Dynamic range expanders

[scifi]

I tried hooking up two stereo dynamic range expanders (between the Sansui QC-04 and front and back stereo amps) last night and listened to a couple CD-4 records with amazing results. The improvement was far better than what I expected. I tried them with stereo (2 speakers) a couple times before, but didn't expect the dramatic difference with a quadraphonic system. The results were a significantly more natural and realistic sound and spreading out the sound giving a more surround sound effect instead of sounding like most of the sound is coming from the speakers, ie. a better ambience effect. I recently got a RG Pro-16 expander from an Ebay seller which I used on the front channels. I used a Pioneer RG-2 on the back channels. I bought that years ago used, I think from a pawn shop or music store. There's a couple Pioneer RG-2's on Ebay right now. The 3 band DBX expanders might be better, but cost more.

http://www.audiokarma.org/gallery/showphoto.php?photo=1600&size=big&cat=

 

[EMB]

I've found the use of range expanders variable; ultimately, it depends on the source, I think, as much as the quality of the units themselves. On my UK stereo slab of SGT. PEPPER, for instance, the crescendos of "A Day In The Life" were more dramatic and impressive. Since vinyl by nature tends to use masters that are compressed to fit on a 45 or Lp (or intentionally Eq'd or compressed for effect), some recordings (and songs within albums) would come off better than others.

For compact disc, I found the results less impressive, partly because (and I'm guessing here), using uncompressed mixdown tapes, or remixes from session tapes tends to eliminate not only the compression, but the need to attempt to expand dynamic range that should already be at or near the best the recording has to offer. But, used judiciously, they can make a big difference, but I also found that sometimes they added mild distortion, or made the sound seem, well, strange rather than natural. YMMV....

ED

 

[Disclord]

Often a far greater improvement can be had by using an expanders (if it has it) Peak Unlimiting function; that way, everything but the very peaks are kept the same and only the peaks are expanded louder - 'released' as it were - from the limitations of an LP or FM broadcast. I used Peak Unlimiting with BTSC Stereo Broadcasts when watching television in the NTSC days - most shows had a somewhat limited dynamic range and instead of wholesale compression, engineers would apply moderate peak limiting just before the stereo encoding. A mild peak unlimiting expansion ratio of 1.2 or 1.4 would, often drastically, improve the final sound quality of a broadcast. This was recommended to me by Dolby's Mark Davis - the guy who invented the form of dbx Noise Reduction + variable emphasis used in the NTSC Stereo Broadcast System. Older FM analog-only LaserDiscs can benefit from Peak Unlimiting too. While MCA DiscoVision and Pioneer used separate 1/4 inch mag tape (with Dolby A and later Dolby SR) locked to the Sony 1-inch C-Type or IVC-9000 VTR master via timecode, they often applied peak compression so as not to overload the FM modulator. CX-encoded LD's with mild expansion from a dbx unit can create some really spectacular sound.

I LOVE my dbx 128 Expander and Type-II Noise Reduction unit. Even with minimal expansion, the 'sound' of the dbx VCA's was totally unique and, like tube amps, quite euphonic, adding a "pleasant" distortion to the signal that made it much more listenable and enjoyable.

 

[scifi]

The Pro-16 can be switched between what looks like a combination of peak unlimiting and expansion, and linear expansion. I found if I set both the Pro-16 and RG-2 to 10 db expansion, it works good. Any higher and the expanders don't track to well.

 

[scifi]

Here's an article about tubed dynamic range expanders. Years ago, I tried 2 or 3 different types of pentagrid converters, IIRC, with the corresponding circuits in fig. 1 and 2 on the first page of the article and decided that the sound quality is too low to be practical. I also tried the circuit in fig. 8 on the third page which uses light bulbs connected across the audio transformer and speakers. The tracking was poor and when I turned up the volume, the light bulbs burned out. I'm thinking of trying the Masco circuit in fig. 5. I have a feeling this might give good results.

http://www.fileden.com/files/2008/8/24/2063601/electronics/CompExp-p41-900.jpg

http://www.fileden.com/files/2008/8/24/2063601/electronics/CompExp-p42-900.jpg

http://www.fileden.com/files/2008/8/24/2063601/electronics/CompExp-p43-900.jpg

 

[TVB]

I use a DBX 3bx ds and a dbx 3bx III for my quad records and Q8s... It is amazing to listen with them over a period of time and then byass them..You will wonder where the music went! (huge difference) !!! I wouldnt want to live without mine..I have purchased three of these units from 2nd hand stores for $15 $15 and $24. My third dbx unit, a DBX 3BX, is hooked into one of my high end stereo systems on which I listen to cds... The dynamic range with CDs and DBX is mindblowing..

 

[scifi]

Here's an article about tubed dynamic range expanders. Years ago, I tried 2 or 3 different types of pentagrid converters, IIRC, with the corresponding circuits in fig. 1 and 2 on the first page of the article and decided that the sound quality is too low to be practical. I also tried the circuit in fig. 8 on the third page which uses light bulbs connected across the audio transformer and speakers. The tracking was poor and when I turned up the volume, the light bulbs burned out. I'm thinking of trying the Masco circuit in fig. 5. I have a feeling this might give good results.

http://www.fileden.com/files/2008/8/24/2063601/electronics/CompExp-p41-900.jpg

http://www.fileden.com/files/2008/8/24/2063601/electronics/CompExp-p42-900.jpg

http://www.fileden.com/files/2008/8/24/2063601/electronics/CompExp-p43-900.jpg

I moved the article here http://antiquesci.50webs.com/CompExp.htm

I tried making a stereo version of the Masco circuit (fig. 5) and found that it works better than the other ones I tried. I substitued 12ax7 twin triodes for the 6SL7 tubes and am using germanium diodes instead of the V2-b triodes operated as diodes. Its definately hi fidelity.

I noticed that the 0.1 microfarad capacitor between V2-a and V2-b and the 100k cathode resistor on V2-b look like they might act like a high pass filter. I made some calculations (f = 1/2piRC) and put in a stereo 3 way switch which can switch between 3 different capacitors (in both stereo channels) which affect the frequency components of the control voltages. When switched to the 0.1 capacitor, the expander reminds me of a bass expander I saw in a store in the 1980's. Switching to a lower value capacitor seems to mainly expand the mid range and gives it more realism.

Changing some of the resistors to variable resistors in the attact/recovery circuit could also be used to alter the response.