Schematic for Pro-ject phono box - Page 2 - diyAudio
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Old 2nd June 2004, 05:42 AM   #11
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Location: Croatia
My phono-box.
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Old 2nd June 2004, 05:55 AM   #12
Zombie is offline Zombie  Sweden
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Good morning Dio!
Looks cool!
Did you replace the opamps or any other capacitors? If you did the mods above (or other mods), what effect did it have on the sound?

Cheers,
Tom
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Old 2nd June 2004, 06:05 AM   #13
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I replace:
R12 with 1,5kohm
R10 with 220 ohm
C1 with 1mF WIMA MKS4
cut R9 from mass
put 10microF and 100nF near OP-amps
Replace filter capacitors with 2200 microF
bypass regulators with 100nF
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Old 2nd June 2004, 06:14 AM   #14
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Little mistake,

Cut R9 on left side of schematic and put it to mass.
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Old 2nd June 2004, 06:18 AM   #15
Zombie is offline Zombie  Sweden
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Hello Dio!
mass = ground? 0V?
Did you replace the opamps?

Tom
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Old 2nd June 2004, 06:20 AM   #16
Werner is offline Werner  Europe
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Default Re: Modding the phonobox?

Quote:
Originally posted by Zombie

Earlier some people suggested there were some "faults" in the circuit, is there anything one can do?
Just about everything in the Phonobox is either wrong or just stupid and wasteful engineering. Just what went on in the mind of the 'designer' is something I can not grasp, when it is perfectly possible to make with 50% of the parts and just two 5534 opamps something that outperforms this one easily.

Keeping the circuit and dropping in expensive opamps and capacitors makes things only worse, as such parts should be put to better use.

Dimitri goes some way to redressing the circuit errors present.

I would go further: throw away the innards, keep the box and the power supply, and put in any of the simple opamp-based phono circuits that circulate here on the forum.


A DC servo fed back to the cartridge input ... sjeeeez ....
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Old 2nd June 2004, 06:28 AM   #17
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Location: Croatia
mass=ground

I don't replace OPamps.
It's possible to replace JRC4580 with better dual ultra-low noise OP maybe OPA2227 or something...
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Old 3rd June 2004, 11:03 PM   #18
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Location: Prague,Czech Republic
Default Stupid thing

This preamp comes not from fa Project, but from my friend Dr. Sıkora and I was the first, which was build it. In original was there two NE 5534 and in servo loop TL 071. As input cap was there foil polyester, any bipolar. This connection is about sixteen years old and was designed ASAP cheapest. When it was new, in many comparisions every win against all preamps in tests. Later it was published in one Czech electronic magazine and was ( and still is ) in our country very popular. Probably from this magazine it was stealed by fa Project and later reduciert to the form, which show Dimitri. This amp is very simple, but have very good sound and noise parameters thanks to " active damping " ( very low current noise ). Dr. Sıkora is not fool - to this time he develope many better preamps - in this time he's working for fa Clearaudio.
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Old 4th June 2004, 05:41 AM   #19
Zombie is offline Zombie  Sweden
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Hello Upopa!
Very interesting information. Have you got a link to the original schematic?
Have you tried to "restore" the phonobox to the original Sykora?

Cheers,
Tom
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Old 4th June 2004, 07:05 AM   #20
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Location: Prague,Czech Republic
Default Stupid thing, part two

To Zombie : " restoration " is easy. Resolder both opamps and get there precidip sockets. If is PCB made for dual opamp, get there NE 5532 and instead 061 give 071 ( or AD 711, LF 411 etc. - any low noise JFet opamp with low offset ). Change input cap, get there PP or PES with the same value. With NE 553. family of opamps is SNR of this connection in MM mode better than 86 dB, which is 1 dB up theoretical value of noise of typical MM pickup ( 85 dB ). This preamp is noise optimalised for MM pickups, in MC mode is it " only " 68 dB ( noise floor is refered to 5 mV and 0,5 mV ). Value of others devices stay the same, but on output give serial resistor 100 R for better stability. That's all. Now exist better solutions, I will try to get it on this pages - it is not exist in electronic form.
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