How to make a DBX 161 Balanced? Pictures of 160/161 innards

GroupDIY Audio Forum

Help Support GroupDIY Audio Forum:

This site may earn a commission from merchant affiliate links, including eBay, Amazon, and others.
T

tubejay

Guest
Someone on the old forum (can't remember who) mentioned that it would be very easy to make the DBX 161 transformer balanced in and out. Does anyone know how to do this? Is it as simple as hooking up a line input 600:600 ohm transformer on input and the output, and adding an XLR jack? Does anyone know exactly how to wire this up? Can anybody recommend a reasonably priced transformer. I'm looking to get sound out of it, and really don't want it to necessarily be transparent. Does UTC make something that would fit the bill?

Thanks,

:guinness:

Here's pictures of a DBX 160 and 161 side by side to compare. It seems like there's actually quite a bit more going on in the 160. They appear to be the same PCB though. Anybody have any schematics????? Anybody know if I can just pop in a pair of Cinemag transformers 600:600? Is there more to it than that? Anybody got any info?

Here's a far shot of a DBX 160VU first, then a 161VU. Notice all of the goods missing in the middle of the pcb on the 161:

160_VU_far.jpg

161_whole_far.jpg


Here's a close shot of the middle of the board where the 160 is heavily populated, and the 161 below it is not:

DBX_160VU_close_a.jpg

161_close_a.jpg


Last, here's a close up of the area near the VCA, where it appears that there are also some differences:

160_VU_Close_B.jpg

161_VU_Close_b.jpg


Anyone have any thoughts on this? Anybody ever made a 161 balanced before? Am I in too deep???

THANK YOU!!! :guinness: :guinness: :guinness: :guinness:
 
For instance, would these do the trick?

http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&category=7275&item=2250497861&rd=1

Here's the info on that auction:

Description
UTC A-20 AUDIO INPUT TRANSFORMERS

Specification:
Primary impedance: 50, 125/150, 200/250, 333, 500/600 ohm
Secondary impedance: 50, 125/150, 200/250, 333, 500/600 ohm
Frequency range: 10 ~ 50000 Hz +/-2dB
 
I'd say yes to all your questions... I don't know about those particular UTCs though. The max dBm aren't specified. Cheap OEPs could fit the bill also..
 
Hi Jay,

I don't know if you've got the schems for the 160 and 161, but the input circuit is very similar- in fact, I wouldn't be surprised if the holes on the 161 board allow you to wire it as a 160 and vice-versa.

The input would be the easiest to mod for a balanced input- you basically wire the op-amp to allow a balanced input (the "unused" input in the 161 is grounded) Slapping a 600R:600R input transformer on the input would work (try it and have a listen!) but a 10k:10k transformer would probably work better.

The output balancing circuit of the 160 is quite elaborate with booster transistors to increase the output drive capability, and what I think must be a "ground sensing" circuit to allow unbalanced one-side-grounded operation without any smoke. The empty zone in the middle of the board is where this would live. It looks like the same board is used for both models.

You could try adding a 600R:600R output transformer directly to the unbalanced output- have a listen. I don't know how it would cope if it was actually driving a true 600R line at high levels- you might want to add an output cap before the transformer, just in case there is a DC offset from the output of the op-amp. Any DC offset from the VCA will be transferred through the final DC coupled op-amp stage.

Get some iron and give it a go!

If you need schems, e-mail me.

:thumb:

Mark
 

Latest posts

Back
Top