REL Subwoofers, Class D Amps and Neutrik Cables.

I have a Rel 505 and just purchased a a Peachtree grand integrated amplifier which is a class d amp. Unfortunately the Negative speaker terminals on D amps in which the neutrik cable connects to are not a ground which could cause damage to the amplifier. I contacted Sumiko (Rel) and they confirmed this. It sound the like best solution would be to use a neutrik cable that has "Caps" on the black wire or something. I've seen them selling on Audiogon A few years ago but not lately as Rel's new subs do not have the issue. Does anyone have any knowledge of this or has anyone seen seen this type of cable anywhere lately?
I don't know what "caps on the black wire" may refer to in this case. But an approach that should work fine is to obtain a simple RCA plug, perhaps at Radio Shack, solder the black wire to the ground sleeve connection point of the plug, while leaving the center pin unconnected, and inserting that plug into an unused RCA connector on the integrated amp. That would establish a circuit ground connection between the amp and the sub. Don't connect to one of the galvanically isolated digital inputs on the amp, though. And connecting to an analog output jack might be slightly preferable to connecting to an analog input jack.

Another approach that might work ok, depending on the internal grounding configuration of the amp, would be to simply connect the black wire to a chassis screw on the amp.

Good luck. Regards,
-- Al
Hey Puff,

Al nailed it - I have one of those cables you speak of, and that's exactly how it works. Music Direct used to sell them, I'm not sure why but they don't anymore. The cable has three wires on the amp end - two positives that connect to the two positive speaker posts on the Grand, and the black cable has an RCA connector that connects to an analog input or output jack for grounding.
I did get one of those cables made with the RCA ground from my stereo dealer, however I'm not sure if they modified the plug in such a way that the center of the plug is not affected per Almarg.

I spoke to Sumiko and they would not commit on a RCA ground as a safe way to go. I also spoke to a gentleman who used to manufacture cables specifically for this purpose and he is now convinced that any high level connection will eventually harm a digital amp and only reccomends using the low level connection.

In regards to the "Caps Thing' I was referring to how the hot leads are modified with 10 UF film caps. Which I know nothing about. l will reference an old post I found on from 09/08/2011 : (not from me)
I know a little about the problems with some Class D amps (as well as class A/B balanced output amps) and using high level inputs to subs, as recommended by Rel.
It is important to understand that all class D designs are somewhat different in this regard, so what applies to one amp will not neccessarily apply to another. My experience is with IcePower based amps, specifically ones using the ASP series Ice modules. These modules have 40 VDC on their speaker output terminals in relation to amplifier ground, and the amps are balanced output, so the black terminal is not ground, the ground is usually found at the chassis. The solution for a Rel sub with this amp is to put a filter on the speaker outputs to block the DC: so the two hot leads get a 10 uF film cap in series and are hooked up to the appropriate speaker terminals. Then the ground lead is hooked up to the chassis, making sure it makes good contact (one may need to scrape of paint or anodising to expose bare metal.
I believe the newer Ice modules are different in this regard.
All balanced output amps (not just class d) need special consideration to hook up to Rel style sub input. For example, my Pass x150.5 is balanced output, and has a separate ground terminal on the back panel: the ground wire from the Rel goes to the ground terminal, and not to any speaker posts, and the two hot leads go to the appropriate speaker posts.
If you are at all unsure how your amp operates, be sure to contact tech support of the manufacturer of your amplifier, and explain to them what you are doing, and ask them to provide an appropriate solution.
BTW: I am a big believer in hooking up subs this way (even subs which do not have a high level input stock (like JL) can be adapted to use the amplifier connection with the appropriate additional circuitry to match impedance/levels) as this connection method tends to make it easier to get a seamless transition between the main speakers and sub(s).
My experience is with IcePower based amps, specifically ones using the ASP series Ice modules. These modules have 40 VDC on their speaker output terminals in relation to amplifier ground....
I was not aware of that. If that is the case with your Peachtree Grand then, yes, as the person you quoted stated you would need to have capacitors in series with the red and yellow wires. Assuming, that is, that the sub itself does not have capacitors in series with its high level inputs. (When you said that "Rel's new subs do not have the issue," I'm not sure how they could be immune to 40 VDC at their inputs unless their inputs were AC-coupled, presumably with capacitors).

Have you asked Peachtree if the Grand Integrated has a significant DC voltage such as 40V on its outputs? FWIW, its manual does not have any cautionary statements regarding the presence of DC on its outputs. Also, they would be the ones, not Sumiko or REL, who presumably could best advise as to the suitability of using an RCA shell for the ground connection.

Also, you could use a multimeter to measure whatever DC may be present. With no signal going into the amp, you would measure between each of the output terminals and the shell of an analog RCA connector.

And if you have or can obtain a multimeter, by measuring for continuity or resistance you could use it to determine if on the cable your dealer supplied the ground connection of the Neutrik connector is connected to the ground sleeve of the RCA plug, and that the center pin of the RCA plug is connected to nothing.

Good luck. Regards,
-- Al
Thanks Al.
Thanks for the thread and I will read along and try some of the suggestions here. I moved from a multi-channel amp to mono amps recently.

I am now having the same issues as my negative posts are live on my Simaudio mono amps. I have tried the connection to chassis to no avail.

When my amps go into standby I get a pretty loud hum from my REL B1. When moved from standby to on humm stops. Ugh.

Got frustrated and disconnected the Neutrik cable but really want this to work of course.

Will follow the thread if okay and watch for additional suggestions.

REL B1 and Simaudio 400M mono amps.

Thanks Rick
Actually the stupid light bulb just went off. I'm using the new monos for front three and am having the issue with humm at idle. Ground to chassis did not resolve as I stated BUT I just ordered a stereo amp yesterday to drive my rears. It didn't even cross my mind that I should now be able to ground on the new stereo amp as negative terminal is not live. I hope this works. It didn't even cross my mind that ordering a stereo amp for rears yesterday may also solve my REL issue. Will know later in week when it arrives.

If I still have an issue will be at a loss but this should work.

Thanks again for letting me tag along with your suggestions above.

Al, Icepower uses only positive supply voltage and "H" Mosfet bridge for the output. That way at zero output (50% duty cycle) both speaker terminals have half of supply voltage vs. GND.

Hypex usue positive and negative voltage plus only two output Mosfets.
Kijanki, thanks. Your expertise on Class D is always valuable.

Rick, as a point of information REL usually recommends that if a single sub is being connected to monoblock amps it is usually best to connect the black wire to a ground point on the preamp. Ideally, IMO, to a circuit ground point such as an RCA shell, but preamp chassis might work just as well, depending on the specific design.

Also, since your Simaudio's are Class AB, the DC offset issue that has been discussed isn't a concern in your case.

-- Al
I have a REL G2. I tried connecting it to my McCormack DNA 500 amp in the "standard" manner. It got so hot it shut down my amp. I then determined the DNA 500 is a "differential" amp. I then connected as per REL's instructions for Class D and Differential amps. Simply find a screw on the back of your Peachtree, unloosen it, slip the spade of the black wire into place and retighten the screw. This will ground the connection and should solve any problems.
I have a pair REL Studio III connected to a pair of monoblock Spectron Class D amps. The Spectron amps are running as differential amps since they are bridged so the hook up is a little different but I don't use the black wire.