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new KEF KC62 dual 6.5" subwoofer

DrStuhl

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The sensitivity difference is because the MAIN IN is expecting to be given the output of a preamp, but you’re plugging in a line level output - consumer, I presume, so -10 dBV nominal:
https://en.wikipedia.org/wiki/Line_level

As such you’re over-amplifying the noise floor of the KEF sub output. Since you have a line level output, you just need to plug it into a line level input. Nobody is to blame per se, it’s just simple gain structure :)

Is there a particular reason you wanted to use the MAIN IN of the NAD amp? From what I can tell, that negates the use of the remote control as well as the front volume dial, which seems like you’re giving away a lot of convenience!

Thanks for clarifying but I think I am missing out on something here? Since I'm also using the preamp (pre-out) before going into the kc62, the volume control / remote is still controlling the overall volume and also the kc62 volume as well.
The you mean Tape in/Out - right? They are not controllable as I understand it.
1631014779062.png

If I would buy another Power Amp and just use the NAD for the Preamp, would that solve that? What would I have to look for that it would work out just fine?
 

kyle_neuron

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Sorry if I wasn’t clear. You’re now using the setup in your most recent set of photos, right? In that configuration, the remote should work so happy days! Although you’re not using the NAD preamp to drive the KC62, so I don’t *think* it will follow the volume adjustments there.

Just to clarify, I haven’t got or used any of the components of your system. I just have a lot of experience chasing down easily-missed gain staging to resolve hiss or hum problems from homes to venues :)

I was referring to the previous configuration, where you connected the output of the KC62 to the MAIN IN on your NAD amp. The manual suggests that connection bypasses the volume dial and remote, which control the preamp part of the NAD. Does that make sense?

I don’t think you need to replace the NAD now - unless you’re wanting something different for other reasons. If you did, then you just need to connect it the same way you have now, KC62 line output to amplifier line input
 

KMO

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The KEF subwoofer is designed to be inserted between the pre-amp and the power-amp. At least, that's the use-case shown in the manual.

Given that it needs to receive the pre-out, volume-adjusted, then, it what it passes out will be the volume-adjusted signal, ready for the power-amp.

But I've not seen any detailed specs on those inputs and outputs - what their actual maximum voltage is.
 

DrStuhl

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Sorry if I wasn’t clear. You’re now using the setup in your most recent set of photos, right? In that configuration, the remote should work so happy days! Although you’re not using the NAD preamp to drive the KC62, so I don’t *think* it will follow the volume adjustments there.

Just to clarify, I haven’t got or used any of the components of your system. I just have a lot of experience chasing down easily-missed gain staging to resolve hiss or hum problems from homes to venues :)

I was referring to the previous configuration, where you connected the output of the KC62 to the MAIN IN on your NAD amp. The manual suggests that connection bypasses the volume dial and remote, which control the preamp part of the NAD. Does that make sense?

I don’t think you need to replace the NAD now - unless you’re wanting something different for other reasons. If you did, then you just need to connect it the same way you have now, KC62 line output to amplifier line input

No, my standard-setup is going out through Pre out (9) to the KC62 into the Main in (10). Volume control is definitely working. Basically this is my setup to the kc62:

1631021550693.png

The KEF subwoofer is designed to be inserted between the pre-amp and the power-amp. At least, that's the use-case shown in the manual.

Given that it needs to receive the pre-out, volume-adjusted, then, it what it passes out will be the volume-adjusted signal, ready for the power-amp.

But I've not seen any detailed specs on those inputs and outputs - what their actual maximum voltage is.

Exactly :)
If I would get another amp, isn't there the same risk of getting that mismatch of sensitivities?
Sure - one that has LFE and integrated HPF would solve it.
 

b7676

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Hard to beatphysics. Can't imagine wanting such a bass module (hard to call it a sub).
I think good oppositional setups start to achieve infinite baffle type acoustics where the driver excursion into the room generates tones and spl, not the box. A good 6.5 can sound like a 12 and deliver fine spl mounted in the right wall.
 
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Chrispy

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I think good oppositional setups start to achieve infinite baffle type acoustics where the driver excursion into the room generates tones and spl, not the box. A good 6.5 can sound like a 12 and deliver fine spl mounted in the right wall.

Yes, a good sized dual opposed sub can be a good thing (I have a dual opposed 15 myself, and a diy project for an 18 if I ever get off my butt). Its just a sealed sub rather than an IB, tho. What does driver excursion into the room even mean?
 

