Submit Search

HAUPTWERK READY! Midified Gulbransen Rialto K Theatre Organ

Hauptwerk and sample sets *not* permitted. Audio and MIDI hardware for use with Hauptwerk, organ consoles, parts, computer equipment.

HAUPTWERK READY! Midified Gulbransen Rialto K Theatre Organ

Postby mick333 » Wed Feb 15, 2017 7:35 am

Fully midified Gulbransen Rialto K Theatre Organ with two Isomonic Leslie speakers (102 & 103), Keyboard Systems Midi Controller, two 61-note wood core keyboards, 25-note pedalboard, and matching walnut bench. Ideal for your Hauptwerk VTPO project, but on its own merit the Rialto K design culminated years of research and development to create a beautiful theatre quality Isomonic sound system with golden voiced tibias. By adding Hauptwerk to this midified organ you will have the best of both worlds! This is the 1135 model which contains the additional features of celeste, piano, and "wah wah" knee lever. Pipes are not included. All offers considered.
Posts: 3
Joined: Tue Jan 13, 2015 5:05 am

Re: HAUPTWERK READY! Midified Gulbransen Rialto K Theatre O

Postby organtechnology » Wed Feb 15, 2017 11:13 am


At the risk of falling off the Hauptwerk possibilities for your posting, I am interested in the definition of an 'Isomonic' sound system. My search turns up an iso-monic Acid as a bacterial cleansing agent but nothing for isomonic sound. Just curious as to what it is. You could answer me privately, if you think it more appropriate.

Complete VPO systems powered by Hauptwerk™. Real Wood Consoles, PC or MAC Computer Sound Modules, Audio for Home or Church.
info (at)

Authorized Hauptwerk Dealer; Milan Digital Audio Dealer..
User avatar
Posts: 1813
Joined: Sun Aug 02, 2009 5:58 pm
Location: DFW, TX USA

Re: HAUPTWERK READY! Midified Gulbransen Rialto K Theatre O

Postby engrssc » Wed Feb 15, 2017 1:41 pm

Hi Thomas,

It's "interesting" verbiage for a vintage Leslie Model 102, you know the one(s) that Hammond folks used to "enhance" the trem effect. I gave mine away countless years ago along with the B3.

How about a pair of Epique's -
(Just kidding) :roll:

User avatar
Posts: 5974
Joined: Mon Aug 22, 2005 11:12 pm
Location: Roscoe, IL, USA

Re: HAUPTWERK READY! Midified Gulbransen Rialto K Theatre O

Postby mick333 » Mon Feb 20, 2017 4:51 am

With all due respect to Ed, his attempted explanation of the "Isomonic Sound System" falls short of the mark. This system has absolutely nothing to do with Hammond organs or the "Hammond sound", but was an extensive endeavor to create a realistic emulation of the theatre pipe organ. It was engineered by Don Leslie in collaboration with Dick Peterson at Gulbransen specifically for the Gulbransen Rialto K electronic theatre organ, which incorporated the pairing of Leslie speakers 102 and 103 and rotosonic drums, as opposed to the other Leslie designs used on Hammonds and others. Since Don Leslie's passion centered around theatre pipe organs, he considered his Isomonic system to be his crowning achievement, and rightfully believed that the Gulbransen Rialto was the best sounding electronic theatre organ ever made. He actually had a very low opinion of the Hammond sound even though he gained most of his fame and fortune through his association with it.

The Isomonic sound system is derived from the words "Isolated" and "Harmonics", and separates notes into two different channels (C and C#). The "C" channel contains the C,D,E,F#,G#,A# notes. The "C#" channel contains the C#,D#,F,G,A,B notes. The C/C# setup somewhat mimicked the diachromatic positioning of organ pipes on a pipe chest to prevent adjacent notes from negatively influencing each other since they tend to draw each other off tune, and it helped solve the problem of single channel intermodulation distortion in the electric organ. This system prevents musical intervals of the fourth and fifth from mixing in the amplifier or the speaker. Instead, the notes are mixed in the air acoustically as in an orchestra or pipe organ, and the result is a glorious three dimensional stereo effect that radiates throughout the room.

Unfortunately, YouTube videos completely fail to capture this. It has to be heard in person and requires the two Leslie configuration to experience it properly.
Posts: 3
Joined: Tue Jan 13, 2015 5:05 am

Re: HAUPTWERK READY! Midified Gulbransen Rialto K Theatre O

Postby TheOrganDoc » Mon Feb 20, 2017 9:28 pm

I had one of those Gulbransen's in my living room, many years ago along with the Isomonic Leslie's,
I found the biggest problem with them, (I was a Gulbransen repair tech.) was the rotary Contact devices (Mercotac's) that were utilized to pass the amplifier outputs, to the Rotating 6" x 9" Speakers that were mounted on the rotating drums. They used Liquid Mercury as one of the rotary Contacts, and a ball bearing assembly as the second speaker wire. :?

Great idea,,,,, "Except the mercury oxidized, and they then became very intermittent" ,
By now I doubt that any of the Mercotac's that were made back then, are working at all ! :oops:

Shaking them like a thermometer would fix them momentarily,
but replacement was usually necessary !
I personally replaced dozens of these devices !

I remember buying a carton full of these devices, from their manufacturer a few times,
and they were not cheap. :roll:

Allen's Gyro-phonic, speakers went an expensive step beyond,
by using Commutator Rings with Contact Brushes to feed audio through to their rotating speakers,
to (almost achieve), Leslie's rotating effects !

Hauptwerk's audio settings easily [simulate] the same effect, (C-C# Split), If not improve on it,
Especially as far as 100 % Reliability is concerned !

The Speaker cabinets for the Hammond X66 an X77, produced a somewhat similar effect,
but they achieve their effect", by using motorized, Rotating Variable Capacitors,
to provide what they called their, (Space Expander- Iso-Monic ?), and also Vibrato effects !

(I do love my Hauptwerk Organ, Thank You HW.) Thank you for your Replies !
User avatar
Posts: 786
Joined: Sun Sep 19, 2004 11:13 pm
Location: South East, Florida, USA

Return to For sale / wanted (classified ads for private individuals)

Who is online

Users browsing this forum: No registered users and 2 guests