Dominator Mod DIY



Dominator II 720 modification instructions.

Update: Please be sure to read the end of this article for updates about the mods. I have received quite a few emails from people successfully completing the mod. There were problems (user error) here and there and I tried to help as much as I could with limited time. I thought it would be a good idea to post some of that help.

I’ve been messing around with Dominator’s for quite some time. The Dominator II 720 is a unique piece of analog kit in that it has a level you can set and there will be no overs above that level no matter what. It employs a clipper circuit in addition to a multiband compressor to achieve this. There is a knob called “Density” that determines how much of the signal goes to the compressor and how much goes to the clipper. More signal to the multiband compressor means a more “squeezed” compressed sound that is too heavy handed for modern day mastering. But when the signal is balanced towards the clipper, you can achieve at least a couple dB’s of limiting before you hear distortion. The clipper is really good! So I set about to make the compressor side less “grabby”. I wanted it work less on the mid-range which gave everything a scooped sound.

The unit also employs pots that don’t track that well left to right, so right there, it wasn’t fit for precision mastering. Adding resistor ladder switches fixes this but most rotary switches are pretty big and don’t fit properly in the 1U box with a PCB close to the front of the panel. So there wasn’t a good way to get switches in there without putting everything in another chassis. Recently I found some cool mini stepped switches on eBay that would fit in the original chassis. This got me thinking about a full modification that would make the Dominator suitable for real mastering or mixing. You can pick them up on eBay for $150-$200 which is a steal for something so cool. Although I haven’t used it on the buss for a mix session, I would think that it would be a great glue machine. Maybe even better for mixing than mastering!

What follows is my Dominator swan song modification documented and open for anyone to try.

Here are a couple audio examples I whipped up. Please use headphones or some decent speakers to listen. I’m digging in pretty hard to show what this thing can do, but at the same time, a cell phone speaker might not translate so well. Using some old jams so I hopefully I can keep this up for a while…

You’ll see (hear), as the “density” and “release” pots go CCW things get more grabby. Especially with the “lift” switches down. Turned to the right, CW, everything loosens up and things start to sound pretty big. Towards the end of the first video I switch up the low “lift” switch and the kick really comes through. A good example of how to fatten things up.

Perfect pop song.


Groovy band I mastered a while back.


Want punchy drums? Call Rich Costey, Lol.


*Butts cut off because this is a family website.




I do not preform this mod for people. This is a Do It Yourself project. I’m not responsible for things going wrong or unusable Dominators when done. If your interested in doing this, make sure you read all the information on this page FIRST. I DO NOT do repairs and WILL NOT respond to emails for trouble shooting help. Not trying to be a dick, I just don’t have the time…

AND, since I don’t know who will be doing this, there’s no way I can guarantee the work or promise it will work out for everyone. Of course I’ve made a few of these and I think they sound great. Everything has to be done at your own risk. There is 120V AC coming into this box so there is a risk of getting shocked and even death! In other words if it doesn’t work or you die, its not my fault!


This isn’t a beginner project so if you don’t have a lot of experience soldering and fixing audio equipment I would recommend getting an experienced audio technician to perform the modification. A good technician should be able to get it done in around 4 hours. Give or take. Depending on how much a tech charges the whole thing should be under $800. Again I’m just guessing and not guaranteeing someone else’s work.

If your an experienced tech and something isn’t clear, go ahead and email me at Since this is new right now, I do want it to be successful for people and if I can make things clearer I will.

Its an interesting read regardless so here we go!


First thing to do is go to eBay and get yourself some small stepped switches:
At the time of writing this, the eBay link below has the switches I used. There are many auctions selling this type of switch. You want the 10K audio taper version. You also want the “D shaft” version which will fit the Dominator knobs. They are very affordable and you need 2 of them…

A word about these:

The taper is more logarithmic than the original pots in the Dominator so I added some resistors to make them provide unity gain with both input and output knobs at the 12 ‘o’ clock position with a little adjustment to the gain trims in the unit. A very useful part of this modification is the addition of an output gain knob. In order to make that 12 o’ clock position work, the output knob will bump the level up 6dB on the last step of the CW rotation. So be careful about testing this out at first. Don’t have your speakers cranked in other words. Up until that last step the volume moves up in very small increments, close to 0.5dB steps. It changes (db/step) throughout the rotation and isn’t perfect, but works well.

