Frequently Asked Questions
How do you connect and setup the SUT?
1. Connect the RCA cables from the turntable to IN on the SUT.
2. Connect a set of RCA patch cords between the OUT on the SUT to the inputs on your phono preamp, preamp or receiver where it says phono.
3. Connect the turntable ground wire to the lug on the SUT and add an additional ground wire between the lug on the SUT to the Ground Lug on your Phono Preamp.
There are 2 switches: One is ground / lift and basically you switch it to whichever position gets rid of the background hum. The other switch is high/low, and again, you switch it to whichever one sounds better. No need to disconnect anything when using the switches and you can't hurt anything by using them. They have silver contacts and it is safe to switch even in the middle of a song.
Do the switches impede the performance of the SUTs?
Yes, anything you use in a circuit has an effect on the output. When the Ground / Lift switch is in the “lift” mode, the switch is not part of the circuit. An A-B test of a SUT with and without the Gain Switch did not have an appreciable effect on the output. I exclusively use switches with silver contacts, which as you know is a great conductor. They are so quiet that you can switch them in the middle of a song and not hear anything but the change in gain. My wiring is all silver and I use resistance soldering exclusively. Even when the switches get old, silver actually becomes a better conductor if it is corroded, so they will still be quiet.
What kind of interconnects do you recommend?
Use interconnects that are grounded on one end only and are built with twisted pair wires.
Bobs devices do supply custom cables designed solely to protect & transmit the delicate signal
The cables will all look the same on the outside. It depends on how they are constructed. The RCA plug has a + and a - . The - is the outside part and the + is the pin in the middle. What you want is a cable that has 2 wires inside a shield. You would use one of the wires as a + and one as a -. You would connect the shield at only one end. But when you look at the cable it will not look any different. Sometimes they are called directional cables and have arrows on them. You would look for a cable made from 2 conductor twisted wires with a shield. Most likely it will be built properly. The shield is sometimes called a drain. Any SUT including these, will work with a standard RCA set of cables, but if you hook it up and are experiencing some hum, the cables could be the culprit.
Are your SUT’s quiet?
Yes. These SUTs are stone cold quiet. However, SUTs sometimes have a reputation for having a “hum.” This may be due to several causes including improper installation and wiring of the SUT itself, use of improper cables, ground loops from too many ground wires, and location of the SUT and interconnects. I have done extensive testing to ensure that there is no noise from the SUT. The ground/lift switch takes into account different types of setups that are commonly encountered.
Introduction of ground loops can occur with the installation of any equipment, and if you have that problem, I will gladly help you troubleshoot that. See the section on GROUNDING for tips on that.
Now, having said that, you can’t put the SUT next to a big power transformer, motor or power cables and expect it to be quiet.
How do MC Step Up Transformers (SUTs) work?
With Step up transformers, you are converting the current (which the mc cartridge has an excess) to voltage. The physics are such that the square of the step up ratio is equal to the internal impedance of the transformer. So, for example, if a transformer has a step up ratio (for voltage) of 1:10, then the internal impedance is 10 x10 = 100. To use this number, you would divide 47000 by 100 to get the reflected impedance to the cartridge of 470 ohms. So when the step up ratio is increased, the reflected impedance is increased exponentially. So, it has to be a balance. When cartridge manufacturers quote impedance, they usually do so for sizing head amplifiers, which are different from step up transformers. With step up transformers, you mainly care about converting the cartridge voltage to between 2.5 and 10 mV, which is what a MM input is designed for using RIAA standards. Now all manufacturers have different specs on their phono stages. Some may have higher or lower sensitivities or ceilings. That information is not always published.
Why do we use the MM inputs when using a SUT?
