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Old 24th February 2009, 03:43 PM   #241
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Default I have removed the USB

I have removed the USB pigtail/ ground loop on the computer... It did not help the sound. I was wrong. What was happening was the outside shell of the usb cable was making a bad/lossy connection to the port on the Mac Mini. So when I put the wire in between the two connectors it helped make a better connection. So now I have a new USB cable that is up to snuff and makes good contact. The addition of the ground loop to the new cable make the whole thing sound rather DIGITAL and unfocused.
But the looped grounds on the speakers are good.

Analog and Looped Grounds... Good
Digital and Looped Grounds... Bad
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Old 24th February 2009, 08:59 PM   #242
BudP is offline BudP  United States
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In my own experiments, adding loops to digital ground was a serious mistake. I was worried I had missed something when Phil reported the opposite, but thought I would wait and see what turned up, since I am used to being incorrect.

Thanks for that Marce, very nicely done. Do put some loops on your EnABL'd drivers though, and don't hesitate to put them on the other analog pieces of gear, that do not have a poured ground plane. And if just one of them has an actual circuit mirror ground plane, then it is very unlikely that anywhere but the speakers will be helpful.

Bud
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Old 25th February 2009, 12:23 PM   #243
marce is offline marce  United Kingdom
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Hi Bud,
when I get chance I am going to give it a try, working 24/7 at the moment takes up all my time unfortenatly. Just by coincidence I am on a course for SI and such like for some new layout tools that we have got at work, to try and speed things up while controlling what is going on on the PCB to a greater degree.
Now this following tale I think you and hopefuly others will find of interest on the subject of listening tests, ability to measure etc.
We design communication systems at work, based around Bells midrange frequency range. Our systems have to work 100%, and have to be clear and audible in all situations, there is no deviation from this. We can measure just about anything, and do using a wide variety of very expensive equipement. But we still rely on listening tests for final quality tests etc of our designs. Because listening tests can be subjective we have set up a listening evoironment with a very (very) expensive head and torso model that mimics the humans binaural hearing ability. This gives us a listening test envoironment, where as well as real humans doing the listening we have a reference listener who dosn't have a bad day, gets colds or has a hangover when doing the tests. It also gives us a reference for collating what we here.
So even with ALL the measurement equipement and ability to measure to the nth level we still rely on EARS for the final assesment of our products.
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Old 25th February 2009, 01:02 PM   #244
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Quote:
Originally posted by BudP
In my own experiments, adding loops to digital ground was a serious mistake. I was worried I had missed something when Phil reported the opposite, but thought I would wait and see what turned up, since I am used to being incorrect.

Thanks for that Marce, very nicely done. Do put some loops on your EnABL'd drivers though, and don't hesitate to put them on the other analog pieces of gear, that do not have a poured ground plane. And if just one of them has an actual circuit mirror ground plane, then it is very unlikely that anywhere but the speakers will be helpful.

Bud
What about class D amps?
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Old 25th February 2009, 03:55 PM   #245
BudP is offline BudP  United States
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Okay everyone. Grab your socks. The following is a report from Dave Davenport, the brains behind Raleigh Audio and Rak Dac fame. Attached is a text file with his initial questions and my pseudo answers. I will admit to holding on to this document since mid year 2008, just in case Dave got far enough ahead of his business requirements to do the objective tests he has in mind and they are in his mind, not mine.

Hi Bud,

I have been experimenting with the loops that you sent me as well as some other things. I want to give you an interim report of my findings because prototypes for my new product came in from the assembler today so I will need to give that my attention this week and I am going on vacation next week so it will be a while before I can get back to the loops.

Since I use my system to evaluate products and changes to the products, I have voiced it to be very revealing, perhaps bordering a bit on the analytical. It has extremely high resolution and exposure of detail. As per you suggestion I chose to attach the loops in my system at the ground connection between the DAC board and the analog output board. This point is called “REF” for reference because I am very particular about separating the different grounds. The two boards have differential circuits which are connected together with five, 2” wires: a twisted pair (+/-) for each channel and a voltage reference (ground) for the differential signals. The REF is directly connected to a solid internal ground plane in the DAC board, which is 2.35” wide by 4.9” long. The loops were connected to the REF at the analog output board.