The important part is you get perfect tracking level wise between left and right with the input and output knobs.

Other than the pots, you will need the basic tools for soldering and audio equipment repair. You will need some small gauge wire. I used colored ribbon cable because it looks neat in the box but regular loose wire will work too. It can be small… 22 – 24 gauge is fine. Wire clippers, needle nose pliers, a solder sucker, and a small eyeglass screwdriver for the adjustment pots for calibration. 1/4″ nut driver and Phillips screwdriver. And of course a nice soldering iron. You also need a drill and assorted bits to make the holes for the mini DPDT switches in the front panel.

Parts List:

(1) Dominator II 720. The first version Dominators won’t work with this mod so make sure you get the II 720 version. UPDATE. The Doninator II 723 versions also work with this mod. They just have some extra EQ (emphasis/de emphasis) circuitry on the clipper board that can be disabled with a switch on the back of the unit.

(2) 10K stepped switches (from eBay) – For input and output pot replacement.

(2) DPDT mini toggle switches – “lift” switches

(4) 200 OHM 1/4W resistors – For “lift” switches

(4) 560K 1/4W resistors – For release adjustment

(2) 3.3K 1/4W resistors -For output pot

(2) 2K ohm resistors – For input pot

(5) 10K ohm 1/4W resistors – for release resistor replacement and fine thresh replacement

Shielded 2 conductor studio wire. Small size similar to whats in Mogami snakes.


That’s about it!


Throughout this I did some of these mods in a different order than I’m laying it out as shown. Some closeups of the board may not have parts removed in previous pictures. Or I have pictures of different PCB’s with slightly different part types. I’ve done a couple of these… but whatever.

2 screws on either side of the unit will get the cover off…

take the knobs off, remove the pot nuts, and remove the front panel:

The pots have little spacer washers on them behind the panel, make sure you save these and put them back on.

Pull the three power connectors off the main board, the ALT board (upper PCB behind the pots) and the clipper board.

Unscrew the screws for the XLR’s

Unscrew the three screws holding the ALT board down, and the two screws holding the clipper board in the rear on.

Pull off the ALT board and clipper board:

Use the nut driver to remove the front and rear mounting posts.

Now you can remove the main board.

In general, its hard to remove parts from the Dominator PCB because the way the parts were clipped after they were soldered to the board. The parts have little “tabs” from the clipping process that make them hard to pull through the small PCB holes. I’ve pulled up a lot of traces trying to get parts out so the tabs (nubs) should be clipped off before part removal can be done. It might take a couple tries if your not an experienced tech. Try not to burn the crap out of the solder holes.

First parts to remove are the attack resistors that make the unit “grabby”. this will loosen up the compression. The parts are numbered with a “H” “M”, and “L” suffix for the three bands since the circuit is exactly the same for all 6 bands. the attack resistors are R317. We are going to take out the attack resistors for the “L”ow and “M”id bands only. The High band can be done as well but I didn’t think it really needed it. They are 4.99K and we will be replacing them with 10K. The value of 10K was on the original schematic funny enough. Someone decided to make it faster with 4.99K and sound worse. Lol.

This picture shows the two on the left side of the board, there are another two on the right side that need removal as well.

Put in new 10K resistors

We are also going to replace resistors in the release circuit to make the release knob have greater range on the fast side. There are 4 of these
and the original value is 1.5 meg. We are going to remove R319L, R319M, R419L, and R419M. Replace then with the 560K resistors. Two R319’s
are on the left side of the board and the two R419’s are on the right side of the board.

Next we are going to disable the phase flipping circuit that was important for broadcast but sounded better to me when disabled. It basically detects the phase of the loudest peak at any time and flips the sidechain signal accordingly. Cool but not something that is done in any regular audio compressors that I know of. This is a step you can skip if you want to lessen the mod time a bit, but I think its worth it.

