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Rel Dual Sub High Level connection to Halcro MC20


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Hi guys, 

 

I have a Rel T9i and Halcro MC20. 
 

I have followed Rel’s instructions re connecting yellow and red cables to positive and negative on the amp and ‘floating’ the black ground cable, then using the LFE connection to a receiver to ground the unit. 
 

I’m still getting some hum though. 
 

I now have a second T9i on the way and would love some advice how best to connect both subs. 


Really, my question is whether the MC20 negative speaker terminals are true ground, the Rel info on Class-D amps having variable voltage on the black terminal really threw me a bit. 
 

Thanks everyone and anyone for any advice!

 

Cheers, David


 

 

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The MC20 is a power amp, right?  You didn't mention what preamp you're using with it but why not take a feed from the RCA out terminals on the preamp into your RELs (instead of using REL's high level (ie. spkr level) connection from the Halcro)?

 

Unless you are also hearing hum from the spkrs which the MC20 is driving, using the low-level connection will kill your hum.

 

Andy

 

 

Andy

 

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23 minutes ago, andyr said:

The MC20 is a power amp, right?  You didn't mention what preamp you're using

 

Hi Andy, thanks for response.

 

I am using one of Chris Daly's passive pre's, I only have a single set of balanced outputs going to the MC20.

 

I want to use the High Level connections for the Rels.

 

The hum that I mentioned is coming from the speakers (and actually the MC20 unit itself) now that I've wired in the first subwoofer. 

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If you use rel supply cable, the yellow and red cable should connect on each positive terminal  power amplifier. The black should connect to negative power ampl terminal neither left or right. 

Class D amplier negative might not connect directly to the ground.

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3 minutes ago, tripitaka said:

I recall @Ittaku mentioning that class D have floating ground, but I also might have that all wrong😀

Yes that's correct, as do bridged amplifiers. Connecting both terminals to a Rel subwoofer will blow your amplifier.

Edited by Ittaku
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The attraction of high level sub connections makes absolutely no sense without the option to bypass the sub's DSP, which is never explained amongst all the marketing BS.

 

That's quite apart from problems with blowing up your amp ☹️

 

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52 minutes ago, tripitaka said:

The attraction of high level sub connections makes absolutely no sense without the option to bypass the sub's DSP, which is never explained amongst all the marketing BS.

 

Not quite understanding you there, T (in terms of "the option to bypass the sub's DSP")?  :(

 

I assume you mean the subs' HP output filter - but when you feed the subs from the main spkrs' terminals ... you have no ability to deliver a HP filter to the mains.  (So you must run them full-range.)

 

Andy

 

 

 

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3 minutes ago, davewantsmoore said:

Why?

Ive heard Rel sell it as a way of bringing the phase of the sub output into line with the phase output of the speakers.

But DSP introduces a substantial phase delay.

Doesnt it?

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3 minutes ago, tripitaka said:

But DSP introduces a substantial phase delay.

Doesnt it?

No.

DSP doesn't have any inherent delay.

 

 

Linear phase filters have delay which gets longer as the frequency gets lower.... These types of filters are only (easily) possible on a DSP.

 

So every time you see these filters used, it's on a DSP.     Perhaps that's where you got the idea that DSP => delay.

 

The delay comes from the filter programmed in the DSP.... not from the DSP itself.

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11 minutes ago, tripitaka said:

Ive heard Rel sell it as a way of bringing the phase of the sub output into line with the phase output of the speakers.

 

This would only happen if there was phase shift in the speaker amplifier.

 

This would be unusual.

 

Their claim is marketing department nonsense.   Sad.

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5 minutes ago, davewantsmoore said:

No.

DSP doesn't have any inherent delay.

 

 

Linear phase filters have delay which gets longer as the frequency gets lower.... These types of filters are only (easily) possible on a DSP.

 

So every time you see these filters used, it's on a DSP.     Perhaps that's where you got the idea that DSP => delay.

 

The delay comes from the filter programmed in the DSP.... not from the DSP itself.

 

Which just goes to prove NOTHING is simple in hifi😏

 

...yet another of my (few remaining) assumptions bites the dust 😀😀 

Thanks for the clarification🙏

 

Dave, how would one know whether a linear phase phase filter is programmed into the DSP? Are these filters common?

 

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the key thing to remember is that "all filters cause delay" - this is baked into the universe we live in....

