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Old 25th March 2010, 07:13 AM   #1131
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Quote:
Originally Posted by Audiofanatic View Post
Hi Joachim, Jan,

I'm gonna order a few LME49990 and make a nice little amp with them and will post my result when ready.

Thanks for the info!

Best regards,


Audiofanatic
Josť, I don't think they have samples available yet.

jd
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Old 25th March 2010, 07:16 AM   #1132
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When i ordered samples they said that they come from Singapore in 5 to 15 days.
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Old 25th March 2010, 08:30 AM   #1133
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Default Samples

Quote:
Originally Posted by janneman View Post
Josť, I don't think they have samples available yet.

jd
Hi Jan,


I've ordered a few samples yesterday and will have them within a few day's!

So If you want to try them out, just log in and order them asap.

These OPAmp's looks Goooooooood

Gr,


Audiofanatic
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Old 27th March 2010, 02:23 AM   #1134
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I have not posted for a while because i was very bussy building the RIAA Encoder and make it work reliably and precise. That was bigger of a task that this seemingly simple circuit sugests. Finding precise resistors and caps was not easy. I have no problem measuring them to better precission then 0.5% but i got a bit fanatic and had to drive into town many times to buy some and get some from a friend. It is now a wild combination of Wima FKP1, Silver Mica, Dale RS55 and normal 1% metalfilm that i selected out of my waiste bin.
Then i ran into trouble with the servo and then the second amplification stage did not work. The mistake was so ambarassing stupid that i spare you the details. I looked several hours into the box and could not find it. Let me say so much that building this out of double OPamps was not a good idea. After i got it working i found that measuring at that low level over such a wide bandwidth is a challange in itself.
Some hours ago i got it finally working and have first results.
I measured the High Z MPP with Inductive RIAA and in the audible band i found very similar results then what i had measured over the DAAS. The DAAS limits measurements to 20kHz and one of the advantages of this encoder is that i can measure over a much wider high frequency bandwidth.
One very telling test is a 1kHz or even 10kHz quarewave. In an ideal situation the combination of Encoder and RIAA gives a perfectly quare quarewave.
What i found with the Inductive RIAA is a 7dB overshot at over 400kHz. If that is the result of the Encoder or the Inductive RIAA itself i will find out tomorrow.
For other purposes i had build a little wideband linear measurement amp from an OPA627 that should be very flat to over 10Mhz. With that amp and my Sennheiser Tube
Voltmeter i will test the setup.
My next post shows some pictures i collected over the last hours.
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Old 27th March 2010, 02:58 AM   #1135
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Here some pictures. First the measurement setup.
From left : DSD generator, RIAA Encoder in small metall box. 40MHz Digital Scope,
Sennheiser Tube True RMS Meter ( bandwidth 1MHz)
1kHz Quarewave over Encoder, High Z Mpp - Inductive RIAA
1kHz Triangle .... same...
Attached Images
File Type: jpg RIAA Encoder Measurement Setup.jpg (621.7 KB, 303 views)
File Type: jpg 1kHz Quarewave Inductive RIAA.jpg (635.7 KB, 291 views)
File Type: jpg Triangle Inductive RIAA.jpg (626.9 KB, 248 views)
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Old 27th March 2010, 03:04 AM   #1136
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Does it give you the same soft down tilt you got for your Riaa on the DAAS? What was it, something like 0.2dB 10kHz less than 1kHz.

P.S. Dedicated work, congrats. What is the model of your TFT DSO?
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Old 27th March 2010, 03:08 AM   #1137
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Next is the peak at 450kHz and then the level in the audioband.
The Inductive RIAA measured + 0.5dB at 20Hz and then better then +- 0.25dB up to 200kHz so the peak is very narrow.
Attached Images
File Type: jpg 7dB Peak at 450kHz.jpg (634.7 KB, 232 views)
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Old 27th March 2010, 03:12 AM   #1138
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Here is 200kHz and 1kHz.
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Old 27th March 2010, 03:26 AM   #1139
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I have some trouble uploading the files.
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Old 27th March 2010, 03:37 AM   #1140
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I try one more time.
Left: Level at 200kHz
Right: Level at 1kHz

Well uploading does does not work. I try again tomorrow.

Thinking more about the ringing at 450kHz i think the reason is in the Encoder.
The opamp will reach its output swing at some point higher up and then a forth time constant is established.
I will look into that in more depth when i find the time.
Until 100kHz everything seems ok.
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