Any phono pre-amp recommendations?

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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
 
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.
 
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.
 
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.
 
Konnichiwa,

bm_mode said:
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:

http://www.diyaudio.com/forums/showthread.php?s=&threadid=14904

These should get you started....

Sayonara
 
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/ampins/discrete/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.
 
In the moving-magnet mode, the circuit in the LT1115 data sheet is a good example of a grossly suboptimal design with respect to noise. The LT1115's current noise (with unmatched impedances driving the + and - inputs) is much too large for a moving-magnet cartridge. Replace the LT1115 with Self's discrete op-amp or with an OPA627 and you get a reasonably good MM amplifier.
 
I thought that I make a few points about this thread.
First, most MM cartridges today don't have as much inductance as early types. Think it through. As the effective stylus mass is reduced by improved design, then very high inductance will tend to roll-off the cartridge too much. This, of course, must be balanced by higher effective output, per turn, to make up for any lost inductance. Most MM cartridge manufacturers have addressed this issue, so that it is not much of a problem, anymore.
Second, NEVER put a 100 ohm resistor in the gate of a 2SK147. You will compromise its noise significantly, and increase high frequency non-linear distortion.
Third, it is usually best to use a FET input op amp or discrete design, so that no added current noise or DC base current is put through the phono cartridge.
I will leave it at that. Good luck, and have fun.
 
MarcelvdG said:
In the moving-magnet mode, the circuit in the LT1115 data sheet is a good example of a grossly suboptimal design with respect to noise. The LT1115's current noise (with unmatched impedances driving the + and - inputs) is much too large for a moving-magnet cartridge. Replace the LT1115 with Self's discrete op-amp or with an OPA627 and you get a reasonably good MM amplifier.
LT1115/1028 is not optimal I'll guess for MM pickups (better for MC) but it's not noisy in a practical circuit. :no: My vinyl amp has a very pleasant low noise level even for MM catridges.
 
Seeing as how opamp based ccts have come into this discussion anyway I'll throw my hat into the ring.

A while back in the search for a ludicrously simple phono amp i stumbled across the kits link at the bottom of the diy site and followed it to Lidstrom audio where they had the following:

I built my first version using +/- 12v battery power and kept the feedback resistor to ground at 10 ohms but incresed the load of the feedback RIAA network by 10 times (resistors up by x10 and caps down by x10) to give me sufficient boost for MC purposes.

Not the last word at present but it's currently implmented with really cheap caps and resistors and NE5534's. Still sounds good though. i believe there's alot of potential for tweaking.

My next build will keep the same schmea as I'm using now but with Caddocks, Auricaps and AD797's.

food for thought and WAAAY simple

Drew
 

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For MC use, current noise of bipolar inputs is not as important as voltage noise (source impedance reasons). I've had trouble getting FETs to work well without some heroic efforts. What DID work well was the AD797- extremely low voltage noise and extremely high PSRR, which takes a lot of criticality out of the power supply design.

For MM, I'm still a tube guy, though I'll admit that there's FETs in my preamp, too.
 
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