Yes, you definitely want to use the MM inputs, since there is a published standard for them. There is no standard for MC inputs and manufacturers frequently have internal adjustments for the MC inputs. A standard RIAA phono preamp is designed to handle between 2.5 mV and 10 mV, conservatively. The RIAA standard is designed around 5mV and 1 kHz. Usually you will not start overloading a phono stage until after 10mV, and I find that the highest gain sounds the best, as long as:
1. You do not drive the phono stage to distortion.
2. You do not provide too much reflected impedance to choke out the cartridge.
Since this device of yours is a transformer, does it thus still need a phono input on my pre-amp or can it go into any line level input?
You will need to connect the output of the SUT to a Phono Preamp magnetic cartridge (MM) input. It will not work into a line level input.
How about the RIAA equalization? Is that inherent to the transformers, or to your design? or Does this pass an unequalized signal to the phono input of the preamp which then applies the equalization?
The SUT design assumes that your phono preamp uses RIAA equalization. It is designed to pass the unequalized signal through, just as you stated, where the MM phono input provides the equalization.
How do I trace the ground leads from the turntable to find ground loops?
Start from your cartridge and follow the wires, looking carefully for any places where the negative terminals of the cartridge (let’s call them system grounds) are connected to equipment grounds (let's call them chassis ground, sometimes referred to as drain wires). We only want one chassis ground connection between pieces of equipment. When there is more than one chassis ground connection, there is the possibility of a ground loop (The electrons don't know which way to go, so they keep on moving and generate noise.)
Since most of us use RCA cables from the turntable to the phono preamp, the negative (system ground) wires have to be shielded with a chassis ground. Some turntables connect the shield of the RCA cables to the chassis ground wire at the turntable, and some do not. You only want them connected that way at one end, hence the ground / lift switch. So, here is the short answer. Remove the ground wire connecting the turntable from the phono preamp. Connect ONLY the ground from the turntable to the Box you got from me. Don't connect the wire from the box to the Phono Preamp just yet. Now, make sure that you use interconnect cable between the transformer and the Phono Preamp that have 2 wires inside (positive and negative) and the shield is connected to the outside (chassis ground of the cable) at only one end. (The cable will have the negative lead and the ground attached to the outside of the RCA connector at one end. The cable will only have the negative lead (Not the ground) attached at the other end.) Now, with everything hooked up, turn it on and listen to the hum. Then move the switch to whichever position offers less hum. Then touch the preamp ground wire to the ground lug and see if it is less or more noisy. Then remove the wire from the phono and see if it is quieter or not. Then touch the phono wire to the preamp wire and see if that is quieter.
Sounds like trial and error. It basically is, but the idea is to make sure that everything is grounded, and only grounded once, and the all the audio cables' shields are grounded, and only grounded once.
The other type of noise is interference (you get that from any parts of your system wires running too close to power transformers, power cords, or any kind of AC power.)
Even after much reading on your site and others, I am still not fully grasping the impedance issues
Transformers are basically voltage changing devices. When used as step up devices for MC cartridges, it steps up the voltage from one that is too low for the phono preamp to use to one that is in the range. A secondary effect of transformers is that it multiplies the impedance by the square of the step up ratio. (read that twice.) For example, a step up ratio of 1:10 has a secondary impedance multiplier of 10 x 10 = 100. So if the cartridge has an output of say .5mV, the 1:10 step up raises it ten times so the output is 5.0mV.
We work the impedance backwards, since most phono preamps have the RIAA standard of 47,000 ohms impedance. So in our example you would divide the 47,000 by the 100 to get 470 ohms impedance to the cartridge.
All of this is pretty straight forward. The part that is not so straight forward, and there are considerable disagreements over the proper impedance to load a cartridge using a step up transformer. Many have experimented with different values and there are varying opinions. You definitely do not want the impedance to be less than the cartridge impedance, and, as a general rule of thumb, you want it too high, rather than too low. So if you have a cartridge with an impedance of say 40 ohms, you want the impedance to be much higher than that. I feel comfortable with 10 times, but it depends. Each cartridge manufacture recommends an impedance for loading but they do not always provide the best information. The cartridge database has general loading information for each cartridge, and it is usually stated as >100 ohms, or something like that.
