SUT or SS LOMC preamp

Re: SUT or SS LOMC preamp

Postby Bob » Wed Mar 14, 2018 10:38 am

Caveat, This is Bob from Bob's Devices.

Several years ago a group in the Los Angeles area compared the Hashimoto to the 1131 Bob's Devices. Consensus was that the Hashimoto added some smoothing to the sound and colored it a bit. Some said that it sounded a bit fat or bloated. In comparison, the 1131 did not color the sound and it appeared to be more clear and open. Since then, the 1131 was improved with a redesign. The SKY was designed with an unprecedented low inductance to better match moving coil cartridges. The SKY is currently in the Stereophile Magazine A list.
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Re: SUT or SS LOMC preamp

Postby Bob » Wed Mar 14, 2018 10:40 am

Why should you use an external MC step-up transformer into a MM phono stage, versus using a self-contained phono preamp that does it all?

Background: Matching Moving coil Cartridges to phono stages is a difficult process. For MM cartridges it is relatively easy since there is a standard for MM cartridges at 5mV and 47k Ohms. With MC cartridges, there is a wide spectrum of output voltages and internal impedances, as well as a variety of inductances. For a Phono stage manufacturer, it requires some serious design considerations.

Basically, almost all MC phono stages have a MM mode. The designer in most cases, builds a second stage to convert the signal from a MC cartridge to the MM level. Most do this with an active stage designed and built with FETs. Some use internal step up transformers. The challenge is accommodating a wide variety of MC cartridges. This is typically accomplished using a set of switches or jumpers on a circuit board. Many have adjustments for impedance and output voltage (different gain settings). If you look at the specs of each phono stages and compare them for MC cartridges vs. MM cartridges, there is usually a significant different in signal to noise ratio, except for those that use internal step up transformers. For active stages, the ratio is lower by about 8-10dB for MC cartridges vs. MM cartridges. This results in a louder background noise floor for MC cartridges. Additionally, adding switches to low output signals is very difficult to do without degrading sound.

For those phono stages that use internal step up transformers, there is a limited range for MC cartridges and typically, the internal step up transformers are not as good as some of the best in the industry. One step up transformer cannot be made to work properly with most MC cartridges.

A stand-alone step up transformer can be used to better match a cartridge to a MM phono stage, instead of using the internal active stage or the internal step up transformers. You can use a step up transformer ranging from 1:5 to 1:40. For those who say that using a stand-alone Step up transformer is not a good idea because it adds an additional set of interconnects; well, the active stage or internal step up transformers are connected by wires or printed circuits inside the phono preamp. Perhaps one could also say that a console stereo or integrated receiver is better than separates since no interconnects are required. There are many excellent interconnects and connectors that are very transparent.
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Re: SUT or SS LOMC preamp

Postby adeep42 » Wed Mar 14, 2018 11:19 am

I am the happy owner of a Bob's Devices VPI SUT. I can add that Bob is a delight to work with. He is also a VPI dealer. If you are concerned with an additional set of interconnects, The VPI SUT that mounts right to the VPI tone arm base is an elegant solution. The surgery required is simple and Bob's instructions are very clean and clear.
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