I’ve changed my mind about the importance of this part of the mod, and feel its not worth the work, the change to the sidechain performance is very subtle. I’m making the pictures small to indicate this part doesn’t need to be done.

First clip out all the J113 fets from the top of the board. There are six of them parts Q301. DO NOT clip out the near by Q302 transistors!!!

Then we solder together the Source and Drain pads of the removed Q301’s on the bottom of the PCB. I just used a bit of resistor wire to short them out. Without doing this the Dominator won’t work.

Do this to all six Q301’s you clipped out:

That concludes the phase flipping mod.

Now lets remove the level circuitry because it only adds a bit of distortion and we will be using the unit as a +4 level device only. We also need the space the switch takes up for our output knob. Take out the U102 and U202 chips.

You can make jumpers out of resistor leads and put them into the IC sockets like pictured, or better yet solder the pins together on the bottom of the board corresponding to, and instead of the jumpers.

Next remove the level push button switch from the front of the PCB. This will be a test of your solder sucking skills!

Now for the input pot. First remove the input pot from the PCB. Solder suck the pins then bend the pins that were bent to hold the pot on for soldering. Once the pot is removed get the new switch ready to install. It might be easier to just clip the pot legs before unsoldering, then just suck out the remaining legs.

We don’t have to use all the holes on the pot and two 2K ohm resistors need to be put on the switch along with some wire. Make sure the wire is long enough for it to wrap around the side of the PCB.

Solder the wires to the empty holes on the PCB as shown in the picture. Solder to the bottom of the board not the top as the switch will take up all the space above the PCB

Put a piece of tape over the solder pads so the metal housing on the pot doesn’t short out the contacts. It will be a tight fit when putting the pots in.

Now to add the output Switch. Behind the level chips previously removed, clip out resistors R135, R136, R235, and R236.

For the hookup wire you should use the 3 conductor shielded wire. That’s a hot and cold wire shielded by the ground wire. I scratched off a little solder mask to solder the ground (shield) wires to. The hot and cold of the left output wire go to either side of R136 and the right hot and cold go to either side of R236. You can just tag the wires on as I did, or you can remove the remaining resistor nubs from the holes and insert the wire leads into the holes. Like I said before, its kind of hard to get those nubs out but its less messy looking when done right.

The other end of the two shielded wires hook up to the 10K stepped pot like in the picture. Attach two 3.3K resistors to the CW lugs on each section of the pot like shown. The ground (shield) wire does not need to be used on this end and can be tucked under the heat shrink on the wire. Its only to shield the signal for lower noise.

There are two controls that essentially do the same thing. The Peak level switch and the “fine” peak level adjust. We are going to take out the fine peak level pot so we can put in compressor “lift” sensitivity switches in the space it took up.

Put in one 10K resistor and jumper as shown in the fine peak pot holes. One resistor is all that’s needed. This makes a virtual fine threshold pot turned all the way up.

Put a piece of tape over the solder pads.

Time to add the sensitivity switches for the mid and low band of the compressor. These switches will lighten up the threshold on those two bands giving the engineer some more control over the compressor sound. I call them “Lift” controls. With the low flipped up it lets a little more low end punch through when compressing. Same with the mid range.

So first we will pull the power wires from the power switch and take the switch out. MAKE SURE THE UNIT IS NOT PLUGGED IN. Wiggle the wires off the switch carefully. Remember what colors go to what tab. Green and red on the right side vertically aligned and black and white on the left side vertically aligned. The switch can be pushed out from the back with the help of a screw driver to push the plastic tabs down that hold the switch in place.

We need to drill two holes for two DPDT mini toggle switches. Use the pictures to determine where to drill. If you don’t have a drill press, use a small bit and work your way up to the larger holes.

For the “lift” switches we need to put two 200 ohm resistors on the middle lugs of each switch.

Attach wires as shown

What we’re doing here circuit wise is shorting out part of the circuit with 200 ohms. So when the switch is up it puts a 200 ohm resistor from one point to another swamping some of the sidechain signal to the VCA. When the switch is down it opens the circuit and nothing is changed from the original circuit.

Before we tag the wires to the board, lets put everything back together. Install the switches and stepped pots into the front panel. Pop the power switch back in and attach the power wires.