Tokyo_John

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The KEF KC62 and KF92 both have this path for the high pass through to speakers:
RCA analogue input -> ADC -> DSP -> DAC -> RCA analogue output -> Power Amp -> Speakers

If your original source is digital, then it would be like this:
Digital Source -> DAC -> RCA analogue input -> ADC -> DSP -> DAC -> RCA analogue output -> Power Amp -> Speakers

Wow...that is an AWFUL lot of stuff happening in between the Source and the Speakers. A lot of things can go wrong. And the fidelity of the final result at end of this chain has to be limited...
 

KMO

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Which is why it makes far more sense to do all this stuff in an AVR, or something active like the LS50 Wireless II.

Digital Source -> DSP -> DAC -> Power Amp -> Speakers

But even passing through a KC62/KF92, the benefits of adding the crossover should be far more audible than any fidelity loss through the extra DAC/ADC cycle. At least, in the absence of an apparent noise fault, like the one above.

This should work fine, in principle.
 

Tokyo_John

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Which is why it makes far more sense to do all this stuff in an AVR, or something active like the LS50 Wireless II.

Yep...or miniDSP, etc..

Digital Source -> DSP -> DAC -> Power Amp -> Speakers

But even passing through a KC62/KF92, the benefits of adding the crossover should be far more audible than any fidelity loss through the extra DAC/ADC cycle. At least, in the absence of an apparent noise fault, like the one above.

This should work fine, in principle.

It depends. I've encountered a lot of garbage ADCs and DACs in my time, especially stuck in devices that have a relatively small budget for such components. I'd like to see these KEF electronics and high pass signal tested by somebody competent...somebody like @amirm. Actually, this would be a very interesting test, just to see what it does and how it works.
 

Dennis_FL

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Update: from Kef USA There is a fix for that known.


That's good to know. I'm in the market now and will see if I can get an updated unit. I noticed the Roon post with a workaround is for an LS 50 wireless II. I have the metas and use an AVR receiver. Is this loss of auto on the sub an issue with just a wireless LS50 ?
 

Dennis_FL

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The KEF KC62 and KF92 both have this path for the high pass through to speakers:
RCA analogue input -> ADC -> DSP -> DAC -> RCA analogue output -> Power Amp -> Speakers

If your original source is digital, then it would be like this:
Digital Source -> DAC -> RCA analogue input -> ADC -> DSP -> DAC -> RCA analogue output -> Power Amp -> Speakers

Wow...that is an AWFUL lot of stuff happening in between the Source and the Speakers. A lot of things can go wrong. And the fidelity of the final result at end of this chain has to be limited...


I was reluctant to get the wireless for that reason. I have a $500 DAC and was wondering if I'd lose fidelity with the conversions from analog to digital and back after my DAC. My AVR receiver does the same thing if I don't choose PURE. I'm still not sure how it does volume control. I may just do volume control in Roon and bypass my preamp altogether (Source->Roon->DAC->Amp->KEFs)
 

Tokyo_John

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I was reluctant to get the wireless for that reason. I have a $500 DAC and was wondering if I'd lose fidelity with the conversions from analog to digital and back after my DAC.

Yes of course you will. I have a Topping D90 -> March P252 (no pre-amp) which is just super clean and transparent, amazing 2 channel setup with the LS50 Metas. I've grown to like it quite a lot, which is why I'm concerned about putting my post D90 signal through a ADC->DSP->DAC cycle downstream, which are secondary components in the device. I'm sure that you gain a lot by DSP, and maybe the KEF KC62 has a DSP that handles its non-linear response, but all of this seems to be pushing it.

My AVR receiver does the same thing if I don't choose PURE. I'm still not sure how it does volume control. I may just do volume control in Roon and bypass my preamp altogether (Source->Roon->DAC->Amp->KEFs)

I ordered a miniDSP SHD which arrived yesterday...haven't had time to play with it. Initial adjustments with REW with calibrated microphone measurements has gone very well and I've found a good flat response for bass down to ~25 Hz, but still some troublesome dips at higher frequencies (~100 Hz, well above the crossover and so nothing to do with the sub) that I can't get rid of by other adjustments. I'm hoping that the SHD can smooth out the rest of these wrinkles with Dirac. Either way, it should be a fun learning experience.
 

