• The move to the new server is done. There are some software and database maintenance updates in process. This has us passing the hat around to help out. We appreciate any donations. Seriously, even a dollar helps. The payment page may be found here - https://www.audiokarma.org/support.html

dbx gurus - 10/20 EQ & prototype 3bx S-I skore / Nudies

w1jim

w1jim

I can fix it but good...
Subscriber
Now here's a pair of interesting new additions - the dbx 10/20 10 band "Computerized Equalizer / Analyzer" and a prototype first generation dbx 3bx dynamic range expander.

I bought these from a former dbx employee.
The EQ he had purchased on ebay and seems to work 100%.
Unfortunately it is missing the calibrated analyzer microphone but I made one from a generic electret mike that I got at RatShack - works but the calibration is likely non-existent.
I found the operations manual online (BTW - submitted it to hifiengine) so that was a big help in figuring out how this works - not all that intuitive!

I also got a engineering prototype dbx 3bx. This allows for individual level and threshold adjustments for each of the 3 frequency bands. The faceplate looks like it was cut by the new guy with a metal cutter in the lab. Then the individual slots for the sliders were milled from the original face.
I found that the guts are significantly different from my other 3bx (series 1). The prototype has all of the audio circuitry on a single PCB whereas my other unit has 9 (vertical) daughter boards that plug into the mother board. Additionally, the prototype has far superior film caps in the audio path and only a handful of tantalum caps in contrast to the other unit which has a lot of electrolytics and tantalums in the audio path (unit shown has been recapped).

So now a question for the dbx gurus - is the PCB on the prototype unit an early (or late) production version or something completely unique?


attachment.php



attachment.php



attachment.php



attachment.php
 

Attachments

  • dbxEQ3.jpg
    dbxEQ3.jpg
    28.3 KB · Views: 304
  • 3bxc.jpg
    3bxc.jpg
    63.3 KB · Views: 387
  • 3bxb.jpg
    3bxb.jpg
    143.7 KB · Views: 301
  • 3bxa.jpg
    3bxa.jpg
    135.8 KB · Views: 304
Register to hide this ad
Looks like a lot of possible adjustments in that prototype.

I'm glad they went with the single piece front panel the all black 3bx looks better.

The prototype has individual Low Middle and High Frequency Expansion and Transition adjustments, interesting.
 
Been having more fum with the proto dbx-3bx.
Replaced the electrolytics with Nichicon brand caps and also replaced the cruddy old RCA connectors with some Chinese goldplated parts...



attachment.php
 

Attachments

  • P1191152.jpg
    P1191152.jpg
    136.3 KB · Views: 219
I was curious as to how (or if) the dbx 3bx would distort or alter it's input signal.

I fed a sine wave (lower trace in the photos) into the unit and observed how the output (upper trace in photos) looked.

The first photo shows zero gain whereas the second picture shows the gain set to maximum.

It was a positive sign that the output signal is smooth and similiar to the input signal.

While this is a simple/static representation and doesn't reflect the complexities of the actual music it is an interesting demonstration of what is going on.
Adjusting the gains on the other gain controls (outside the frequency band) alters the signal very little.




attachment.php




attachment.php
 

Attachments

  • P1191150.jpg
    P1191150.jpg
    63 KB · Views: 214
  • P1191151.jpg
    P1191151.jpg
    66 KB · Views: 214
Wow... it looks like there's some shielded small signal transistor pairs there (little grey bags with pink stripes). Very very cool!
 
I should hook one up to my distortion meter and see what it looks like.

I have a 3bx-DS that's wonkey and needs attending to as well. However, I don't hold much hope I can DIY fix it.

With separate frequency band control, I'd almost think that was an early prototype for the 4bx sans the digital control.
 
thefragger said:
Wow... it looks like there's some shielded small signal transistor pairs there (little grey bags with pink stripes). Very very cool!
Click to expand...

