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EQUIPMENT FORUMS >> MINI TORII >> Lifted the ground
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Message started by hifitubes on 07/07/10 at 19:19:06

Title: Lifted the ground
Post by hifitubes on 07/07/10 at 19:19:06

About a month ago after trying multiple PC systems, grounding schemes, power cords, conditioners, and 2 locations, I floated the ground on my my PC (music server, HTPC, DAW, whatever the hell we call them these days).

Then I was going to add a linear supply that I have here, but I'm lazy, so first floated the ground which eliminated the EMI/RFI that was creeping down my AES cable to my external DAC.

I got a new expensive DAC and the noisefloor was worse than my $300 DAC which has an IEC socket; the $$$ DAC has AC wall wart. I would swap the DACs using the exact same power, single-ended RCa, and AES cable from PC. The $$$ DAC had at least 10db higher noise floor.

I floated the ground on the Mini-Torii and it's dead silent.

Does the Mini have anything like:

[edit]a 10 - 47 ohm resistor between signal ground and electrical ground will usually solve ground loops. This is a much better way than fancy ground loop isolators. [/edit]

Now that the PC and Mini-Torii have floated grounds, if I attach their chassis' together with a ground wire, the noise returns. I'd like to make this setup safe as possible and not sure if that means grounding the chassis of each unit to Earth separately or what.

What's the grounding scheme in the mini like? I also had to reverse the + - at my subwoofer or it would short the signal coming off the Torii binding posts. Everything was sharing a common ground?

Everything runs into an Exactpower EP15 regenerator.

Title: Re: Lifted the ground
Post by dank on 07/08/10 at 11:49:13

Hifitubes

I think the first step is going to have to be to figure out if, in fact, the + outputs of the mini-torri are connected together as it appears they are. Power down your system, get out your ohm meter, disconnect your speaker cables and measure the 4 terminals of your mini-torri. Are they all infinite? Are the blacks (-) connected? Are the reds (+) connected? If the reds are connected, I'm 99.9% sure this is NOT the way its suppose to be, and this should probably be corrected before you go any further.

Next, I'd disconnect all your earth grounds, including your sub amp, and check the noise in your system, is it ok for both DAC's?

If so, I'd add the earth grounds back one at a time. What is the noise like with just the sub amp earth grounded? Does the sub amp's polarity switch make a difference in the noise? What is the noise like with just the PC earth grounded? What is the noise like with just the minni-torri earth grounded? The answers to these questions will dictate what to do next.

Dan

Title: Re: Lifted the ground
Post by hifitubes on 07/08/10 at 14:21:57

From memory, there is continuity from either output tranny to all the binding posts, as well as between + & - binding posts.

I don't know if the + are tied; will check.

I currently have the sub grounded, PC floated, Torii floated, DAC grounded. This is VERY quiet.

I tried floating the DAC last night and ground loop returned. I can try floating the sub ground next and then try the DAC again, as well as polarity switch. There is a TINY amount of hum on the monitors which is very acceptable now.

Title: Re: Lifted the ground
Post by dank on 07/08/10 at 15:23:30

Hifitubes

"From memory, there is continuity from either output tranny to all the binding posts, as well as between + & - binding posts"

Oh yea, forgot about those pesky output transformers. OK, right side + to - ought to be somewhere between 1/2 - 1 ohm (transformer secondary). left side + to - ought to be somewhere between 1/2 - 1 ohm (transformer secondary). - to - ought to be zero or infinite (depending on the mini-torri design), and + to + ought to be (zero + 1/2-1 ohm) or infinite.

If you are getting 0 for + to + and 1/2 to 1 ohm from - to - there is a problem that should be resolved.

I'm wondering if you have a red binding post shorted to the chassis.

Could some other mini-torri owner out there measure their amp and tell me if the outputs are common ground or isolated? (what resistance reading do you get from black to black, power off, speakers disconnected?)

