Cartridge incompatibility, Soundsmith and Luxman

Please note CHANGING the internal resistors does NOT inhibit you in the least from other cartridges in future; it is totally the way to go (assuming the simple  change works for this circuit).  If you go to 470, or 1000 Ohms, you can ALWAYS use an external metal short RCA Y adapter ($12) with two female/one male RCA and insert RCA plugs with resistors soldered inside. Parallel resistors will bring it down to what ever you  need in future.  (product of values divided by sum of values). We have seen this ONE load value in this model before, and it is very short sighted in my NSHO.  The proper way is to have 1000 -2000 internal and at LEAST some open RCA females jacks on the rear apron, allowing you to put loading plugs in at will. If someone who knows circuitry can verify this circuit allows the 100 ohm resistors to be changed, let him know.....OR send ME the schematic. That is the lowest cost way to make this unit flexible like almost all models of MC preamp designs. Our high gain MCP-2 phono preamp ($1199) has a variable control to go from 10 Ohms to 5K Ohms. Another option. 

Peter Ledermann/Soundsmith

Great post! Thanks.

Unfortunately the specifications on the phono section are sparse so it is unclear what the input configuration is.  The fixed 100Ω value is an odd choice unless there is an internal SUT for the MC input.  To further confuse things the E-250 phono has an internal SUT and lists gains of MM: 38dB, MC HIGH: 57dB, MC LOW: 66dB and input impedances of MM: 34kΩ/47kΩ/56kΩ/100kΩ(switch selection) MC HIGH: 40Ω, MC LOW: 2.5Ω.   When I do the math the numbers do not add up without some overly complex switching and loading arrangement.   The MC high setting it adds 28dB of gain which suggests a 1:26 step up ratio.  That means that the impedance ratio is 1:676 so if the 2.5Ω value is indeed the actual value then the secondary of the SUT would need to be terminated with 1700Ω which is highly unlikely.  Looking at it from the other direction and assuming the 1:26 and a 47kΩ load the input impedance would be 70Ω.  If you work out the same numbers for the MC Low they are equally confusing.  This leads me to believe that 2.5Ω and 40Ω numbers are not the actual input impedance but rather the suggested cartridge impedance which is how many Japanese companies specify phono inputs.  The E-500 lists that it uses 4 SUT's rather than the tapped unit in the E-250.  

Since the specifications of the phono section of your integrated do not list the MM and MC gain, it seems the only way to find out for sure is to measure the DCR of the input of the phono and see what you get.  If it is 100Ω then that is likely your actual impedance value and it may be possible to change that to a higher value.  If it is around 1Ω then it likely has a internal SUT with a step of ratio of ~1:20.  My guess is it is the later at which point while increasing the load value is possible it may lead to less than desirable results.  

dave

Dave, the Luxman website page on the 590ax2 ( not the 250 or 500) indeed gives very little useful information regarding the phono section, but the many photos of the many PCBs reveal no evidence of a SUT anywhere. Furthermore the unit seems built with discrete components rather than op amps and SMDs. So I am guessing it would be easy to remove the putative 100R load resistors and replace them with 470R or higher. I’d use 1000R or even higher, unless PL has a preference for exactly 470R. I knew that Luxman use a SUT in their flagship 500 phono stage, so my a priori expectation was to find there is a SUT also in the OP’s unit, but that doesn’t seem to be the case so far as I can tell from the scant information.

@intactaudio ​​​​@lewm Thanks guys. The information is indeed very limited... all the website gives is this:

PHONO (MM): 2.5mV/47kΩ
PHONO (MC): 0.3mV/100Ω

Basically no information expect that the loading for the MC is very low, which explains why the Soundsmith Zephyr Star MIMC is not very happy. The sound is really wide and you can clearly place each performer in their space, but there's no highs at all.

I'm not much of an DIY guy and the prospect of opening up the L-590AXII to replace a resistor is not something I feel comfortable with. I sold all the separates to simplify things and having to modifying a new amp isn't very appealing. I think changing the cartridge is the easiest and best solution.