REL + Class D poweramp advice

[G-Dubz]

Hi there, 

 

I've managed to complete my 2.1 setup thanks to all the help I've received at SNA and have been really happy with my setup. 

I recently purchased the last item (for now), a REL R305 sub for a bass boost to Kef LS50's in an apartment living area. They are driven by a Primare SP33 pre/pro and 30.7 Class D poweramp. 

 

I've connected the R305 to the 30.7 using the hi/lo speakon cable that came with the REL. I haven't got an LFE RCA cable just yet. I've connected the hi/lo speakon cable according to the manual with the black & red to +/- input and the yellow cable to the other + input of the Kef's and have run the system for a day or so and everything seems to work fine - no hum, bass sounded great.

 

However, I was reading about LFE cables online, then ran into some quite alarming warnings about REL's and Class D poweramps such as the Primare 30.7 - the official REL website has explicitly said that the black cable should not be connected to the (-) port and should be left disconnected and covered with electric tape due to something with Class D amps not being fully grounded. They warned about potential heating damage to the REL +/- the amp. 

https://relsupport.zendesk.com/hc/en-us/articles/115004486607-Class-D-Amp-Connection-Methods

 

However, when I disconnected the black cable there was a loud hum on the sub. The article then went on to suggest earthing the sub using the LFE RCA channel, so I've ordered a cheap subwoofer RCA cable off ebay (gold plated/double shielded) one to see if that will fix the hum and earth the circuit. 

 

Whilst that is arriving, I was just wondering if there are any other REL owners out there who have experience with connecting them to class D poweramps?

 

If the RCA works, is a better shielded/more expensive subwoofer specific cable necessary for a musical 2.1 setup as I would need a 3m length? And also whether the black cable should definitely be left free and if the RCA cable does not fix the hum and earth the circuit, what troubleshooting options might there be? 

 

Many thanks in advance!

 

 

 

[Ittaku]

I'm not sure about the specifics of class D power amps, but bridged regular amps will burn out if connected to Rel high power inputs because they expect their negative terminals to be grounded. I know of someone who burnt out some very expensive bridged monoblocks this way. Presumably the class D amps have the same problem - no ground on the negative terminal?

[G-Dubz]

5 minutes ago, Ittaku said:

I'm not sure about the specifics of class D power amps, but bridged regular amps will burn out if connected to Rel high power inputs because they expect their negative terminals to be grounded. I know of someone who burnt out some very expensive bridged monoblocks this way. Presumably the class D amps have the same problem - no ground on the negative terminal?

Cheers for the reply - very alarming indeed!

 

The articles from the REL official websites/blogs suggest that class D amplifiers are 10-15 volts above ground on their black terminals which actually draws current in a circuit setting which is meant to be zero. Their workaround was to disconnect black & then earth the sub via an RCA connection from the REL LFE. 

 

I guess one of my main questions is when you have separates will earthing still work the same? ie. the high level speakon cable from the sub connects to the class D 30.7 primare poweramp

but the LFE RCA will have to connect to the SP33 Primare pre/pro RCA subwoofer port for grounding. 

 

One of the REL videos also shows the black cable being grounded by contacting it with a screw on the back of the poweramp. 

 

Have spent many months slowly but surely building the system, so very keen to give it the proper due diligence and avoid any electrical disasters, particularly for my first setup. 

 

Any advice welcome! Cheers. 

[tubularbells]

The issue with Class D and bridged amps is the negative speaker terminal is not grounded to earth as is the case for more mainstream amps therefore if you connect the REL's black wire your effectively creating a short circuit which will either blow the amps fuse, trigger the protection device (if your amp has one) or destroy the amp.

 

Ive used REL's on a few class D amps connecting just the yellow and red wires to the + terminals. If you experience hum simply attach the black wire to the chassis of the amp or another piece of grounded equipment in your rack (a phono ground screw is useful for this) but DO NOT connect to the speakers negative terminal.

[G-Dubz]

7 hours ago, Tubularbells said:

The issue with Class D and bridged amps is the negative speaker terminal is not grounded to earth as is the case for more mainstream amps therefore if you connect the REL's black wire your effectively creating a short circuit which will either blow the amps fuse, trigger the protection device (if your amp has one) or destroy the amp.

 

Ive used REL's on a few class D amps connecting just the yellow and red wires to the + terminals. If you experience hum simply attach the black wire to the chassis of the amp or another piece of grounded equipment in your rack (a phono ground screw is useful for this) but DO NOT connect to the speakers negative terminal.

Thanks for the confirmation & advice. 

 

Would it be ok to stick the black wire (with screwed in banana plug) down to the chassis of the amp with electrical tape to ground it? 

[tubularbells]

35 minutes ago, G-Dubz said:

Thanks for the confirmation & advice. 

 

Would it be ok to stick the black wire (with screwed in banana plug) down to the chassis of the amp with electrical tape to ground it? 

