Beyond the Ariel - Page 746 - diyAudio
Go Back   Home > Forums > Loudspeakers > Multi-Way

Multi-Way Conventional loudspeakers with crossovers

Please consider donating to help us continue to serve you.

Ads on/off / Custom Title / More PMs / More album space / Advanced printing & mass image saving
Reply
 
Thread Tools Search this Thread
Old 15th November 2010, 02:56 PM   #7451
diyAudio Member
 
Join Date: Mar 2006
Location: SE Wis
Quote:
Originally Posted by panomaniac View Post
In the USA we don't have the option now with polarized plugs.
You can either use a heavy duty wire cutters or a Dremmel to remove the tabs on a polarized plug and then you can plug the plug into the receptacle either polarized or non-polarized.
  Reply With Quote
Old 15th November 2010, 03:55 PM   #7452
AR2 is offline AR2  United States
Master Burner
 
AR2's Avatar
 
Join Date: Dec 2002
Location: San Francisco, California
Quote:
Originally Posted by panomaniac View Post
OK, this makes a bit more sense now that I've slept on it.

If the high capacitance side of the transformer is more likely to couple noise into the chassis, you would like the electrical supply wire closest to ground potential to be connected there. Thus less noise coupled into the chassis.

Of course both sides of the mains supply carry current, but the neutral is nominally at ground potential in many systems.

I do remember from the "old days" in the USA before polarized plugs (and also in France where they didn't use them), that swapping the plugs back and both could really result in lower noise. Getting the right combo was often tricky. In the USA we don't have the option now with polarized plugs.
.
OK, simplified, does that means that dot marked point on primary side of transformer should be connected to the phase and the not marked connector neutral?
__________________
www.burningamp.com
  Reply With Quote
Old 15th November 2010, 04:25 PM   #7453
diyAudio Member
 
dantheman's Avatar
 
Join Date: May 2008
Location: Mountain View, CA
Quote:
Originally Posted by soongsc View Post
The absolute value is not accurate, that is why I did not show the scaling.
So how about just telling us how large of a value change between the lines? That way we can get a feel for the amplitude variation.

Thanks,

Dan
__________________
My Blog
My Music Recordings
  Reply With Quote
Old 15th November 2010, 05:46 PM   #7454
Pano is offline Pano  United States
diyAudio Moderator
 
Pano's Avatar
 
Join Date: Oct 2004
Location: Milliways
Blog Entries: 4
Quote:
Originally Posted by AR2 View Post
OK, simplified, does that means that dot marked point on primary side of transformer should be connected to the phase and the not marked connector neutral?
Yeah, I think that's what Bud and Lynn are saying.
  Reply With Quote
Old 15th November 2010, 06:27 PM   #7455
BudP is offline BudP  United States
diyAudio Member
 
BudP's Avatar
 
Join Date: Feb 2007
Location: upper left crust, united snakes
yup..that's what I'm sayin.....
__________________
"You and I and every other thing are a dependent arising, empty of any inherent reality" Tsong Ko Pa
  Reply With Quote
Old 15th November 2010, 06:35 PM   #7456
AR2 is offline AR2  United States
Master Burner
 
AR2's Avatar
 
Join Date: Dec 2002
Location: San Francisco, California
Good, without knowing the detailed description, I was kind of intuitively doing the right thing. Sort of makes sense. Thank you BudP for describing the logic behind.
__________________
www.burningamp.com
  Reply With Quote
Old 15th November 2010, 08:44 PM   #7457
diyAudio Member
 
Lynn Olson's Avatar
 
Join Date: Jul 2004
Location: Northern Colorado
Default More Measurements

This isn't an area where we have to guess or do a lot of audiophile listening - we can measure and get the right answer. All you need is a modern high-impedance DVM. (A sensitive capacitance meter is optional.)

Connect device A and B (say, a linestage and a power amplifier) to the AC wall socket. DO NOT interconnect them. Turn them both on. Measure the AC Volts potential between the two chassis. I've measured anywhere between 3VAC and 70VAC between pairs of chassis, on a North American 120VAC system. These voltages appear on two-prong (ungrounded) and three-prong (grounded) equipment, and are the result of small leakage currents (specifically, stray capacitance) between the primary of the power transformer and chassis.

Next, measure the potential between the chassis of device A and the ground pin of the wall socket. Ideally, float the chassis of the device by using a 3 to 2-prong "cheater" plug, although this poses a serious user hazard if there is a fault condition in the device. Wearing gloves is a good idea when doing things like defeating safety features.

Note the measured potential will NOT be zero. Repeat for device B. Keep the gloves on as long as the device is plugged into the "cheater" adaptor. (Common fault conditions include miswired or defective power switches.) The device with the higher AC potential between chassis and ground is most likely the one with the reversed primary winding. A more rigorous method is to directly measure the capacitance between the chassis and each side of the incoming AC line - with everything turned off and disconnected, of course.

Connect the two pieces of equipment with your favorite audiophile interconnect. (If using unbalanced RCA's, turn off the second device before connecting together, then turn it on again after connecting.) Measure the voltage potential between the two devices - it will probably be in the small millivolt range, or lower. Don't smile too quickly; that same voltage, which is very noisy AC, will appear as a common-mode signal at the input of the second device.

