current amplifying phono stage

[fdegrove]

Hi,

I'm interested to see what happns when you treat a fairly crappy cartidge like the Stanton 680 as a current source operating into a low impedance summing node.

FWIW, the Stanton 68x series aren't even MM cartridges but rather of the moving iron variety.
Not that it would matter for what you're trying to do but still.

Jan Didden used a similar circuit quite a while back as an I-V converter for a 1541 DAC.

Dunno what exactly it was JD did but I know a few reasons why one would go down that road for I/V conversion in a DAC (not all of them) iso using say, a resistor, resistively loaded xformer or the ubiquitous opamps.

Catridges aren't DACs and vice versa....so I second Analog_sa 100% here.

Cheers,

[angel]

Originally posted by john curl
...
This overdamped the MC cartridges. I proved this by rewiring the design to be switchable to either 100 ohms input or grounded base (very low Z) and listened to the difference. 100 ohms input won the contest.

Could you please elaborate as to the sonic difference between the two approaches? There tends to be some differences of opinion about which sound more closely approximates the source. And, I'm curious about whether the sonic improvement was, as you say, due to reducing the cartridge damping, or due to other things, such as increasing the damping of the Q of the inductor, etc..

[patriz]

Just curios to discover if anybody has built any phono from what it has been discussed here?

[Onvinyl]

Originally posted by scott wurcer
Brian - If you want a quick try on this, take the lowest _voltage_ noise CFA you can find, use the cartridge resistance as gain resistor and an appropriate resistor as feedback resistance to get the gain. So if you have a cartridge that measures 5 Ohms say use a 500 Ohm feedback resistor. I don't think any offsets get in the way current or voltage (a few microAmps one way or the other flow in the coil). OTOH you might want to select for lowish Vos or tweek it (pot on the rails with a big divider to the +input, for instance).

Hi,
in my current project (a deviation from rjm's phonoclone), I use the AD811 in the way Scott described here some time ago. I've tried some other chips here, (both cfa and 'normal'), but that one works best. That with -probably Ri-wise- suboptimal DL103.
But, I have a strange issue: without tweaking the offset, I have an input offset of around 0.2 - 0.4 mV. It works with the denon cartridge, but i fear it would fry a cart with say Ri=1 Ohm.
However, if I tweak the offset to zero as described by Scott, the sound gets dull as if the tweeter is missing. Can that be? Or is this something else going wrong?
Rüdiger