So I was wondering why my Ground Loop isolators made such a difference to the sound....

When I had the Aerpro RCA leads, the isolators made no difference to the sound quality.

I got some nice Stinger RCA's and wondered why there was no change... so I removed the Ground Loop Isolators and well!!!!!!
the transformation was incredible.

This got me to thinking - what do these things really do.

I have done some preliminary measurments and calculations... anyone care to comment on my maths?

SGLI Input Inductance 1.25 Henrys, Output 0.75 Henrys (isolation transformer).

I have assumed from this that the turns ration is about 1.66 to 1

so then I calculated the impedance for 20Hz to 20kHz, XL = 2 * pi * F * L

from the circuits I know that the output impedance of the PXA is 340 ohms, so then I used a voltage divider calculation to determine the output voltage of the SGLI based on the impedance of the SGLI compared to the impedance of the PXA...

Also, I calculated the phase shift due to L in the output circuit...
Click to view attachment

Now it all seems pretty basic to me, and without actually measuring the input/output response... am I on the right track, or am I missing something?

I'm happy to email my spreadsheet if you want to check the calcs.

ok, so I found out some new information:



So I re-did the graph:
Click to view attachment

That looks a bit more realistic - insertion loss at -1.1dB
-3dB point is around 16Hz which is better, but such a slow roll-off.

since removing the SGLI's, I had to reduce the subwoofer level quite a bit (about 6dB), and the midbass is better now too, so perhaps there is more losses than the theory (so far) dictates.....

jeesus...

the difference in your results means that I'd be checking the maths a couple of times...

and not ever using ground loop isolaters ever again...

(is that the right answer?)

Couldn't you just cut the shield on the RCA?

A lot of the problem stems from the output impedance of the PXA being pretty high, if it was lower, say 100ohms, then we'd only be losing 2dB at worst, but the phase shift would still be there.

LDC7 goes into this a bit. think it is in chapter 8? measuring the T/S of a woofer.

need to calculate the impedence of the system (ie source then amp and in ur case, the ground loop isolators)

im @ uni so i cant recall the page number. im pretty sure all the LDC's go into this when they explain how to measure T/S specs.

im sure u have the gear to measure the impedence, from there u can calculate the phase angle shift. that would simplify the mathematics a lot.

on the face of it, the second graph correlates more with what u appear to be hearing. the first graph idicates only very little shift.

i'd imagine u have already clac'ed out the phase shift with the 701? could u chuck it up if u have?

altho i dont kno the maths behind this. i found using LOCS and isolation transformers that u do loose a bit of mid bass and bass. ive got nothing to back it up tho. tho ur calcs do seem pretty on the money.

What sort of phase shift in the 701 do you mean? the output is resistive... if you mean the filter ouput of the DAC...

Click to view attachment

Solid line is amplitude (left scale), dotted line is phase (right scale)

na, i got retarded. i was thinking of the 701 as a unit inline with the signal, ie that the source was say a D310, instead of the source being the 701.

just ignore that bit

also, ignore most of my post. i thought for a moment that we were talking the complex impedence at the speaker (ie, the impedence the amp see's). which is silly.

how does the 701 react to a change in impedence it see's? does it change at all? i know virtually nothing about electronic. im just trying to apply some transducer logic to it all.

Probably one of the better papers on ground loop isolators and balanced CMRR circuits.

http://www.jensen-transformers.com/an/an003.pdf

So, you compared Aerpro and Stinger cables with the Ground Loop Isolators, and tried the Stinger cables without the G.L.I's, but did you try the Aerpro cables again?
Or did I miss something and this is implied?

I originally had the Aerpro cables, no SGLIs.
When I added the SGLIs, I did not notice a difference in the sound, but a lot of the alternator whine was gone.
I put the Stinger RCAs in with the SGLIs - still no difference.
Removed the SGLIs - much improved.

I guess I could put the old RCA's back in to see, but I'm not really interested. The fact that the SGLI's had such a negative impact on the sound is enough for me, and the point of this thread.

Abmolech - yes, saw that when I was looking for an "equivalent" to compare.

This is a graphical representation of the circuit inside an SGLI.
Click to view attachment
There's no ground connection as such, but a flying lead out of each end of the unit - one is connected to the input right ground, the other is connected to the left output ground... :frowns:.

Fair enough, I probably wouldn't want to try them again either
Just another small query though, have you run the Stinger cables along the same path as the Aerpro ones?
i.e. have the Stinger cables lowered the the whine that was evident when you were running the Aerpro cables without the SGLI's?

I'm asking these questions because i've just bought a new car, need new RCA's and tossing up between high end Aerpro, or low end Stinger.
The Aerpro ones look mighty nice for the price.
I've got some temporary cables in and can't here any noise, but maybe it might be nice to have extra 'protection' if it's available.

Keep in mind, though, it's never going to be a high end SQ system.

Same route

The actual first reason for removing them was to see if the noise was still there after I may have found the original problem... haven't checked yet.

Isn't it better to find the cause of the noise, instead of installing GLIs?

yes, but in the short term....

anyway, the noise is now gone - it seems that the Aerpro RCA's allowed noise to enter the system.

Hmm might be a good reason to replace my aerpro RCAs

I get slight alternator noise sometimes and iv tried everything but new RCAs