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rbrooks7
02-12-2005, 08:25 PM
I was thinking of building a dynamic range expander for my setup, but I have not done any op amp work in a while and need some help.

What is a high quality audio op amp for a good price. The price factor is crucial as i will need some 10-15 devices for the project. Also, I was hoping for them to be a Norton amp so I would only need a single sided supply.

Also, I've heard horror stories about hte use of dynamic range expanders blowing drives. Any input? I am running a pair of L100's with a Threshold FetTwo preamp, Threshold S/500 amp (it is so sweet!!), Yamaha EQ-70. I was expecting to have to fuse the tweets to protect them.

Any input helps. Thanks

duaneage
02-13-2005, 05:34 AM
I was thinking of building a dynamic range expander for my setup, but I have not done any op amp work in a while and need some help.

What is a high quality audio op amp for a good price. The price factor is crucial as i will need some 10-15 devices for the project. Also, I was hoping for them to be a Norton amp so I would only need a single sided supply.

Also, I've heard horror stories about hte use of dynamic range expanders blowing drives. Any input? I am running a pair of L100's with a Threshold FetTwo preamp, Threshold S/500 amp (it is so sweet!!), Yamaha EQ-70. I was expecting to have to fuse the tweets to protect them.

Any input helps. Thanks

I built a DRE using an NE572 many years agao. I used TL084 Mosfet op-amps. You can use LM324 as well if you want to run a single end supply. the LM324 is a FET based amp that is cheap and good enough for audio use. It basically takes the Vcc and internally splits it so the amp gets it 's split voltage. I have data on the NE572 ( andthe 571, 573 cousins) but I think they are out of production. Are you creating a gain cell from scratch? Here is a source for this chip. It is a stereo chip so at least you get two channels for one price. I would consider two or three bands for this
http://www.midwest-analog.com/catparts.html#NE572

If your going to go discrete all the way matching the components is key. Variable gain cell circuits are suseptable to heat and noise because of the gain curves used. Integrated Circuits solve these problems because tolerances can be very tight and temperatures are uniform.

I have a DBX 3BX-DS , have owned it for 18 years, and really like it. It can generate very high levels above what the input is. You have to be moderate in what a DRE is used for. THe idea is not to jack everything up, rather expand downwards the quieter passages. THis gives you the dynamic range expansion your really after. The threshold at which a DRE goes from attenuation to gain is critical, as is the attack rate and decay value. My DRE has a high speed amp for transient restoration which can surprise speakers sometimes.
I would use thermistors on the tweeters for protection. They open up when needed and automatically reset themselves. Values have to be calculated based on current flow.

rbrooks7
02-13-2005, 08:27 PM
Thanks for the info. BTW how much do the DBX units run? Would it be cheaper to just buy one? I have installed them in concert halls, etc. when I worked for a large audio engineerig firm, but I never priced them.

duaneage
02-13-2005, 09:11 PM
Thanks for the info. BTW how much do the DBX units run? Would it be cheaper to just buy one? I have installed them in concert halls, etc. when I worked for a large audio engineerig firm, but I never priced them.

Ebay is the pbvious answer but there are other on line resources for them. There were several models, I prefer the "DS" series. The 5BX was the big boy. 700 dollars new , they go for more sometimes because they are rare. I paid 350 for my 3bx in 1988, I have seen them go for 250 to 450 depending on how bad someone wants it.


I truly feel the dbx expanders are the best. Started in 1962, dbx perfected expansion and compression. They make studio and pro stuff today but the home equipment is more of what your looking for because of teh input and output connections and generally the specs are suited more for home use. My 3bx has a single knob that goes from expand to compress and a nice led display to keep tabs on levels. The high frequency and low frequency bands are also adjustable. The older, black face models are not as refined and IMHO are not as good.

i am thinking of making a expander for my car that switches to fixed compressor using the NE572. But time is in short supply anymore.

Tezza
11-02-2005, 12:54 PM
Hi,

Does anyone have any pictures/details/specs for the dbx 5bx DS? I'm thinking of upgrading my 3bx II.

Cheers,

Terry

toddalin
11-02-2005, 02:46 PM
I have a dBx 119 that I no longer use as expansion and compression are included in my Yamaha RX-Z9. Works fine.

You can have it for $75+shipping.

The thread will take you to a discussion on the 119 and includes a picture.

http://www.recordingproject.com/bbs/viewtopic.php?t=8142