REL High level input with class D The unsolved mysteries

[Cerwin]

Hello. I´m a little bit nervious because after reading all of you after one year finally I´ve decided to write here.

I´m not new in the audio hobby, but sometimes you get stuck and you need de knowledge from the very experienced friends.

Until today I was using my REL sub with he high level input with my MC2 S800 amplifier using the standard high level connection scheme without problem because is an AB Amplifier.

Need to say that I love the high level connection input because I always go with spare devices, In this case is a stereo systems, so ,no AV receiver with sub out, etc. The high level input always has been a plus for the bass stage in my system.


OK at this point everything is ok, here comes the tricky part. I decided to buy a Class D power amplifier. I will not tell the brand, but I will say that is stereo with purifi modules. So can be the same for a variety of amplifiers : VTV, Boxem, NAD, Audiophonics, Apollon, etc.

OK I seach and i find a nice video from rel "how to connect your rel using high level input into a class D amplifier", ok nice.

Here is the problem: I have seen that some class D amplifiers works at the outputs with phase shifting.

So the standard class D connection from REL is this:

OK, it´s true with the black to the ground chassis the HUM noise disappear. That´s ok , now you be to be aware in class D amplifiers Where is the lighting symbol, because (as I understand tells you if your amplifier is working with phase shifting or not.

NAD M33 the "hot is in one positive and other the negative"

Boxem Arthur 4216

In my case my amp has the following config

I have performed some test with this results ( so be aware)

Bass in the sub but no too much punch

Same result that test A

So it´s clear at the "hot terminals" you have signal and inside the rel with the ground chassis crew you have signal with no HUM.

Here´s is the tricky part:

You can think.. OK red wire to left hot positive and yellow to Right hot negative . REL also says this for NAD M33 Users :

So should be like this

So this does not work for me, I don´t know if some NAD users has tested.

The only right configuration may be have dual subwoofers and simulates the monoblock connection like this:

So conclusions:

- If you know the solution to connect ONE sub using high level input with this phase shift amplifiers please share.
-If I use the standard class D connection from REL I´m missing the bass info from one channel
-It´s clear that yellow and red wires are signal summed inside rel sub and complete with the chassis ground (OK)
-In this kind of amplifiers the summatory of the HOt signals produces and out of phase almost null signal.
-Be aware if you want to use high level subwoofer with this kind of amplifiers. Are becoming so common to avoid the pumping effect for the power supply , ( I have read this)

some models that uses this config: NAD m33. BOXEM Arthur 4216/E2, Audiophonics 400 y 450Et models.

Other references:

Please if you consider that i have made any mistake or have wrong info about the amplifiers mentioned I will be happy to edit.

PD: Sorry for my English, sometimes is not very good.

Regards.

 

[somebodyelse]

A couple of problems leap out:

1. It's not about amp class, it's about having the -ve speaker terminal driven. This happens in bridged Class AB amps too.
2. There's another problem with some amps - the speaker terminals float at a voltage different to chassis.

I don't think 1 needs further explanation. For 2 we see it most often recently with the TPA325x amps, but it could happen with any bridged amp with single sided supply. Both outputs are driven but they float at half the supply voltage relative to ground. The speaker doesn't see this - it only sees the difference between the speaker terminals. If you connect the REL input between chassis and ground the REL is going to see the large DC offset, and the amp may go into protection - the TPA325x has a protection mode for if a speaker terminal gets shorted to chassis, but others may not. I don't know whether anything damaging would happen to the REL in such cases.

You'll see that NAD used blue rather than black for the -ve speaker terminals. This is an indication that they aren't grounded. Unfortunately the manufacturers of many bridged amps don't use this convention, so it can't be relied on.

Short version: when using speaker level sub inputs, be sure that you know the details of the amp outputs and sub inputs, and that you understand the potential problems. If in doubt check with the manufacturers.

 

[Cerwin]

Hi @somebodyelse thanks for you explanation. In that case, I don´t know how REL make a video so generic about to connect them to a class D amps, because they can cause so many problems to the users.

So If I have understood. There is no solution for this. Or the manufacturer needs to know the REL connection type and tell you if its suitable or not and what is the right and safe way to do it , right?

It´s a pity. My REL sub sounds really great in a stereo system. But now I can enjoy the crystal clear audio quality of the purifi amplifier without REL bass improvement.

 

[somebodyelse]

So If I have understood. There is no solution for this. Or the manufacturer needs to know the REL connection type and tell you if its suitable or not and what is the right and safe way to do it , right?

No solution for subs already made anyway - REL aren't alone in this. The real solution is for sub manufacturers to use a differential input that can accept significant common mode voltage offsets, not to assume that all amps have a grounded speaker terminal. Having said that, speaker level inputs aren't ideal anyway - line level with a high pass for the mains us usually preferable.

 

[Audioagnostic]

I am using the line out of my hypex NCore NC122MP as you wired your a/b amp, in my rel sub. Audiophonics built amp.

Did some reading and for the hypex modules this should be fine.
But I do admit to not comprehend the issue completely... Rel claims wrong wiring could damage the sub but since mine is working for a year+, I presume it is ok.

 

[Cerwin]

I am using the line out of my hypex NCore NC122MP as you wired your a/b amp, in my rel sub. Audiophonics built amp.

Did some reading and for the hypex modules this should be fine.
But I do admit to not comprehend the issue completely... Rel claims wrong wiring could damage the sub but since mine is working for a year+, I presume it is ok.

If the outputs of your ncore amp does not work in phase shifting configuration. You should have no problem. If your amp uses phase shifting configuration between channels, quite probably you’re missing the bass of one channel.