Here is a log of my experiments:

1. Attached a bare loop to the REF pad. There was a noticeable sonic result in two areas. First, it sounded like there was an increase in the upper midrange. (no attempt was made to measure this.) An example of the effect of this is a sharpening in the upper range of female vocals. Second, A slight smearing of the music was greatly reduced. I had not noticed this smear before and was evident only by comparing the sound with and without the loop. The effect was an increased coherence in the music.

2. I removed the loop. The sound returned to as it was originally.

3. I re-attached the loop to the REF pad. The results were as before.

4. Played music continuously for 19 hours. The change in coherence was the same as before the break-in period, however the upper midrange was still increased but not as much as before the break-in period.

5. I removed the loop. The sound returned to the original.

6. I attached the same bare loop to the same REF pad through an 8” piece of #20 Teflon insulated stranded wire. The sound was the same as that with the loop directly attached to the REF pad. (4. above)

7. I removed the bare loop and attached a cotton-shrouded loop to the REF pad. There was a noticeable result. There was the same increase in the coherence as with the bare loop, but without an apparent increase in the upper midrange.

8. Played music continuously for 24 hours. The coherence increased slightly.

9. I removed the loop. The sound returned to the original.

10. I prepared a copper plate by sweat-soldering a piece of 6” long, #20 Teflon insulated stranded wire to the center of the short side of a 10” x 4” x 0.025” copper sheet. I attached the wire to the REF pad. The copper plate was away from the electronics by the length of the 6” wire and lying flat on the top surface of a wooden cabinet. The electronics was mounted open on a glass plate by stand-offs. The glass plate was on the cabinet.

There was a noticeable result. The sound exhibited the same increase in coherence as with either of the loops when first attached. There was a slight apparent increase in the upper midrange, but less so than when the bare loop was first attached.

11. I wrapped the copper sheet in a single layer of a cotton terry cloth dish towel. There was a very subtle diminishment in the apparent increase in the upper midrange.

12. I left the towel on the sheet and played music continuously for 24 hours. The increased coherence was still present but there no longer was an apparent increase in the upper midrange.

13. I removed the towel from the sheet. There was a slight apparent increase in the upper midrange. This apparent increase was less than that with the bare copper plate before the break-in period.

14. I removed the plate and wire from the REF pad. The sound returned to the original.

End of report.

My general observation is that attaching copper to the REF increases coherence (reduces smear) and causes an apparent increase in the upper midrange. Applying a cotton shroud to the copper reduces or eliminates the apparent increase in upper midrange. There is a time, break-in, factor involved.

I must admit that I found myself shaking my head and laughing in disbelief several times, particularly when experimenting with the towel on the copper plate. However, I heard what I heard and will stand by that.

All for now, talk to you later,

Dave
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File Type: txt electron pool q&a.txt (7.8 KB, 213 views)
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Old 25th February 2009, 04:01 PM   #246
BudP is offline BudP  United States
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What about class D amps? Well, they must have an analog portion to be able to drive speakers. I would put a pool right on the return point for the speaker outputs, see what happens.

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Old 25th February 2009, 04:30 PM   #247
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Very interesting, those results are not far off what I've heard using the loops, except I've not used any cotton. The midrange "colouration" went away for me, at least any negative part of it. And it might not even be colouration, but a revelation.

Simon
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Old 25th February 2009, 04:54 PM   #248
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Quote:
Originally posted by BudP
I would put a pool right on the return point for the speaker outputs, see what happens.
Many Class-D amps are BTL so don't have a grounded return.

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Old 25th February 2009, 10:41 PM   #249
BudP is offline BudP  United States
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I was asked for an annotated version of the Q&A document, so that it was clear who was asking intelligent questions and who was providing pseudo answers. So here it is as another attachment.

Bud
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Old 27th February 2009, 08:51 PM   #250
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HI,is the same matter ?

from humblehomemadehifi
"The second tweak was to short the chassis of the driver to the minus pole of the connector. This is easily done by soldering a short piece of wire from the minus pole to the centre connection screw that holds the solder tab in place (see photo). This gave improved midrange clarity with a smoother treble and more punch in the bass amazing for a 5-minute tweak that costs absolutely nothing!"

Click the image to open in full size.
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