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In Reply to: RE: LCR Phono posted by Jeff Davison on March 09, 2009 at 17:49:18
Jeff,
I mentioned this before. There can be no internal termination of 600 ohms since that would draw excessive current through the inductors when direct coupled. The warning to not exceed 100V simply means that the caps used have a 100V rating.
I have also mentioned (and documented via spice) that the input impedance of the LCR is ~600R independent of the load placed on the secondary. Leave the secondary open and it is 600R. Short the secondary to ground and the source still sees 600R.
The situation where the 300R number comes into play is when you attempt to load a pentode with a 600R resistor in order to define the source Z feeding the network. In this situation, the 600R plate load is in parallel with the 600 LCR network (which is 600R independent of secondary termination) which nets a 300R load on the pentode.
What I find clever about NAZ's design is that he dispenses with the 600R termination altogether which nets him an extra 6dB of overall gain (6dB less loss in the network) at the cost of a drop of in LF response. In order to get back the LF loss, he terminates the network with a CL resonant circuit and tunes it to get back the bass response. If you look at the frequency response plots you will see him flat to around 23hz and then -4dB at 20hz with a steep slope. I don't have a problem with this since the LF behavior is essentially from a few stacked filters rather than a single complex one and I'm a firm believer that keeping extreme LF behavior out of a phono pre is actually a good thing.
dave
Follow Ups:
I'm flip flopping whether or not to build Naz's circuit with the Silks as there is no way to determin what's actually happening in side their module. I have it on good authority that it is not a "drop-in" exact replacement for the S&B or the Tango, and that a lot at "circuit tuning" must be done around the Silk to work in a circuit designed for the S&B and Tango.Naz was suggesting that maybe we / I should work with you as you did with Andrew in your forums postings? The Silk is starting to scare me because of the lack of information about it and the secretivness of Kittipol on his proprietary design.
I was also thinkin of possibly using this (expensive) solution as it IS a drop in replacement:...
JD
Edits: 03/10/09
I find this page very confusing. They mention the Tango and show the same picture from Hiraga, yet show a schematic that is different using what is equivalent to the middle method of the hiraga diagram which will allow direct coupling up to the rated cap value at a small penalty in overall accuracy. In the same schematic they designate the two inductors as the "EQ-2L" as if they are a stand alone module so I am unclear what you would be purchasing.
below is the actual Tango EQ600P drawing from the spec sheet.
dave
Tango did do a module with just the inductors...
me too :(
Although I sent them an email to se if it would be a 1 to 1 replacement for the Tango in any given circuit.
JD
Jeff, I responded to Lars who provided some useful input at Dave's site. We may be getting somewhere.
Naz
Naz, I got a reply from Acoustic-Dimensions in the Netherlands who also make an LCR. They say theirs is an exact replica also exact in that theirs, and the Tango, have no tolerence to DC at all..... which unlike the Silk that allows up to +100vJD
Edits: 03/11/09
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