There was a great thread in this back from 2016 started by Brian Gupton in relation to his Hommage T2. In that thread it was said that the step up ratio for the T2 is somewhat high approximately 1:40. I went on to play with the math a bit, and a 1:40 SUT should result in an impedance to the cartridge of approximately 29 ohms (47,000/40x40). The T2 is supposed to be voiced for the EMT TSD15. That cartridge, though, has an internal impedance of 24 ohms. That would mean that the impedance of the SUT would match the cartridge almost 1:1, which violates the goal of having the SUT impedance to the cartridge be approximately 10 times the internal impedance of the cartridge. On the other hand, the Ortofon SPU A, which is the cartridge the Hommage T1 is voiced for, has an impedance of 2.5 ohms. Is it possible that the source of the step up ratio confused the T1 and T2? The 2.5 ohms would be just about spot on the 29 ohm SUT impedance to the cartridge. And if the inverse is also true, can we assume that the T2’s impedance is closer to 10 x 24 ohms or 240 ohms? This would result in an approximate 1:14 ratio for the T2. Am I off base? Probably the best answer to to simply ask the designer or the distributor. Just curious if anyone else may have figured this out.
The 10x ratio suggestion is for resistor terminated, voltage input, active phono preamps, not transformers. Many designers, past and present, choose to match the transformer and cartridge impedance since it is a power transformer, not just a voltage transformer. And often it is mentioned in cartridge specs that the recommended load impedance is for active gain stages.
Bob’s devices mentions the 10x ratio as the general target for passive gain stages (SUTs). In fact, on their website they have a chart with cartridge gain on one axis and internal impedance on the other. Using that chart, and using the specs for the SPU and TSD, they would result in recommendations of 1:40 for the T1 and 1:10 for the T2. Seems too much of a coincidence.
That's fine, I'm just telling you there isn't an agreement on the best way to match a transformer to a moving coil cartridge. Look at the Luxman EQ-500, one of the best phono preamps in the world, they favor impedance matching as opposed to the 10x ratio rule, and they've been designing and building high quality moving coil transformers for decades longer than Bob has been in business But who knows, I think we talked before in another of your threads about the Auditorium ratios, and I don't know any details.
Appreciate the conversation! It wasn’t me in other threads...I just started looking into this. I’m kind of interested in the science. Makes the hobby fun.
Yeah me too. Where’d he get to? Looks like he’s still alive which is good! https://www.linkedin.com/in/briangupton
I found this thread because I just ordered a T2 to pair with my Ortofon A95. Dealer (Matt Rotunda at Pitch Perfect) said that was the right way to go as opposed to the T1. Anyone have experience with this combo?
I don’t doubt that he steered you in the right direction, but I’m curious if he mentioned why he recommends the T2 with the A95 instead of the T1? The A95 output and impedance are low, much like the SPU the T1 is designed for. I imagine the T2 sounds great though.
I don’t recall as I ordered this back in January and still hasn’t arrived! I’m going to cancel if it isn’t here by August.
This is where matching load Z to source Z comes from. Maximizes SN. It was applied to audio from instrumentation, which audio is, transducers, amplifiers, etc. The optimum Ro for the Rl in the sec is: xfmr ratio n^2 ~ (Ro for Rl) / Rs Rl = n^2 x Rs If Rs = 10 and n = 1:20 Rl = 400 x 10 = 4000 Ohm sec Reflected to prim ~ 400/20^2 = 10 Ohm Rl = Rs Good night to all!
