DBX NX-40 Setup

[pderousse]

Does anyone have any experience with DBX decoders and the basic wiring set up? I can't tell whether I have a bad unit or I've somehow set it up wrong. When I found a DBX NX-40 on ebay for $25, I thought it was worth an experiment. I normally run the turntable directly into the phono input of a McIntosh C49, so I thought I could run the signal from two spare RCA outputs to the NX-40 input labled "From RCVR Tape Output" and then from the its output labled "To RCVR Tape Input" another two cables to spare RCA inputs on the preamp. This seems to be what the instructions require to play a "disc" (by which is meant a record); however, turn the unit on, push "DBX disc decoder," and - no sound. I can't tell whether I have a bad unit or I've somehow set it up wrong. BTW, I have no interest in the recording functions; I accidentally bought one of these peculiar records.

 

[cgallery]

I don't think it will work like that because when you switch to the input # where this is connected on the receiver, the output on the receiver is no longer playing the turntable.

You need a tape or processor loop on the receiver to use the DBX. Or you could get an external phono preamp.

 

[pderousse]

I suspect you're right. With all the programibility of the C49, I had thought it may be possible. A proc loop can no longer be assumed.

 

[voodooless]

Why use a device that is made for tape on a spinning platter anyway?

 

[MaxwellsEq]

This device, like a Dolby encoder/decoder, is for compressing signals when recording on to analogue tape and for replying previously DBX encoded source material. The only thing it can possibly do to an LP playback setup is to significantly mess the sound up!

 

[pderousse]

Thanks for your help.

This device, like a Dolby encoder/decoder, is for compressing signals when recording on to analogue tape and for replying previously DBX encoded source material. The only thing it can possibly do to an LP playback setup is to significantly mess the sound up!

It does everything you say it does for both tape and LP (see first image)

 

[voodooless]

Thanks for your help.

It does everything you say it does for both tape and LP (see first image)

Where does it say that it works for LP?

 

[pderousse]

I was a bit incredulous too at first and only stumbled upon this device because I accidentally purchased a dbx encoded LP (which sounds atrocious if you play it without a decoder). The Nx40 is incompatible with my system, but I’m really intrigued by this proto-CD lost tech. The answer to your question can be found in the owner’s manual which is easy to find online. Discogs also has a whole area devoted to these special LPs. Thanks again.

 

[voodooless]

The Nx40 is incompatible with my system, but I’m really intrigued by this proto-CD lost tech.

Your McIntosh can't output two different sources over the two outputs? If so, set up output one to output the photo output, then connect the box between it and another input and set the second output to that input. That way it should work (if supported).

The answer to your question can be found in the owner’s manual which is easy to find online.

Ah, now I get it, you were referring to the disc decoder button.

 

[pderousse]

It appears (again no expert on this) that what I need is a pre that will accept a phono input but “monitor” a different input, the one from the processor. The c49 is highly customizable, but from what I gather from other Mac fora, it can’t do that, and ‘tape-Mon’ is no longer a common feature consumers want. I wonder, if I used a separate phono pre and split its output into both the c49 and the processor, I could then use the pre to select the different inputs.

 

[NiagaraPete]

Does anyone have any experience with DBX decoders and the basic wiring set up? I can't tell whether I have a bad unit or I've somehow set it up wrong. When I found a DBX NX-40 on ebay for $25, I thought it was worth an experiment. I normally run the turntable directly into the phono input of a McIntosh C49, so I thought I could run the signal from two spare RCA outputs to the NX-40 input labled "From RCVR Tape Output" and then from the its output labled "To RCVR Tape Input" another two cables to spare RCA inputs on the preamp. This seems to be what the instructions require to play a "disc" (by which is meant a record); however, turn the unit on, push "DBX disc decoder," and - no sound. I can't tell whether I have a bad unit or I've somehow set it up wrong. BTW, I have no interest in the recording functions; I accidentally bought one of these peculiar records.

