I've got my eye on an expensive Phono stage that only accepts balanced inputs - from my experience about 99.9% of the tables out there are single ended only. Is there a cost effective way to convert an single ended turntable to supply a balanced input of a phono stage (without compromising the signal)? thanks for any input.
You can run cart. balanced into phono pre with RCAs if cables and input jacks are wired that way. That is the way I run mine. XLR jacks are too big to fit through my arm mounting hole (OL arms use Rega mount with hard wired cables). In my case using XLRs would require unsoldering them every time I needed to pull the arm. :~( No real penalty to using RCAs wired balanced IMO. The shield can be grounded at the turntable which is then grounded with the TT ground wire.
Mordante, your best option in this case is to replace the junction box with one for XLR cables, and run everything balanced. The advantage of doing this is that the cables will have less overall effect on the sound- they will be more neutral.
English is not my native language and I don't really know that much about cartridges. But if I were to buy a phono amp like the Blue amp Surzur, which to my knowledge is of a fully balanced design would I benefit from using XLR cables. The junction box on my VPI scout can be replaced by a XLR junction box. Or should I just use RCA cables.
In addition does anyone have any experience with a blue amp Surzur?
Dgarretson has got it pretty close. The gain of the preamp is unaffected by using only one input single-ended; the problem with that is noise that is now available at the input of the preamp, whereas if you use the signal balanced, the noise can be rejected, and just as important, the input cable will have less artifact.
I am really impressed at the increase in knowledge in the community regarding this subject!! Only a year ago there would have been a lot more myth-information present on a thread like this, so far the only such posts have been two from one 'goner. Well done!
I haven't yet taken the time to go through the thread Dave linked to. But I would expect that a factor that would in some cases be decisive regarding the advisability or inadvisability of using an rca-to-xlr adapter which grounds pin 3 (as opposed to an adapter cable which does not) is:
IF the phono stage and part or all of the subsequent signal path and components in the system are fully balanced designs, then using an adapter which grounds pin 3, in addition to ruining common mode noise rejection capability at the phono stage input, will result in the sacrifice of some of the key advantages of fully balanced design in those subsequent parts of the system. Including cancellation in those components of some forms of internally generated distortion, and, particularly in the case of the power amplifier, reduction of power supply-related noise.
Also, if the entire signal path is balanced, a considerable fraction of the amplifier's power capability (as much as 75%) will probably become unavailable.
It should be noted, though, that grounding pin 3 and thereby in effect making the subsequent parts of the system single-ended in those respects, will NOT degrade the common mode noise rejection capability of balanced interfaces that may be present at points in the signal path subsequent to the phono stage input.
Gain is not lost in single-ended vs. balanced wiring of cartridge, as the voltage output of the cartridge is what it is in either scenario. Some state that dividing this voltage across the two phases of a balanced amp may reduce s/n ratio. Others believe this is off-set by the advantage of common mode noise rejection in a differential circuit. Others state that the reduced capacitance that the amp sees from the source in a balanced hook-up may be advantageous.
Al, Interesting point you make re not losing signal strength. That runs counter to my actual experience when I accidentally grounded one half of the signal in a full balanced set-up. But now that you say it (and now that I realize I knew it, and you are correct), I can think of another reason why I definitely lost at least 6db of signal strength until I un-grounded the 2nd of the two signal-carrying conductors. (Note I have avoided using the terms "positive" or "negative", which are merely conventions and could also be confusing.)
As to my statement regarding the "negative half of the signal", I know very well what is happening. I had just been criticized for being too pedantic, so I decided not to elaborate on that statement for fear of confusing someone. Perhaps my over-simplification could also be confusing, so thanks for mentioning it.
I should have added that IF one does use an RCA cable to carry a balanced signal, then one must lift the chassis ground connection on the RCA jacks, for sure. Else, like Dave said, you will lose the negative half of the signal to ground. This equivalent to a 6db loss in signal strength.
