Summary
The DBX 163x has to be one of the most challenging mods I have come across. Not because of the technical side of soldering components but because there are so many variations on a theme and it is choice overload. Sometimes, choice has arisen due to the ability (or lack of) to get hold of parts, sometimes due to experimentation, sometimes due to attempts to retain character. After spending many hours reading through the the different forums, my conclusions are several nice options that can make a positive impact on the compressor.
The big changes to the DBX 163s are as follows:
1) PSU mod
Changing the electrolytic capacitors for the PSU removes a significant amount of noise from the compressor. While 2200uf is the recommend value being banded around but I have not seen much feedback about the impact of going in over 1000uf 35v (the most commonly used capacitor). Nichison HE series are often recommended due to a property in that type of capacitor. Panasonic is mentioned quite a few times too.
- PSU Capacitor Discussion at GearSpace (Link) Get lowest impedance.
- 2200uf Nichicon (Link) possible height issue. I One model lent them over slightly.
- Nichicon HE series capacitors 1000uF 35v (Farnell Link) (Link) (Link)
- 1000uF 35v Panasonic FM
2) Opamps mod
Changing out the OPAMPS cleans up the sound significantly. OA1, OA2 are an essential upgrade and clean up noise. OA3 and OA4 are recommended. OA3 and OA4 are the side chain control.
- THAT OPAMP (Link)
- Milmax machined sockets
3) HPF Capacitors mod
Changing/removal of some HPF capacitors around, before and after the opamps with ceramic caps open up the high end. In some mods, there are greater removals but going too far will cause oscillation on the compressor. A good move is to improve the quality of the existing capacitors. Most of these capacitors are 0.1uF and 0.01uF. Possible links to the board, C3 & C4 (Input), C8 & C9 (Output), C6 (possible C7 too) = LPF at 80Hz, C17 (HF suppression) high roll off,
- HPF Capacitor Discussion (Link)
- The cap near line input (Link) C1 (low capacitance 120pf)
- TapeOp section on HF caps (Link) . Replace those lentils!
- Vishay 0.1uF from AudioPete’s list (Mouser Link) (DigiKey Link)
4) Resistors mod
Changing some of the resistors to metal resistors improves the sound quality.
- R2, 100K Dale RN55 mentioned by Sean (Link)
- Dale CMF55 metal film mentioned by Brian M Boykin.
Additional changes that make a difference include:
5) Small capacitors by PSU
Changing two small capacitors near the power supply, 0.01uF but there are variations of C23/24 or C25/C26. This area is confusing and I cannot see any real explanation of how the location makes a difference.
6) Ferrite Bead
This mod involves replacing C2 with a ferrite bead. As mentioned on TapeOp, there is not much capacitance here anyhow. It is recommended but the original bead change is no longer available due to being discontinued. AudioPete includes an alternative in his shopping list but whether this is a good alternative, I do not know. On the later mods, it is often just skipped.
- C2 capacitance notes (Link)
- Ferrite bead discussion (Link) Panasonic EXC-ELSA39
- AudioPete’s list alternative (Link)
There are quite a number of variations, the main versions are as follows
Jim William’s mod. (Link 1) (Link 2)(Link 3)
The original mod? This mod offers opamp upgrades, psu electrolytic capacitors, changes to 01uF and 0.01uF capacitors, metals resistors and the ferrite bead. It involves a bypass on the bottom of the board. I like Brain M Boykin’s explanation of the bypass in the ApronBeatz variation.
Sean Variation. (Link)
Very interesting mod. Using lots of additional WIMAs. Know someone with this mod and it sounds great.
GearSpace (2016) ApronBeatz Variation. (Link)
This mod offers opamp upgrades, psu electrolytic capacitors, changes to 0.1uF and 0.01uF capacitors, metals resistors and the ferrite bead. However, it offers different locations for the 0.1uF and 0.01uF caps and there are some inconsistencies between the diagram and description. I really like the circled areas in the photo and this provided me with a great start by helping me understand the locations of key items on the board. The thread contains lots of useful information by Brian M Boykin.
GearSpace (2013) Doulos Variation. (Link)
This mod offers opamp upgrades, psu electrolytic capacitors, changes to 0.1uF and 0.01uF capacitors, metals resistors and the ferrite bead. Different locations for the 0.1uF and 0.01uF caps. I like the simplistic approach of this mod with straight swaps of 0.1 and 0.01uF capacitors. I like the colour coding between the 0.1 and 0.01uFs and it helped me understand more about the location of the different capacitors on the board. The photos are very useful.
Mod Defecator Variation. (Link)
This mod offers opamp upgrades, psu electrolytic capacitors, changes to 0.1uF and 0.01uF capacitors, metals resistors and the ferrite bead. Different locations for the 0.1uF and 0.01uF caps (C23/24). This mod offers information about enhanced heatsinks for the PSU. Very useful, large photos of the mod in progress, attached to a Facebook account.
Famous Beagle Variation. (Link)
Waiting on this mod.
Other useful links
AudioPetes Parts Lists (Link)
The TapeOp Thread (7 Pages)(Link)
“If it signal path stuff, go low ESR, if it’s power supply or filtering, go with Low impedance, and you can get some with both characteristics.” Brian
Current thoughts are to go for Jim’s mod, plus all HF cap swap out, all metal resister mods, plus UK PSU mod.