How technical are you?

DaveyF · Dec 7, 2011

Yesterday, I spoke to the tech at Audio Research... i think his name was Chris. Anyhow, we spoke about an issue that I am having with my REL sub connection to my ARC D70Mk2 amp. The amp uses the 4ohm tap as a ground and the REL uses a ground connector ( or something like that, anyhow I had been warned not to connect the REL in the usual manner to the amp for fear of something ( cannot remember what but it wouldn't be good

)....).The tech was very obliging and tried to explain some of the electrical and scientific properties of the amp to me...DUH!!

I just really didn't get it.

I have to admit that my technical understanding of our hobby is very limited

. I know some of the posters on this forum are highly competent in this area and some are like me.....where do you fall

Johnny Vinyl · Dec 7, 2011

I don't have a technical, scientific, mathematical bone in my body! It's all just gibberish to me! Must be my genes, although one of my brothers lives for that kind of information. Personally I could care less ( for the most part), but I deeply admire people who can make sense out of it all. That's not to say I haven't tried to learn, but I just cannot grasp it, so I gave up trying to understand it all years (make that decades) ago. Maybe that's why I am so much more of a media/content fan...and sometimes pretty knowledgeable about that side of the hobby as well ( or at least think so).

fas42 · Dec 7, 2011

I'm an ideas person, love developing an understanding of something technical; come from a long line of doctors and engineers, so that probably has something to do with it! Doesn't mean I have a vast storehouse of technical knowledge, especially as I got sidetracked into computing during my working life, but delve into the into the nuts and bolts of things with the energy of a highly enthusiastic "amateur". I believe I have good abilities to learn, understand something new, and then come at a problem from new directions ...

Biggest downer is that the brain is slowing down, starts to "smoke" if I put too much pressure on it, so often have to take things easy ...

And I'm no musician: a disappointment is that I've tried several times but it just doesn't click, at least to the point where I get ongoing enjoyment from making the effort.

Frank

DonH50 · Dec 7, 2011

ARC grounds the 4-ohm tap so the output using the 8-ohm tap is "balanced" in their design. That is the signal swings equally about the 4-ohm tap but in opposite polarity at the 8-ohm and ground taps.

My technical level? Middling, anyway...

And, I am a musician, or at least I try, and local groups keep asking me back. Just got home from a rehearsal, as a matter of fact.

DaveyF · Dec 8, 2011

Don, That's not what I understood the tech to tell me at ARC...But then, like I said, I listened but he talked way over my head

I was told to connect the REL hot and neutral to the 8 ohm taps and the ground to the 4 ohm tap...apparently that will result in a 4ohm connect to the REL and not a ground loop ( at least that's what I thought i was told

) At the same time, my speakers are running off the 4ohm tap..
With my extremely limited understanding of this stuff, I have no idea whether I understood him correctly or not...

Luckily, I guess when it comes to understanding musical instruments I fair much better

jadis · Dec 8, 2011

On electrical matters, technically zero. If biasing using those friendly pots at the back of my ARC amp counts, then maybe 1, out of 100.

On mechanical stuffs, a lot higher. I worked in my father's aluminum extrusion plant for 22 years so I am familiar with tool and dies, measurements and the like.

When it comes to crossover cut-offs in bi-amping, I get confused easily. Though I really ought to learn these things one day. I feel that is the ultimately audio set-up.

Phelonious Ponk · Dec 8, 2011

Technically, davey, I suspect I'm closer to you than Don. Musically? I'm an ear-trained rock/pop/country musician not a jazz or classical virtuoso, but I front bands as well as participate in them, I'm pretty good at it, and have never had any trouble finding a gig. I attribute that not to hard work or skill but enthusiasm. I love it.

Tim

microstrip · Dec 8, 2011

DonH50 said:
ARC grounds the 4-ohm tap so the output using the 8-ohm tap is "balanced" in their design. That is the signal swings equally about the 4-ohm tap but in opposite polarity at the 8-ohm and ground taps. (...)

.

Don,

Just a small detail - the full balance of the ARC output transformer is at the 0 and 16 ohm, not the 8 ohm.
.
If you want to use it as a balanced output for a XLR type subwoofer input you connect pin 1 of the XLR to 4 ohm, 2 to the 16 ohm and 3 to the 0 ohm.

Some people using 4 ohm speakers with by-wiring capability connected 0 and 4 to the - and + of the bass and 4 and 16 to - and + of medium/treble using two pairs of speaker cables.

DonH50 · Dec 8, 2011

Hmmm... You are probably right, but that does not jive with my memory of the windings on my old D79. That amp has moved on to mep and I lost (misplaced, technically, since they are in the house someplace) the schematics (not sure they showed the actual winding configuration anyway; I had to measure that). I plead forgetfulness, senility, whatever and bow to your knowledge.

Not sure I ever saw anyone connect with bi-wiring that way but (despite working for a dealer) I don't recall a lot about their specifics... It does sound familiar; I saw a lot of "interesting" wiring configurations, including those who thought putting the 0-4 and 4-8 (or 8-16) ohm taps in parallel on a 4-ohm speaker would double the output power...

microstrip · Dec 8, 2011

You can find many schematics of old ARC gear at the Audio Research database site,

http://www.arcdb.ws/

including the great D79:

Grainger49 · Dec 8, 2011

Davey,

Pretty technical here, I'm a retired EE. But I used to be an audio salesman before that. So I understand that many guys out there are not following.

