Guess what ? This crazy thing is playing ! It hums a bit. Most of it comming from the motor in my turntable. I was able to reduce that quite a bit by moving the stage further away from the turntable. I will try other things like shielding with Mu-Metal but i can say right away that tonal balance is not much off. I can not say for now how much wideband noise it has. The hum is too dominating so i have to work on that to find it out.
This is by far the most unlikely stgae i ever build and it is ultry simpel. Edgar, you are a funny chap and isn´t it the fun that drew me again into DIY ?
This is by far the most unlikely stgae i ever build and it is ultry simpel. Edgar, you are a funny chap and isn´t it the fun that drew me again into DIY ?
I was able to get the hum down enough to do some serious listening. Putting an alumimum
plate over the coils helped a lot. I tried also to encase them in one of my infamous cookie boxes but that RAISED the amount of hum maybe because they are magnetic. I am sure a well made Mu-Metall coil from Sowter whould be dead quiet but again not really cheep.
Maybe i find a solution that works without costing a fortune. Besides the small hum the stage is dead quiet. I listened to a diet of Melody Gardot, Valery Carter and Sting ( Symphonicities ) and found the sound very balanced, kind of sweet and liquid and superbly low in disturbing noises. This is really easy listening but the stage was wide, high and deep too. I realy think this priciple is a valid alternative and provided the hum problem is solved i see no reason why a state of the art stage could not be made that way. It works of cause only when the Impedance of the cartridge is taken care for.
plate over the coils helped a lot. I tried also to encase them in one of my infamous cookie boxes but that RAISED the amount of hum maybe because they are magnetic. I am sure a well made Mu-Metall coil from Sowter whould be dead quiet but again not really cheep.
Maybe i find a solution that works without costing a fortune. Besides the small hum the stage is dead quiet. I listened to a diet of Melody Gardot, Valery Carter and Sting ( Symphonicities ) and found the sound very balanced, kind of sweet and liquid and superbly low in disturbing noises. This is really easy listening but the stage was wide, high and deep too. I realy think this priciple is a valid alternative and provided the hum problem is solved i see no reason why a state of the art stage could not be made that way. It works of cause only when the Impedance of the cartridge is taken care for.
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I persuaded Jürgen Hensler to make me two of his wounderfull coils. They will be 1mH, 1.5 Ohm so the noise contribution will be even less then the 0.75mH, 4 Ohm i am using now. The coils will be wound on double e-core audio material. That way the coils are much smaller and less prone to hum pickup. I will also try Mu-Metal shielding. This is scheduled to be ready on wednesday evening, one day before ETF, so this is tight.
Thanks John, for that advice. Sofar i have some experience with Lundahl and Sowter products in MU-metal cans but honestly i am not measuring distortion much at the moment.
My transistor circuits get simulated so i see if i land in the ballpark. Usually i design for better then -80dB distortion at 20kHz into 600 Ohm at 1V, mainly second harmonic. Better is fine and i was able to design open loop circuits that are better then -100dB but i did not find a direct correlation if that sounds any better. I focussed more on listening recently. When i want very low distortion i am using modern Opamps or a combination of Opamps with discrete Output or Input stages or both. Together with my Josi team i also designed a discrete Opamp with very low distortion. The PCB´s are ready but we did not find the time to stuff them. But listeners tell me that they like my discrete designs better. Again something i can hardly prove by measurements. Are we still measuring the wrong things ?
My transistor circuits get simulated so i see if i land in the ballpark. Usually i design for better then -80dB distortion at 20kHz into 600 Ohm at 1V, mainly second harmonic. Better is fine and i was able to design open loop circuits that are better then -100dB but i did not find a direct correlation if that sounds any better. I focussed more on listening recently. When i want very low distortion i am using modern Opamps or a combination of Opamps with discrete Output or Input stages or both. Together with my Josi team i also designed a discrete Opamp with very low distortion. The PCB´s are ready but we did not find the time to stuff them. But listeners tell me that they like my discrete designs better. Again something i can hardly prove by measurements. Are we still measuring the wrong things ?
Thanks Sam, when i have luck it will all come together. I talked to Jürgen Hensler today and typical for him he said :" I whould not like to waiste time so i make you some coils that are tapped at 0.56, 0.75 and 1mH". Fine, then i have some fexibility. Playing around with the big air coils to reduce the humm i put a small piece of Mu-Metal over them and could hear the sound of metal over the speakers !!!!!! Cristal clear ! First i thought this is really bad but then it occured to me that i should try the oposite and make the hum stronger. After fumbling around a bit i got the sound of the motor in the speakers. I use a silicon belt that is glued and not cast so at the joint there is a small discontinuety. I could clearly hear the sound it makes when it passes the pulley at each revolution. Tack, Tack, Tack... Whow, this is not only a musical intrument and an electromagnetic microphone but also a superb analysing tool. Strange enough that i also was on the other hand able to reduce the hum to a point where decent music reproduction could be heard. Let´s see what Jürgens coils will bring to the table " ...... will pot them in wax... very small airgap located at the inner...... " It whould not be the first time he surprises me.