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Old 31st December 2012, 02:23 PM   #31
PMA is offline PMA  Europe
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Quote:
Originally Posted by PMA View Post
3rd image is a noise plot of the preamp with real turnatable and cartridge Shure M35X connected to the input.

The results are:
.
.
.
- noise level of the preamp with input connected to the real turntable cartridge is -90 dBFS
I have a new measurement of the noise level of the preamp connected to the turntable and cartridge. The previous one was done on the prototype placed in a provisional case. The new measurement is made with preamp and PSU in a final case 19" 1U, one can see improvement in the noise level a HF resonance pickup.
Attached Images
File Type: png openamp1+SL1200+M35X_new.PNG (82.1 KB, 389 views)
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Old 3rd February 2013, 03:33 AM   #32
mlloyd1 is offline mlloyd1  United States
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PMA:

Just curious - why you chose not to add the R-C at the output that ADI used to "tighten" the RIAA accuracy at high frequencies.

I like the design by the way. I use something similar but using some old National buffers I like that are now NLA - the LM6321.
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Old 3rd February 2013, 10:46 AM   #33
PMA is offline PMA  Europe
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Hi mlloyd,

something similar is done by R2 + C2 (at the input). This prevents the gain plot from remaining at 0dB at high frequencies. I want to maintain "strong" output, and the circuit works well even into 50 ohm or 32 ohm. 2nd reason not to add resistance is to keep 51 ohm output impedance (and thus low influence of interference in case one uses the 50 ohm coax.).

Anyway, it is the cartridge inductance that dominates in overall HF behavior.
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Last edited by PMA; 3rd February 2013 at 10:49 AM.
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Old 3rd February 2013, 01:28 PM   #34
mlloyd1 is offline mlloyd1  United States
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understood. thanks.

mlloyd1
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Old 4th February 2013, 01:13 PM   #35
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Wow! Great project PMA, thanks so much!

Well thought out, well engineered, good design cycle, exact testing, thorough documentation ... even nice pictures!



Oh yeah, and kick-*** performance!

I absolutely LOVE the idea of plugging headphones straight into this! It seems so obvious in hindsight --- beefier output to drive lower-noise feedback and enough output for ... headphones! Brilliant!

It doesn't get any more direct than that! Forget cables, forget preamps, forget extra amplification/current stages ... s i m p l i c i t y !

Now, I've got to find that headphone extension cord for my shorter headphones ...

PMA:
"Normally, OPA627AP/BP and APG4/BPG4 should be OK. Let's hope they are genuine. I have built my preamps from the old stock of Burr-Brown OPA627AP genuine components, but unfortunately I have no more pieces. "

Could you say more about these different grades and production runs of 627? How do we tell them apart? (Or should this be another thread?)

Here's my old ones:
old OPA627AP.jpg

Cheers,
Jeff

Last edited by AudioLapDance; 4th February 2013 at 01:22 PM.
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Old 5th February 2013, 01:02 AM   #36
nezbleu is online now nezbleu  Canada
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Hi Pavel:

I am having a little trouble with the BOM. You list part numbers for Farnell and something called GME. I am not familiar with the latter and have been unable to locate them. I am familiar with capacitor types FKP2 and and X7R, but what does CF3 mean? Under the columns "Library" I assume something like "C-5" means 5mm lead spacing, is that correct? Are the CF3 caps just polyesters of the appropriate lead spacing? I assume 50V or better is sufficient for all the capacitors? Resostors: all 1% metal film, 1/4Watt OK?

Thanks.
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Old 5th February 2013, 02:19 AM   #37
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.. Under the columns "Library" I assume something like "C-5" means 5mm lead spacing, is that correct? ...
Nice! 2.5, 5, 5.5, 7.5mm!

Quote:
Originally Posted by nezbleu View Post
...Are the CF3 caps just polyesters of the appropriate lead spacing? I assume 50V or better is sufficient for all the capacitors?
openamp1_1_orig.JPG



C4.jpg

105J63

Cornell Dubilier, Film Capacitors, Polyester , 1 uF, 5 %, 63 V, 7.5mm

167105J63C-F Cornell Dubilier | Mouser


Last edited by AudioLapDance; 5th February 2013 at 02:21 AM.
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Old 5th February 2013, 07:25 AM   #38
PMA is offline PMA  Europe
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Quote:
Originally Posted by nezbleu View Post
Hi Pavel:

I am having a little trouble with the BOM. You list part numbers for Farnell and something called GME. I am not familiar with the latter and have been unable to locate them. I am familiar with capacitor types FKP2 and and X7R, but what does CF3 mean? Under the columns "Library" I assume something like "C-5" means 5mm lead spacing, is that correct? Are the CF3 caps just polyesters of the appropriate lead spacing? I assume 50V or better is sufficient for all the capacitors? Resostors: all 1% metal film, 1/4Watt OK?

Thanks.
Hi nezbleu,

sorry for confusion. GME is a Czech store GM electronic - elektronika, kterou znáte... and parts with their code are not critical. All resistors are metal film 1% 0.4 - 0.6W. CF3 is a MKP (polyester) capacitor. Arcotronics R66 preferably. C-5 means 5mm spacing, C-7.5 means 7.5mm spacing etc. Critical parts are FKP (polypropylene caps, WIMA) and parts from Farnell or RS components.
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Old 5th February 2013, 07:26 AM   #39
PMA is offline PMA  Europe
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AudioLapDance,

thanks for your kind words and for your help!

Your OPA627AP look OK (I hope). I am attaching a photo of the genuine OPA637. (but 637 MUST NOT be used in this phono preamp).
Attached Images
File Type: jpg OPA637.JPG (38.4 KB, 255 views)
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Last edited by PMA; 5th February 2013 at 07:32 AM.
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Old 5th February 2013, 01:03 PM   #40
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Maybe we should start a new thread about the 627, I'm sure others (not building PMA's phono) would want to know! What should it be called, "Genuine OPA627?" or "Are your OPA627 real?" in order to get their attention!

Sorry, I haven't been in the industry for a while, I don't get why there is an issue? Did production change to "china" at some point or is there just that much counterfeit? Was there a buyout and then production standards changed? What is going on?

Can you tell by the codes?

My 627
0104WM4410

So is this 2001, 04 month (April), at the WM plant, 4410?
Or is it the 44th week, 10th production run

Your 637
34ZKPB7

?!?

Cheers,
Jeff

PMA, I also have some more technical questions about the use of 627. Should I start a new thread for that?

Last edited by AudioLapDance; 5th February 2013 at 01:11 PM.
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