balanced vinyl

If the two leads of each channel of a phono cartridge are kept isolated from the system ground, from cartridge to phono preamp input, using a differential input preamp, is this sufficient to produce a functional balanced circuit? Is this often done to reduce external source hum and noise?

If the two leads of each channel of a phono cartridge are kept isolated from the system ground, from cartridge to phono preamp input, using a differential input preamp, is this sufficient to produce a functional balanced circuit? Is this often done to reduce external source hum and noise?

This is the normal way to balance circuits w.r.t. ground, yes. The degree of balance (the common mode rejection ratio, AKA CMRR) will depend entirely in this case on the accuracy of the preamp balance. Inherently it won't make any difference to the system noise, and the effectiveness at LF depends on other factors to do with the cable, etc as well. It doesn't just work with cartridges; it is commonly used with dynamic microphones as well in exactly the same manner.

I have my catridge connected this way. You need some work on the arm to replace those wires with fine twised pairs as well. It will certainly void any warranty The preamp is a balanced design that was once published in ETI (middle 80's I think).

Does it make a difference? Well for me it does. I made some recordings while I set up my turntable including the switch from unbalanced to balanced. Each time recording 1 minute and then looking at the spectrum. And the reduction of 50Hz was important. However as Steve said it isn't automatically, it also depends on cable and even more on the routing of the cable. Using balanced connections I was able to keep 50Hz much lower after finding the best cable routing compared to the same excercise using unbalanced cabling/preamp. But the largest difference was with much less harmonics of 50Hz. How much of that was due to the preamp is another question of course because both cabling and preamp changed at the same time.

There might be some remains of that on the old forum.

I have contemplated doing this in the past - but at present I have a preamp that works remarkably well without needing a balanced input at all - indeed, it won't take one.

I can't say that I'm that surprised that to get the very best out of this arrangement, you've had to dress the leads. To reduce all interference, you probably need the conductor pair twisted reasonably tightly to ensure both freedom from inductive interference and a good overall CMRR.

The neatest arrangement I've ever seen in terms of eliminating rubbish in balanced systems and making staggering improvements to the CMRR was from Bill Whitlock of Jensen Transformers. You can read about it here - unfortunately this is still very much under patent protection!

Well, I twised some 0.2mm magnet wire together rather tightly and ran this straight from the cartridge to the preamp with only some connectors at each end. Twist is about 3mm pitch. The preamp has to be adjusted for CCMR at LF and HF interactively. It takes a bit of time and gear but isn't that hard either. The biggest contributor to hum turned out to be the turntable drive itself. there was a transformer in the plinth. Removing this to his own box a meter further made the largest difference.

I'll read this paper at ease tomorrow. Thanks for the link.

PS balancing doesn't help to keep interest. The system has been shut off for more than 5 years now. I can't stand the tought of having to record an LP and treat it anymore. There are still GB's of recording on the HD waiting, probably forever.

In my view there is certainly no reason to argue against balanced wiring whenever this is possible. But in the case of most turntables for vinyl there is little reason for changing the common unbalanced wiring. I assume the use of one of the common MM cartridges which call for a terminating resistance of 47 k Ohms and low capacitance. In case of a low impedance MC cartridge, things are different and may require balanced wiring.

The S/N that may be expected from a good vinyl pressing is rarely above 60 dB, already excluding the very low frequency components originating from playback and cutting rumble which often are considerably above that. There is the disadvantage of a further boost by the RIAA playback characteristic in the order of 15 dB mainly being responsible for 50/60 Hz hum. Thus, as long as the floating pick up reads a figure of -75 dB or better with respect to the peak amplitude, balanced wiring will not do any better. This holds even more when the figure gets worse with the pick up above the turntable. In most cases, the residual hum is due to magnetic stray fields of the turntable motor to the catridge itself. Such hum induced will not decrease by balanced wiring. Keep a pragmatic view before doing unnecessary rewiring as in most cases a well shielded cable not running in parallel with the mains cord will do the job !
 

This holds even more when the figure gets worse with the pick up above the turntable. In most cases, the residual hum is due to magnetic stray fields of the turntable motor to the cartridge itself. Such hum induced will not decrease by balanced wiring. Keep a pragmatic view before doing unnecessary rewiring as in most cases a well shielded cable not running in parallel with the mains cord will do the job !

The majority of earlier turntables behaved better from the radiated hum point of view - they were made of either something cast, or at least sheet steel, and reasonably heavy. Some of the newer, more recent ones may have wonderful balance, etc although the plastic ones have lousy screening capability. But yes, the hum from this source won't balance out, and in order to reduce it significantly, you often have to do a lot of work to the turntable.

I forgot to include one frequent source of interference. Many turntables have small neon lamps as speed indicator referring turntable speed to mains frequency. These often are a capacitive source of a minor high frequency buzz as they flash with 100 Hz or 120 Hz. I had this problem with my Lenco L 833 DD. For elimination I added a small grounded mesh to the cartridge that overlapped the unshielded wires and plugs. You may also use any metal tape instead.

Forgot to add the picture !

I forgot to include one frequent source of interference. Many turntables have small neon lamps as speed indicator referring turntable speed to mains frequency. These often are a capacitive source of a minor high frequency buzz as they flash with 100 Hz or 120 Hz.

I've replaced the neon with a LED on one turntable - not had any problems with that at all. In an ideal world, I'd drive it from a crystal-locked source, but I haven't gone quite that far with it yet!