Potato Cakes

DBX 160A mod notes
« on: November 19, 2018, 01:29:52 AM »
Hello, everyone,

Without going in to all the details of a particular project, I am in need of building or acquiring a 1U compressor. After looking around at different kit options, I thought about acquiring a dbx 160A and doing the tweaks on it that I have read about from other internet users and it seems it would be a decent option. The 160A itself can be had for pretty cheap in the used market and the additional materials would cost less than $100USD to the mods. I was wondering if anyone here has performed any of these procedures on the 160A and if they would be willing to share any notes. One area I am not sure about is any changes to component values in the PSU that would provide some improvements.

There are a number of other DIY options that I have looked at, but considering the time I would have to spend working on this project, modding a 160A seems like a quick and cost effective route.



Potato Cakes

Re: DBX 160A mod notes
« Reply #1 on: November 19, 2018, 11:00:19 AM »
Here are notes that I have so far from other internet discussions. They come from Jim Williams at Audio Upgrades:

 - The 160A is nearly identical to the 160XT. The XT uses a LM353 input opamp and a 5534 output opamp, the A uses 5532 opamps. Both differ from the X by having an opamp based balanced output, the 160X uses a current buffer around a LF351. The XT and A also have this circuit in addition to the cleaner balanced opamp outputs. The A has a cross coupled output with a servo.
 - Both the XT and A are superior to the X as they each incorporate the non-linear timing capacitor circuit which speeds up attack time and lowers low frequency THD. These circuits can be inproved by replacing the cross coupled 1N4148 diodes with green LED's.
 - All can be improved by replacing the VCA with a that 2180A. Remove the 51 or 47 ohm resistor from the trim to pin 4 and remove the trim circuit feed 100k resistor as these are pre-trimmed at the factory. On an A it's R110 and R111. On an XT it's R9 and R10. On an X it's R9 and R10.
 - When I do the mod on them the VCA is replaced with a that 2180A, the opamp is changed to a National LM6172, the trim circuits are removed from the VCA, the electrolytic coupling cap is replaced with a Wima 4.7 uf mks-2, bypassed with a MIT .01 PPMFX. Power supply cans are replaced and enlarged and some phase compensation and power supply bypass caps are added. Bandwidth is raise up one octave. Slew rate is increased. Distortion is lowered. Fog is removed. All is well.
 - Transformer is a JT-123-DBX. They can be had for just under $60USD.

Though I believe I found a different solution to my project, I think this might be good project to look into if it yields noticeable "better" characteristics that can be measured and heard as the total cost would be about $300, depending how much is spent on the 160A itself.

I'm going to be doing some traveling so I won't be able to get to looking into this for the next couple of weeks, but I would like to know if anyone here with a schematic of the 160A/X/XT can verify any of this information.




Re: DBX 160A mod notes
« Reply #2 on: November 20, 2018, 05:28:40 PM »
You did not set a single goal of what you set to achieve with this random set of changes and anecdotes from questionable sources. But go for it if you just want to replace parts for roughly equivalent parts for no particular reason.

I mean just plain soldering is fun after all.


Re: DBX 160A mod notes
« Reply #3 on: November 20, 2018, 07:45:05 PM »
A drawback of the 160A is that there appear to be no schematics available.

I think you'll find most you see now will have a THAT VCA already so there's not much to be gained by changing it. I've seen Jim comment that the inductors on the input sound bad and that he replaces them with ferrites. They have three legs so I imagine they have input / ground / output

One audible difference between the A and the X/XT is that there is more contrast between Over-Easy and Hard Knee modes on the A. I quite like that

I think the board layout & lack of schematic makes the A a more difficult prospect to hot-rod than an X or XT. Easiest is the XT as the top & bottom panels are removable. On the X and the A you have to remove the PCB to solder anything  which makes testing mods really hard work

The 160A / X / XT is a one-trick pony in many ways but it is a good trick. If you wanted a more flexible single-channel 1U compressor have a look at a Symetrix CL150, a JBL / UREI 7110 or anything by Valley People / International

Nick Froome

Potato Cakes

Re: DBX 160A mod notes
« Reply #4 on: November 20, 2018, 08:19:11 PM »
For project that sparked this thread initially, I was told that Colin is supposed to have the ez2254 kits back in stock at the end of the week, that will satisfy that need.

Here is a schematic that is supposedly for the 160X, and I think areas where I would be doing the changes are the similar if not the same to an A. It should be a helpful starting point at any rate.

I agree that these compressor are useful in a narrow scope of audio situations (subjective opinion notwithstanding), however what I have read, which is always true, with the changes the compressor characteristics seem more helpful in a wider range of applications. I don't know that if it does not perform as well with the tracks or program material which is was originally designed to handle. 

I think I'm just going to have a get 160A and start poking around. The information whether good or bad will be worth it. It probably won't be till around Christmas time before I can look in to this.




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