KRK Rokit 8 Gen 2 Upgrade

[Bobby Baird]

Upgrading my set of Rokit 8's from NJM4580 & STTL074CN with OPA2134, OPA4134 Op-Amps & better capacitors. One board is the preamp. The other is the power amp and power supply together on one board attached to a large heat-sink. Here are the schematics KRK. Here are the replacement parts for the preamp minus op-amps. https://www.mouser.com/ProjectManager/ProjectDetail.aspx?AccessID=15f6d907b9. Bom is for one speaker.
Here are the replacement parts to Re-cap your original amp board https://www.mouser.com/ProjectManager/ProjectDetail.aspx?AccessID=bc1f41b20f. Bom is for one speaker. BOM for new Rev.1.1 amp board here. https://www.mouser.com/ProjectManager/ProjectDetail.aspx?AccessID=d0bdab8e9c Bom is for one speaker. New Rev.1.1 power amp board project folder attached.

 

[Bobby Baird]

Preamp Stock

 

[Bobby Baird]

Stock Power Amp with replacement power supply caps from previous repair.

 

[Bobby Baird]

Preamp mod with all new caps and sound plus TI OPA2134. Night and day difference in sound way more clarity and punch. I A/B with the stock speaker. Now I need to promptly mod the other monitor. Notice the 8-pin DIP to SIL adapter.

 

[Bobby Baird]

Power Amp and supply upgrade. All new caps, power supply voltage dropping resistors, and audio driver OPA4134 amp on SOIC-14 to 14-pin DIP adapter.

 

[Tubetec]

Ive got 20+ years from set of Behringer Truths , Neumann under Sennhieser sold you a bucket of top spec gear thats engineered to crap out in a matter of years , class D /smps biggest load of ******** I ever heard of,
Well done Bobby.

 

[3nity]

Ive got 20+ years from set of Behringer Truths , Neumann under Sennhieser sold you a bucket of top spec gear thats engineered to crap out in a matter of years , class D /smps biggest load of ******** I ever heard of,
Well done Bobby.

How you liked those thruths?

 

[amplexus]

A note to anyone doing this- make sure if any of that black glue/goop used on the caps is on the pcb to remove it entirely, esp if it's on any component leads. That stuff is prone to go conductive over time and then bad things happen!

 

[Tubetec]

The Truths were a very reliable speaker for me , I prefered to sell them in the hifi shop to DJ's and musicians over hifi speakers which didnt give good value for money at all .I installed them in pubs/clubs where they continue to work to this day as backround music and sound reinforcement if required.
The amp modules are traditional class A/B , very powerful 150w bass 75w tweeter , linear toroid psu, they last for years ,decades even .

Ive moved on from using the truth as my reference monitor but I still have a pair handy when I need them , they make a great studio monitor for listening or fold back , I might re-purpose a pair of Truth amp modules to power a set of more modern monitors who's Smps/Class D amps have fused out, Sennhieser KH-120 being the obvious candidate with DAC/DSP based EQ to iron out the bumps.

 

[Nina Beh]

Would you say that these are the exact parts I need to buy for my R6 G3? I tried Google search but apart from your post and another Wordpress article on the R5, nothing came out. I'm good with the soldering iron but I know nothing about electronics.

 

[sisepuede]

Would you say that these are the exact parts I need to buy for my R6 G3? I tried Google search but apart from your post and another Wordpress article on the R5, nothing came out. I'm good with the soldering iron but I know nothing about electronics.

Hi mate,
Do a favour to yourself, open one of your monitors and do a BOM (bill of materials) that you need for the repair/upgrade just to be 100% sure.

Take note of the uF and volts of every capacitor, buy those thar are rated 105C, they work longer than 85C for obvious reasons (inside the monitor gets hot!)

On the power section try to use as much as possible good film capacitors like panasonics, specially replacing the old mylar green caps on those the sound depends and ceramics are excellent for PSU filtering but a bit harsh for audio.

I wouldn't mess with the opamps, they are just fine in that circuit and faster opamps without adding extra decoupling capacitors might bring some unwanted high frequency oscillations.

If you can replace all the high watt resistor by metal film that would be great, as termal noise is something to be avoided.

Take care of measuring diameter and pitch of electrolytic capacitors (here size matters!) and buy from reputable sellers like Mouser, Farnell, TME, Digikey, RS, etc, depending in your location.

I have an old pair of KRK Rokit V1 from 2007 about 18.000hs of use and the power supply caps were very bad (original caps are very cheap chinese and most of them were out odf specs).
After removing the whole black glue I replaced all the electrolytics by Panasonics and Nichicon, and the 100nF by Panasonic and Wima. Also some resistors. Now they work as they should, after more than 15 years of using them in my job every day I am so used to their sound that I really was missing it.

Bytheway, Neumann KH120 have the same power IC, I saw a pic of the inside, just the version for 60volts and they have a regulated PSU (I believe) ofcourse drivers maybe better and other plus like dacs and room correction circuit, but KRK are like standard sound on home recording studios, I love mine.

Good luck!

 

[Bobby Baird]

Added some more heat-sink to keep those class ab amps cooler.

 

[Bobby Baird]

Pulled up RTA mic in the sweet spot in my untreated room and the frequency response was pretty reasonable. No more than 6db dips or peaks. I just made corrections to response with my DBX231 graphic eq. Sounding pretty flat now.

 

[Bobby Baird]

Tired of the old amp board. Gonna layout a 2oz copper pcb.

 

[Bobby Baird]

Modified power supply.
I will replace the cheap obsolete 647, 667 transistor buffered zener shunt approach to a regulated power supply using LM317, & LM337 regulators. As well as, trimmers for fine tuning voltages. Attached is the original schematic vs. my modification Rev.1.1. This will hopefully provide stable power to the preamp thus feeding cleaner signal to the amp.

 

[Bobby Baird]

I have also, decided to swap out the obsolete TDA2052 with the modern equivalent the TDA7296 although in a Multiwatt 15 package. The newer part has a slew rate of 10V/μs, double that of the 2052 spec @ 5V/μs. Hopefully this will improve the high end transient response. This is the final layout.

 

[Bobby Baird]

New Boards.

 

[Dylan W]

If you’re going to the trouble of designing a new PCB, you might look into making this a “composite” design (putting the TDA7294 inside a nested feedback loop with an op amp). This has been a popular approach with LM3886 for a while (search “myref amplifier”), by all accounts it reduces distortion tremendously and sounds much nicer than stock.

Some details for the 7294 here:
https://www.kaltecs.com/tda7293-composite-amplifier/

 

[Bobby Baird]

Boards were delivered today. Hopefully get them built this weekend.

 

[Bobby Baird]

Got it working no more annoying random sounds and pops. New TDA7296 has more clarity than the old obsolete TDA2052. Revealing more details in the mid range. I have a few more boards left if anyone has a pair of these old speakers and they need a re-vamp.