Hi Lew,
That's not true in the case of a phono cartridge, as I indicated above. There would be a 6db loss in signal strength in the case of an actively driven balanced pair of signals, such as between powered components (that are not transformer coupled), but that is a different situation altogether.
And again, I suggest that you not refer to "losing the negative half of the signal." That would imply that half of the waveform, and the corresponding signal information, is lost, which as you probably realize is not what happens.
Elizabeth, Keep your shirt on. Nothing I wrote was incorrect. And it may help the OP, if the OP is concerned with the details of this hobby. And most of us here are already nuts enough to be that way. On the other hand, your comment that cartridges do not have three-wire outputs may reflect a lack of understanding on your part. As others wrote, nearly all cartridges are inherently balanced devices, and the two sides of the coil deliver a balanced signal. What you are grounding in an SE phono stage is what would otherwise be the negative phase of the signal PLUS the shield on the cable, ALL going to chassis ground at the phono stage, typically.
I should have added that IF one does use an RCA cable to carry a balanced signal, then one must lift the chassis ground connection on the RCA jacks, for sure. Else, like Dave said, you will lose the negative half of the signal to ground. This equivalent to a 6db loss in signal strength.
A standard RCA/XLR converter plug may not work, as these typically short XLR pin 3 to ground.... As suggested by Lewm, if in an RCA configuration cartridge negative phase and shield to RCA barrel share a common wire, then grounding the shield to pin 1 or chassis will have the effect of shorting out and eliminating one half of the balanced signal.
Actually, that is not correct. The phono stage will see the same signal amplitude whether or not pin 3 is grounded. There will be the same difference in voltage between pins 2 and 3, as generated by the cartridge, either way. The cartridge will not "care" whether those lines are referenced to the phono stage's ground, or are floating.
The difference will be, as I said in my post immediately above, that the impedances of the two signal lines relative to ground will be unequal if pin 3 is grounded. That will severely degrade rejection of common mode noise, but will not affect the amplitude of the signal that is processed through the phono stage.
Essentially, it would convert the balanced input stage into a single-ended input stage, but with no change in signal amplitude.
And again, to be precise, it is one polarity, or one of the two signals in a balanced pair of signals, that is shorted to ground, not one half of a signal. Each of the two signals comprises a complete waveform containing all of the signal information, and the waveforms on the two signal lines are identical except for being inverted relative to each other.
(I was just about to click "submit" on the following, when I saw Dave's (Dgarretson's) post above. Thanks Dave).
I should have added at the end of my previous post that there is a second reason why it is preferable to use a properly designed adapter cable, rather than an rca-to-xlr adapter.
Most or all commercially available rca-to-xlr adapters connect xlr pins 3 and 1 together (i.e., they ground the "cold" or inverted signal polarity). The resulting difference in the impedance of pin 2 (relative to ground) and pin 3 (relative to ground) will pretty much negate the common mode noise rejection capability of the balanced input.
To simplify, the two-pin cartridge coil is inherently a balanced signal generator. On one channel map cartridge Red to XLR pin 2 and cartridge Green to XLR pin 3. On the other channel, map cartridge White to XLR pin 2 and cartridge Blue to XLR pin 3. The cable's RFI shield should float unconnected at the the arm and be grounded to XLR pin 1. A separate ground wire may be run from physical tonearm to phono stage chassis.
A standard RCA/XLR converter plug may not work, as these typically short XLR pin 3 to ground and elimininate one phase of balanced signal from circuit. To pass a fully balanced cartridge signal to the phono stage you need a converter plug that maps RCA pin from cartridge positive phase to XLR pin 2, cartridge negative phase from RCA barrel to XLR pin 3, and floats XLR pin 1 unconnected.
As suggested by Lewm, if in an RCA configuration cartridge negative phase and shield to RCA barrel share a common wire, then grounding the shield to pin 1 or chassis will have the effect of shorting out and eliminating one half of the balanced signal.
