[PaulFolbrecht]

Hello,

I "discovered" VMPS very recently in my search for SET-friendly time&phase accurate speakers.  I was able to hear the RM30s yesterday at a local owner/dealer and was pretty impressed.  In addition, Brian took the time to respond to a flurry of emails from me as well.  I had a couple other questions I thought I'd post here to allow Brian or someone else to respond.

1) Sensitivity ratings vs. the variable output: are the numbers you quote (93/91dB ribbons/bass) with the outputs maxed??  Or the stock/default levels?  That could make a big difference, no?

2) Caps & crossovers.  Since 1st-order crossovers are employed, I would think this implies a minimum of parts?  Such crossovers can be (aren't always) implemented with just a single cap/inductor.  That said, I'm wondering why the fairly steep Auricap/TNT upgrade prices.  Might I ask how many Auricaps that $550 is buying?  I'm just curious; I don't know enough to fault the x-over design and that's not my intent.  I know there is generally very, very good value here as well, and I'm sure nobody is being "taken" by these upgrades.  I'm just wondering how much these caps really go for each!

Thanks!

[Brian Cheney]

The cap values are large due to the low crossover points.  That's why the expense.  It takes about 16 individual TRT's to make a pair of crossovers, for example, plus the time it takes to trim them to very small tolerances.

To take maximum advantage of the sensitivity of the system use the PBS to control the woofers.  Then there is only one Lpad (the mids) which is reduced only about 3/4dB relative to the trebles.  Lpads are reduced about 3.5dB when the system is operated full range from a single amp because, as usual, woofer sensitivity is less than that of mid and treble.  With the PBS woofer level can be boosted to match the balance of the drivers.

Try your SET fullrange on the 30's and see if there is enough output for your needs.  If not go with the PBS and use the SET only on the mids and trebles.  Full up those drivers come in at around 95dB/1W/1m.

[PaulFolbrecht]

Thank you for the reply, Brian.

Ah, lots of caps for the woofer x-overs.  That makes sense.

The problem with trying my amps on your local dealers' speakers is that that pair has the 10" woofers and since you told me yourself you now prefer the speakers without these, I'd definitely not be getting them.  Those 10" woofers are doubtless going to add a quite substantial load to the amps, so I don't feel that this trial would likely give me good information.

On paper, from what I've read before, the speakers look like an entirely reasonable load full-range for 30W tube amps with high-current capability.  The site says 91.5 & 93dB for the woofers/ribbons, impedance 4-8Ohms.  That's quite doable.

That led me to the question on the L-pads and sensitivity, and now as a further question I have to ask if the 91.5dB figure corresponds to the old or new woofers and includes the 10-inchers or not.

Could you tell me this: what is the full-range sensitivity of the current 30C model run full-range in dB/W/m?  I would guess you are setup to be able to measure this pretty quickly?

I'm sorry to be a pain.   Really.  You have to admit, this is a pretty basic spec for what is now the most common/recommended setup. 

Bi-amping is possible, but I admit I'm biased against it as I've always found it to be slightly less coherent overall.  I avoid it if at all possible.  With the C models going down to 40Hz or so, and my sub filling in that bottom octave or more, I can stand a little roundess in the bass - in fact, I sometimes prefer it.

Thanks!!

[Brian Cheney]

There are two 89dB woofers in parallel, or 92dB nominal.  So that's the maximum sensitivity of the system fullrange.

[PaulFolbrecht]

92dB full-range is quite good.  I could always buy the speakers without the PBS with the (sensible) hope that my amps would power them full-range very well.  I think that is very likely.  Remember, I don't listen above 90dB peaks anyway.  If not, I could add the PBS.

I would be getting the OXO.  So if I decided to "upgrade" to PBS in the future I could get the bare (standalone) PBS modules and that would be that.

This is probably published somewhere, but what is the input impedance of the PBS amps?  Since I run the passive (TVC) linestage that is important.

[John Casler]

92dB full-range is quite good.  I could always buy the speakers without the PBS with the (sensible) hope that my amps would power them full-range very well.  I think that is very likely.  Remember, I don't listen above 90dB peaks anyway.  If not, I could add the PBS.

I would be getting the OXO.  So if I decided to "upgrade" to PBS in the future I could get the bare (standalone) PBS modules and that would be that.

This is probably published somewhere, but what is the input impedance of the PBS amps?  Since I run the passive (TVC) linestage that is important.

Input impedance of that amp is 12K ohms if I remember correctly

[Brian Cheney]

The OXO is a big step forward sonically so get it by all means. 
It also permits easy crossover/parts upgrades later on.

The PBS is available as a standalone chassis or as a plate amp that mounts inside the OXO.

[PaulFolbrecht]

FWIW, the maker of my TVC linestage (Audio Zone) says that a 12K input impedance is not at all a good thing.  They recommend 50K ohms or higher (when bi-amping, I assume).

Hmm.  12K is not an extremely low Zin for a SS amp, so I find this to be an.. annoying, shall we say, restriction (if that's what it is).

If I bought the RM30s, I'd hopefully not want/need to bi-amp, but it would be nice to have that option available.

Does anybody know how resistence combines when two sinks are driven in parallel?  That is basic electric stuff; I should know that.

Maybe the maker is just being overly "cautious" in their recommendations.  Or maybe this is one situation you just can't have your cake and eat it too.  It is interesting to note, if nothing else.

[John Casler]

FWIW, the maker of my TVC linestage (Audio Zone) says that a 12K input impedance is not at all a good thing.  They recommend 50K ohms or higher (when bi-amping, I assume).

Hmm.  12K is not an extremely low Zin for a SS amp, so I find this to be an.. annoying, shall we say, restriction (if that's what it is).

If I bought the RM30s, I'd hopefully not want/need to bi-amp, but it would be nice to have that option available.

Does anybody know how resistence combines when two sinks are driven in parallel?  That is basic electric stuff; I should know that.

Maybe the maker is just being overly "cautious" in their recommendations.  Or maybe this is one situation you just can't have your cake and eat it too.  It is interesting to note, if nothing else.

Hi Paul, the 12K is for the "plate" version.  I have not seen the component specs, but would assume them similar.

[DSK]

...Does anybody know how resistence combines when two sinks are driven in parallel?  That is basic electric stuff; I should know that....

Paul, I believe the generalized formual for impedances/resistances in parallel is
Rt = (R1 x R2) / (R1 + R2)