Connecting HiFi Amplifier High-Level Outs to Subwoofer Low-Level Ins - AVS Forum

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Subwoofers, Bass, and Transducers

04:13 PM Liked: 0
post #1 of 14
07-29-2014 | Posts: 6
Joined: Jul 2014

I have an oldish Denon 375rd, with 2 zones but no pre-amp nor subwoofer outputs.

I just got a Focal Cub 3 without realizing it's more of a Home Cinema subwoofer and it has ONLY Low-Level Inputs and NO High-Level ones.

Now, I'm inquiring if I can give this back but I'm not sure - sure, the seller should have told me, but maybe I wasn't clear enough of my setup. Anyway, I guess the question in general could be of some use to other people!

Can I connect the High-Level outs from the amplifier to the Low-Level inputs on the Sub?

What about audio quality, what about electrical safety of the equipment?

THanks for your help!
BassThatHz's Avatar BassThatHz
01:35 AM Liked: 440
post #2 of 14
07-30-2014 | Posts: 3,267
Joined: Apr 2008
The Denon doesn't have a subwoofer out?
Time to upgrade to something made this century dude.

This (but preferably something much better.)

Like this, say...
fatbottom's Avatar fatbottom
03:29 AM Liked: 202
post #3 of 14
07-30-2014 | Posts: 3,890
Joined: May 2003
Originally Posted by BassThatHz View Post
The Denon doesn't have a subwoofer out?
Time to upgrade to something made this century dude.

This (but preferably something much better.)

Like this, say...
Ignore that person.

Going from a hifi amp to AVR isn't an "upgrade"

Either replace your sub with one with high level inputs, or buy a high level to low level converter.
04:19 AM Liked: 0
post #4 of 14
07-30-2014 | Posts: 6
Joined: Jul 2014
Thanks fatbottom!

Ok I will look for a high->low converter... do you have any experience with them - about potential quality loss?
that is, if I can't get the sub back and exchanged! Which still sounds a better option from your answer.

BassThatHz, thanks but I'm trying both to save some money and keep using that Denon that for audio only is great, and this is my bedroom setting so no need ever for 5.1, only 2.1 'coz the speakers are compact and lack some depth!
qguy's Avatar qguy
04:33 AM Liked: 61
post #5 of 14
07-30-2014 | Posts: 935
Joined: Dec 2008
Does the Denon have headphone outs ? if yes, you can try a headphone jack to RCA cable.

No audible degradation on the speaker level to line level converters. The same principle is employed for subwoofers with speaker level inputs.
04:41 AM Liked: 0
post #6 of 14
07-30-2014 | Posts: 11
Joined: Jul 2014
I don't know what your skill level is but it would be real easy to go inside the receiver and separate the preamp section from the power amp section and mount some RCA female jacks on the back of the receiver. If your not up to the task then take your receiver to your local HiFi shop and ask them to do it. One this is done I would use two y-jacks one for each channel and normal the preamp to the power amp for each channel and this will leave you one output left from the preamp. I would then patch this to your powered subwoofer.

I see no advantage to purchasing a different piece just so you have preamp outputs. If I had it in front of me I could do it in about 1/2 hr or less.

The Y cables I am talking about have two male RCA's and one Female RCA jack.
05:01 AM Liked: 0
post #7 of 14
07-30-2014 | Posts: 6
Joined: Jul 2014
Thanks qguy!!

Yes indeed it has front headphones out, so that could be a simple option indeed!
I will go and check that it doesn't disable the speakers out though (i think I remember it does).

Thanks 6bg6ga!

that's also an interesting idea, and indeed it make much more sense to get the pre-amp out rather than amplify it, then bring it to low again
My skills are limited and, much worse, my electric equipment is close to none though, but I will try to find soldering tools and give it a try, unless:

I just realized my amp also has tape out:

Is that a proper low-level output? or not?

(I just realized that tape-out is probably fixed volume... which means I would have to adjust my sub volume all the time... not really ideal!)
11:14 AM Liked: 0
post #8 of 14
07-30-2014 | Posts: 6
Joined: Jul 2014
For your information, and while the generic discussion about how to connect an amp without proper low-power output with a sub without high-power inputs is still valuable, I contacted the customer support of Focal and they said this amp is simply not suited to audio quality, regardless of the possibility of connection, because of the nature of the filtering on the sub!

