Attaching subs to class D amps?
- Thread starter candleman
- Start date
Tony L
Administrator
I did try using two Topping TP20 T-Amp and nothing blew up. I've no idea whether I was lucky or whether the fact I used a stereo pair of subs was a factor, but I've read many times it's a bad idea. I since discovered you can actually spec the BK subs to be used with a T-Amp, I guess they alter the grounding somehow.
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johnhunt
pfm Member
I had a sub connected to some ice monos some years ago...had to get a special lead supplied by rel. the amp supplier warned of thunder and lightening if I tried connecting them with the standard high level connection
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Julf
Facts are our friends
Some subs have "high level" inputs intended to be driven from power amp outputs.
Ok, then in this case yes the amplifier architecture should have an impact...
Obi1
Swedish HiFi enthusiast
I dont think it is a Class-D issue as some other already stated.
It is a earthing issue. I know that Rel subs dont play nicely with true balanced amplifiers (or bridged amps) if you connect it in a traditional way (high level). There is even risk of damaging the built in amplifier.
And this has to do with having two "hot" leads, when the amplifier needs one of the leads to be earth/zero potential.
It is a earthing issue. I know that Rel subs dont play nicely with true balanced amplifiers (or bridged amps) if you connect it in a traditional way (high level). There is even risk of damaging the built in amplifier.
And this has to do with having two "hot" leads, when the amplifier needs one of the leads to be earth/zero potential.
occamsrazor
pfm Member
Hi Julf, any info on connecting a single sub via high-level inputs to a pair of Hypex Ncore monoblocks which are in turn run from MDAC via balanced XLR? Or would it be better to connect to the MDAC's RCA line-level outputs (though I read a couple posts saying that "may" degrade the quality of the balanced outputs.)
Second question, and a more general one, when you run an amp to high-level sub inputs, is the amp powering the sub driver directly and bypassing the sub's amp, or does the sub still use its own amp and just take a signal from the high-level inputs?
Thanks in advance...
davidjt
pfm Member
Pending a more knowledgeable reply from Julf, if you Google 'REL ST manual' you'll find connection instructions. (Ideally, according to REL, you'd want one sub for each channel: but then they're in the business of selling 'em
)bennyboyph
pfm Member
Try one of these
http://www.profusionplc.com/pro/gex/pcatdtl0?ipartno=AMS1000-2600
http://www.profusionplc.com/pro/gex/pcatdtl0?ipartno=AMS1000-2600
The REL subs are a bit special on this ( and for the price they could have done better i think ).
Most SS and almost all tube amps are single ended. Common ground for both channels, and then there own positive rail. That's why there is only 3 wires to the REL sub.
Truly balanced amplifiers ( technical more advanced design, many classD is balanced ) have NOT a common ground, but their own ( just like two mono blocks )
The trick is to take the two positive signals and feed them to the REL, and then fish a ground somewhere else ( I use a phono plug on my pre amp, but it could also be as simple as the chassis ) for the 3 wire.
No need to make it more advanced than that
Super sub by the way
Theis
Most SS and almost all tube amps are single ended. Common ground for both channels, and then there own positive rail. That's why there is only 3 wires to the REL sub.
Truly balanced amplifiers ( technical more advanced design, many classD is balanced ) have NOT a common ground, but their own ( just like two mono blocks )
The trick is to take the two positive signals and feed them to the REL, and then fish a ground somewhere else ( I use a phono plug on my pre amp, but it could also be as simple as the chassis ) for the 3 wire.
No need to make it more advanced than that
Super sub by the way
Theis
Julf
Facts are our friends
Hi, Ben - and thanks for poking me, I haven't logged into pfm in a while, as I got too tired of all the silly faith-based arguments.
As Reenberg states, REL are a bit special - but all they need is for both power amp channels to have a common ground - true for normal amps and many ncore setups, but not true for bridged amps.
The issue might be your monoblock setup, where the only common earth is through the input connectors gong back to your MDAC - makes for an awfully long ground path. I would power the subwoofer from the MDAC RCA outputs - I would love to hear a rational reason for why that would degrade anything.
The sub still uses it's own amp, with the input signal suitably attenuated.
occamsrazor
pfm Member
REL crept in somewhere in this thread, which to be fair isn't my thread, but I'd likely be looking at an ATC C1 subwoofer, if that makes a difference.
I see your point there....My Ncores are grounded to the Ghent case chassis like this (as per your recommendations):
1. Mains earth to chassis close to IEC socket.
2. Pin1 of XLR socket to the "ground contact" of XLR socket (which in turn connects to shell and chassis)
3. nAmpon wire to chassis
4. SMPS is connected directly to chassis via the metal spacer
....so isn't there also a common earth via the mains earthing wire, or doesn't it work like that? What are the implications of not having a common earth?
There were a couple of posts by JohnW about it, I can only find two now, the conclusion was unclear to me but maybe you understand the science better:
http://www.pinkfishmedia.net/forum/showpost.php?p=1576173&postcount=3
http://www.pinkfishmedia.net/forum/showpost.php?p=1790758&postcount=261
Ona semi-related note, I read the RCA outputs are by design 6db lower than the XLRs, which would necessitate additional gain on the sub I guess. Is this a non-issue?
Julf
Facts are our friends
It does - the ATC C1 has a 4-pole hi-level connection, unlike REL that has a 3-pole connection. Thus you have nothing to worry about.
Yes - there is a common earth, but in a monoblock setup, the ground current has to travel all the way either down the mains earth wire to the distribution block and back up, or down to your DAC and back up - a fair bit of distance and wiring.
Yes, and I agree with his points. As the MDAC doesn't have a separate output buffer for balanced and unbalanced, you would put a very slightly unbalanced load on the balanced outputs - but as the output impedance of the MDAC is probably tens of thousands of ohms, we are looking at a 0.01% inbalance - not really significant. As John stated, "nobody so far has reported any degradation from using both sets of outputs".
It is a non-issue, as you need to adjust the level of the subwoofer to match the gain of your main amps and the sensitivity of your speakers in any case.
occamsrazor
pfm Member
Thanks for clearing all that up Julf, seems like no issues with either high or low-level inputs with this particular setup.... which makes life easier. Cheers....
lawrence001
Basic Member
Very old thread I know but I'm facing the same issue here. I need to run my Rel sub (using the high level inputs) from an ice power 1000asp amp, the sub being wired in parallel with the two main L/R speakers (the bananas being piggybacked). Is there a risk of damage to the amp or sub as a result of the amp topology?
I would use the low level, but it is single channel LFE and my pre only has L/R outs.