LME49990 design note - Page 3

BigE · 9th October 2012, 10:46 PM

Thanks for the drawing ahaja!

A pic of the boards is in post 19 here.

The Phono Stage

The dual hole marked SG is signal ground on the phono board. This is connected to power supply common between C4 and C5. This is also where the TT ground is connected.

Here, signal ground SG = power PG = TT gnd.

The input is directly above it. Cap C1 is connected *behind* signal input. I am going to connect the RC network between the two holes marked SG and IN.

ahaja · 10th October 2012, 12:10 AM

You can try solder RC combo on the rca socket.

BigE · 10th October 2012, 12:20 AM

ok.

I only have a mica 470pf. Hopefully that will solve the problem, and I can get some good ones later...

BigE · 10th October 2012, 01:22 AM

RC network in place.

No significant change with the OPA627 - I did not break it....

Need parts for bypassing the LME49990 at the adaptor level. This is the next step.

Will keep you posted.

qusp · 05:07 AM

yeah well in the headphone amps and low power poweramp designs by opc he gets essentially perfect results (-160db with all spurs under -148db) heres comprehensive measures of the headphone amps (only the SE-SE and BAL-SE are using the lme as front end) no rail to rail bypasses, just main slightly 'remote' 330uf polymer caps, 10uf X7R ceramics on the buffers rails and 1uf on the 49990 rails, both directly on or very close to the pins and shunting to the solid ground plane. with good PCB layout and careful wire/connection routing, there is no need for so much parallel capacitance.

BigE · 10th October 2012, 12:20 PM

What can you do without a ground plane?

sachu888 · 10th October 2012, 12:25 PM

Hi,
If you see closely my DIY CNC phonostage,you will find 4 (yello colour) .1uf 50V multilayer Ceramic caps very close to Opamp socket pins.They are there to stop oscillation from Opamps.

Regards,
Sachin

qusp · 10th October 2012, 02:50 PM

Quote:

Originally Posted by BigE

What can you do without a ground plane?

use a solid piece of copper foil and make it your ground plane, or you can buy soic adapters that already have bypass cap positions

BigE · 10th October 2012, 08:58 PM

Could you tell me please, where can I find those soic adapters?

The goal here is to replace a socketted opa627 with the LME49990.

I got my LME49990s pre-mounted from proto-advantage.com. They are Canadian, and ordered the opamps for me, thus extreme shipping costs.

sachu888 · 11th October 2012, 02:59 AM

Quote:

Originally Posted by BigE

Could you tell me please, where can I find those soic adapters?

The goal here is to replace a socketted opa627 with the LME49990.

I got my LME49990s pre-mounted from proto-advantage.com. They are Canadian, and ordered the opamps for me, thus extreme shipping costs.

Hi,
Cheapest I have found here 2* Dual SOIC to DIP-8 Convert PCB Adapter SMD OPA627 | eBay
BTW PM me if you want to try CNC MM Phonostage ,(see my signature)This is the best Phonostage I have ever heard and can be built under $50.

Regards,
Sachin

10th October 2012, 12:10 AM	#22
ahaja diyAudio Member Join Date: Oct 2004 Location: Poznań	You can try solder RC combo on the rca socket. __________________ Dual mono preamp Turntable

10th October 2012, 04:51 AM	#25
qusp is choosing a less facetious title... diyAudio Member Join Date: Oct 2009 Location: Brisbane, Australia	yeah well in the headphone amps and low power poweramp designs by opc he gets essentially perfect results (-160db with all spurs under -148db) heres comprehensive measures of the headphone amps (only the SE-SE and BAL-SE are using the lme as front end) no rail to rail bypasses, just main slightly 'remote' 330uf polymer caps, 10uf X7R ceramics on the buffers rails and 1uf on the 49990 rails, both directly on or very close to the pins and shunting to the solid ground plane. with good PCB layout and careful wire/connection routing, there is no need for so much parallel capacitance. Last edited by qusp; 10th October 2012 at 05:07 AM.

10th October 2012, 12:25 PM	#27
sachu888 diyAudio Member Join Date: Jul 2010 Location: Nashik	Hi, If you see closely my DIY CNC phonostage,you will find 4 (yello colour) .1uf 50V multilayer Ceramic caps very close to Opamp socket pins.They are there to stop oscillation from Opamps. Regards, Sachin __________________ CNC super high end DIY MM Phonostage DIY Simple Active Preamp

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9th October 2012, 10:46 PM	#21
BigE diyAudio Member Join Date: Aug 2008 Location: Toronto	Thanks for the drawing ahaja! A pic of the boards is in post 19 here. The Phono Stage The dual hole marked SG is signal ground on the phono board. This is connected to power supply common between C4 and C5. This is also where the TT ground is connected. Here, signal ground SG = power PG = TT gnd. The input is directly above it. Cap C1 is connected behind signal input. I am going to connect the RC network between the two holes marked SG and IN.

10th October 2012, 12:20 AM	#23
BigE diyAudio Member Join Date: Aug 2008 Location: Toronto	ok. I only have a mica 470pf. Hopefully that will solve the problem, and I can get some good ones later...

10th October 2012, 01:22 AM	#24
BigE diyAudio Member Join Date: Aug 2008 Location: Toronto	RC network in place. No significant change with the OPA627 - I did not break it.... Need parts for bypassing the LME49990 at the adaptor level. This is the next step. Will keep you posted.

10th October 2012, 12:20 PM	#26
BigE diyAudio Member Join Date: Aug 2008 Location: Toronto	What can you do without a ground plane?

10th October 2012, 08:58 PM	#29
BigE diyAudio Member Join Date: Aug 2008 Location: Toronto	Could you tell me please, where can I find those soic adapters? The goal here is to replace a socketted opa627 with the LME49990. I got my LME49990s pre-mounted from proto-advantage.com. They are Canadian, and ordered the opamps for me, thus extreme shipping costs.

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