I believe it will work ok either way, but connecting sub negative to amplifier chassis ground is probably preferable in that it would avoid possible problems or damage if at some point in the future the sub ground inadvertently became common. The minor downside of connecting that way is a 6db reduction in the signal amplitude going into the sub, which most likely just necessitates a corresponding increase in its level setting.
Basically, a balanced output has signals on its two output connectors (or connector pins, in the case of line-level xlr connectors) that are equal in amplitude but inverted in polarity, relative to each other. Components with single-ended outputs (or inputs) have their return connection grounded to chassis. Components with 3-prong power plugs have the ac safety ground prong also tied to chassis.
So if you were to connect the two sides of a balanced output into a single-ended input, and both components had 3-prong ac plugs, you would be grounding one of the two balanced signal outputs. Depending on the design of the output circuit, that could conceivably cause damage.
In this case, that situation is avoided because the sub amp's signal ground is not common with ac safety ground. However, as I say connecting it's ground to amp black would create the risk of damage if the sub chassis inadvertently came into contact (either directly or via a cable) with the chassis of any other component that had a 3-prong plug.
By connecting sub negative to amp chassis ground, the sub input will only see half the amplitude that it would see if it were connected between the two equal but opposite polarity signals that are present on red and black. Hence the need to increase the sub's level setting by 6db, which won't be a problem unless there is a gain or sensitivity mismatch somewhere in the system.
Re your final question, the sub leads should ideally be connected at the amp end of the speaker cables, not at the speaker end. That way the current drawn through those cables by the main speakers, and any consequent voltage drops that might result from interaction of that current with cable impedance, will not affect the signals to the sub.
Regards,
-- Al |
So if you were to connect the two sides of a balanced output into a single-ended input, and both components had 3-prong ac plugs, you would be grounding one of the two balanced signal outputs. Depending on the design of the output circuit, that could conceivably cause damage. To clarify my statement a little further, if both amp & powered sub had 3-prong power cords, the path by which the negative (black) output of the amp would be grounded is: Amp black to sub chassis ground to sub ac safety ground to safety ground pin on sub power plug, then via ac wiring to ac safety ground pin on amp power plug, then to amp chassis ground. Also, I'll add to my previous comments that another way in which sub signal ground could conceivably become common with ac safety ground is if an internal short were to occur within the sub amp. That is very unlikely if it is well designed, but if a short were somehow to develope between its signal ground and the neutral prong of its 2-prong ac power plug, that would create such a situation since ac neutral and ac safety ground are tied together back at your ac service panel. Regards, -- Al |
Al,
You are very good at explaining things! you must be a physics teacher or something. I am familiar with how balanced connections work to cancel noise by summing inverted signals. Your explanation has helped me to understand the issue of the interaction with grounds.
Since I have also done home wiring, I also get your point about the possibility of the negative lead going to common ground through a short of the amp.
I think it makes good sense to use chassis ground (per Ayre's recommendation). It is helpful for me to understand why this is so. I don't think the 6db drop will be a problem.
thanks alot Al - I have seen some of your other posts and appreciate your involvement in the Audiogon community.
drew. |
the sub leads should ideally be connected at the amp end of the speaker cables, not at the speaker end. That way the current drawn through those cables by the main speakers, and any consequent voltage drops that might result from interaction of that current with cable impedance, will not affect the signals to the sub. This is as debatable as the long interconnects vs. long speaker cable argument, as there are pros and cons to each approach. While a technical argument can also be made for connecting the sub the speaker's binding posts, simple logistics makes the strongest argument. |
almarg,
A follow up on this.
I connected my r/l speaker outs to the sub, red to speaker positive input and black to chassis ground. The sound was good but not what I expected from the Ayre, the soundstage was compressed into the center and some harshness in instruments such as trumpets etc. As I listened to more music, I definitely felt as though something was not right and started swapping cables. I found that with the either input pulled from the amp, I still got sound from both speakers. Connecting the negative speaker leads both to chassis ground created crosstalk (at about -6b) and so I basically had a very expensive mono system.
