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Old 21st April 2004, 01:32 PM   #21
Onvinyl is offline Onvinyl
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EC8010:
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You really don't want to use a FET input op-amp in this application. As a broad generalisation, FET op-amps are dominated by voltage noise, whereas bipolars are dominated by current noise. When you use a moving coil cartridge as the source, its low source resistance means that the current noise hardly develops any voltage, meaning that bipolars are quieter. AD797 might be a good choice.
The Nature of Noise (ehm...) and the right choice of op-amp was a topic in the asylum thread as well. There wasn't a consent conclusion, so I'm looking foward to build a hack next weekend (hopefully...) and see how things perform, trying out the opa2604 I have around.

Maybe a discrete topology of this approach might work well, but that is way beyond my capabilities.

Rüdiger
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Old 21st April 2004, 01:35 PM   #22
Onvinyl is offline Onvinyl
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Werner,
did you try it with frozen cart? Balanced? What is your issue with the lack of flexibilty?

Rüdiger
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Old 21st April 2004, 02:07 PM   #23
Werner is offline Werner  Europe
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Single-ended, no frozen cartridges. As if I had cartridges to waste ...

Compatibility? I have cartridges of 5 Ohms, and I have cartridges of 150 Ohms or so. See?
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Old 21st April 2004, 02:41 PM   #24
Onvinyl is offline Onvinyl
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Werner:
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As if I had cartridges to waste ...
If they are wasted or not, is a main topic of the discussion

Rüdiger
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Old 21st April 2004, 03:03 PM   #25
analog_sa is offline analog_sa  Europe
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current amplifying phono stage
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If they are wasted or not, is a main topic of the discussion
It certainly is an interesting topic. I think Kinergistics had a loony variation using a whole lot of junk in the NFB loop. An MC cart, a tape head, lots of poor solder joints and god knows also what. From the reviews it sounded amazing on some recordings (probably on bad ones) and dreadful on others.

JR's concept makes a lot more sense. I'll be very interested in your findings. Maybe we'll all start buying cartridges in pairs
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Old 21st April 2004, 05:44 PM   #26
sreten is offline sreten  United Kingdom
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Quote:
Originally posted by peranders

Didn't you misunderstood me? What happens if the load is zero ohms, using a true I/V amp?
Just exactly as I stated for the first case.

Its a voltage source driving the coil resistance and inductance
into a short circuit, output is current.

The F3 is stated for current output, not voltage for the first case.

For the second case output is effectively voltage, though there's
no reason you can't add a series resistor to the cartridge to drive
the virtual earth point, in this case F3 is also for current output.


sreten.
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Old 21st April 2004, 06:32 PM   #27
sreten is offline sreten  United Kingdom
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I'll also add a cartridge body in the feedback loop will be next to
useless to balance the cartridge inductance by a factor of the gain.

Plain commonsense engineering should prevail here.

Using the cartridge DCR as one resistor in a shunt feedback
arrangement, effectively the cartridge driving the shunt feedback
virtual earth point, so gain depends on cartridge DCR will roll
off the treble, particularly for highish output MC's.

Its not for nothing MC's have recommended minimum loading.

sreten.
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Old 21st April 2004, 07:05 PM   #28
Elso Kwak is offline Elso Kwak  Philippines
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Lightbulb Balanced MC amp

Hi, the Moving Coil catridge is a natural for balanced operation. You will need some kind of instrumentation amplifier.
http://db.audioasylum.com/cgi/m.mpl?...04&r=&session=
Replace the noisy zener by 5 LEDS in series. Now we are talking about REAL HIFI!! etc.,etc.
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Old 21st April 2004, 07:10 PM   #29
platenspeler is offline platenspeler  Netherlands
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Hi,

I'm listening to this amp at the moment. I use a LT1115 for input opamp and OPA 637 for the second one (my cartridge is Dynavector DV17 with DC resistance of 38 Ohms).

I have another pair of AD797 which I want to try as well, but the LT1115 does quite well. In fact, I'm listening to it right now (Pink Floyd, Delicate Sound of Thunder playing)

About a second cartridge in the feedback loop ... can anybody help me explain to my wife why I would buy a "dummy" cartridge somewhere in the box?

Maarten
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Old 21st April 2004, 07:12 PM   #30
john curl is offline john curl  United States
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The summing resistor to lower impedance was part of my JC-1 patent, first submitted in 1974. We have gone away from short circuiting the input for MC's, because it usually sounds worse than a higher impedance in modern MC cartridges.
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