View attachment 232077View attachment 232078View attachment 232079

This is not the right DBX. You want the dynamic range expander. I think it was a 224 It also reduces his and noise. Back in the day it was great for improving video audio and records that had lot's of noise between tracks.

 

[pderousse]

It’s the correct dbx. They made many vinyl decoder models. From the NX40 manual:

 

[MaxwellsEq]

Thanks for your help.

It does everything you say it does for both tape and LP (see first image)

Only if you have a DBX encoded LP. It will completely mess up the sound of a non-encoded LP.

 

[DVDdoug]

Of course, you can check the rest of your setup by bypassing the DBX box with a direct RCA connection. Then if you get nothing through the DBX box you know it's broken.

I had a cassette deck with DBX but I don't remember the vinyl version...

Try putting it between your preamp and power amp. It might want a "hot" line-level signal so it will probably work best if your power amp has a volume control that you can use. Also, the expansion will make the preamp volume control a little weird (exaggerated).

Another solution would be to get a separate phono preamp. You shouldn't need a "great" phono preamp because the expansion will improve the signal-to-noise ratio. (But it will also exaggerate any frequency response variations.)

P.S.
Since it is a dynamic expander, quiet sounds will be very quiet so with weak signals you might not think it's working.

 

[Eurasian]

What dbx record did you get? There couldn’t have been many produced/sold.

I only heard this technology demonstrated once and it was quite impressive. Iirc, the expansion was more dramatic than the usual dbx boxes, so a very flat cartridge/pre amp combo was required. I remember being startled by the explosive dynamics and low surface noise.

 

[pderousse]

Of course, you can check the rest of your setup by bypassing the DBX box with a direct RCA connection. Then if you get nothing through the DBX box you know it's broken.

I had a cassette deck with DBX but I don't remember the vinyl version...

Try putting it between your preamp and power amp. It might want a "hot" line-level signal so it will probably work best if your power amp has a volume control that you can use. Also, the expansion will make the preamp volume control a little weird (exaggerated).

Another solution would be to get a separate phono preamp. You shouldn't need a "great" phono preamp because the expansion will improve the signal-to-noise ratio. (But it will also exaggerate any frequency response variations.)

P.S.
Since it is a dynamic expander, quiet sounds will be very quiet so with weak signals you might not think it's working.

The amps have only XLR inputs. I received a phono pre this evening and will report back soon whether it works.

 

[pderousse]

What dbx record did you get? There couldn’t have been many produced/sold.

I only heard this technology demonstrated once and it was quite impressive. Iirc, the expansion was more dramatic than the usual dbx boxes, so a very flat cartridge/pre amp combo was required. I remember being startled by the explosive dynamics and low surface noise.

The LP is Cal Tjader, La Onda Va Bien. Your experience is what Ive heard from others. That, and because I’m a huge Tjader fan is why I’ve chased this phantom. Once I get a chance to run the signal through a phono pre, I’ll report back. It sounds like a real shame that it did not catch on before the CD replaced it.

 

[pderousse]

So I changed the signal path to turntable > Rega Fono MM Pre > NX40 DBX Decoder > preamp, and I could not hear anything, I mean absolutely nothing, no hiss, no pops, no music, nothing, until I cranked the volume and realized it was playing music. I dialed back the gain knob of the on the NX40, and I was in business. There is indeed no record noise whatsoever. Transients of Tjader's vibes and Lateano's percussion are super crisp and right there. The sound stage very natural and articulated. I did some preliminary A/B testing with the Toping D90SE DAC and adjusted the trims on the inputs to the same levels, so as to avoid loudness falacy. In a casual listen, I found hard to tell the difference between a 44/16 FLAC output through the DAC and the DBX record; some slight forwardness in the record maybe over the DAC, but definitely nothing obvious. This will require much more careful listening. These records are really cool.

 

[Eurasian]

I’m glad you got it working and liked the results. I bet there are still some of these records floating around that would be worth a listen.