Personally I have tested a dozen or so cartridges and have communicated with many individuals who have collectively have probably 50 different cartridges. So, between the cartridge database and the feedback from customers, we can pretty well judge what works well and what doesn’t.
A few questions: – (1) in respect of the interconnect between the SUT and phono stage: (a) Is the shorter the better?; (b) Can I get away with not using a shielded cable and use say an interconnect comprising a 3 wire braid of solid core single crystal 6N copper sheathed in cotton?; and (c) In the case of a shielded rca interconnect, should the shield be connected at the “receiving” end or the “transmitting” end of the cable? (2) Clarification on grounding. I am using a Terminator tone arm and there’s no ground lug like the VPI tone arm I was using previously.
The cables between the SUT and your phono preamp are the most important cables in your system. The SUT has converted the amperage from your cartridge into voltage and so there is no current to spare. It is also highly susceptible to electromagnetic radiation. You can try a non-shielded cable, but I doubt that it will be quiet.
You should shield that cable and keep it as short as possible. Also, it doesn’t matter which end the shield is grounded on, as long as it is only one end. We do that to avoid ground loops. We only want one route for the ground to take.
After you connect everything and run a ground wire from the SUT to the Phono stage, take a second ground wire and attaché one end to the SUT and try touching the other end on the turntable motor. Try the ground lift switch in both ground and lift modes with the wire touching and not touching the motor frame. A good way to run this test is to turn up the volume on your preamp while the needle is not on the record. That way you can easily hear the background noise. The goal is to get it as quiet as you can. On my system, it is with a ground from my turntable to the SUT and a ground from the SUT to the preamp, with the switch in “lift” mode. It is most likely going to be different for you.
You might want to think about your turntable cables also. Since your tonearm doesn’t have a ground, you might want to build the same type of cables with the ground connected at the SUT end, so the cables from your turntable are shielded.
I have two phono stages both with 47K ohms loading. I am checking on the gain on my McIntosh C15 preamp which has a standard moving magnet phono section. My cartridge has an internal impedance of 7.2 ohms. It has a 0.3 mV output. People selling step up transformers out there do not give the important information or if they do, they do it in a way that someone like myself cannot understand as I do not have a technical background. The ratio stuff just goes over my head. Hope you can help me understand what type of SUT would work best for me.
You generally want at least 10 times the internal impedance, except for some Denon Cartridges. There are always exceptions to everything, including this statement.
You didn’t tell me what cartridge you are using so I will speak in generalities.
A standard MM Phono preamp is set up with 47,000 ohm input resistors (They are sometimes easily changed and I recommend that folks change them to 100,000 ohms if they can do so, which will allow a higher gain step up and also put less resistance in the way of the signal.
All MM Phono stages are different, but most of them will accept a load between 2.5mV and 10 mV. If you know the sensitivity (low number) or the overload voltage (high number) you can substitute those in the equation.
Basically, take both values and divide by the output voltage of the cartridge to get the range of step up ratio that will work. Then take the input impedance of the phono preamp and divide it by the minimum impedance that the cartridge wants to see (10 times the internal impedance). Take the square root of that number and that is the highest step up ratio that your cartridge can use without choking it out.
Compare that to the max and min voltage calculations and you have the range of step up ratios that will work.
Here is your specific calculation to get step up ratios, based on a standard RIAA MM Phono preamp and a cartridge with .3mV output and 7.2 ohms internal impedance:
10mV / .3mV = 33
2.5mV / .3mV = 8.35
47,000 ohms / 72 ohms = 653, sqrt of 653 = 25.5
So, you need a step up ratio of between 1:8.35 and 1:25.5
Usually, the ratio at the highest end of this scale works best.
Is a burn in period required?
Yes, there is a burn in period. The first 10-20 hours are the most noticeable with it becoming less critical after that. However, the burn in continues forever with diminishing returns. So, if you compare on that has hundreds of hours on it with one that has say 20 hours on it, there will be a perceptible difference.