Could work but thats a very dodgy way to do it. Try it first by touching the black wire to and exposed screw on the amps chassis or another piece of gear just to see if that stops the hum your experiencing (it should).

 

If so then see if theres some easy grounding point on the amp or other equipment otherwise you could loosen a screw on the rear panel, wrap the wire around & re-tighten as an alternative or better yet buy an RCA plug and solder the black wire to the outer connector and plug into an unused RCA jack

[doogie44]

May I add a comment here? For many years I used a Wyred4Sound Class D stereo amp in my system (with 2 REL Storm 5 subs) and took those REL warnings seriously. I changed from connecting the subs at the amplifier terminals (using the 'speakon' connections) to going 'LFE' from my preamplifier subwoofer outlets, thence to the subs.

 

People say that you get better bass and such using the amplifier connections. Well, this might be technically correct I can't agree with that because I can't tell the difference in my system. The cutoff is set at 30Hz with the LFE but the quality of the sound overall--in every way--is very good. The convenience and absence of worry about the connection rules.

 

Now I am using a different amplifier but I still use the LFE path. I am a REL fan for decades and they have never made a bad product in my opinion.

 

Just my 2c worth

[blybo]

On 03/04/2019 at 11:01 AM, Tubularbells said:

better yet buy an RCA plug and solder the black wire to the outer connector and plug into an unused RCA jack

@G-Dubz I'm pretty confident the store you bought your Rel from would happily modify the cable for you in this manner.

 

 

[G-Dubz]

Thanks for the comments. 

 

I actually bought it second hand from an SNA member. 

 

Interesting re: using LFE only! 

 

My plan currently is to electrically tape up the black port on the speakon cable, making sure there is no metal exposed and then let it float. Then ground the sub by getting a sub RCA-LFE cable. Hopefully that will do the trick. 

[blybo]

3 minutes ago, G-Dubz said:

My plan currently is to electrically tape up the black port on the speakon cable, making sure there is no metal exposed and then let it float. Then ground the sub by getting a sub RCA-LFE cable. Hopefully that will do the trick. 

I'm sure that will work, however the other solutions are a more elegant option and I'm sure a member here could do the soldering for you if you aren't confident yourself. YouTube is awesome for learning DIY tasks.

[andyr]

I'm confused! 

 

I thought REL subs were powered subs - ie. they have their own built-in amplifier?  (So why do you need to connect them to a power amp?)

 

If this is because of REL's "USP" - that by connecting the amp to the REL's spkr inputs, you get a more integrated sound with the satellite spkrs - well that is just marketing BS by REL (to give them a Unique Selling Proposition), IMO.  The normal connection for spkrs & sub - in my world, anyway - is at line level ... ie.:

• an RCA cable from preamp to the power amp which drives the satellites
• and an RCA cable from preamp to the sub(s).  This doesn't have to be a special "sub RCA cable" - just a normal shielded RCA.

 

Andy

 

[markm1111]

This is also an issue with Bel Canto Class D amps. There is, or at least was a few years back, a white paper on the Bel Canto site which details the issue, and gives reasonably thorough instructions on how to safely connect the Rel high level cables to the Bel Canto amps. This should be applicable to your Primare amp as well.

 

My understanding is that the Rel subs perform much better for music listening duties with the high level connections. I currently have Bel Canto Class D amps and a Rel sub, but as I only use it for HT duties, it is connected via LFE from the AVR.

 

If I can find it I will post a link

[markm1111]

I knew I had discussed this before!

 

Also try http://www.belcantodesign.com/pdfs/e_OneTOsub.pdf

 

 

 

[andyr]

18 minutes ago, markm1111 said:

 

My understanding is that the Rel subs perform much better for music listening duties with the high level connections.

 

 

Where did you get this understanding from, Mark?

 

(Reading REL mktg blurb ... or actually comparing both ways of connecting up a REL?)

 

Andy

 

[markm1111]

Just now, andyr said:

 

Where did you get this understanding from, Mark?

 

(Reading REL mktg blurb ... or actually comparing both ways of connecting up a REL?)

 

Andy

 

Bit of both probably Andy. I often wonder about me hearing what I am "supposed" to hear.

 

When I ran the Rel connected high level to a Burson PI-160 for 2.1 duties, I felt it sounded tighter than hearing it connected via LFE to the AVR. The Burson and the AVR were in the one system, using the same main speakers and sub, and an Opp 95 as source (HDMI to the AVR, single ended stereo output to the Burson, playing a CD). Whether or not that was imagined is up to interpretation, and it certainly wasn't a double blind test, but I was fairly confident there was difference in favour of the high level connection. Having said that, connection wasn't the only variable. YMMV

[andyr]

3 minutes ago, markm1111 said:

Bit of both probably Andy. I often wonder about me hearing what I am "supposed" to hear.

