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DBX 4BX Mods


babadono

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7 minutes ago, Westcoastdrums said:

Mostly we use gates when needed.   I guess "on paper" I understand.   We had primarily used outboard gear in the past.   I mean for budget gear that "expands" my question is, do the pros really outweigh the cons in terms of SQ and SNR?  I kind of doubt it.   Hearing is believing I guess.   

The effects are subtle but still audible. You can adjust the threshold way wrong and try to upward expand everything and the result is not good(to my ears). It also divides up the frequency of the signal into 3 bands and performs its magic on the 3 separately to avoid the lows effecting the highs and vice versa. As far "budget" is concerned this unit when in production had the best VCAs and RMS level detectors that DBX produced. i.e. the same ones that went in their studio gear. My modified units now have the best VCAs and level detectors made by THAT Corp. And IMHO the best audio Opamps ever made the LME49720.

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Original PCB is on the right side.  The DBX expanders also serve as a noise gate when performing their duties.  The 5BX-DS was the most sophisticated of them all but very rare.  It had five  idependently adustable bands for range expansion, compression and most importantly impact restoration.  For a time I use two of them one for each channel monoed via Y adapters so left and right were totally independent they really can bring the music to life.  The first time I heard a DBX 3BX-III (lesser version of the 4BX) I was sold.

DBX 5BX-DS Pair.jpg

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My understanding of the 5bx is any signal over the threshold got left alone or compressed depending on the settings. It is not a linear expander but a downward expander and compressor combo. I have no experience with these units but that's my understanding. With compressed recordings I want linear expansion. If its too loud I can turn it down or use one of the compressors in my mixer.

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6 hours ago, babadono said:

I looked briefly for a expander plug in for a DAW that was not just downward expansion and came up empty. If you know of one please post a link. 

 

What type? vst, au, aax? Windows, OSX, Linux?

 

Bruce

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11 hours ago, babadono said:

My understanding of the 5bx is any signal over the threshold got left alone or compressed depending on the settings. It is not a linear expander but a downward expander and compressor combo. I have no experience with these units but that's my understanding. With compressed recordings I want linear expansion. If its too loud I can turn it down or use one of the compressors in my mixer.

You are absolutely correct the only upward expansion comes via the impact restoration circuits.  Most people do not realize that it is a downward expander which can be useful with today's way oversaturated recordings.  I like yourself prefer upward expansion.  I parted with them and used a pair of DBX 3BX-DS's instead as the expansion on the digital series units is far smoother than its predecessors.  The 4BX is an expander only and offers no compression ability or ambience circuit.  The 3BX-DS also displays all three bands of impact restoration while the 4BX displays one even though it is performing it on all three bands.  The Impact Restoration on the 4BX is also more aggressive offering 12db difference compared to 10db of the 3BX-DS.

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13 hours ago, Marvel said:

 

What type? vst, au, aax? Windows, OSX, Linux?

 

Bruce

Jeesh, how complicated can it be:)? Marvel I really have no idea. I would assume if I ever get that far it would have to be something that runs on a Windows computer. Right now the mixer I have only has a firewire interface and therefore has never been hooked up to a computer. I am assuming if I really want to get involved with this the first step will be getting a new mixer with USB or AVB interface(s).

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I was just curious, because I had copied a 1/4 track stereo tape a few months ago and did some expansion on it, but I will have to open up the session file to see what I did. The tape I had was a bit compressed. I didn't change it much, but it is a bit more lively. The DAW software I use has some default plugins, but they are in LV2 format.

 

Bruce

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  • 2 weeks later...

Well the first unit is done and passed the smoke test last evening. Now to run some tests.

Added balanced inputs using Jensen line input transformers, balanced outputs matching the impedance on pin 3 of XLR with the impedance on pin 2. Balanced or unbalanced operation is selectable by rear panel switch. Another rear panel switch selects mono/stereo operation. I did not want to have to add a Y cable externally to get the level detectors to work in single channel mode. Added nice gold plated RCA connectors for the unbalanced main I/O. I really do not care about the tape loop RCA connectors(who uses that sheet anymore?) so I left them as is. Also added DC power inputs so I can run unit from a remotely located power supply(I hate transfomer hum) 

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I still have my original 117 and it still works great. 4BX in my main system. I can hardly listen to LPs without one unless they are in the top couple of percent of pressings, and even then they will be compressed unless it's chamber music or something of limited dynamic range to start with. 

 

As mentioned, I think it sad no one has brought this wonderful tech back for the modern resurgence. Once you have one and learn to set it properly, there is no going back. I keep hoping someone will duplicate the functions in realtime software. It would be nice for stuff on music servers. 

 

Dave

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52 minutes ago, Westcoastdrums said:

I understand trust me.  Sarcasm.   Strong work on the mods. What were the results?

Taking first unit back home tonight, it appears to perform on bench as envisioned. I'll hook back into system over 3 day weekend(yea). I am suspecting it will behave just as before except now its got balanced I/O as an option.

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46 minutes ago, Mallette said:

I still have my original 117 and it still works great. 4BX in my main system. I can hardly listen to LPs without one unless they are in the top couple of percent of pressings, and even then they will be compressed unless it's chamber music or something of limited dynamic range to start with. 

 

As mentioned, I think it sad no one has brought this wonderful tech back for the modern resurgence. Once you have one and learn to set it properly, there is no going back. I keep hoping someone will duplicate the functions in realtime software. It would be nice for stuff on music servers. 

 

Dave

If I were a DSP wizard I would pursue this. I've got the chops for the analog I/O but not the DSP. What a fun learning experience it would be.

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46 minutes ago, Westcoastdrums said:

without having a sound signature of its own

DBX has none IF you have a good ear and learn to set it just right. Some find it easy, some take a while. In my case I've used them so long if an adjustment is needed it's a matter of no thought and just doing it. In most cases I already know what I want and when it's off I recognize it immediately. 

Dave

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