Implementing the same profile filters in analog passive components (caps/resistors/coils) vs active analog low level components (ie op amp or transistor) will have identical delay.

A woofer in a sealed box has a high pass filter response - this also has delay

 

All of the above filters have delay that varies with frequency - which is defined as Group Delay, and they are Infinite Impulse Response (IIR) filters.

 

Linear Phase filters have zero Group Delay - they still have delay (see above - all filters have delay), but the delay is the same for all frequencies, and they are Finite Impulse Response (FIR) filters.

 

The steeper and lower the filter the more delay it has - ie a 4th order filter will have more delay than a 2nd order filter at 100Hz, and the same order filter will have more delay at 50Hz compared to 100Hz (regardless of whether FIR/IIR, linear phase/non-linear phase).

 

DSP can implement FIR or IIR filters - think "linear phase" or "analog" filters

 

Implementing (edit most  IIR) filters in DSP will have "almost" the same delay as passive or electronic analog - the inherent delay caused by the filter will almost always be higher than the "processing" delay of the DSP, such that the DSP delay can "mostly" be ignored.

 

Linear phase FIR filters (edit which can only be implemented in DSP) take more time to compute the lower and steeper you go, and my DEQX (as an example of a DSP solution) will recommend using IIR filters down low with steep filters...(edit as FIR/linear phase filters have too much delay).

 

(edit) IIR filters are easy to implement at line level for any "order of crossover/steepness", but as you go lower with the Xover frequency, with passive components, the component values get much larger and are  (end edit) not realistic with passive inductors/caps/resistors.

 

Mike

Edited by almikel
clarification
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3 hours ago, almikel said:

 

Implementing most filters in DSP will have "almost" the same delay as passive or electronic analog - the inherent delay caused by the filter will almost always be higher than the "processing" delay of the DSP, such that the DSP delay can "mostly" be ignored.

 

That was a very interesting post, Mike👍

But just circling back, because we are talking here about a high level input, I am assuming that what is going on within the sub is:

ADC ->DSP -> DAC (coz modern subs don't seem to use passive analogue filters).

So it's not 'just' the filter time delay that we are interesting in.

🙏

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8 hours ago, almikel said:

the key thing to remember is that "all filters cause delay"

 

Given the context of the question.... this is (true, but) likely very confusing.

 

 

DSP delay = ~1ms

 

IIR / analogue delay = for LF, it could be lets say half a cycle at 20Hz for an extreme-ish example.    That's 25ms....  but, but not audible as a "delay".

 

FIR delay depends on the frequency resolution.... and so for a LF filter, we might want.  3Hz.... that's 300ms.   1Hz is 1 second.   These are "echo echo echo" types of delay.   😆

 

8 hours ago, almikel said:

Linear phase FIR filters take more time to compute the lower and steeper you go

 

 

FWIW.... and hopefully not to lurch off topic or into something confusing..... it isn't because low, or steep, per se .... but because of the frequency resolution that is desired to represent a fast changing response at LF.    Eg. if you have a steep rolloff at 20Hz (for example) .... then you want a certain number of data points vs Hz to represent that.    You could have a data point every 0.5Hz ... for a filter delay of ~2 seconds..... or a data point every 5Hz (which would be ugly) for a delay of 200ms.

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5 hours ago, tripitaka said:

ADC ->DSP -> DAC (coz modern subs don't seem to use passive analogue filters).

 

So there's 1ms for the DSP/ADC/DAC.

 

.... and then the amount of delay depends on the filter.    If it's an IIR type, then it's just the same as an analogue filter.    It's directly related to the amplitude .... and so might be (for example) up to 25, or even 50ms for a big filter like a highpass or low pass filter.... but it's probably lots lots lower.

 

However if you are filtering the mains the same (which you should be, eg a complimentary high pass and low pass filter) .... then the phase distortions are matched (and blend together).

 

 

However for a FIR filter (which most people associate with DSP, as they are only possible on a DSP) ..... then you might have 10x or more delay.

 

 

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8 minutes ago, davewantsmoore said:

 

So there's 1ms for the DSP/ADC/DAC.

 

.... and then the amount of delay depends on the filter.    If it's an IIR type, then it's just the same as an analogue filter.    It's directly related to the amplitude .... and so might be (for example) up to 25, or even 50ms for a big filter like a highpass or low pass filter.... but it's probably lots lots lower.

