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Old 5th July 2007, 07:50 PM   #1
Tolu is offline Tolu  Germany
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Default New preamp with LME49710

Hi,

I just finished my new preamp with the LME49710NA from National.

I plugged it to my power amp (Atoll AM 100) and listened my favorite songs. It should replace a not so bad passive preamp TCC TC-754 (80$ class).

Remarkable was the clearness of sound without any noise. So much details did I never heard before. But, something was missing. The warmth and the full sound in the lower mids and the basses were thin and dry. I switched to an OPA604. The sound was much "earthier" and darker but there were no details anymore. Not as good as the TC-754. The sound stage wasn't as deep and wide as with the LME.

So, 100 Euro without satisfaction, or? Is there a possibility to pimp up the circuit or would it better to replace the opamp.

The details in the music were great but I am missing the lower frequencies. Would an OPA627 be better? Or which one is a good compromise between details and warmth?

Has anyone a good working circuit for it?

Thanks

Tolu
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Old 7th July 2007, 03:46 AM   #2
trats is offline trats  United States
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hi Tolu, if you'd prefer to stick to 8-legged single opamps, I'd suggest ad843 as it would give great bass, a fuller sound, yet dynamic with details. Other good singles that I've used are LM6171 and LM7171 (watch the gain, >2), but these are more neutral sounding than ad843. Carlosfm's ad815 is much better than any of the above, http://www.diyaudio.com/forums/showt...255#post480255
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Old 7th July 2007, 07:51 PM   #3
Tolu is offline Tolu  Germany
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For better understanding, here is my thin sounding circuit:
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Old 8th July 2007, 04:02 AM   #4
trats is offline trats  United States
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Tolu, have you tried 100n bypass instead of 1uF, and also 100-470n from +v to -v. Btw, the other ends of 49.9k/470p/1k are grounded on the pcb, right? So, the gain = 4x in the preamp. I'd first try a lower gain, say, 2x or just use the LME49710 as a buffer.
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Old 8th July 2007, 08:10 AM   #5
Tolu is offline Tolu  Germany
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Quote:
Originally posted by trats
Tolu, have you tried 100n bypass instead of 1uF, and also 100-470n from +v to -v. Btw, the other ends of 49.9k/470p/1k are grounded on the pcb, right? So, the gain = 4x in the preamp. I'd first try a lower gain, say, 2x or just use the LME49710 as a buffer.

I haven't tried 100n instead of 1F, but what do you mean with 100-470 n from +V to -V?

What do you mean with the other ends of 49.9k/470p/1k are grounded? It is like on the picture. Eingang stands for Input and Ausgang for Output. There is only the Input and the Output Cinch grounded and the rest as on the pic.

The gain is 4x. Do you think gain x1 will warm up the sound?

Regards
Thomas
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Old 8th July 2007, 08:44 AM   #6
Tolu is offline Tolu  Germany
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Oh sorry, I know what you mean with grounding the input section!

I had a look on the original circuit drawing and found that I had forgotten the grounding for Input section and the feedback resistor. But it works although! I am no electrician but a business man so I have sometimes problems of understanding!

What will be the effect of grounding correctly? With an OPA604 there is enough bass. I tried the OPA604 in Class A mode (I took Pin 5 in replacement for Pin 6). It sounded very good but there was very much noise and plops when the cd player stepped from song to song! The missing ground could be the reason, or?

Regards

Thomas

OFF TOPIC

Dear mods,

when can you make an own preamp section in the forum?
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Old 24th June 2011, 05:43 AM   #7
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I HAVE USED LME49710 AS LINE PREAMPLIFIER WITH GREAT RESULTS.YOUR CIRCUIT IS WRONG.YOU MUST GROUND THE OTHER END OF 49,9K.ALSO BYPASS THE SUPPLY WITH SMALLER CAPS,SAY 100NF.YOU MUST ALSO CONNECT IN SERIES TO OUTPUT A 47-100R RESISTOR TO ISOLATE THE IC FROM CAPACITIVE LOADS.TRY THESE AND...NO PROPLEMS,IT SOUNDS GREAT.
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Old 24th June 2011, 11:02 AM   #8
SY is offline SY  United States
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It might help if you turned off the "caps lock" so it doesn't seem like you're SHOUTING.
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Old 20th December 2011, 12:27 PM   #9
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hi,

would like to build this preamp using LME49710HA (they probably would perform even better than NAs). The scheme mentioned is very simple and reminds me the one that is used in Grado RA1 headphone amp. However I have still few questions to clarify, maybe someone could help

1. Input section.
So it should be grounded as on Grado's scheme. What blue alps pot should be used? 20k or 100k?

2. PSU. Would lm317-337 circuit be fine with this preamp? Also what caps should be used to bypass the supply? Now it's 1uf mks, 100uf elko, 10n fkp. Should I add 100n also? Would it be fine to feed the preamp with +-12v?
Quote:
Originally Posted by ARTISAND View Post
ALSO BYPASS THE SUPPLY WITH SMALLER CAPS,SAY 100NF.
3. Output
Quote:
Originally Posted by ARTISAND View Post
YOU MUST ALSO CONNECT IN SERIES TO OUTPUT A 47-100R RESISTOR TO ISOLATE THE IC FROM CAPACITIVE LOADS.
What does that mean?

To lower the gain to 2-3x 3k resistor on the scheme above should be less, right?
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Old 22nd December 2011, 07:40 AM   #10
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anyone
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