current amplifying phono stage

[BrianL]

Onvinyl:

"if offset is no problem"

OPA2604s are FET-input. You really don't need to match the
impedances to compensate for bias currents as they are
essentially zero. Also, the resistors you need are equal to
roughly half the cartridge coil's resistance which is pretty
small for the MC cartridges. You're not likely to budge any
DC offset by fiddling with pots on the +inputs.

Could the low interest in this thread be because most people
don't "get it"? I see that there are at least two audiophile/engineers
reading and commenting, both of which are involved in high-
performance semiconductors as a profession.

-----

Scott: That's "BB/TI", not "TI/BB" ! ;-)

I agree that the photodiode ap-note is not that relevant

[peranders]

Originally posted by Onvinyl
Hi,
Recently, I finished (?) my version of the la bohème stage
www.klaus-boening.de

Can you show us pictures of your unfinished(?) work?

[Onvinyl]

Hi,

I get my digital back in few days, meanwhile, here is a
detail:


Rüdiger

[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).

Originally posted by BrianL
Onvinyl:

"if offset is no problem"

OPA2604s are FET-input. You really don't need to match the
impedances to compensate for bias currents as they are
essentially zero. Also, the resistors you need are equal to
roughly half the cartridge coil's resistance which is pretty
small for the MC cartridges. You're not likely to budge any
DC offset by fiddling with pots on the +inputs.

Could the low interest in this thread be because most people
don't "get it"? I see that there are at least two audiophile/engineers
reading and commenting, both of which are involved in high-
performance semiconductors as a profession.

-----

Scott: That's "BB/TI", not "TI/BB" ! ;-)

I agree that the photodiode ap-note is not that relevant

[peranders]

I think this is a rather interesting topic. What happens if you take out the current from the pickup with no voltage across it (= zero Ohms inimpedance) compared to "measuring" the voltage (=high inimpedance) and take out no current?

[sreten]

Originally posted by peranders
I think this is a rather interesting topic. What happens if you take out the current from the pickup with no voltage across it (= zero Ohms inimpedance) compared to "measuring" the voltage (=high inimpedance) and take out no current?

Theoretically not much except the inductance comes into play much earlier.

For my MC15 inductance is not given but I believe its 50uH to 100uH.

Lets assume 100uH (50uH) with specified DCR of 6R.

F3 = 9.6KHz. (19KHz)

Which ties in with recommended loading of > 20R.

F3 = > 40kHz. (80Khz)

sreten.

[EC8010]

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.

[SY]

AD797 might be a good choice.

Funny, though, the 797 designer uses discrete FETs in his phono stage.

[peranders]

Originally posted by sreten


Theoretically not much except the inductance comes into play much earlier.

For my MC15 inductance is not given but I believe its 50uH to 100uH.

Lets assume 100uH (50uH) with specified DCR of 6R.

F3 = 9.6KHz. (19KHz)

Which ties in with recommended loading of > 20R.

F3 = > 40kHz. (80Khz)

Didn't you misunderstood me? What happens if the load is zero ohms, using a true I/V amp?

[Werner]

As said, not much happens: the record plays, the music flows ...

I tried Scott's suggestion years ago with AD811 or LM6181, using an Ortofon MC25FL. Worked rather nicely, but I abandoned the scheme because I desire more flexibility/compatibility from an MC-preamp. And anyway, I changed over to a medium-Z medium-output cartridge shortly after.