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Old 7th February 2013, 02:16 PM   #61
PMA is offline PMA  Europe
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This is the MEASURED frequency response. Both channels (blue and black plots) in same graph. Y-axis is in dB, but please forgive the constant shift (card not calibrated to preamp). At 1kHz, gain is 40dB.
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Old 9th February 2013, 02:16 AM   #62
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Quote:
Originally Posted by PMA View Post
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.
Sorry for another silly question... The 51 Ohm resistors (R3, 5, 9): is the value critical? Since some of them are in the signal path I am tempted to splurge on some nice parts (low tempco, low noise, tight tolerance for matching), and I can get 50R of the type I want to buy, but not 51R. Alternatively I can get some at 51R1 which look OK. I assume a 1 Ohm difference for R3 won't have a significant effect, but R5 and R9 are before and after the RIAA network. Would I be better off getting precisely 51R for those, or would 50R be OK?

Thanks.
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Old 9th February 2013, 03:06 AM   #63
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The 51 ohm resistor are not critical.

The 51R1 you mentioned should be 51.1 ohms which is perfect. Buy a bunch and select the 51 ohm ones if you really wanna get crazy!
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Old 9th February 2013, 06:09 AM   #64
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51R resistor values are not critical at all . Important are resistors and capacitors in the feedback network, indexed 50 and above (150 and above).
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Old 10th February 2013, 03:08 AM   #65
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Pavel,

Is it possible to get board dual mono(if not already built). Up to date , dual mono phono always sound better ! I really don't know why .... but ready to pay extra for.
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Old 10th February 2013, 03:51 AM   #66
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I'm sure Pavel tested between channels and may even have a niffty graph but I think his design is at such a high level of technical performance that going full dual mono would be verrrrrry diminishing returns.

Besides, this is phono! What sort of separation, channel immunity, etc ... do you think you get from the cartridge?

Also, Pavel is a busy guy and this type of audio is just his hobby ... I'm surprized he actually got the PCB up!
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Old 12th February 2013, 02:47 PM   #67
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Default PCB Update?

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Originally Posted by PMA View Post
MLStrand56, not yet as a kit. But PCBs will be available by the end of January 2013.
Here we are at mid-Feb. Any update on the PCB's or kits?

I too would like to see a optional MC stage.

MLStrand56
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Old 12th February 2013, 03:09 PM   #68
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PCBs for OPENAMP1 phono preamp are available. I am sorry but kits will not be available, at least not in near future like 6 months - 1 year. The time I can spend with audio is very very limited.

Pavel Macura audiopage
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Old 22nd February 2013, 03:04 AM   #69
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Crap! That didn't last long. The pricelist lists the PCB selling out on Feb 14!

Yikes, you snooze, you loose I guess.

I've emailed Pavel about a possible next order and will post his response.
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Old 22nd February 2013, 08:37 AM   #70
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I am sorry but I am completely occupied with work on industrial automation projects and plasma spraying. Thus, I really have not enough time for PCB production and distribution to customers, which is time consuming. I have offered the completely open project and I believe that it provides enough information for potential builders, even if they had to design their own PCBs. Sorry for any inconvenience.

Schematics and assembly instructions (in one document) and BOM may be downloaded for free from my webpage:

Preamplifier for MM cartridge
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