suggest all this as I gave up on vinyl years ago. So what I say should be taken as idle talk over a couple of beers.
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Old 26th August 2003, 04:06 PM   #10
sam9 is offline sam9  United States
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Default oops

"TL1115" should read "LT1115"
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