Looking at the above schematic, and I may have missed the tie point, the 0 point of the output transformer secondary is tied back somewhere in the circuit (I'm not tracing it closely) and the 4 ohm tap is tied to what I call circuit common. This is a point where many of the signals are "referenced." When you measure a voltage it is from one point to another. One of those points is the reference. The reference is often ground, the chassis or a point that is just common to the RCA inputs, power supply negative and center taps on transformers.

This is just the kind of point that is also connected to the 4 ohm output tap in the schematic above. That point is some ohms above "common." You will see the word "common" on a line that will trace back through two resistors to the "0" connection on the output transformer. So it is allowed to "float" a little.

The pragmatic thing to do is to check the resistance from the "0" connection on the amp to the chassis of the amp. That gives you some idea of the isolation between the two points.

The same thing should be done for your REL. Check from its input to the chassis. See if they are tied together.

To get a grasp on the absolute resistance you are reading touch the meter leads together and see what the internal resistance of the leads is. Ignore this much resistance when you measure the others.

I hope this helps.

DonH50 · Dec 8, 2011

@microstrip: Thanks for that! I see you are right...

@Grainger49: Nice to have another EE on board! Looking over the schematic, I see the common is used as the common for everything in the signal path and all power supply secondaries, but see no tie to chassis ground. I thought there was; my old ARC preamp has a low-value resistor connecting chassis to signal ground at one point. I had thought that was a code/UL requirement, but it either isn't (wasn't) or I simply didn't find it in my look at the D79 schematic. The 0 and 16 ohm taps provide feedback.

DaveyF · Dec 8, 2011

Grainger49 said:
Davey,

Pretty technical here, I'm a retired EE. But I used to be an audio salesman before that. So I understand that many guys out there are not following.

Looking at the above schematic, and I may have missed the tie point, the 0 point of the output transformer secondary is tied back somewhere in the circuit (I'm not tracing it closely) and the 4 ohm tap is tied to what I call circuit common. This is a point where many of the signals are "referenced." When you measure a voltage it is from one point to another. One of those points is the reference. The reference is often ground, the chassis or a point that is just common to the RCA inputs, power supply negative and center taps on transformers.
This is just the kind of point that is also connected to the 4 ohm output tap in the schematic above. That point is some ohms above "common." You will see the word "common" on a line that will trace back through two resistors to the "0" connection on the output transformer. So it is allowed to "float" a little.

The pragmatic thing to do is to check the resistance from the "0" connection on the amp to the chassis of the amp. That gives you some idea of the isolation between the two points.

The same thing should be done for your REL. Check from its input to the chassis. See if they are tied together.

To get a grasp on the absolute resistance you are reading touch the meter leads together and see what the internal resistance of the leads is. Ignore this much resistance when you measure the others.

I hope this helps.

Grainger49 Thank you for your description...Unfortunately, I am still at a loss trying to figure out what is the possible outcome IF I hook up the Rel incorrectly. The tech at ARC told me to attach the left hot Rel output to the 8ohm left tap, the right neutral to the right 8ohm tap and the Rel ground to the 4ohm tap. He said in that way the Rel would see a 4ohm load along with my speakers, which are attached to the 4ohm tap and the 0 ohm tap....( At least that's what I thought I heard him say

) My understanding of all this, and of the subsequent explanation to me of why and how the ARC's of this vintage utilized a grounded 4ohm tap, went way over my head

Am I understanding the tech correctly in his set-up topology or am I about to potentially blow everything up

microstrip · Dec 9, 2011

DaveyF said:
Grainger49 Thank you for your description...Unfortunately, I am still at a loss trying to figure out what is the possible outcome IF I hook up the Rel incorrectly. The tech at ARC told me to attach the left hot Rel output to the 8ohm left tap, the right neutral to the right 8ohm tap and the Rel ground to the 4ohm tap. He said in that way the Rel would see a 4ohm load along with my speakers, which are attached to the 4ohm tap and the 0 ohm tap....( At least that's what I thought I heard him say ) My understanding of all this, and of the subsequent explanation to me of why and how the ARC's of this vintage utilized a grounded 4ohm tap, went way over my head

Am I understanding the tech correctly in his set-up topology or am I about to potentially blow everything up

Does your REL subwoofer have a Neutrik speaker cable with a Red, Black and Yellow cable?

Anyway, you were given the correct indication - the main reason for using the 8 ohm taps is to have the less gain as possible. If you hook the Rel ground incorrectly you can risk shorting the output of the ARC and, even if it works , you will get a strange proportion of the left and right channel in the subwoofer mix!

DaveyF · Dec 9, 2011

Hi Micro, the REL does use a Red,Black and Yellow cable with a speakon connector. So, the tech at ARC said place the yellow on the left 8ohm tap, the red on the right 8 ohm tap and the black on the 4ohm tap.
Meanwhile, my speaker cables are attached to the 4ohm tap and the 0 ohm tap, both left and right. ( at least I think that is what he said, he went over the circuit topology and also the electrical properties with me as well, which basically made my head spin

)

I haven't tried this yet, since I am using my Rowland as the amp of choice for the moment and still trying to dial in the sub with this amp in the system.
Thanks.

DaveyF · Dec 11, 2011

I was talking to a fellow a'phile last night, who also happens to be a EE. He laughed when I told my story about the tech at ARC

My friend told me that in his opinion the funniest thing about the situation is that the tech at ARC probably knows very little about the current science in the field....why, because they haven't taught tube theory or as he put it-" how to figure out if steam is rising and at what rate" for years, today they are teaching a lot more advanced stuff. To which he continued that if I thought that the stuff that I was being told from the ARC tech was making my head spin, then don't talk to any of the current guys at the SOTA...

I'm sure glad I'm NOT in that field

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