I'll really try returning it before trying anything else!
qguy's Avatar qguy
03:04 PM Liked: 61
post #9 of 14
07-30-2014 | Posts: 935
Joined: Dec 2008
Out of curiosity, would you send an email to Focal customer support and asked what kind of filtering does this subwoofer employ and what would be the ideal filtering be for audio quality.

Since your getting a new subwoofer for audio.. Check out Rythmik subwoofers Their filtering is designed for audio quality
04:24 PM Liked: 0
post #10 of 14
07-30-2014 | Posts: 6
Joined: Jul 2014
what they wrote me is:

" même sur ses entrées RCA, la fréquence de coupure haute du CUB 3 n'est pas réglable mais fixe ; à cet effet son usage reste réservé au Home-cinéma ."

which translates to:

"Even on the RCA inputs, high-cut frequency isn't customizable but fixed. For this reason, its usage is really limited to Home Cinema".

Of course, if I can't parametrize the high-level frequency filter I can't have the sub seamlessly "merge" with the fronts, which is why he's suggesting to look at another model/brand.
So basically it's a classic low-pass filter, just with no configuration it's no good for high-level inputs and in general for music configurations.

In my personal opinion the Cub 3 might actually work if your amplifier has a good audio processor and can correctly configure the LFE out (my HC Anthem is actually very good in 2.1 audio too)

I did a quick search for Rythmik and Unluckily I couldn't find them here (France) definitely not in the shop I use that has almost every brand you can find in the country... and where I'm hoping to get a replacement!
For the price, and with high-level ins, I can get an Elipson (French) or a Tangent (Danish).
qguy's Avatar qguy
07:01 PM Liked: 61
post #11 of 14
07-30-2014 | Posts: 935
Joined: Dec 2008
B&K subwoofers is another brand you may want to look at, its Brit and might be available in your shores
05:17 AM Liked: 0
post #12 of 14
07-31-2014 | Posts: 11
Joined: Jul 2014
Regardless of the subwoofer you have or choose the main problem is still the fact that you don't have a preamp level out. I really believe that someone has gotten some double talk from an uninformed customer support person. I've never seen a powered sub that doesn't have a internal crossover. That crossover generally has some type of adjustment for frequency and level.

Put some full range material into it and see what comes out. If you don't have suitable frequency then add a crossover into the chain.

. People for the most part simply do not understand how a subwoofer should be setup. Most will duplicate the frequency already provided to their main speakers and this is incorrect. Proper setup is as follows... The subwoofers frequency is adjusted by means of an internal eq filtering in the processor or an crossover. If for example you dial in 20-80hz at a 24db per octave then you should adjust your frequency that your main speakers receive to from 80hz on up. Most will duplicate what is already going to their speakers and this ends up with a questionable response.

You can easily build a mono summing electronic crossover with less than $50 worth of parts or pick up a piece of commercial audio gear that is used for less than $100

I am currently using a Marantz SR4021 in my theatre and it has no sub out. No problem because I simply built one with a response of 20hz to 74hz at 24db per octave slope. The mains are limited from 74HZ- 20K. It takes full frequency and filters it and presto I run the output to a power amp and set the level with pink noise and a sound level meter.
fatbottom's Avatar fatbottom
05:27 AM Liked: 202
post #13 of 14
07-31-2014 | Posts: 3,890
Joined: May 2003
It's possible the input could have a fixed crossover, some older subs did.

I can see only one dial- volume? so it's possible!
11:35 AM Liked: 0
post #14 of 14
07-31-2014 | Posts: 6
Joined: Jul 2014
Yes fatbottom you are right - fixed crossover (though it's not old), that dial is the volume!

Yes I agree not having pre-amp outs is not ideal... but I don't want to change the amp yet. Thus I'm looking for a cheap but decent sub (to fill up the basses in a bedroom with compact BW speakers), spend nothing more in connections (I'd rather put them in a better sub or a new amp!), and get this going.
Putting 50 or 100$ in additional connectivity is as much as the amp would be worth today, probably! (even though it's still a nice and satisfying amp). And I might not even build it right

Anyway, I got hold of the shop and they will change the sub no problem, though the only choices in that price range (200e / 250$) and with high-level in are Elipson CB 102, Highland Dord 165 and Artsound Tutto 1
I would love a BW 608 but that's twice the budget... B&K sounds like a nice option, I'll see if the shop can get them and what price.
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