Feeding one power amp from two pre-amp simultaneously using a passive mixer?

[PHD]

Hi

I have dual Hypex NC400 power amps with both single-ended and balanced inputs. I want to use the amps as external front channel power amps with my Denon X4800H as well as a hi-fi power amps for my NAD C658 preamps.


Instead of looking for a remote-controlled switch box solution, I was thinking of using a passive line-level mixer, such as this one:

Mix 2:1 - Radial Engineering

The Radial MIX 2:1 is a simple yet highly useful mixer that passively sums two audio channels down to one.

www.radialeng.com

https://www.radialeng.com/wp-content/uploads/2021/09/mix-21-manual-WEB-09-2021.pdf

It's a balanced two-input to one-output passive mixer. What if I use two stereo dual RCA to 1/4" TRS cables and connect both L/R outputs of the Denon AVR and NAD preamp which will trick the 2:1 mixer into thinking it's mixing two balanced inputs where in fact it's mixing two stereo signals L1+L2, R1+R2 ?


Will this work? Would it impact sound quality or channel separation? Ground loop isn't an issue because the two preamps share a common ground with the power amps using separate grounding wires (phono Denon to NAD to Hypex chassis ground).

Is there a better alternative to share one power amp with two preamps?


Thanks

 

[Blumlein 88]

If you just want to switch between the AVR and the NAD preamp I think these simple switchers are better. If you want to feed and blend both at the same time then the Radial is the ticket, but I don't know why you would want that.

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I have one of the above I use for much the same reason. I usually have my front speakers as part of a 5.1 system and the fronts fed by a large power amp. I sometimes use a separate DAC or something like a BabyFace to feed music just for stereo. This lets me switch between the two. In fact I could switch between a 3rd source if I wanted to do so.

IF the Denon only has RCA out, then you need to use an RCA to XLR cable which may or may not get enough output from your power amp. The Denon lists the analog output as 1.2 volts.

 

[PHD]

If you just want to switch between the AVR and the NAD preamp I think these simple switchers are better. If you want to feed and blend both at the same time then the Radial is the ticket, but I don't know why you would want that.

Nobsound 3-IN-1-OUT XLR Audio Switch Review

The $200 more for wooden end caps. The one reviewed here is hard to beat. Worth the price for the Neutrik connectors alone. Well, if they're real. The ones I have recently bought from Douk Audio don't have the Neutrik logo/writing on the XLR connectors. The logo is the one of Yongsheng (Ningbo...

www.audiosciencereview.com

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Nobsound Little Bear Mc103 3-IN/1-OUT XLR Measurements Hi folks, Here is a quick measurements write-up of the Nobsound Little Bear Mc103 XLR line selector. This is the three inputs/one output configuration, pretty much similar to the "Pro" version @amirm reviewed a while ago. It has been...

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I have one of the above I use for much the same reason. I usually have my front speakers as part of a 5.1 system and the fronts fed by a large power amp. I sometimes use a separate DAC or something like a BabyFace to feed music just for stereo. This lets me switch between the two. In fact I could switch between a 3rd source if I wanted to do so.

IF the Denon only has RCA out, then you need to use an RCA to XLR cable which may or may not get enough output from your power amp. The Denon lists the analog output as 1.2 volts.

I prefer a switch, but I couldn't find one with an IR remote control that I can program into my Harmony Elite/Hub/ I did order one from Aliexpress, but It had non-standard OR codes that cannot be programmed into the Harmony remote...


Can I use just one Radial 2:1 mixer for stereo blend or should I buy two, one for each channel? If I understand correctly, the Radial uses separate mixing paths for the positive and negative signals, which could also support two positive left/right signals. The question is whether channel separation could be affected if only one mixer is used?

The Hypex NC400 has enough gain even for a low 1.2V single-ended.

 

[Blumlein 88]

The Radial is a summing mixer. If you connect the Denon and NAD, then both signals will be combined. And yes you will need two. Now if one source is off while the other is on I guess it would work. I see no advantage vs the switches I listed.

I have seen rca switching boxes with remote for AV. Maybe some of them are still available.

 

[Blumlein 88]

Upon further reflection I think I see what you had in mind. That you could connect both devices. Then turn on the Denon remotely, use it for AVR. Turn it off remotely. Turn on the NAD remotely and use it for stereo.

What might be a problem is the Denon would see the output impedance of the NAD, and the NAD would see the output impedance of the Denon. That likely is 300 ohms or less. It wouldn't effect anything channel to channel, but each device was not built for those kind of low impedance loads. Plus some devices when connected and turn off can act something like diodes and add distortion.