What causes this? There's a small leakage current, mostly capacitive, and thus tilted towards HF noise, between the incoming AC and the chassis of the device. The best way to reduce this leakage current is use specialized medical-grade low-leakage power transformers, but this rarely done due to cost and size considerations.

The shield, or "ground" side of the interconnect creates a metallic connection between the two chassis. Since it has a finite resistance (no, it's not a superconductor, despite what the advertising says), there's a voltage drop that appears across the length of the cable. This voltage drop translates the small chassis-to-chassis current flow into a voltage, which then appears at the (voltage-responsive) input of the second device.

How to improve this situation, which unfortunately applies to all interconnected pieces of equipment that are not transformer-isolated from each other? It may not be practical to rewire the offending devices, although that is the most permanent solution. An even better solution (and less practical) is to throw out the high-leakage power transformer and replace it with a medical-grade low-leakage transformer - these use foil-shielded windings that are on different sides of the core, thus no direct physical contact between the primary, core, case, secondary, or anything else. (A generic power transformer depends on the enamel coating of the primary wire for all shielding and isolation - think about it! All it takes is a pinhole in the enamel coating for things to start to go wrong very quickly.)

If you add a heavy chassis-to-chassis braid that covers and shields the audiophile interconnects and presents a lower impedance than the signal-return of the interconnect, that decreases the voltage drop between the chassis, and offers a lower-impedance path that does not carry audio currents. Crude-looking but effective.

Balanced XLR interconnects and circuits offer improvement, but as long as there is a metallic connection between the two chassis, AC noise currents will flow, and it is up to the CMRR rejection to the second device to get rid of this noise. In effect, you're using pair-matching, feedback and gain to get rid of a problem that shouldn't be there in the first place.

When you have to transport audio signals over long distances (20 meters or more), active CMRR solutions cannot handle the safety hazards of equipment plugged into dissimilar AC systems, nor can they reject the large amount of induced common-mode noise of long (balanced) cables. Think about what it takes to reduce induced noise in a large studio for television or sound movies that have a huge number of noise sources - motors, light dimmers, various gizmos of all different kinds, and long connections between audio gear. This is where transformers with high isolation ratios come in; to break the grounds, filter off RFI, and deliver very good balancing (on both send and receive) that is independent of the CMRR figures of active electronics.

Anyway, this is why I'm a little skeptical of cable comparisons in typical audiophile systems with hard connections between different devices. Low-level noise, particularly hashy noise from the incoming AC line, can mimic sonic colorations when it is below directly-audible thresholds. (In other words, you might have to be right next to the speaker to actually hear the hash or roughness, but it will be audible as a coloration when sitting further away.) There are good reasons for the pro world to go to the lengths they do to get AC noise as low as possible - and there's no reason we can't follow suit with our equipment.

Last edited by Lynn Olson; 15th November 2010 at 09:12 PM.
  Reply With Quote
Old 15th November 2010, 09:24 PM   #7458
diyAudio Member
 
Lynn Olson's Avatar
 
Join Date: Jul 2004
Location: Northern Colorado
By the way, I want to thank all of my transformer-building friends - Bud Purvine, Dave Slagle, Per Lundahl, Mike LeFevre, John Atwood, and many others for all the good info they've given me over the years. Also a big thank-you to Gary Pimm for educating me on instrumentation design and shielding techniques, and another big thank-you to John Atwood for vacuum-tube physics.

When you know more about how devices actually work, you don't need to resort to audiophile hand-waving. You know where to look, and what to measure for. All physical devices depart from the pretty little models; real engineering is knowing how the physical devices depart from the models, and how to design around that. (Tektronix 101, but I'm sure Bell Labs and Hewlett-Packard did things this way too.) Watching things getting built is very educational - you can then see why the device has the little peculiarities it does. Something as minor as the choice of voice-coil glue (doesn't sound like much, does it?) actually has an effect on the sonics of an entire audio system. Similarly, physically mapping out the capacitive leakage path from primary to chassis is very informative. Stray capacitance is everywhere, so you might as well know what it's doing to your circuit and the system as a whole.

Last edited by Lynn Olson; 15th November 2010 at 09:45 PM.
  Reply With Quote
Old 15th November 2010, 09:26 PM   #7459
Pano is offline Pano  United States
diyAudio Moderator
 
Pano's Avatar
 
Join Date: Oct 2004
Location: Milliways
Blog Entries: 4
+1
  Reply With Quote
Old 15th November 2010, 10:13 PM   #7460
TerryO is offline TerryO  United States
diyAudio Member
 
TerryO's Avatar
 
Join Date: Nov 2002
Location: Seattle,Wash.
Quote:
Originally Posted by panomaniac View Post
+1
Ditto here as well!
__________________
"If you have to ask why, then you're probably on the right track."
quote from Terry Olson's DIYaudio Forum application
  Reply With Quote

Reply


Hide this!Advertise here!
Thread Tools Search this Thread
Search this Thread:

Advanced Search

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off



New To Site? Need Help?

All times are GMT. The time now is 02:27 PM.


vBulletin Optimisation provided by vB Optimise (Pro) - vBulletin Mods & Addons Copyright © 2014 DragonByte Technologies Ltd.
Copyright 1999-2014 diyAudio

Content Relevant URLs by vBSEO 3.3.2