Topping PA7+ Class D with older Rel Quake Subwoofer - compatibility

[guston]

Hi everyone,

I have been lurking for a while now and have a question to ask - I have really tried to find a definitive answer to this but cannot. Go easy on me - I'm eager to learn but am relatively new to this and technically have a lot to learn. Hoping this post will help others too....

Recently I setup a Topping PA7+. It is powering some Yamaha hifi speakers (6ohm). Through research into subs with high level connections I believed that I could incorporate a powered sub. The PA7+ being bridged setup, I concluded that the setup in the diagram below should work. I picked up an older REL sub (see photo below) - I haven't connected anything yet as, as I was waiting for it to be delivered I contacted Rel to check that it would be compatible - they were very helpful and got back to me, but unfortunately did not recommend I connected this older type of Rel sub. Here is a snippet of their response:

'The Quake subwoofers were designed before Class D amplifiers were common in consumer audio, and as a result they do not feature necessary circuitry for being able to connect High Level to Class D amplifiers. Instead, the Quake (and all other "Q Series" models) can only be connected High Level to Class A/B amplifiers that reference to electrical ground at their negative speaker output terminals. Unfortunately, this means that the Quake should not be connected High Level to your Topping PA7+. Instead, in this system we recommend connecting the Quake using it's RCA input to an open output on your system's preamp.'

Worst case scenario - it really doesn't work, I sell it and think about finding a more modern sub with high level inputs.
Best case scenario - Rel team are not incorrect, but are playing it safe (understandable) - and possibly there is a work around and this sub can be connected. (I will be happy).

If anyone has any thoughts or think this can be solved, I would be very interested to know! Thanks in advanced

​

 

[somebodyelse]

The PA7+ and similar amps aren't just bridged - the outputs float at half the supply voltage. If you try ground referencing them as per that diagram you'll be exposing the REL inputs to ~24V of DC offset which they probably weren't designed for, hence the advice not to do it. Do you not have a preamp out or similar line level output you can feed it with?

 

[guston]

I’m guessing more modern subs are designed to handle this dc offset. Is there a term to look for in the specs of a sub that would determine this? If I could find a sub that would work via high level input with the PA7+ that would be great.

No preamp. But I use a Xone 92 LE for mixing music, which is why I picked up the PA7+ (so I could connect the mixer via balanced XLR’s to the PA7+ inputs - prefere hi-fi sound for mixing music). Maybe the subs high level speakon could be split to two TRS/TS which could be connected to the ‘mix 2’ output on the 92…

Thanks for your response

 

[dagfinn]

Maybe the subs high level speakon could be split to two TRS/TS which could be connected to the ‘mix 2’ output on the 92…

No, but you could feed the lowlevel output from mix 2 to either to LFE or PC input.

 

[somebodyelse]

I’m guessing more modern subs are designed to handle this dc offset. Is there a term to look for in the specs of a sub that would determine this? If I could find a sub that would work via high level input with the PA7+ that would be great.

Unfortunately it seems not to be something that gets into the specs very often. The high level input needs to be differential, but beyond that it gets complicated. If it's AC coupled it should be fine. If it's DC coupled you get into what the DC offset tolerance is, and whether the systems share a ground reference somehow (mains ground, some other interconnect etc.) or are fully floating. That's why the advice is to confirm compatibility with the manufacturer.

This sidesteps the point that speaker-level inputs should be the last resort not the first choice. With speaker level inputs the speakers have to be driven full range and the subwoofer matched to their acoustic roll-off, rather than having a controlled crossover. Maybe look at studio-oriented subs that have balanced inputs and outputs, and include high pass filtering for the outputs. The sub would sit between your Xone 92 LE and the PA7+ so your speakers wouldn't be exposed to LF content they can't reproduce. That would result in reduced cone excursion and reduced power dissipation, in turn reducing IMD and thermal compression.

 

[guston]

No, but you could feed the lowlevel output from mix 2 to either to LFE or PC input.

Nice. Although the Mix 2 on a xone92 is a balanced output (or at least in the manual it states - 'It is not usual for unbalanced equipment to be used here.') so I could try, with an RCA splitter/Y cable, to connect the sub to the 'record out', or I could connect it to the 'Booth out' which takes balanced and unbalanced cables - either of these to the LFE input on the sub.

Unless this doesn't work/i'm missing something, I will try this as a work around.

 

[guston]

Unfortunately it seems not to be something that gets into the specs very often. The high level input needs to be differential, but beyond that it gets complicated. If it's AC coupled it should be fine. If it's DC coupled you get into what the DC offset tolerance is, and whether the systems share a ground reference somehow (mains ground, some other interconnect etc.) or are fully floating. That's why the advice is to confirm compatibility with the manufacturer.