Dan

Title: Re: Lifted the ground
Post by hifitubes on 07/10/10 at 17:33:36

Running out the door but I quickly checked with everything still connected and there is continuity between + > + and everything else.

Title: Re: Lifted the ground
Post by hifitubes on 08/20/10 at 02:24:07

Quote:

If you are getting 0 for + to + and 1/2 to 1 ohm from - to - there is a problem that should be resolved.

Sorry for the delay. Powered down, left IEC power cord into Torii as well as RCAs coming from preamp, but all speakers cables unhooked.

Continuity

L + < > R +
L - < > R -

R+ < > R -
L + < > L -

Output trannies have continuity with one another

Resistance

L+ resistance to L- = 1.5ohm

R+ resistance to R- = 1.5ohm

L+ resistance to R+ = 0ohm

L- resistance to R- = almost 3ohms

Title: Re: Lifted the ground
Post by dank on 08/20/10 at 13:40:17

These resistances confirm that your + speaker terminals are connected together, which is not right. Some amps have no speaker terminals connected (isolated), other amps have the - speaker terminals connected (common ground), but no amps that I know of have the + speaker terminals connected. I would suspect a wiring error in the amp or maybe its as simple as the red and black plastic color rings on the speaker connections being installed backwards.

I'm looking at the mini-torri picture on the web site...are your black speaker connections (-) towards the back of the amp like the picture?

If the +/- placement looks right, you may have to call in the pro's and ask if the mini-torri design has isolated outputs, common ground outputs, or common positive outputs (like yours has now).

Dan

Title: Re: Lifted the ground
Post by hifitubes on 08/20/10 at 14:16:15

Yes, IIRC the negative terminals are in the back.

From what your saying though, it sounds like common positive outputs are something unheard of? How does this affect performance, as things sound pretty good right now.

What's happening, IYO, with it wired this way as opposed to the other two options you mentioned (common ground, isolated)?

thanks Dan,
j

Title: Re: Lifted the ground
Post by dank on 08/20/10 at 15:05:58

Isolated, common ground, or common positive will have no effect on sound if you are using the amp by itself with just 2 speakers. The problems come when you try and use the amp with something else.

As you've experienced, if you connect a common ground plate amp (which many plate amps are) you get a dead short. You are lucky that this didn't damage anything.

As long as you know, there's nothing really wrong with it. Connecting to a plate amp by reversing the speaker polarities will work just fine sonically. You just have to be darn sure to always connect them "reversed" rather than "normal".

Dan

Title: Re: Lifted the ground
Post by hifitubes on 08/20/10 at 15:22:08

Thanks Dan. Steve offers this amp with the RCA outputs that are tied to the output transformers so maybe that has something to do with this.

Title: Re: Lifted the ground
Post by Steve Deckert on 08/20/10 at 17:09:17

The Mini Torii has the color codes of the output speaker jacks reversed. Red is actually negative and black is actually positive. This was done to maintain the desired absolute phase.

Steve

Title: Re: Lifted the ground
Post by hifitubes on 08/21/10 at 02:31:56

I'm admittedly a bit confused.

So connecting just my bookshelves, I'm ultimately wiring + to - and vice-versa for absolute phase.

When adding the plate amp, I need to compensate and truly wire the - to - and + to + due to the common ground.

Does this mean the phase switch should be set to Reverse on the plate amp?

Title: Re: Lifted the ground
Post by dank on 08/21/10 at 12:52:04

Many plate amps are common ground. This means that the two negative terminals are connected togeather. When connecting a common ground plate amp to your mini torri you must connect - to + or you will short out your mini-torri outputs.

I would then tend to think that the plate amp phase switch should be set to reverse, but there are other factors involved, so the only proper way to set the phase switch is to listen and set it to the position that sounds the best (loudest = most in phase IMHO).

I would continue to hook your speakers up + to +, although you could certainly hook them up + to - / - to + without harm and give them a test listen to see if you can hear any differences and then hook them up the way that sounds best to you.

Dan