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In the Forum: Off Air Audio
In the Thread: Rohde & Schwarz EU-6201 Tuner

Post Subject: The Schwarz runs from crystal oscillator!Posted by Romy the Cat on: 8/27/2011

It was a bit tricky to make it works. The Schwarz original crystal is imposable to get and the new one that I got from ICMC had different internal capacitance, so I was forced to shut them with additional inductance to let the oscillators to fire up in the Schwarz circuit. As the result I have the tuner frequency reference running from pure, super stable, ultra low noise oscillator. The Schwarz has internal capacity to measure the output of crystal oscillator and to fine-tune the tuner’s front end to the same frequency reference. That is very good but the greatest thing is that by flipping a switch on the front panel I can defeat the quartz oscillator with fix frequency and to engage the local electronic oscillator that follows the returnable front end. This is the ultimate thing that might be done in a Superheterodyne tuner.

Now, leaving all technical nuts and bolts aside the main question is: how the Schwarz driven from crystal oscillator sound different compare to the Schwarz driven from the local oscillator? This is $64000 question, isn’t it? Well, the jury is still out about it. The difference is near negligible. I would say that the difference does exist but it is so insultingly small that it in a way defeats all my efforts I spent. I have short fragments that recorded with both oscillators, I can post it and you will be a judge. This test is one more indication of how superbly Rohde & Schwarz is built that a crystal oscillator can’t overperform the unit local electronic oscillators. Dima explained to me that the quality of the Schwarz’s post oscillator filtration and the all silver retuning capacitors is so high in Schwarz that he is not surprised with my results. Well, the question I ask then is why Rohde & Schwarz is made the provision for crystal oscillator then. The stability is not truly a factor as the stability of Schwarz tuning with local oscillator is phenomenal. In addition then Schwarz is tuned to a station and reaches own cruse temperature it has a provision to mechanically lock all tunable caps and then the frequency control is dead stable. So, it has to be a reason why they did it.

I will keep to fine tune the .23-.27uH cap that I shunt my crystal oscillator and perhaps I will be able to get something out of it. The crystal oscillator shall demonstrate less noise no matter what, why I do not hear it. Well, partially is because the noise level that I am getting is not restricted by my receiver by the noise level of WCRB transmitters. Still, I would like to explore this subject to the very end.

The Cat

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