So I changed to connecting negative to black speaker input and now everything sounds as it should - which is terrific: great bass, expansive soundstage, space and transparency of instruments (the Ayre is a very musical amp).
Seems to me that the only option is to make sure the sub has no common ground (ground lug on the plug) and connect to the speaker terminals unless I am missing something.
Drew. |
Hi Drew,
Not sure what you mean by "with either input pulled from the amp, I still got sound from both speakers." Are there two subs, or one? I assumed there is only one sub, and its amplifier has inputs for both the left and right channel outputs of the main power amp, which it sums together to feed a mono signal into the sub's driver. The left and right main speakers are separately connected to the left and right amp outputs, and I assume are unaffected by whether or how the sub is connected. Correct me if I'm misunderstanding the situation.
If my understanding is correct, my suggestion would be to try connecting sub left red to amp left red; sub right red to amp right red; and one and only one of the two sub amp black inputs to amp chassis (leave the other sub black input unconnected).
Regards,
-- Al |
Drew -- A further thought: Try connecting as described in my previous post, but with the sub black terminal connected to preamp chassis, rather than amp chassis.
Regards,
-- Al |
Al,
One subwoofer only. What I meant to indicate was when either the left or right input from the DAC is pulled from the Ayre AX7 integrated amp (only one stereo side connected) I hear output from both main speakers (whether or not the sub was on)with the alternate speaker down about 6 - 10 db. When the black leads were removed from the subwoofer amp chassis, there was no crosstalk. Meaning the energy from the balanced negative speaker outs was crossing over and back the negative leads to the main speakers.
So, you are correct and I am having a "duh" moment. When Steve at Ayre suggested grounding the subwoofer speaker connections to chassis ground, he meant on the Ayre, not on the subwoofer. (not a pre-amp chassis as the Ax7 is an integrated that actually doesn't have a pre-amp stage per-se).
I think I get it now and will try the grounding sub negative to the Ayre and not to the subwoofer amp chassis. Although I am still confused about one piece.
Should I do this:
1. Positive speaker outputs on Ayre connected to red speaker inputs on sub.
Negative leads from speaker out to chassis on Ayre - seems like this would ground the mains to chassis as well?
or
2. positive the same
negative from chassis ground on the Ayre to black speaker outputs on sub.?
Drew. |
Ouch! Yes, by all means what was meant was sub black to amp chassis, not vice versa. Keep in mind that with a fully balanced amp, both the red output and the black output of the amp have signals on them (in fact, the same signal except with opposite polarity, as you now appear to realize). When you connected both of the amp's black outputs to sub chassis, you were connecting two different amp output signals together, a definite no no!
I don't quite follow the two alternatives you listed at the end of your post, but let me re-state how I envision the connections should be made:
-- Left main speaker red to Ayre left channel red.
-- Left main speaker black to Ayre left channel black.
-- Right main speaker red to Ayre right channel red.
-- Right main speaker black to Ayre right channel black.
-- Sub left channel red to Ayre left channel red.
-- Sub right channel red to Ayre right channel red.
-- One or both of the two black terminals on the sub to the chassis of the Ayre. I suspect that it won't make any difference whether you connect both of them, or only one of them, since they are most probably connected directly together within the sub's amp.
Regards,
-- Al |
Al,
I get it and appreciate your help - now I am going to leave things as they are and enjoy it.
drew. |
This is an interesting and timely topic as I just today picked up an AX-7 to play around with. I connected my REL to it the way I normally would, with the one black lead connected to one channel's "-" terminal. Drewh1, did Ayre suggest what to use for chassis ground on the unit? There are no obvious screws on the back to use.
(In case anyone at Ayre is reading this, the Cardas binding posts are not ideal when you are connecting a subwoofer this way because you end up tightening down for the terminal with the subwoofer lead and then it's not tight enough on the other pole.)