 

However if you are filtering the mains the same (which you should be, eg a complimentary high pass and low pass filter) .... then the phase distortions are matched (and blend together).

 

 

However for a FIR filter (which most people associate with DSP, as they are only possible on a DSP) ..... then you might have 10x or more delay.

 

 

 

Thanks Dave, I must admit I thought that ADC and DSP (IIR)  processes were slower than that

👍

 

Edited by tripitaka
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12 hours ago, andyr said:

 

Not quite understanding you there, T (in terms of "the option to bypass the sub's DSP")?  :(

 

I assume you mean the subs' HP output filter - but when you feed the subs from the main spkrs' terminals ... you have no ability to deliver a HP filter to the mains.  (So you must run them full-range.)

 

Andy

 

 

 

 

This thread has been quite instructive for me - though it confirms that high level sub inputs are still pointless😀😀😀

 

Andy, to clarify my original premise, I had previously seen value in high level inputs only IF they could avoid time delays from the sub's DSP (which of course they don't).  As you say, one would then still need a passive in-line lowpass filter.   BUT, as I have just learned from this thread, there is nothing to be gained (phase-wise) even in that hypothetical scenario!!

Edited by tripitaka
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15 minutes ago, tripitaka said:

though it confirms that high level sub inputs are still pointless

Why?

 

15 minutes ago, tripitaka said:

Andy, to clarify my original premise, I had previously seen value in high level inputs only IF they could avoid time delays from the sub's DSP (which of course they don't).

Subwoofers (almost always) don't use FIR filters in their DSP .... because those filters have much too much delay.

 

Even in a system where an equal amount of delay can be applied to the mains... you then need to delay the video too.... it's very problematic.... which is why it's rare that it is used.

 

 

 

15 minutes ago, tripitaka said:

As you say, one would then still need a passive in-line lowpass filter.   BUT, as I have just learned from this thread, there is nothing to be gained (phase-wise) even in that hypothetical scenario!!

 

DSP filters in a subwoofer (unless they are of FIR type, which they won't be ... see above) ... have identical delay to a passive inline low pass filter (or any other type of analogue filter) 

 

 

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@davewantsmoore if you read more carefully, I was making those exact points on which you are supposedly now schooling me - and giving credit to THIS thread (ie, you) for teaching me. 😃

 

Even so, I would still be interested if you see value in having high level inputs on an ACTIVE sub, since you seem not to agree with me on that point?

 

 

 

 

 

Edited by tripitaka
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13 minutes ago, tripitaka said:

Even so, I would still be interested if you see value in having high level inputs on an ACTIVE sub, since you seem not to agree with me on that point?

 

Yes..... you say they offer no benefit due to the delay issues .... and "this thread confirms for you they are pointless".

 

Think about four subwoofers.

 

1)   Subwoofer with passive low pass filter at speaker level   ....  ie. driven by an external amplifier with with low pass filter inside the subwoofer box  (ie.  a typical ordinary oldschool subwoofer).

 

2)  Subwoofer with passive low pass filter at line level .... ie. driven by an external amplifier with the LP filter at line level between source and amp.

 

3)   Active / DSP subwoofer.....  The sub has a line level input.    So:   Source (line level) > ADC > DSP (low pass filter) > DAC > Amplifier > Woofer

 

4)   Active / DSP subwoofer .... The sub has a speaker level input.   So:   Amplifier (speaker level) > ADC > DSP (low pass filter) > DAC > Amplifier > Woofer.

 

 

They all have identical delay.

 

 

 

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@davewantsmoore it's useful to have those scenarios laid out, side by side,  as it explicitly confirms what has become apparent throughout this thread (from you and Mike).

 

From this, I would once again conclude that having high level inputs on an active sub brings no benefit.

 

But, I guess you are saying that they also 'do no harm', so that's fair enough. 

Edited by tripitaka
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7 minutes ago, tripitaka said:

From this, I would once again conclude that having high level inputs on an active sub brings no benefit.

 

I guess it allows you to add subs when you are using an integrated stereo amp or HT amp which doesn't have 'pre outs'?

 

7 minutes ago, tripitaka said:

But, I guess you are saying that they also 'do no harm', so that's fair enough. 

 

Shirley they do harm - in that if your subs are fed from your main spkrs ... you must be running your mains full-range (rather than rolling them off to match with the sub's roll on).  This has several disadvantages, compared to putting a HPF on the mains.

 

Andy

 

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