Johnson Wu has extensive experience performing modifications to electronics, and recently started to modify crossovers for himself and his customers. Here is an e-mail I received from Mr. Wu, commenting on the OIMP series V-Caps he installed in JM Labs Micro Utopias.
"I am an avid 2-channel audiophile for 32 years. I've been modifying my own gear for almost 10 years now, having started with the usual tricks of re-cap, Schottky, choke, resistors, and progressed on to fixing the flaws of Chinese amps, and recently moved on to building my own amps.
I recently took on modifying and building amps for fellow audiophiles. I've had little experience with speakers and crossovers, none other than recently repairing and upgrading the crossover for my Quad 989s and a supertweeter for my Diatone 610s.
"What? You buying a pair of home-theater speakers?" a friend comments as I made my decision to pickup a pair of JM Lab Diva Utopia speakers. "Love the beryllium tweeters. The size is right." I said. "We heard them at the dealer before, don't you remember?" the friend exclaimed. "No decay, wooden bass and dead sound. You are a sucker for punishment!"
Currently I own Quad 989s and Avalon Eidolons (the latter are my perfect reference but both pairs have a tendency to overwhelm my room). The Eidolons are current on loan (boy has it been a long while) to a fellow modder friend.
12 years ago I almost bought a pair of Mezzo Utopias. Too bright, I passed. Then a few years ago while helping a friend pick up new speakers we auditioned the Micro, Diva, and Alto. The Diva was actually the worst of all three, it had a wooden and dead sound. The friend ended up buying the Altos (priciest, and as expected, it's the best of the 3).
The Alto Utopia has a deep but a bit flabby bass. However, with the right upstream gear, it has transparency that rivals the best of electrostatics. Very transparent, but even more so very critical of upstream components. Anyway, I kept thinking there has to be a way the Diva Utopia can sound good. The form factor is what I want in my listening area.
Recently I had the opportunity to re-cap (more like resolder instead of recommend and install) and replace resistors (with Mills NIWW of the right rating) on a pair of Micro Utopias that distorts and saturates when stressed. The owner bought four V-Cap OIMP 6.8 uF to be installed in the HF portion of the crossover. "You are taking a huge leap of faith here." I said, "the tweeters are voiced with the stock caps and as far as I remember the sound is not bad. You are betting big money buying these expensive caps." "The V-Cap TFTF's worked well for me on my heavily modded Jolida." He said. "Well I know they're good. I'm using V-caps in my Altavista NP220. But these OIMPs are completely different. These are lower voltage OIL caps."
Few hours on the bench with a soldering iron and the end result was stunning. I was floored and the owner and I were ecstatic when we listened to the speakers with the resoldered crossover. The Micros successfully pulled the trickery of convincing us they are not mini-monitors. The sound stage was huge, the dynamics awesome (still a boom due to its slotted design interacting with my room). But talk about detail, decay, and dynamic headroom of anything above 100 Hz. They are so stunning it revived my interest in the Diva Utopias enough to look for a pair for myself. "Same configuration, same crossover point for mid and tweeter." I said to myself, "they can't be bad."
A few weeks later I found a pair on Audiogon and the owner was local. Got a deal and the owner told me he was driving them with a BAT VK75SE. He said he didn't get them to sound right until he borrowed another VK75SE to drive dual mono. "Wait. This can't be. Aren't they supposed to be 90 dB/W speakers?!?!" Anyway, transaction done, and I hauled them home.
Excerpting from on AA forum thread: "There is a 5-6 dB suckout between 80 and 230 Hz ...lacks the soundstaging magic of the 907's ... voiced a little hotter on the top ...soundstage sounds narrower and flatter than the 907's..."
Sadly, other than the "little hotter on the top" this writer's right... Major bass suckout. But I think the top is not hot. It's hashy. Lack's air compared to other Utopia's. Nothing wrong with this particular pair. They're pretty much the same as the pair I heard at the dealers.
Within an hour's listening. I pulled out the Torx wrench from my toobox and popped off the back plate where the binding posts are to see the crossover. "2 crossover boards? No. one is a crossover board, the other is the Zobel circuit to stabilize the impedance of the 2 woofers."
Taking a closer look at the main crossover board. I realized why the Diva's don't sound even as good as the Micros. Focal JMLab committed the SAME CRIME Quad commits: Using a 180uF bipolar lytic as a coupler for the midrange driver. This lytic is supposed to cutoff low frequency to let the woofers takeover. But as a coupler it is now filtering anything between 100Hz (yea right!) and 2500Hz. For the tweeter there's a Solen/AXON 3.3uF 250V cap that's known for its raspiness. This can't be right. Aren't these supposed to be high end speakers? I am almost inclined to call up my friend who has the stock Altos and open them up to check on the caps.
Based on TJN's measurements. The bass suckout can be explained by the LF cutoff being tuned too high. OK, since I am doing away with the lytic I might as well get a bigger cap to lower the cutoff point. Does anyone make a 220uF film cap? It's Solen, of course. And heck I have to stick with the raspy 250V ones. Well, at least they are much much better than lytics based on my experience fixing my Quad 989s. The 220uF should lower the 3dB drop point of the midrange a bit to narrow the midbass suckout.
For the tweeter, I do have a pair of Jantzen Audio Superior caps of the same value. I popped out the AXON 3.3uF for the tweeter and replaced them with the Jantzens. Sound stage opened up. Less of the hashiness. But a sense of dryness came with the Jantzens. It's a little bit like that of Infinicaps used in high voltage bypass in amps. The sense of clarity and openness comes at a price. Now I hear what some people would refer to as Beryllium ringing. Tried to band-aid that with Russian K40 PIOs. The mid high became very colored and resolution actually suffered.
The mids and highs are definitely not good enough compared to the modified Micros. Time to bit the bullet and get the same caps in the modified Micro. Got a pair of OIMP 3.3uFs and you were nice enough to match them for me.
Took me no time installing them. The leads on the input side remain a bit long because I didn't want to solder point-to-point to the resistor yet. But the output side goes straight to the HF output of the crossover board bypassing the traces.
Even with only 10 minutes run-in I can already recognize the sound. That's exactly what impressed me the most with the Micros that were modified. A reviewer / manufacturer, most of whose opinion I agree with and respect a lot (in fact I bought many of his surplus caps used in his shootout tests), once wrote and that the OIMPs sound uninvolving. I beg to differ this time. In both the Micro and the Divas the OIMPs are anything but uninvolving. Do the V-Cap OIMPs have a sound? Yes, it's the V-Cap house (Haus... pun intended?!) sound. Fast, yet always under control, extremely airy with no analytical coolness, and never any overshooting or saturation. This, in my opinion, is exactly what modern tweeters need. Subjectively I feel that these are like Jensen copper oil caps with much less color and much more honest and accurate headroom. Some caps are de-focused, most caps glare. Most caps sound beautiful when playing simple stuff but goes non-linear or thins-out when dealing with complex passages. The V-Caps (both TFTF and OIMP) in my applications are completely free from that. The smear-free delineation of strings in symphonic passages, while maintaining texture is what separates V-Caps apart from all others.
Too bad there is no way I can open the crossovers of the Eidolons, otherwise I bet $$$ the V-Cap OIMPs can get rid of the slight grain of the Accuton tweeters.
My next step? Let them run-in for a while. Perhaps get a pair to bypass the Solen 220uFs (risky bet, some caps cannot be bypassed, it smears). The woofer integration is a different story. It will take me some time to really address the problem of the still remaining mid-bass hole.
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