Regards

Regards

 

[jck2001]

I think there are a couple of ways you can proceed here with a rel sub. If memory serves, rel uses dc coupled mosfet amp. Not sure if there is dc blocking in their input filters, but to be sure, you could put 10uF caps in the red and yel signal paths and connect those to the amp + for R and L with black to chassis ground. If the amp is supplying any DC bias on the speaker outputs, the caps will block it and that should allow the sub amp to produce the proper output and you get the full bass output (because the driver is no longer constrained by the dc bias)

THe second thing you can try is to use the balanced High input of the rel. Here, you would choose a channel from the amp, L or R and connect the red to +, the yel to -, and black can float (since you are now going to have the sub amplify a differential signal). If you do this, BE SURE TO CONNECT to the HIGH level BALANCED Neutrik socket and not the usual Neutrik socket (and definitely not the low level balanced XLR input.) Yes, the other channel will be lost but for low frequencies, say below 50hz, the two channels should be carrying nearly identical information anyway so really nothing perceptible missing as long as you cutoff below 35-40 hz.

one final note, that lightening bolts only means "high frequency switched outputs". Nothing else. They warn of this because at these swithching frequencies, its possible to get shocked touching these speaker terminals in operation.

 

[Everett T]

Hello. I´m a little bit nervious because after reading all of you after one year finally I´ve decided to write here.

I´m not new in the audio hobby, but sometimes you get stuck and you need de knowledge from the very experienced friends.

Until today I was using my REL sub with he high level input with my MC2 S800 amplifier using the standard high level connection scheme without problem because is an AB Amplifier.
View attachment 480854

Need to say that I love the high level connection input because I always go with spare devices, In this case is a stereo systems, so ,no AV receiver with sub out, etc. The high level input always has been a plus for the bass stage in my system.


OK at this point everything is ok, here comes the tricky part. I decided to buy a Class D power amplifier. I will not tell the brand, but I will say that is stereo with purifi modules. So can be the same for a variety of amplifiers : VTV, Boxem, NAD, Audiophonics, Apollon, etc.

OK I seach and i find a nice video from rel "how to connect your rel using high level input into a class D amplifier", ok nice.

Here is the problem: I have seen that some class D amplifiers works at the outputs with phase shifting.

So the standard class D connection from REL is this:

View attachment 480856


OK, it´s true with the black to the ground chassis the HUM noise disappear. That´s ok , now you be to be aware in class D amplifiers Where is the lighting symbol, because (as I understand tells you if your amplifier is working with phase shifting or not.

View attachment 480859
NAD M33 the "hot is in one positive and other the negative"

View attachment 480860

Boxem Arthur 4216

In my case my amp has the following config
View attachment 480864


I have performed some test with this results ( so be aware)
View attachment 480866
Bass in the sub but no too much punch

View attachment 480867
Same result that test A
View attachment 480868

So it´s clear at the "hot terminals" you have signal and inside the rel with the ground chassis crew you have signal with no HUM.

Here´s is the tricky part:

You can think.. OK red wire to left hot positive and yellow to Right hot negative . REL also says this for NAD M33 Users :

View attachment 480870

So should be like this
View attachment 480871
So this does not work for me, I don´t know if some NAD users has tested.

The only right configuration may be have dual subwoofers and simulates the monoblock connection like this:

View attachment 480872

So conclusions:

- If you know the solution to connect ONE sub using high level input with this phase shift amplifiers please share.
-If I use the standard class D connection from REL I´m missing the bass info from one channel
-It´s clear that yellow and red wires are signal summed inside rel sub and complete with the chassis ground (OK)
-In this kind of amplifiers the summatory of the HOt signals produces and out of phase almost null signal.
-Be aware if you want to use high level subwoofer with this kind of amplifiers. Are becoming so common to avoid the pumping effect for the power supply , ( I have read this)

some models that uses this config: NAD m33. BOXEM Arthur 4216/E2, Audiophonics 400 y 450Et models.

Other references:

Please if you consider that i have made any mistake or have wrong info about the amplifiers mentioned I will be happy to edit.

PD: Sorry for my English, sometimes is not very good.

Regards.

Darn, REL really makes it tough for their users. There is a simple solution for them, but I digress.

 

[Chr1]

Curious if this just relates to high level inputs to REL subs, or high level inputs to subs in general?
Ta.

 

[Sokel]

Curious if this just relates to high level inputs to REL subs, or high level inputs to subs in general?
Ta.

In general, and not only that:

It's not only about reversed phase Class D as of OP ones but all bridged amps (so, higher power class D as well) who must NEVER see Ground at their terminals.

 

[Everett T]

Curious if this just relates to high level inputs to REL subs, or high level inputs to subs in general?
Ta.

I believe that they confuse their customers without science. I understand that there are cases where high level inputs are needed, but they tell their customers to use that option when those customers have bass management options that would benefit them much better.

I'll admit they are trying to change, but they have a boat load of marketing to overcome.

 

[Chr1]

Got several subs with high level options and have to say that I like to have the option. Sometimes a line level connection, though preferable, is not always possible.

 

[Everett T]

Got several subs with high level options and have to say that I like to have the option. Sometimes a line level connection, though preferable, is not always possible.

I understand where that is the only option.

 

[somebodyelse]

Curious if this just relates to high level inputs to REL subs, or high level inputs to subs in general?
Ta.

Best to ask the manufacturer as it depends on implementation. REL certainly aren't the only one where bridged amps won't work, but it isn't universal.