'zactly - those are matched pairs in a single 5-pin package - they share a lead.

brutal said:
With separate frequency band control, I'd almost think that was an early prototype for the 4bx sans the digital control.
Click to expand...

That's a possibility I hadn't considered. I have a friend with a 4bx (picked up at the MIT Flea for $15!). I'll have to take a look in there at some point to see if there are similarities.
 
I have a variety of dbx products here but unfortunately I don't have a functioning series 1 3bx. The one I have has an issue where one of the left most daughter PCBs is defective. Depending on the slot I put it in (low-mid-hi frequencies) it boosts that band to the max. I've built a cable that allows me to have it connected 12" from the mother board for diagnostics but so far I haven't been able to determine the problem :scratch2:. I've posted a request for parts in the AK classifieds to no avail.

I have however compared the proto 3bx with a 3bx Series II and I feel the proto generally sounds smoother. It is hard to compare them since it appears that the HF band is different between the 2 units.

Also the proto, while offering significant more adjustability with the individual bands is correspondingly more tricky to set up but eventually leads to a more satisfying effect. It just feeds one's Audio Obsessive Compulsive Disorder far more then an EQ or regular dbx range expander could.

I was trying to determine where in the dbx hierarchy and time line this would have fit. The 4bx appears to be a later product - offered alongside the 3bx Series III and the PCB layout appears to be significantly different from the Series II units. Therefore I am of the opinion that this was a later development of the Series I (which it resembles). I am curious if anyone has opened up their Series one device and seen a PCB like in this prototype?

I've done a bunch of poking around the www.vintagedbx.com website to reach my conclusions. I've emailed them but suspect they aren't actively supporting that at this time.
JimB
 
Based on the numerous 3BX pieces I've had, I would bet heavily against it being built around an early 3BX design. Those should be the version with the daughter boards.

John
 
Old thread , I know, but does anyone know how the mic for the 10/20 is calibrated? I have a nice 10/20 which is missing the mic and was wondering why a stock electrect with the same specs wouldn't work or at least be made to work ? . How was the original mic calibrated and would the people at DBX have any info on obtaining a replacement? TIA for any help.
 
I would think you could get good (or at least consistent) results with a generic "calibrated" electrolet mile.
You'd want to tune to taste afterwards anyway.


Tapatalk
 
The generic capsules work acceptably well. Experiment. dbx the company is dead and gone. Yes I know the name lives on, but not the people who did these units.

More importantly... rta eq'ing in the field is usually a 2 or 3 db per octave rolloff starting at 1k or 2k. I'm partial to 3 db /oct starting at 1k.
 
Thanks for the reply. I don't know quite what was meant by 'calibrated' in the first place. I thought the microphone just had to be accurate in what it picked it up in the listening position over the audible range within a certain accuracy - +- 1 db according to the manual -so that the onboard computer could adjust the output of the speakers to achieve the desired flat response. I have someone interested in purchasing the unit but he says it has to have the original mic for it to work properly. I got a reply from the tech dept at DBX but they were useless - it was as if they didn't know what I was even talking about.
 
Calibrating a mike means it's either electronically matched for a specific box, or it's response is compensated via software, or both. Depending on how accurate you want the results, you may even need to recalibrate an identical replacement mike, more than likely via pots on the internal board.

Good example of how calibration can get complicated is a Behringer EMC8000 - those microphones have a couple thousand unique calibration files available for matching to hardware via a software patch.

I suppose you could always calibrate using the Mark One Ear and make notes as to how much you need to change the automatic results to make it sound "right". If nothing else, you'll be a lot closer than you'd probably get trying to start from scratch manually ... having some good target ranges to start with make the tweaking a whole lot easier.

Also worth mentioning, "correct" eq is ultimately in the ear of the beholder, so you'd more than likely make some flavor tweaks even with the correct mike.

PS ... I have a series one 3BX, and would never part with it. I've tried a couple software expansion packages on my media server, and they don't hold a candle to the real deal.
 
You must log in or register to reply here.
Back
Top Bottom