Jeff Rowland model two sounding thin With Mini Utopia


Hello everyone, 

i have been following the forum for years, but never had the chance to have an active participation.
I apologise if there are any errors but english is not my native language, as i am Portuguese.

I have recently added a Jeff rowland model 2 to my system, in order to give my beloved Bat VK60 some res,t due to high hours of usage.

Much to my surprise, the Model 2 paired with the preamp Bat Vk5 and driving JM Lab Mini Utopias sounds quite
"thinner" then the VK60. I don't think it is just the "valve vs transistor" sound diference, and i am wondering what are the causes.

I have chosen the high input impedance 36Kohm and normal 26dB gain to match with the Vk5, and altought have yet to change the pinout of the xlr's (waiting to receive some Neutrik NA3FMX wich is a phase inverter between pin 2 and 3 (BAT uses pin 2 hot and JF Model II has pin 3 hot) i have tried inverting the speakers phase but with no sucess in regard to achieving somewhere close to the sound i had with the VK60.

Everything else in the system remains the same, apart from the power cable of the Model 2, because i am waiting for a IEC Tupe 19 i orderes from the States, in order to be able to use my power cables from Van den Hull.
Have tried to change the nordost valkyria between amp and preamp for another one i use for the cd palyer, but with no improvments.

With the Model 2 i have lost the wheight in the midband as well as a certain roundness in sound. The model 2 is quite smooth, but the analogy that comes to mind i is like you are feeling a fresh wind instead of a warm wind embracing your body. Everything else is as expected, good image and tonal accuracy. Harmonics are not as good as VK60, bass response surprisingly presents itself  leaner compared to the vk60 wich is quite good (had a Krell KSA 200s before tjhe Bat so i could compare both). All in All a less satisfying sound.

I have opened the Model two and it looks in pristine condition (inside and out), and becasuse the capacitors are hidden, can not see how they are looking.

Is this a mismatch between the model 2 and the Mini Utopias, the current phase inversion, the caps that are due for a replacment, bias adjustment (no idea if it even usess bias adjustmente) or anything else i am skiping?

Your thoughts will be apreciated, as i keep on trying to squeeze the sound i was hoping for.

PS: the next JF dealer is over 800kms away in another country, so i would rather sort it out first before i think of sending them the amplifier for a check in. Also currently still waiting for a reply from the Jeff rowland site, with no replys.




c_n_m
No impedance mismatch here at all as the specs for your preamp is 1100 ohms balanced; 850 ohms single-ended. This works fine with your 36k input impedance. I do think it is simply two different sounding amplifiers with your speakers. What is the size of the output cap on your preamp? I think they are 1 uf right? You either have two 1 uf caps in parallel or the 6 pak option? So your output cap value if too small can roll of bass.  However 2-6uf should be plenty on the output.  

I am afraid you are hearing the sound difference of the amp/speaker combo.    
Is that Rowland amp a Class D amp?   If it is, that could account for the thinness?  Make sure your speakers are in phase, is it possible you reversed one of the wires on one of the speakers?
@stereo5 The Model 2 is an old school mid-90s Rowland amp. Guessing it's just the different sound of the two amps i used to run the Micro-utopia with a PP EL34 tube amp and it never sounded thin.