 

Yes, that is indeed a valid point, Mark.  I tend not to trust my ears but rely on the hearing acuity of my 'golden-eared panel'.  (You know who you are.  )

 

3 minutes ago, markm1111 said:

When I ran the Rel connected high level to a Burson PI-160 for 2.1 duties, I felt it sounded tighter than hearing it connected via LFE to the AVR. The Burson and the AVR were in the one system, using the same main speakers and sub, and an Opp 95 as source (HDMI to the AVR, single ended stereo output to the Burson, playing a CD). Whether or not that was imagined is up to interpretation, and it certainly wasn't a double blind test, but I was fairly confident there was difference in favour of the high level connection. Having said that, connection wasn't the only variable. YMMV

 

Mmmm, that seems to me to be very different scenarios - which could explain the sonic difference.

 

An example of what I would consider was not a different scenario would be:

• preamp to the power amp driving the main speakers ... plus preamp to sub(s).
• preamp to the power amp driving the main speakers ... plus connections from these speakers to the sub(s).

 

Andy

 

[markm1111]

2 minutes ago, andyr said:

Mmmm, that seems to me to be very different scenarios - which could explain the sonic difference.

 

An example of what I would consider was not a different scenario would be:

• preamp to the power amp driving the main speakers ... plus preamp to sub(s).
• preamp to the power amp driving the main speakers ... plus connections from these speakers to the sub(s).

Fair point Andy. Given the Rel can only connect to low level RCA, or high level at the speaker connections on the amp, probably the only way to truly compare would be to connect to the speaker outputs on the AVR. Given many AVRs these days are Class D, likely to run into the same issue. Don't think I can even do it on my Vitus, as I believe although it isn't class D, it has a similar issue with high level connections (I recall reading that somewhere....). Might just put it in the too hard basket

[andyr]

2 hours ago, markm1111 said:

Fair point Andy. Given the Rel can only connect to low level RCA, or high level at the speaker connections on the amp, probably the only way to truly compare would be to connect to the speaker outputs on the AVR. Given many AVRs these days are Class D, likely to run into the same issue. Don't think I can even do it on my Vitus, as I believe although it isn't class D, it has a similar issue with high level connections (I recall reading that somewhere....). Might just put it in the too hard basket

 

So it seems REL is able to get away with not having their USP (which is: connect through the main speakers to the subs) disproved ... because the people who use REL subs generally have HT systems (and, hence, AVRs) rather than stereo amps in a music system?

 

Andy

 

[G-Dubz]

3 hours ago, markm1111 said:

I knew I had discussed this before!

 

Also try http://www.belcantodesign.com/pdfs/e_OneTOsub.pdf

 

 

 

Thank you for the link

 

I did search SNA before I made my post but missed that thread above, cheers! 

 

My understanding was that because the hi/lo input into the sub is piggy backed off the same outputs as the speakers and the signal is the same that it helps to integrate things a bit more? I'm a complete audiophile novice though. I am very glad though I picked up on this class D issue rather than leaving it for months and months and risking damage to both the sub & amp. 

[robmid]

Thanks. That's something I didn't know. Lucky I read this thread because I was just about to make a BIG mistake.

 

I'm running my older REL Quake with one channel connected as recommended at speaker level with a Hypex amp and it sounds great.

[G-Dubz]

4 minutes ago, robmid said:

Thanks. That's something I didn't know. Lucky I read this thread because I was just about to make a BIG mistake.

 

I'm running my older REL Quake with one channel connected as recommended at speaker level with a Hypex amp and it sounds great.

Glad it helped someone else!

[Serpeant]

Rel also recommends to turn LFE to minimum for music.

 

Maybe I'm not a classy listener but I like to turn up LFE for music.

 

Hip Hop sounds better with bass.

[andyr]

15 minutes ago, Serpeant said:

Rel also recommends to turn LFE to minimum for music.

 

Maybe I'm not a classy listener but I like to turn up LFE for music.

 

Hip Hop sounds better with bass.

 

Everything sounds better with bass, S! 

 

And

 

[Mike13]

I reconnected all my cords and wires and now my Rel T9i’s are switched off because they hum.

 

When I bought my Chord Qutest a helpful sales guy at Carlton Audio gave me half a speaker cord and said to connect it to a metal screw on the amp and a metal screw on the subs. This didn’t work. 

 

I bought something to go inbeteeen the TV aerial and the wall aerial socket. Didn’t work. 

 

I bought an ifi Ground Hog because it is supposed to fix hums. I’ll try it this weekend, however I’m sceptical because I’ve since realised that the straight print on a power cable means it is already grounded. Will report back. 

[Mike13]

On 04/04/2019 at 6:52 PM, markm1111 said:

My understanding is that the Rel subs perform much better for music listening duties with the high level connections. 

That option is still there because it is easier than integrating them using DSP. I can’t see why it would sound better with the high level, but maybe it does!