The main purpose of the pin 1 ground connection on balanced interfaces between powered components is to keep their respective circuit and chassis grounds reasonably common.
Where one or both of the two components has a 2-prong power plug, or is used with a cheater plug, without that pin 1 connection the grounds of the two components may "float" to very different potentials, due mainly to ac leakage paths and stray capacitances in their power transformers. That potential difference may be large enough to saturate the input stage of the receiving component, or at least to exceed its common mode rejection capability.
If both components have 3-prong power cords, then in the absence of the pin 1 xlr connection the grounds of the two components would be kept common only by the ac safety ground wiring, which is not desirable from a noise standpoint.
None of those factors are applicable to a phono cartridge, which has no ac, no power transformer, etc., and which will happily adapt to whatever the ground potential of the phono stage may be.
That said, it may be somewhat beneficial if instead of using an rca cable into an rca-to-xlr ADAPTER at the phono stage input, a twisted pair shielded rca-to-xlr adapter CABLE were used instead. It would be wired such that xlr pin 2 is connected to the rca center pin at the other end; xlr pin 3 is connected to the rca ground sleeve; and the shield is connected to xlr pin 1. Using a cable like that results in the two signal polarities (not signal "halves") on pins 2 and 3 being wired symmetrically (as opposed to an rca cable where the two conductors are not physically symmetrical). That will mean that any noise picked up by the cable will be essentially the same on the two conductors, and therefore rejectable by the receiver in the phono stage.
Just keep in mind that the typical "RCA" cable will have only one conductor for the signal. The "ground" connection in an RCA-terminated cable will typically be carried on the shield that surrounds the "hot" wire. In balanced configuration, there is no "ground". The "hot" wire of an RCA cable fed a balanced signal will carry only the positive half of the signal, and the negative half of the signal will travel on the shield of the cable to the outer ground connection at the RCA plug. Even if you use RCA to XLR adapters, this is the case. Some contend this degrades the signal. Better, IMO, to do a little soldering and change over to XLR, 3-conductor cables all the way.
I think to be truly differential it needs a center-tap 0v. MC cartridges do not have a center tap so the ground (0v) is floating and does not form part of the signal. The ground path of the tonearm should not be part of the balanced signal - pin 1. The chassis is normally pin 1 with 2 hot and 3 cold OR pin 1 CT (center tap), 2+, 3-.
A mains transformer has a center tap for the 0v which the preamp or amplifier uses as the 0 volt reference and is used as the 0 volt reference for the system.
I don't think anyone produces a Moving coil cartridge which is truly balanced - having a center tap. This would mean having 6 pins.
Hope this doesn't go down too badly as my first post! and I was just about to post about getting a new cartridge.
I don't think it is as simple as that.
The problem with running balanced from a cartridge is that the input electronics are doubled which creates 'electronic' noise and not 'common noise' which balancing cancels (CMRR). Common noise in a turntable cartridge system should be nothing significant if your system is setup correctly. Input stage noise though, due to doubling of stages/ components creates more problems than it can solve.
If you have noise or hum from your turntable it is better to look at 'why' than to try and irradicate it using balancing..... prevention is better than cure!
From what I can see, it is a marketing ploy by some phono stage manufacturers, and usually the not so serious ones, and seems to be the fashion for now... I have listen to it and am not at all convinced it is worth the effort and if anything looses some of the 'air' and speed that the single-ended RCA connection gives.
you don't have to do anything the turntable, it is naturally a balanced signal. Its a matter of physical connection. Some balanced phono preamps have xlr inputs instead of rca connectors which require either an adapter or a custom made interconnect, if that is what is needed/can be used, that has rca on the tt side and xlr on the phono pre side. I have used an Audioquest cable made that way and it worked great. Any TT setup can run into a balanced phono pre with the right connection.
Just a matter of changing the connectors and having it wired correct on the Balanced side. There is a great reference doc on Rane.com in the Notes area on wiring, I think RANE NOTE 110..It will show how to terminate correctly..
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