Any phono pre-amp recommendations? - Page 2 - diyAudio
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Old 26th August 2003, 05:29 PM   #11
Electrons are yellow and more is better!
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Quote:
Originally posted by MarcelvdG
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.
Oops, I read it too fast
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Old 26th August 2003, 06:15 PM   #12
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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.
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Old 27th August 2003, 09:20 PM   #13
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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.
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Old 28th August 2003, 08:03 AM   #14
Electrons are yellow and more is better!
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Quote:
Originally posted by MarcelvdG
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. My vinyl amp has a very pleasant low noise level even for MM catridges.
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Old 28th August 2003, 08:44 AM   #15
Electrons are yellow and more is better!
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I think the datasheet of LT1115 has two good basic solutions you should study.

check also Rod Elliott's designs
http://www.sound.au.com/

http://www.borbelyaudio.com/
http://www.wnaudio.com/
http://www.hagtech.com/
http://www.tanker.se/lidstrom/

http://www.fortunecity.com/rivendell...o/aaphono.html
Thorsten Loesch is pushing his stuff (see above) but El Cheapo isn't so cheap. I can agree of most things.

http://www.klaus-boening.de/
http://home.no.net/andiha/articles/audio/riaamp.htm
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Old 28th August 2003, 09:15 AM   #16
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Peranders, over what bandwidth and with what source impedance did you measure your MM noise and SNR? Was that with or without A-weighting?
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Old 28th August 2003, 10:11 AM   #17
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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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Old 28th August 2003, 12:33 PM   #18
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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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