For subwoofers that only offer line level connection, such as the JL Audio subs, how would you connect them to the Ax-7, which has no pre out -- through the tape out? |
I connected my REL to it the way I normally would, with the one black lead connected to one channel's "-" terminal. Drubin -- What model REL is it? And does it have a 3-prong power cord? If so, you definitely don't want to do that. For the reasons I explained above, and also note the cautions on page 5 of the AX7 manual: http://www.ayre.com/pdf/Ayre_AX7e_Manual.pdfRegards, -- Al |
It's an R-205 and, yes, it uses a 3-prong power cord.
I've lifted the ground. Sound seems to be the same either way. |
Drubin,
The R-205 manual indicates in multiple places that for a fully balanced amplifier the black wire of the high level input should go to amp chassis.
Not sure why you didn't hear a difference when you lifted the ground. Perhaps its signal ground and ac safety ground are not common, the way they normally are with amps and preamps. If you have a multimeter, it would be interesting to see if there is continuity between the black wire and the safety ground pin of the power plug.
In any event, even if things are somehow isolated so that you avoid the risk of damage to the amp, I don't think you will get the right sound with the black wire going to the negative terminal of one of the amp output channels.
If we denote the instantaneous voltage between the amp's left positive terminal and the amp's ground as Lvolts, and the instantaneous voltage between the amp's right positive terminal and the amp's ground as Rvolts, the corresponding voltage that the sub provides to its driver should be proportional to (Lvolts + Rvolts), which is a mono signal obtained by summing together the left and right channels.
That is what will happen with the black wire from the sub connected to amp chassis. However, if it is connected to, say, the left channel negative terminal of the amp instead, what will result is ((2Lvolts) + (Rvolts-(-Lvolts))) = (3Lvolts + Rvolts). So instead of the summation to mono giving equal weight to the two channels, the left channel would receive very disproportionate emphasis (the factor of 3 corresponding to about 9.5db).
Drew -- Upon re-reading my earlier post, I want to make sure it's clear that no disrespect at all was intended when I used the word "ouch." We've all made comparable mistakes at one time or another, including me.
Regards,
-- Al |
Drubin,
I have Ayre MXR's and a Rel Studio. I was instructed by Ayre to connect the red wire (positive) from the Rel to one amp's positive and the yellow wire(positive) from the Rel to the other amp's positive terinal. The black wire from the rel (negative) is to be connected to the center post that is used to tighten the Cardas terminals on one of the amps. This gives the black wire a connection to ground. Hope this helps.
Bob |
Thanks a lot, guys. Al, you are a treasure! |
Drubin- It sounds like Al helped you figure this out. Ayre did not give very complete instructions.
FYI- you can't use tape out for subwoofer output because it is a fixed output and not connected through the volume control.
Al -
no offense taken - I am glad it did not seem to have any ill effects. I guess since I connected each black to different screws on the plate amp, there was enough resistance to prevent a dead short. At any rate - the amp is the best that I have heard so far and I really do feel that the speaker connections to sub amp provide a better subwoofer integration than the pre-outs. This has been suggested in other places in this forum.
Hope everyone is enjoying some music on this beautiful Sunday morning (here in sunny CA).
drew. |
Revisiting this topic, one of the downsides of the chassis ground connection scheme, at least with my REL, is that when the Ayre is turned off but the REL left on, the REL hums. Drewh1, do you experience the same thing? |
Drubin,
I am not using this scheme. After researching, I determined that the only way that a ground connect failure could occur is for the subwoofer amp to fail and short everything to ground. Since my O-audio subwoofer amp does not have a common ground connection, I am hooking both negative and positive leads as normal as this is a very remote possibility. Also the O-audio is a digital amp. I do know of someone else using Ayre with Martin Logan subs who connects both Pos and Neg terminals and has no problems.
You must determine that your amp does not have a common ground connection. It may not be enough to simply lift the common ground from the plug if you have one. The amp I have did not have a three prong plug, only two.
