Phono Preamp. With transformer or fully active

With one SUT you can't use all MC cartridges, such phono stage is not universal for all MC. It will work for some of them nicely, but if your cartridge impedance is very low (2 Ohm) or very high (40 Ohm) you can't use one SUT for both of them.

I'll differ from Ralph and agree with chakster 100% on this one.   The thing everyone misses in this discussion is the transformer needs a specific amount of inductance to assure low end extension based on cartridge internal impedance.  If you take a 2Ω cart and use a SUT designed for 40Ω, the LF extension will be down into and past record warp and tonearm resonance and the low impedance drive will cause an underdamped top end (HF peak in response). Depending how close to the audio band this happens, the results can be problematic.  Going in the other direction and using a 40Ω cartridge for a SUT designed for a 2Ω source typically will not have a full bandwidth bottom end and an over-damped top end.   The general solution to this is to design with enough inductance for the highest impedance cart and rely on a network on the secondary to fix all the other issues that arise from any mismatch.  The other typical solution is to use a dual or tapped primary that allows for different turn ratios to better suit a wider range of cartridges.  

For given source and load characteristics a wide bandwidth transformer can be wound to match the situatu

dave

@intactaudio I don't see you commenting about the transformer loading in your post. I know that this bit is problematic:

If you take a 2Ω cart and use a SUT designed for 40Ω, the LF extension will be down into and past record warp and tonearm resonance and the low impedance drive will cause an underdamped top end (HF peak in response)

-because our phono sections go down to about 2Hz, yet there are no problems with record warp and the like. Loading the transformer is well-known to control issues in the high end- the 'underdamped' part to which you refer. So while the inductance of the cartridge certainly plays a role, its not that hard to come up with the correct loading for the transformer to make it work.


However I agree that in most cases this is beyond most audiophiles, but this does not change what I wrote. An SUT made for a specific cartridge was probably made at the behest of the cartridge manufacturer; they would probably not be happy if that transformer were used with some other manufacturer's product. So its not surprising that they don't publish loading charts for other cartridges. But if the manufacturer of the transformer doesn't have a dog in the fight, then things are different- and I point to Jensen Transformers as one of the best examples of that. One glance at all the cartridges they list shows they've done their homework!

The Jensen Transformer website contains or used to contain some excellent white papers on transformer loading, as per the subject of Intact's and Atma's posts.  They show how and why to load down the secondaries to compensate for the effects mentioned.

Dear @lewm :  A dedicated external SUT is not builded exactly the same as the transfortmers used in phono stages where the designer knows that the customer can have different MC cartridges ( needs a gain/impedance selector/alternatives. ) and their designs take in count that issue.

R.

@atmasphere 

Are you the guys who do OTL amps?

I loved your setups with classic & their horn speakers

Do you do “ just” phono pre’s ? 
Jeff