Bend the two LED’s back flat against the board to make room for the switches. Don’t clip them out! The other LEDS won’t work if those two are clipped.

We are going to tag the “lift” switch wires to the PCB now. We can make the left switch “low” and right switch “mid”. The low switch will have its wires going to R321L (and ground pad) and R421L (and ground pad). The mid switch wires
will go to R321M (and ground pad) and R421M and ground pad). This is explained in detail next…

Solder two wires from one side of the switch (plain wire and the wire above it with the resistor on it) to the two spots on the PCB in the picture.

Like this:

Be careful not to get solder blobs all over everything. Luckily the diode (D302) next to R321 is connected to the resistor where we’re making the connection. So you can use both pads. But keep it as neat as possible.

Tag the two switch wires to the other side of the board as well and your almost done.

All tagged up!

Here is whats going on with the switches, simplified.

After the “lift” switch wires are attached to the PCB for the low and mid bands, the ALT PCB and Clipper board can be put back in. Use the nut driver to put the 5 standoffs back on.

Tighten up all the pots to the front panel. be careful and don’t over tighten!

Put the knobs back on. For the input and output, we want to find the 12 o’ clock position. Since the pots are 21 position there is an absolute middle position 10 steps from either side. Once found slip a knob on the shaft with the cap pulled off. Then put the cap back on so the pointer is straight up. Now we can calibrate the unit for unity with both added switch pots at 12 o” clock.

We need to trim the level. there are only two square 10 turn trim pots on the board and these adjust the input level.

Run a 500Hz tone through the unit and with the input and output straight up at 12 o’ clock (middle rotation) adjust the trim pots for unity gain input to output. The actual gain in db’s doesn’t matter because that will depend on what level you put in with your test equipment or DAW. You just want left and right to match, and the level to match with the process button in and the process button out (bypass).

This next adjustment may not need to be done. If the frequency response is flat when checked, your good. If not here’s how to straighten it out:

There are two tiny one turn pots under the ALT PCB barely accessible but with a small eyeglass screwdriver you can get to them. They are on either side of the treble and bass EQ pots. They adjust the high and low boost for unity (flat) with both the high and low EQ knobs at 12 o’ clock. Its easiest to calibrate these with an Audio Precision or similar audio test equipment. It can also be done with a computer program that at least does frequency sweeps. Another way is to use your DAW with a VU plugin on the return track.

The small adjust pot to the left of the treble pot adjusts the left treble response, the one on the right adjust the right response, same thing for the bass pot.There is some nail polish gluing the pot rotation in place but not permanently. So just be careful not to strip out the plastic in the trim pot when trying to adjust them.

Alternatively, if all you have is a DAW, take note of the 500Hz level you achieved when adjusting for unity gain. Say its -18dbFS or 0VU on a VU plugin. You want to set the frequency to 30Hz then tweak the small adjust pots under the ALT board on either side of the bass pot so the level is also 0VU. It should be close to begin with. Then set the tone for 10K and adjust the small adjust pots on either side of the treble pot. to 0VU. So 30hz, 500hz, and 10KHz should all have the same level reading when sending the tones out of the DAW, through the Dominator, and back to a track with the VU plugin on it.

As seen in the pictures from my Audio Precision, you can achieve a very flat response. Equal left and right level. The unit has pretty low THD+N as can be seen on the sweep chart. Mostly around 0.005% THD+N at +10dBu. Pretty awesome for going through a crossover and 3 VCA’s. Which speaks for the quality of the Aphex proprietary VCA’s. Very good indeed!

There are other calibration steps that can be done but not really needed. Again its a good move to find the Dominator II service manual on line. I found it with a google search many years ago and I’m sure its still up there somewhere. Schematics are included in the service manual to help techs with this mod. They aren’t needed but point out what I’m doing to the circuit.

And lastly, put on some P-Touch labeling for the finishing touch. I call this the “MDE DommoD”. The tech should put his initial and the date on it to make it official!


