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Old 4th June 2004, 07:31 AM   #21
dimitri is offline dimitri  United States
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Dear Upupa Epops,

I never had the intention to offend Dr. Sykora, as I haven't heard anything about the man and/or his designs. I have read many times on this forum that you, Czechs, invented so many substantial things in audio in the past, but - I didn't discuss your self-doubt.

I discussed phonobox as it was manufactured. In it present state it contains obvious engineering flaws.

The owner of the Project is in Austria and the production facility is in Czech. I once found the Czech factory web site, where they wrote that they produce automotive electronics for one German company and Project turntables, phono and headphone electronics as by-product.
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Old 4th June 2004, 08:16 AM   #22
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To Dimitri : I take it only like explanation of all story around this preamp and I haven't anything agaist your name for it . It is only about how blatantly somebody ( and in this czech manufacture is sales manager " old bolshevic pig " ) know to stealed ideas of others. As I know, Dr. Sıkora don't get any penny.
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Old 4th June 2004, 12:47 PM   #23
dimitri is offline dimitri  United States
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>I haven't anything agaist your name for it

sorry this is not my design, I don't associate with it, I just gave an example how manufacturer rips off the customers
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Old 10th June 2004, 09:19 AM   #24
maxg is offline maxg  Greece
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Default You all probably know this already...

But if you open the phono stage you will find 3 sets of jumpers - 2 on either side at the top and one set at the bottom slightly to the left as you look at it.

The top 2 jumpers are for gain, the bottom one for selecting operation for either MC or MM.

If you are running an MM cart (or a high output MC design) you can move the top 2 jumpers and get higher gain for an MM cart.

Works very well and definitely improves the sound (even when you balance out the volume gain with the volume control on your amp).

I have tried this with a variety of cartridges (the standard K4 cart that comes from Project on the RPM4, the Blue Point Special and a Clearaudio Virtuoso 2) and all benefited.

Sharing - just in case there is anyone out there that does not know the trick.
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Old 10th June 2004, 10:51 AM   #25
Zombie is offline Zombie  Sweden
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So...now I've done it!
Put sockets for fast opamp change. Tried both NE5554/TL071 and OPA2134/134, 134 preferred. +/- pins have 0,1uF to ground. Low noise opamps on the way.

Shorted out C7 elco and removed R9, R8 changed to 4k33.

R1 to 560 to give correct load to MC used.

I really wanted to get rid of all the ceramic caps close to the signal path, but didn't have proper sizes of values at hand.

The 4,7uF at the input gives me nightmares, but couldn't find anything better that was small enough to fit in...pointers welcome.

1000uF caps in the power supply as well as shottky diodes. Weird the the + and - sides of the psu aren't the same...

If there's any interest I'll report back what the owner thinks about the changes in terms of sound quality.
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Old 28th June 2004, 08:55 AM   #26
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You can put 1microF Wima MKP (or MKS) instead 4.7 microF electrolytic
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Old 5th July 2004, 05:57 PM   #27
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What do you think about the NJM4580s?
Is it worth replacing them with, say NE5532 or
LM833? Are there other suggestions for
drop-in replacements?
From the specs, NJM4580 don't look too bad to me.
Thanks,
Stephan
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Old 6th July 2004, 07:56 AM   #28
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@Dimitri : when investigating my Pro-Ject Phono Box,
it looks to me like C2 and C5 is pico-Farad instead
of nano-Farad.

Also in the pictures in the PDF they look like
ceramic capacitors, beeing physically to small
to be in the nanofarad-Range.

Especially for C2 in the input section, in series
with R2 /47 kOhm this would have some impact on
the calculations of the input impedance,
as a 47kohm in series with 27 pF will not have
too much effect in the audio band...

In my Phono Box C2 is labeled 27 (underlined),
C5 is labelled 12 (underlined), if they were nano-farad,
the labelling should be n27 or 273 AFAIK.

To me it looks that the purpose of the feedback servo loop
is to create a "virtual" cartridge loading, hence the terminology
"ACTI-DAMP circuit for automatic impedance adjusting"
(badly tranclated from german product description
found on the web).

regards,
Stephan
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Old 6th July 2004, 08:30 AM   #29
Zombie is offline Zombie  Sweden
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Hello!
If the ceramic cap has a low voltage rating, even a 0,1uF ceramic is VERY small...maybe better to measure them?

There is an improvement in sound with OPA604, but more noise, especially in MC mode. The OPA2228 (??) is better

cheers,
T
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Old 6th July 2004, 09:57 AM   #30
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Zombie, thanks for your reply. I will measure them
later because I have to unsolder them for measurement.
But I am quite sure they are pico-Farads.

OPA604 has FET inputs as opposed to NJM4580,
NE5532 etc. Many People advise against changing
BJT against FET Types. Did you try OPA604 in the Phonobox?

Also, im am very intersted in Opinions about NJM4580.
It has good-looking specs in my opinion. Some
posts above there was the advice to change them
to NE5532, to come back to the original design.
I have some thoughts that NJM4580 is somewhat
better than NE5532, from the specs.

Thanks,
Stephan
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