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Old 8th April 2012, 06:03 PM   #381
BigE is online now BigE  Canada
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Anyone try AD797 in place of OPA627?
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Old 10th April 2012, 01:11 AM   #382
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Hey Erik,
I think there are a number of drop-in replacements (although they may not be the same package type) for the OPA627/637.
The AD825 is supposed to be quite good and many people seem to prefer it, although there would need to be an adapter to the DIP package in my case.
Otherwise, how about the OPA134 or OPA132? There are a bunch of LM op-amps as well, but I have no experience with them..too bad the other op-amps I have on hand are all duals (I have several 2134 from a CMOY I built!)
There is a fairly long thread about op-amps here, although they are discussing dual opamps
The Best Sounding DUAL opamps
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Old 10th April 2012, 09:31 AM   #383
ahaja is offline ahaja  Poland
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AD797 is not good in this application. Needs another values of feedback resistors.

Good for 1st and 2nd stage are LME National opamps, or for 2nd fet opamps.
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Old 10th April 2012, 12:17 PM   #384
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How about the LME49713? It looks like a good candidate - I ended up using DIP carriages rather than soldering in the 627/637. I wonder if I could just get the TO-99 package and put the legs into it, although I see that it's 3 times the price on digikey over the SOIC package...
byron
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Old 10th April 2012, 01:13 PM   #385
ahaja is offline ahaja  Poland
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LME49713 - this is current feedback opamp. Not for this application. See datasheet.
It's very good in passive riaa as an output stage.

Here - LME49710, very good LME49990 specially as a 1st stage (very low noise).
Or AD8065 but requires max 2x12V supply - 2nd stage. Faster with greater output current.
I think it's much better than OPA627/637 which are overrated. ;-)
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Old 10th April 2012, 01:17 PM   #386
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OPA627/637 are like Black Gate N type, not too many people understand how to use them properly

OTOH, why not try OPA27: Phonoclone 3
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Last edited by Peter Daniel; 10th April 2012 at 01:20 PM.
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Old 10th April 2012, 04:53 PM   #387
ahaja is offline ahaja  Poland
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Yes. ;-)
For example LME49990 has 5 times less noise than OPA627/637.
That's why it should be used as a 1st stage in this application with low source impedance - or another bipolar opamp.
For the same reason fet opamp (627/637/132/134/8065 etc.) should be used in a 2nd stage. Here impedance seen on the inputs is much higher.

All about it is written in great book about phono preamps - Amazon.com: The Sound of Silence: Lowest-Noise RIAA Phono-Amps: Designer's Guide (9783642197734): Burkhard Vogel: Books

BG N & 627/637 are not only recipe for very good sound.

;-)
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Old 23rd May 2012, 01:55 PM   #388
kor952 is offline kor952  Netherlands
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Default More gain.....

If there is more gain needed (+ 15dB), for instance when a Denon DL-103 is used, it is possible to change the second stage as follows.

R2 = R3 = 1k8
R4 = R6 = 1M
R5 = 100k
C2 = 3.3nF
C3 maybe the same (10uF) but may be changed to a 4.7uF

The gain of the first stage is R1 / cart. imp. x loss factor (due to the parallel RIAA cap)

For a DL-103 this will be 1620 / 40 x 0.9 = 36.45 x

The gain of the second stage is R5 / R3

For the original this will be 33k / 3.3k = 10 x

For the modified 15dB + version this will be 100k / 1.8k = 55.55 x

Output of a DL-103 with the original components = 0.3mV x 36.45 x 10 = 109 mV

Output of a DL-103 with changed components = 0.3mV x 36.45 x 55.55 = 607 mV

Difference in output is 14.9 dB

If you want less gain change R2 and R3 to a higher value, for instance 2.2k instead of 1.8k gives -1.74dB (0.818x) less gain.

RIAA filtering will not change while the values of caps and resistors are switched.


My 2 cents,

Ronald.

Last edited by kor952; 23rd May 2012 at 02:06 PM.
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Old 23rd May 2012, 03:47 PM   #389
jtktam is offline jtktam  Canada
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Peter.. is this still available for purchase?

-joe
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Old 26th May 2012, 12:02 PM   #390
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Yes, the boards are still available and I can supply most of the components as well.
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