So additional mods you can do is replacing or removing some of the Electrolytic caps in the signal path. I did it to just be tweaky but it had very little to no effect over the frequency response or the THD+N. And definitely not something I could hear. Cap replacements usually make a difference if the caps are old and dried up. Not something I noticed with the Dominators I have. Another thing people do is switch op amps around. Don’t do it. NE5532’s are pretty much the best audio op amp out there bettered only by the single NE5534 version. Yes newer op amps have better specs on paper but don’t usually produce better outcomes in the real world. Unless you put something in that causes more distortion in the circuit and you like that sound. I’ve done pretty exhaustive testing and listening and op amp swapping is pretty much BULLSHIT. Just my humble (educated) opinion of course.

So the caps you can replace with high quality non-polar types are located here:

The caps in the rear of the board can be completely jumppered by just putting a piece of resistor wire in the empty capacitor holes after removal. There maybe a bit of DC offset on the output since these are the caps blocking the DC for the output driver circuit. But I have not had any problems. If worried about that replace with non-polars.

Like I said, you can easily rip up traces when trying to get parts out. If so, just scratch the green solder mask off the trace with your eyeglass screwdriver and fix with a resistor lead or small solid core wire.

The two caps at the front of the board need to be replaced and can’t be jumppered. If you wish to use a larger value that 100uF and the caps are bigger, bend them over so the ALT board can still be places above them.

Lastly if you want to be weird and must swap an op amp to make yourself feel good, a strategic and easy place to do it is on the clipper board. This is one op amp that both left and right signals go through so any fancy dual op amp can be put here.

Don’t worry about the one behind it, that one only handles DC.



Some have had problems with audible distortion or “fuzz” in the signal. This seems to be associated with the small adjust pots that calibrate the VCA and adjust the center point for the EQ pots. Here is part of our correspondence email.

Because the pots are Log taper there is not much change in level CCW from the middle. There’s probably about a db. The proper pot/switch would be a linear taper. But those are not available unless you buy 20 or so. The eBay seller will make them custom 10K linear switches in quantity. 
As for the distortion, I’ve noticed that sometimes the little adjust pots for the VCA’s will get dirty or heat up over time and get brittle. There are three. A 1k (VR301) on the schematic, that can be removed and replaced with two 500 ohm (510 ohm standard value) resistors. Emulating the pot in the center. And (VR302) 100ohm that can be removed all together. These two pots don’t seem to have much of an effect over the performance of the VCA. Perhaps when really turning down the signal, but most of the time nobody is compressing that much. The third adjusts the DC offset voltage on the op amp after the VCA. you can spray some pot cleaner on it and exercise it back and forth, then put a multimeter on TP 302. With no signal thru the unit adjust VR (303) so there is no DC reading on the test point or as low as you can get it. 0.01mV or something. These three pots are near each of the six VCA’s.
Its possible the tiny adjust pots for the high and low EQ are also dirty. These cannot be removed or simply replaced with 2 equal resistors. They have to be sprayed and exercised. The problem is that some Dominators have the pots with a bit of red glue stuff meant to hold them in place. the glue can get in the pot or I’ve had a hard time with the tiny screwdriver stripping the plastic slot on them. The best way to remedy all this is to order new pots and replace them all, but that’s a pain in the butt…
I would guess that your distortion problem is related to these tiny pots. I have seen them cause it.
Another possibility:
I realized that I set up the gain of the unit for -14dbfs = +4dbu level because that’s the mastering level I use, but most peoples interfaces are set up for -18dbfs = +4dbu. Which would send +4db more signal into the unit. But this should show up as a little compression on the meter. This can be remedied by changing the additional resistors on the switch pots so there is less overall level in the first op amp stage, and a bit more make up in the last op amp stage (output pot). Some experimenting required.
The problem for this fellow turned out to be the EQ adjust pots, so the VCA pots didn’t need attention. So try exercising those first.
If there is still problems, move on to the pots by the VCA’s
****************Added high lift switch****************
I ended up putting another switch for the high band just like the mid and low. I drilled a hole between the density knob and the fine knob and inserted the switch just like the low and mid lift switches. Tagged the wires on to the remaining high band parts same as the mid and low. I find it to be very useful and would recommend the extra effort!