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In the Forum: Analog Playback
In the Thread: The last phonocorrector: “End of Life" Phonostage

Post Subject: Generally the phonocorrector has very low noise.Posted by Romy the Cat on: 4/20/2010

Ok, you are getting somewhere. I am not sure why I used the 100R, 50R and 22R resistors. It is good idea in some cased to list the potential of some circuits but it need to be used ONLY what it necessary. Do not forget that in your case you have 5 chassis: PS, 2 correctors and two transformers. Connection of the two transformers chassis is tricky. In some case you want to connect them together and THEN to connected them to corrector/s. You need to run a few experiments how to do it in your configuration. To connect grounds a few inches here or there might make a significant difference. It looks like one of your channels is fine, now you need to fine tweak the grounding on the second one. The 2Meg resistor is necessary for the second side of the corrector.

Generally the phonocorrector has very low noise. I have it with 27dB gain transformer and 109dB sensitive playback. Running the playback wide open at max gain I have no noise. At max gains I have a very minor “breathing” of my LF arrays but no auditable noise, rather some LF pressure in the room but no sound. I presume that it is sub 20 noise – which is fine by me since I use only class A amps and the ULF harmonics do not drain the PS one my amplification. Mind you that with this phonocorrector and playback at max gain the volume is absolutely insane and I never play it at this volume. My normal listening level is good 30dB below, so whatever “noise” I have at max volume level is absolutely not auditable at listing levels. That all is very nice as the phonocorrector has exposed filtering caps that shall be susceptible to pick up some AC dirt from air. For whatever reason they do not and my corrector has no noise even without box. BTW, the polarity of the air caps might be a factor. Make the AC go enter the air cap chassis and exit from the air cap insert. This way you will have the chassis of the air cap to do some extra self-shielding.

The trick with the air caps is to set them to the correct value. When they are connected then the values are changed. So, you need very accurately up-solder the air caps from the circuit, to measure then with trusted pF meter and then put the wares back. Alternatively you can have high precession RTA and you can run ant-RAAI or a test dist sweep and adjusting the air caps you can get horizontal response. I used both methods and they both give identical result. The only problem with this corrector is that I did not fixate the air caps. They are as they are and I do not shape the corrector. They do hold the values but I guess if I violently shake the correctors then they will not – the same as the tuners. I decided do not glue the air caps. Sometime in future I will make the perm air caps from pure cupper plates – with 100pF and 330pF it will not be too difficult….

The Cat

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