That mixer probably has some resistors to limit that effect. You would need to know how it is setup internally.
EDIT to ADD:
Looking at the Radial manual, it says 8 k ohm input impedance. So that probably takes care of the issue with having both connected. I also notice you loose 6 db for insertion loss. That might make your Denon borderline with the amp.

 

[Blumlein 88]

Amazon.com

Amazon.com

Here are a couple RCA switchers with remote switching. I used a similar device several years back. It worked fine. The one for AV use you just don't connect anything to the yellow composite video. Using an XLR to RCA adapter from the NAD should work okay with these. Then everything goes to the RCA input on your amps.

 

[PHD]

Thanks. What about an active line level mixer? Such as this one :

https://www.amazon.com/Behringer-Micromix-MX400-Low-Noise-4-Channel/dp/B000KGYAYQ/ref=mp_s_a_1_52_vs_ar?c=ts&dib=eyJ2IjoiMSJ9.FvQPwQQxInEJprbxlBf4lpvPFPoZVSHuSlOCIh48B7Xl-EpHWGsxgnltWa9NwZNjiNwj0Oz1G5C-5imhE98ct2qbL5sxrbDw0h3Jpjae4GxkOmlxTjR9oFrQzRIz0JgJYyntMekPpcgtdDZKtpb9OMckVCFq-_nHJWP-RqE7Sw37X412sagGpzxoFFeJNcZd5cPfMLhlhBioDi95x2gc2w.IE5MEt5l16qznofUcjpNJ8svEQP_JMXpo3AGISAK2ak&dib_tag=se&keywords=Audio+Recording+Mixers&qid=1723357852&refinements=p_89%3ABehringer&s=musical-instruments&sr=1-52&ts_id=11974861

Or any alternative which won't degrade sound quality?

 

[Chrispy]

What a weird convoluted setup. I doubt you really have a handle on SQ

 

[PHD]

Well, the bottom line is that I still need to find a way to share one power amp and a set of speakers between two pre amplifiers in the same room. Either by mixing the signal paths or by using a remote controlled switch... I'm now considering buying a cheap hifi preamp with two line inputs to be used as a controlled switch...

 

[Zek]

Such as this one :

This one is mono, you need a stereo mixer, somethin like this

Amazon.com

 

[klettermann]

My scenario is similar to your own, I think, with HT and audio front ends feeding a common amp for the 2ch / front speakers. The speakers are large Magnepans driven by ML No. 332. The HT setup is Denon x3800h (RCA's out) while the 2 ch is a (mostly) Schiit stack (balanced out). I got a Schiit Loki Max equalizer to do the switching. It has balanced and unbalanced inputs that are remote switchable. Different EQ profiles can also be stored and selected by the remote. Works great.

 

[PHD]

My scenario is similar to your own, I think, with HT and audio front ends feeding a common amp for the 2ch / front speakers. The speakers are large Magnepans driven by ML No. 332. The HT setup is Denon x3800h (RCA's out) while the 2 ch is a (mostly) Schiit stack (balanced out). I got a Schiit Loki Max equalizer to do the switching. It has balanced and unbalanced inputs that are remote switchable. Different EQ profiles can also be stored and selected by the remote. Works great.

Can the Loki convert the SE input into balanced and output it via the XLR outputs?

I couldn't find the Loki Max in the Harmony remote database. Is the remote IR-based and uses standard codes that can be programmed into Harmony? The last remote-controlled switch I bought had non-standard IR codes which couldn't be learned by Harmony...

Thanks

 

[EJ3]

Well, the bottom line is that I still need to find a way to share one power amp and a set of speakers between two pre amplifiers in the same room. Either by mixing the signal paths or by using a remote controlled switch... I'm now considering buying a cheap hifi preamp with two line inputs to be used as a controlled switch...

Feed one preamp into a line level input on the second preamp which is fed to the amp. That is how I use my pair of APT/Holman PreAmpifiers because I need more inputs than there are on just one of them. No switches needed.

 

[PHD]

OK. I think I found the right product:

https://www.amazon.com/gp/product/B0CPL46JSS/ref=ox_sc_act_image_1?smid=A15FO7ZPW6GUAV&psc=1

With this switcher, I can use the 12V trigger out of the Denon or the NAD to switch between the FR/FL and sub1/sub2 outputs of the Denon and NAD for both dual subwoofers and the power amplifier.

 

[klettermann]

Can the Loki convert the SE input into balanced and output it via the XLR outputs?

I couldn't find the Loki Max in the Harmony remote database. Is the remote IR-based and uses standard codes that can be programmed into Harmony? The last remote-controlled switch I bought had non-standard IR codes which couldn't be learned by Harmony...

Thanks

Yes, rca's and xlr's both in and out. For the other stuff best to just look the Schiit website for more info.