UCD180 questions

[tiki]

posted by Bruno:
Really, the wire that acts as a screen and connects chassis grounds should not double as a signal wire. ...

In this way, ground currents that flow from chassis to chassis do not flow on the cold wire and place no voltage across it.

This addresses two problems:
1. The screen may act as an antenna, picking up voltages by influence at high impedances, or currents by induction at lower impedances. Well known as screen current(?, german: Mantelstrom) in the RF-area.
2. Equalising currents may reach levels in the upper mA-range, if the mains wiring is distributed (not equalised loads) and if there are loads connected like PCs. Try to measure the voltage between your satellite receiver's case and the coax cable shield. Such voltages may be dangerous to the audio equipment's inputs.

I believe, it is better to have an extra earth cable, which should be connected to the mostly available earth screw at the metal cases (star ground). I would use one-end-grounding of the screen with stationary equipment. It may be not useful with stage equipment, because of the wiring effort.

BTW: not grounded cases may act as an antenna theirselves, influencing the circuits inside, at least in common mode.

Excuse me the off topic issue again, I believe, it is worth to be told for keeping all the wonderful amp's capabilities.

Regards, Timo

[ewildgoose]

Since we are so far OT, perhaps I can ask a fairly basic question:

Based on what is discussed so far on the balanced idea: this seems to imply that the correct design for a balanced interconnect would therefore be a twisted pair for signal wire, with a shield around both of these. The shield should be connected to earth at both ends?

Has anyone experimented with any particularly successful DIY designs for balanced cables, I see mostly unbalanced designs out there?

[FuriousD]

Balanced audio equipment is normally not designed to have a floating ground (it is tied to chassis), simply because ground is not used as part of the signal. The sound quality advantage of correctly designed balanced connections is often underestimated (possibly due to the relative rarity of correctly designed ones).

Bruno,

This is certainly quite a minefield. Unfortunately for those of us who have to make products that will be used in just about every Hi-Fi configuration, the Chassis connected earth is just not a usable reality. Even in a balanced system, there is usually some 0v referenced section and if this is connected to Chassis earth (Even if its only the Unbalanced outputs), then you introduce every switch mode PSU's unwanted garbage into your audio reference point, and its certainly very audible and will only become a problem that worsens as new regulations push more PSU's towards SMPS

To say that its just a case of Balanced = Connected and Unbalanced = Floating, just is not practical as many circuits may have a differential input but then use a single ended amplification stage for one of many reasons (although these are mostly cost of course).

The HF capacitor connection is usually a trade off to try to avoid RF pickup at a high impedance input (that todays great op-amp designs will usually fold down into the audio band for you) whilst trying to avoid a direct connection and hence pollution of the audio reference point (Single ended). I agree this is not ideal.

Most Hi-Fi manufacturers do it their own way. There is no unified earthing policy, and certainly not in the professional field. This leads to trying to deal with all manner of earthing connections at both inputs and outputs. Also a wide range of true and Pseudo differential outputs does not help this either. That said, what is commonly seen amoungst most manufacturers is a floating system 0v. with the Chassis's connected via the Mains earth connection. UK, Euro and US plugs all allow for this. The balanced cable shield connection is then dependant on the input stage design and setup. A bit of each to his own...

Theres alot more to this and I think it is worth exploring on this thread as it has great relavence to the sound quality achieveablewith the UCD modules.

F.

[classd4sure]

Hi,

Rane Audio has a set of articles which cover the interconnection schemes extensively.


Here's the link for anyone who cares,

http://www.rane.com/library.html

Look under "Wiring, Interconnection & Grounding"

Note #110 and #151 "Grounding and Shielding Audio Devices"

Cheers,
Chris

[wytco0]

I currently use an old NAD 116 Preamp with my Music Fidelity Typhoon Power amps (also old ), I am going to replace the Typhoons with amps using the UCD180s and as I was planning to keep the NAD as Pre for now. The NAD has Balanced outputs available, from earlier conversations it seems that it would be best to use the balanced connections to the UCD180's, is that right or have I misunderstood something (quite likely !).

I am pretty new to this DIY stuff but isn't there a better way of controlling volume than using a preamp for digital power amps? I can see that something is needed to switch between inputs but can't all of the volume control be done in the digital domain somehow?

[classd4sure]

Hi,

The UCD isn't a "digital" amp as you seem to be thinking, it's entirely analog, so you can't just throw in a digital volume without degrading the sound quality of it.

I would be using an Audigy sound card as a pre-amp, sadly the outputs are disgusting on it, I can make an adapter but even that is far from ideal, might have to explore that a bit, but a sound card is my goal for a pre amp.

I've a cheap adapter made up with some 12 gauge monster cable that's over a dozen feet long and the audigy is able to drive it flawlessly though, no noise on it at all (audible) until I turn the computer off, then a 60hz hum takes over with a vengeance.

Regards,
Chris

[Jan-Peter]

Wytco0 ,

When you NAD has balanced output, that's great please use this!

The UcD is called a "digital amplifier" but there is nothing difgital inside....... It's an analog modulated PWM amplfier.

Regards,

Jan-Peter

www.hypex.nl

[Bruno Putzeys]

Originally posted by ewildgoose
Based on what is discussed so far on the balanced idea: this seems to imply that the correct design for a balanced interconnect would therefore be a twisted pair for signal wire, with a shield around both of these. The shield should be connected to earth at both ends?
Has anyone experimented with any particularly successful DIY designs for balanced cables, I see mostly unbalanced designs out there?

The shield is at least connected hard to the transmitting end. On the receiving end, it may be connected hard as well, or through a capacitor if the receiving equipment has a "pin 1 problem" i.e. if the shield is connected to the pcb instead of chassis.
For increased rejection of near-field M fields, star quad cables may be used. They are otherwise unpopular with pro people due to their higher capacitance.

[Bruno Putzeys]

Originally posted by FuriousD

To say that its just a case of Balanced = Connected and Unbalanced = Floating, just is not practical as many circuits may have a differential input but then use a single ended amplification stage for one of many reasons (although these are mostly cost of course).
F.

Yes - in that case great emphasis must be put on the ability of differential receivers to reject common mode. And especially in that case, making sure that the shield current goes straight down the chassis instead of into the pcb is of paramount importance. A fully differential design can live with some unwanted earth current through the PCB, a single-ended circuit with balanced drivers/receivers can under no circumstances tolerate ground currents through the pcb. For that reason again: tie pin 1 to case.

This is now an official AES recommendation. Neutrik is supplying XLR chassis parts with pin 1 firmly welded to the chassis.

A problem that can occur with the standard rca-to-xlr cable I described before is when a consumer device (floating gnd) is connected to two grounded balanced boxes. The equalising current flowing between the 2 grounded boxes goes through the consumer device. There, tiki's advice is sound: tie the shield to case, not to the rca ground. The better adapter cable is thus one where the shield comes out with a screw lug, and an rca plug with the hot wire to pin and cold to sleeve.

[wytco0]

classd and Jan-peter, thanks for reminding me that these modules are not digital, silly me

My modules just arrived (arrived yesterday but I was out) they look very nice. Hoping to put them together later this week, I am now thinking of replacing the insides of my MF Typhoons with the UCD modules as I can do them one at a time. I might even be able to use the MF power supplies but I dont have any details of the schematic for them .