This sidesteps the point that speaker-level inputs should be the last resort not the first choice. With speaker level inputs the speakers have to be driven full range and the subwoofer matched to their acoustic roll-off, rather than having a controlled crossover. Maybe look at studio-oriented subs that have balanced inputs and outputs, and include high pass filtering for the outputs. The sub would sit between your Xone 92 LE and the PA7+ so your speakers wouldn't be exposed to LF content they can't reproduce. That would result in reduced cone excursion and reduced power dissipation, in turn reducing IMD and thermal compression.

I'm also looking for an affordable studio sub, as like you have pointed out, a studio sub will be more compatible with this setup - I really appreciate your advice, thank you, and thank you everyone!

This setup is in a temporary studio and is purely low budget and for fun/practice. A more permanent hifi setup is on the horizon once I finish building my house.

 

[dagfinn]

Nice. Although the Mix 2 on a xone92 is a balanced output (or at least in the manual it states - 'It is not usual for unbalanced equipment to be used here.') so I could try, with an RCA splitter/Y cable, to connect the sub to the 'record out', or I could connect it to the 'Booth out' which takes balanced and unbalanced cables - either of these to the LFE input on the sub.

Unless this doesn't work/i'm missing something, I will try this as a work around.

"Record out" is not good, you don't have level control over it, it's a fixed line out level, as is "booth out". The master fader does not affect them, you'd have max level constantly. May be simplest to go from "mix 2" (which is controlled by master faders), to the PC input, 3,5mm - I'm guessing it's stereo. Manual doesn't say. LFE will also work.

Look here too, see post 2 by @staticV3:

Connecting a TRS balanced output line to RCA input

Hey all, I have a Audiobox USB computer interface for recording. I currently have a pair of Mackie studio monitors connected to the only outputs on the device. The Audiobox has a volume control for the line level signal output. The outputs are TRS balanced line outputs. I am wanting to try to...

www.audiosciencereview.com

There are many way to do this, a simple coverter plug could work, not sure what you have access to. Of course, a new sub with balanced in and low/highpass would be best, like @guston describes.

 

[somebodyelse]

I'm also looking for an affordable studio sub, as like you have pointed out, a studio sub will be more compatible with this setup - I really appreciate your advice, thank you, and thank you everyone!

This setup is in a temporary studio and is purely low budget and for fun/practice. A more permanent hifi setup is on the horizon once I finish building my house.

Define 'affordable' - something like the Kali WS-6.2 which Erin liked?

 

[guston]

Define 'affordable' - something like the Kali WS-6.2 which Erin liked?

Well what ever I get for selling the Rel Quake - maybe €200. I have found some KRK S10's for this kind of price. Im not expecting a lot from this system - like I said, it is temporary and the goal is purely for mixing practice. Either way - I hope this thread will help other PA7+ users.

 

[guston]

"Record out" is not good, you don't have level control over it, it's a fixed line out level, as is "booth out". The master fader does not affect them, you'd have max level constantly. May be simplest to go from "mix 2" (which is controlled by master faders), to the PC input, 3,5mm - I'm guessing it's stereo. Manual doesn't say. LFE will also work.

Look here too, see post 2 by @staticV3:

Connecting a TRS balanced output line to RCA input

Hey all, I have a Audiobox USB computer interface for recording. I currently have a pair of Mackie studio monitors connected to the only outputs on the device. The Audiobox has a volume control for the line level signal output. The outputs are TRS balanced line outputs. I am wanting to try to...

www.audiosciencereview.com

View attachment 488402

There are many way to do this, a simple coverter plug could work, not sure what you have access to. Of course, a new sub with balanced in and low/highpass would be best, like @guston describes.

Thanks for the link - I think I understand.

In my case i would be going from L+R TRS ('mix 2' on the mixer) to RCA SE (single end - into LFE on the sub). Are you sure going from a balanced output into an unbalanced input (RCA SE) will not cause damage?

I can solder my own cables - so can make something up if I know what parts to order.

many thanks!

 

[guston]

Anyone have any info or thoughts about running a balanced output into an unbalanced input (RCA SE). Thinking about any possible damage to the mixer as Allen and Heath dont recommend it in the manual.

Pretty sure Im going to sell and find a studio sub. Or add a Fosi ZP3 to incorporate the REL - I believe this will produce a better quality result over running the signal through a studio subs IN/OUTS...

 

[somebodyelse]

Anyone have any info or thoughts about running a balanced output into an unbalanced input (RCA SE). Thinking about any possible damage to the mixer as Allen and Heath dont recommend it in the manual.

We've had whole threads about it. Short version: Unless the manufacturer says it's ok, or you know the details of the balanced output implementation, and fully understand how it works, DON'T DO IT. Use a proper balanced to single ended adapter, whether active or transformer.