LME49990 design note - Page 3 - diyAudio
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Old 9th October 2012, 10:46 PM   #21
BigE is offline BigE  Canada
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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.
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Old 10th October 2012, 12:10 AM   #22
ahaja is offline ahaja  Poland
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You can try solder RC combo on the rca socket.
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Old 10th October 2012, 12:20 AM   #23
BigE is offline BigE  Canada
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ok.

I only have a mica 470pf. Hopefully that will solve the problem, and I can get some good ones later...
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Old 10th October 2012, 01:22 AM   #24
BigE is offline BigE  Canada
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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.
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Old 10th October 2012, 04:51 AM   #25
qusp is offline qusp  Australia
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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.
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Old 10th October 2012, 12:20 PM   #26
BigE is offline BigE  Canada
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What can you do without a ground plane?
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Old 10th October 2012, 12:25 PM   #27
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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
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Old 10th October 2012, 02:50 PM   #28
qusp is offline qusp  Australia
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Quote:
Originally Posted by BigE View Post
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
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Old 10th October 2012, 08:58 PM   #29
BigE is offline BigE  Canada
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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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Old 11th October 2012, 02:59 AM   #30
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Quote:
Originally Posted by BigE View Post
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
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