This doesn't directly answer your question, I know but may give you an alternative connection.
drew. |
Interesting. The REL has a three-prong plug. I will say that I think the system sounds better connected the standard way (i.e., not to chassis ground), but that may be the 6db volume difference at work. I don't want to blow up the Ayre of course, but... |
I have a new question on this subject. How do you connect a stereo pair of subwoofers to a fully balanced stereo amp, such as the Ayre.? The REL cable for each sub has two channels of "hot" (red and yellow) plus a ground. I assume that, for each sub, you would connect both hots (or just one?) to the plus side of the appropriate channel on the amp. But what about the grounds? Would you connect both subs' grounds to the chassis? |
Drubin - you might want to start by calling Steve at Ayre about this one. I am sure they have encountered this issue before. |
Drubin -- Yes, you would want to connect both hots (yellow and red) to the plus output of the corresponding channel of the amp, and both subs' grounds to amp chassis.
The subs' electronics sums the difference between its red and black together with the difference between its yellow and black inputs. If you connect both red and yellow to the + output of a fully balanced amp, and black to ground of the amp, then since two identical signals are being summed together, the mono signal the sub provides to its driver will be proportional to the output of that channel of the amp.
If you were to connect sub black to amp negative for the corresponding channel, then as we discussed earlier in this thread you create, under some scenarios, the risk of damaging the amp. However, fwiw, the other downside of doing that which I had mentioned (creating an imbalance favoring one channel in the summation to mono) would not occur in this situation.
Regards,
-- Al |
Thank you, Al. After i posted my question, I looked around on AA and found a response from a REL representative to a customer in India concerning his hum problem. Since your Ayre amp is balanced and since you are using two subs, you must have a balanced hi level inupt which your model does not have. It is not a product defect. The unbalanced hi-level input can be used on balanced amps so long as there is only one sub. Also, since the black speaker terminal on a a balanced amp is not ground but rather positive-inverse, you must ground to the chassis, any screw that stops the hum.
Therefore you can use one sub on the Ayre with the sub grounded to the chassis, or perhaps just take the ground from the LFE and leave the black wire out of the equation if that works for you.
If you wish to have two subs on this amp, you must have one of the larger models that are equipped with balanced hi-level inputs. This is, in fact the only circumstance (two subs in stereo on a balanced amp) where the balanced hi-level input is used. This also gets wired up quite differently. Each channel is red-positive, yellow-negative, and black to chassis ground. This would suggest that I'm SOL regarding using two subs with the Ayre and will need either different models of RELs or a different approach to amplification, such as separates with two sets of preamp outs, or monoblocks, or an unbalanced stereo amp. However, I'm not sure I believe the guy's answer. I have sent a note to REL and will also call Ayre at some point to try to get more clarity. |
Drewh1, your response slipped in. Yes, I will call Ayre, good suggestion.
Does anyone know if JL Audio subs present the same dilemmas? |
Hmmm (pun intended :)).
I feel quite certain that what I said is correct in terms of basic functionality, but I can't say with certainty that hum won't arise (just as it can arise in any system with unbalanced interconnections).
By connecting the black wires from both subs to amp ground, you are connecting the signal ground of both subs together. If the two subs do not have significant voltage offset between their signal grounds (such as might result from plugging their 3-prong power cords into separate dedicated ac lines), and if their power transformers do not have significant leakage between ac hot or ac neutral and signal ground, I wouldn't think that there would be a problem. Even more so because the signal levels involved are speaker-level, rather than being line-level (at lower voltages).
If a hum problem did arise, conceivably it could be fixed by connecting a heavy wire directly between ground points on the two subs. Or perhaps by using cheater plugs, to isolate each sub from ac safety ground.
That said, both the causes and the solutions to hum problems arising from single-ended interconnections can, as I'm sure you realize, be elusive. If REL answers you similarly to the rep you quoted, I would try as much as possible to pin them down as to whether they are basing that on hands-on real world experience, using their subs with balanced amps, or if they are perhaps just being overly idealistic.
Best,
-- Al |
Drewh1, your response slipped in. Yes, I will call Ayre, good suggestion.
Does anyone know if JL Audio subs present the same dilemmas? |