Matias

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Dennis_FL

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Alternatively one can use fixed analog filters in order to avoid the ADC-DSP-DAC of the subwoofer limiting the performance.
https://www.amazon.com/FMOD-Crossover-Pair-High-Pass/dp/B0006N41JW
https://www.amazon.com/FMOD-Crossover-Pair-Low-Pass/dp/B0006N41EM/


Good area for amirm to explore......how is fidelity affected by AVR receiver or subwoofer analog to digital to analog conversions .

I was going to test going straight from my DAC to the amp but how to wire in the sub? If I use the sub as a filter does it do analog to digital conversions?
 

abdo123

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Lots of audiophile nervosa in this thread lately.

For subwoofers you need ~60 dB of S/N and around -40 dB THD. Even Toddlers can make circuits with such requirements.

my phono stage (Cambridge Audio Duo, the best measured in this site) has mains hum at around -60dB in my system and it's completely inaudible.
 

Dennis_FL

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I have the LS50 metas and just purchased the KC62. I have a few options for setup and will appreciate suggestions. I have a Marantz AVR receiver (with Audyssey room correction) and I use an external Emotiva amp for two channel stereo. 95% of the time I'm playing music through Roon/Tidal to a Gustard X16 DAC and on to the receiver.

So I'm a little fuzzy on the best way to wire the sub as I posted above. If I use Audyssey then the Marantz is taking the analog output from the DAC and converting to digital and then after DSP - converting back to analog. The receiver has a "PURE" setting which bypasses Audyssey but I'm not sure how it does volume control

I was thinking of going straight from the DAC to the amp with Roon as volume control but how to wire the KC62? With the speaker wire output of the amp? Or with the RCA output of the DAC and then the output of the sub to the amp?

Then is this the same thing? Does the sub convert to digital to filter the crossover?

Or am I making too big a thing with the A/D, D/A conversions? Should I just use the Marantz and "PURE" setting.

Signed "Confused in Florida"
 

KMO

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PURE on the receiver is 100% analogue. The volume control and level trims are analogue in all modes.

If intending to use the sub for music, the benefit of the receiver DSP crossover, and potentially Audyssey, should outweigh any potential benefit of a superior external DAC.

I'd just send digital into the receiver, not use pure, and use the 'LFE' sub input.

Would be nice if the receiver offered digital pre outs, so you could stick your DAC in at the end of the digital chain, after crossover. Otherwise, no point inserting it into the chain.

Maybe you could split your digital signal, send it to both DAC and receiver, so the receiver is getting both analogue and digital inputs for that source. You could then temporarily change INPUT MODE to analogue and select PURE to get the DAC output. But then no sub in that mode, without rewiring it. Or maybe select LFE+MAIN and engage HPF on the sub? Anyway, all that omits the crossover, so it would just be an option to allow comparison.
 

Dennis_FL

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PURE on the receiver is 100% analogue. The volume control and level trims are analogue in all modes.

How do they treat the sub crossover?
 

KMO

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How do they treat the sub crossover?

Everything else apart from level trims is digital. Crossover and distance settings will have no effect in DIRECT or PURE DIRECT mode.

(IIRC, in the past a very few high-end receivers have had auxiliary fixed-frequency analogue crossover circuits they could employ, but I doubt yours is one of them.)

When using a digital source in PURE mode, it restricts behaviour to emulate the limitations of the analogue path - it does the Dolby Digital or whatever decode to get the LPCM, and then sends that straight to the DAC, bypassing all the DSP-type stuff.

Now, some Denon, and hence possibly Marantz, receivers do have a "subwoofer" setting that applies only to 2-channel DIRECT modes. I believe that will send a copy of L+R to the SW output, which will allow you to engage the subwoofer. But it won't be doing a crossover - mains will still be getting full-range, and you'd want to engage LPF on the sub. I think the sub will be getting a full-range signal too.

Edit: did a bit more searching. The above might be wrong. Some sources suggest that if the "Subwoofer" setting exists, that may imply the analogue crossover is present, and it will be fixed at 80Hz. The setting will likely only be visible at all when in 2-channel DIRECT mode (including PURE and DSD), in "Surround parameters". The normal digital "crossover" and "large/small" settings will not apply - only that DIRECT-specific analogue "subwoofer" option.
 
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Dennis_FL

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I just looked at the manual and there is only high level input. No output. So the main speakers are wired in parallel? So I set the preamp to send full range to the amplifier and the main speakers (in my case KEF LS50 metas) are getting the full range also? No crossover? What am I missing?


Screen Shot 2021-09-20 at 8.00.58 AM.png
Screen Shot 2021-09-20 at 8.00.58 AM.png
 
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