IRS V in Music Room One gets a new lease on life

Paul, Could I ask you what you are doing with the input to your amps for the IRS? Are you using the stock boxes with the capacitors and resistors to match the amp input impedance? Are you running balanced interconnects from your equipment rack to the amps and if you are, how are you arranging the filter impedance matching using the balanced format?



I made custom boxes for the amp inputs – basically a balanced version of the high pass filter the system requires. And I run everything balanced. I also converted the servo box to a balanced input too, so now everything runs balanced. The BHK amps are 100K input impedance, so that’s what the high pass network was designed for.

Yikes! Does that require doubling the components in the crossover for each leg of the balanced circuit?

Oh, goodness, no. This is on the input only, not the output crossover. The IRS asks for a first order high pass filter on the input of the amplifier. It consists of a single capacitor in series with the input. For balanced, yes, we use two - but that’s not as bad as it sounds were we having to double the speaker crossover.

Paul, as a point of reference, my Vandersteen Model 5 speakers use a high pass crossover for the input to the amp to work with the built-in subwoofer. When Vandersteen first started doing this it was with the 2Wq subwoofer and used a simple capacitor for the crossover, which is what I understand you are doing. For the Model 5 they introduced a fancier version with many components and is battery biased, ala Audioquest cables. They have since introduced an even more advanced crossover for the Model 7 speakers. They are available in single ended and balanced configurations and are fully adjustable for amplifier impedance. If you’re bored (not likely!) you might try the Vandersteen crossovers to see if they make a difference. I know Richard certainly thinks so. Personally I don’t know how much difference they make, when I was using a single ended amp I used capacitor crossovers I made, but when I got the BHK250 I could use the balanced crossovers that came with my speakers. It certainly sounded better, but I was going from single ended to balanced and a much better amp, so it should have!

Paul the literature for the IRS shows the (2) .o1uf caps in parallel on the center conductor of the single ended set up. For 100K impedance is also shows adding a third .01uf cap and a 72.6 k ohm resistor. Did you just use a single capacitor on the + and another on the - path on the balanced cables? To convert the woofer controler box to balanced did you use a transformer in side the box to run the single ended woofer circuit? I would love to duplicate what you have done. I’m handy with a soldering iron and mechanical stuff. any insight you could give me would be appreciated.



Thanks Pmotz, though I am hesitant adding anymore to the input crossover than the caps - I am guessing Ricahrd has other motivations not similar to the IRSV which is quite specific.

To Mike. Yes, instead of the circuit they show which is a .02mFd (they used two parallel ones because at the time the Wonder Cap they liked was only available in 0.01), that gets rearranged, one per balanced input.

On the servo I build a differential input using a NE 5535 op amp. Here’s an example of the circuit. I used the existing power supply in the servo unit to feed a pair of these and all 100kΩ resistors instead of the 10KΩ shown…


Thanks a lot Paul !! I’m talking to Bob who going to help me get me up and running.

I really enjoyed reading about the progress of the IRS V and are looking forward to any further postings.

My listening pleasure over the years has been with the RS1b’s, the speakers being a constant over several changes of amplifiers, cables, positioning, room treatment and source components. I have remained with the old Cogan-Hall cables, a bit unwieldy but they sound right.

Purists may baulk at the bi-wiring modification but experimentation won out. I’m very happy with the system now.

One day I would love to hear the IRS V, I can only imagine what they sound like.IMG_2810-resize.jpgIMG_2812-reduced.jpg

You’d be most welcome

And welcome to the forum Allan!

The new crossovers are installed , working fine. I want to thank all involved in there making of them. Bob stadher of makes both arrest looking product that’s sounds fantastic. How much time it took to arrive at this product I never really know but I can speak of its sound wow. Paul,was kind enough to share its making and kind enough to tell me it’s improvement . Paul it’s way beyond a vail hahahahaha I guess it’s safer to say that and get this response holy cow it’s jaw dropping. It’s smoother while still adding clarity and details. Your amp

in monos up next Paul. Going up against tthe Goldmunds it’s a marvel and I feel it will be just that good. As these speakers give nothing any place to hide lol.

Thanks ps audio as well as mr N and expscially bob S for his producing this fine product.

Paul do the imp high pass box too in balance. If gas increased details as much as the new Crioss over did. The low level details has improved so that I hear things where there was none.

Yes, the input box we did in balanced too.

Hello to everybody,

probably I’m one year late :slight_smile: but I am the (proud) owner of an IRS V, and have some questions about it.

My system is all balanced and between preamp and wings power amps I have a direct wiring (not through servo unit); I’m very interested to change the servo in a full-balanced unit.

The only mod that I’ve done is to change the operational of the servo is to change the old operational with a more recent one (and lighty smoother), because the main problem in my system was the speed difference between wings and towers…

But the possibility to rebuilt wings crossovers and mod the servo into a balanced unit makes me crazy; so I kindly ask you if is possible to buy the two x overs boxes and the balanced servo.

Should be great to have your opinion concerning the speed difference between wings and towers…

Many thanks for read.

From Modena, Northern Italy


Hello, from a fellow IRSV owner. Our chief engineer, Bob Stadtherr can fix you up with rebuilt crossovers and servo system if he’s still up for it.

The improvements, along with a set of BHK amps is nothing short of extraordinary.

If you’re interested, contact me directly at paul @ and I’ll connect you with Bob.

Good morning

PAUL on another forums there is someone persistent in nit having the cross overs be external like ours is.

He swears that even the short cables we have seriously degrade to sound. While I cannot comment I do feel two school of thoughts.

One it’s isolated from vibrations in the towers

second how can it matter when after he crossovers in several feet of wires in fact many feet of wire.

Is he correct ? Any thoughts. ? I feel the upgrade was very good and I have grown to love the improvement

Over the last week one of my towers had a low rumble when playing or not
I read through the service Manuel and made a phone call to mark a very nice guy and knows plenty about infinity speakers
he felt as I did it could be a loose accelerometer in the woofer
I took things apart and found nothing wrong
the connections inside seemed fine and a small rf type shielded coupling is used to remove the woofer
putting it back and turning it back on was a wow moment
has anyone ever heard what 2K watts and 6 12 woofers can do you may be surprised given this is only one half of the woofers.
In trouble shooting first part is to remove the servo sensor
and play this was fine a bloated bass but fine wow does that servo make things good

next a complete reboot
well In playing loud passages I have vibrated various bid to parts as hair yes hair and fat even my eyes lol
but what happened next was an amazing show of thunder in my room like I never have heard before I felt the air as I ran to shut it down.
Anyway a simple loose connection of the servo was the cause no damage and playing fine now.
I truly have a new raspect for these woofer towers now
also for anyone who has a pair the woofers are labeled IRS v and the Amps have two huge toroidal transformers amd 8 large caps the IRS 1/2/3 one 4 caps and one transformer also white woofers.
My resonaing for posting is be aware of our subs with Servos this can happen to other types as well and very not so good experience for those who leave there Amps up and powered all the time as I don’t anymore lol.
Live and learn friends