National opamp inflation

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#222
Hi Mark,

as there is no plot of transimpedance vs. frequency given in the 49713 datasheet, it seems that (by reconstruction from a set of other plots given and a bit of guesswork and comparison with other CFB parts where this spec is given) the transimpedance corner frequency might be on the order of 10..20kHz -- which would be very nice. Would you mind to comment on that, given your specific insight/knowledge of the part?

- Klaus
 
#223
Hi Tolu,

Yes, that combination for your preamp will be the easiest to implement and will work fine. But you might try the 713 for the first stage also. If the low value input resistor is a problem for you then you could try the non-inverting configuration for the LME49713? May or may not be better than an inverting LME49710. If I were still at National I would have done that test for you! Also for a preamp you should use the metal cans! I will be building a Phono preamp sometime soon so maybe I can get a chance to try a few different combinations but without an AP2 Cascade at home I can only listen and I prefer to measure first to make sure I am not "fooling myself" with unknown non-linearities! Listening is more time consuming than measuring so I like to start with a known condition before spending the extra time in my sound room "working-listening" instead of using that extra time for "fun-listening!"

Anyone have an AP2 for sale or trade?

And...

Klaus,

I will check up on that transimpedance graph question with my "Sources" for you. I know we did not measure that and it is a great question!


Mark / Audioman54
 
#225
Hi Ken,

The schematic was never released but it is very simple and very close to identical to the schematic in AN-1490. It uses the same Darlington packages shown in AN-1490. I believe separate devices instead of the darlingtons would be better though. So if you (or anyone else out there) have any suggestions on other driver pairs I would be excited to try them!...after I find a used AP2 so I could measure the results and then listen to it!

Mark / Audioman54
 
#226
Hi Mark,

Panson is building one with a triple descrite darlington configuration. He're the link: http://www.diyaudio.com/forums/showthread.php?p=1904474#post1904474- Post 136 (I couldn't find a link thing like the old forum, so I hope it works otherwise just cut and paste it into your browser) I doing the same triple idea with a 2sa1381/2sc3503 pre driver, MJE15032/33 driver and NJL4302/NJL4281 output transistor. Using his idea of a seperate VAS board (49811) from the output board I'm also building one with the STD03 darlingtons.

Ken
 
#230
Hi Mark,

No I havent. I'm still waiting for details on my DAC changes, and am looking for a machine shop that will make a bending guide for me for both 8 pin dip spacing, and SOIC pad spacing. I have it designed, just need to find someone with a milling maching to fab it for me.

There's a nice note here at Audio Asylum of positive results of using the TO-99 LME49720:

http://www.audioasylum.com/forums/hirez/messages/26/261252.html
 
#232
audioman54 said:
Tailspin,

Have you used the part yet?

Audioman54 / Mark
Click to expand...

Hi Mark,

I have - in an inverting preamp - just got my dc-servo working for it as well. I'm driving a LME9811 with a predriver/driver/Thermal trak output - just listened to it this past weekend. It's pretty wonderful. Still some bugs to work out in the setup - a relay based input selector kit that isn't working - I seem to be able to get the complicated electronics to work, but, am ready to throw the selector kit in round file...

Ken
 
#233
Tolu said:
Hi Mark

what is your suggestion for a very good line preamp?

e.g.
source -> LME49710 (gain?) -> relay pot (kOhm?) -> LME49713 (gain?) -> output
Click to expand...

I am using sources -> relays -> RC filter -> pot (10 KOhm log, Bourns conductive plastic) -> LME49720 (aka LM4562, non-inverting, gain 2) -> 51 Ohm series resistor -> output

The RC filter sets a pole at 100KHz. There are no coupling capacitors anywhere. Offset is very low ~1 mV. Without the RC filter the pre-amp provides gain to several MHz.
 
#235
glennb said:
I am using sources -> relays -> RC filter -> pot (10 KOhm log, Bourns conductive plastic) -> LME49720 (aka LM4562, non-inverting, gain 2) -> 51 Ohm series resistor -> output

The RC filter sets a pole at 100KHz. There are no coupling capacitors anywhere. Offset is very low ~1 mV. Without the RC filter the pre-amp provides gain to several MHz.
Click to expand...

I think that the LME49720 is lower noise than the LM4562, but only by 200pV!
 
#237
4562=49720

Jackinnj,

The LM4562 and the LME49720 are the exact same part! We added the
LME49720 to the LME series to make the new number sequence make sense. I.e. LMe49710/LME49720/LME49740, single/dual/quad. The slightly different specs are another story...

Mark / Audioman54

PS - Anybody heard of any engineering audio jobs out there? 11 months and no work really stinks!
 
#238
Tolu said:
Hi Mark

what do you mean with that sentence? Could you please explain it?
Click to expand...

What Mark didn't explain is that the the LME49713 is a current feedback op amp. The impedance of the output to negative input must be within a certain range for it to work. One of the benefits of the CFB opamp is much higher bandwidth- on the order of 30 MHz full power bandwidth. And it brings associated challenges like stability etc.
 
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