Schematic for Pro-ject phono box

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That pretty stupid thing is here:
 

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Modding the phonobox?

Hello!
I'm thinking about modding or improving the Phonobox.
I have some OPA604, 134 and 637 in my box, are they drop-in replacements?

There are some ceramic caps on the card, too. And elcos
:smash:

Earlier some people suggested there were some "faults" in the circuit, is there anything one can do?

What about increasing the output level a bit?

Got some experience with modding CD:s so difficult jobs don't scare me :clown: - I totally lack theoretical skills, but understand schematics, so if ou can help me - thanx!

Tom
 
Re: Modding the phonobox?

Zombie said:

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 ....
 
Stupid thing

This preamp comes not from fa Project, but from my friend Dr. Sýkora 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. Sýkora is not fool - to this time he develope many better preamps - in this time he's working for fa Clearaudio.
 
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. :cool:
 
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