1147 Kit with C2 Organ and 120 leslie

**Satman3** · 06-24-2012, 07:24 PM

Hello All. I was called in to help a small church set up their leslie 120 speaker with their C2 organ that was initially wired for a 720 leslie speaker that went bad. The organ had also been redone with a trek II solid state preamp. After consulting with the pastor; I ordered an 1147 kit to connect the two together trying to get around rewiring the organ and the leslie as the budget is small. I connected the 1147 kit and it did allow the leslie motor switching and the organ played but there is a great deal of distortion when the volume pedal is pressed down. I did adjust the pot on the kit to no avail. The problem is not with the speaker as it was played on a C3 organ and sounded surprisingly good. I did forget to mention that there is no amp in this 120 so I figured I would try and intercept the speaker wires in the cabinet and insert some type of 20 watt amp between the 6 pin connector box and the speaker. I would also like some suggestions on an inexpensive amp from some of you gurus. However, at this point I need to determine where the distortion is coming from and dont want to add an amp to amplify noise. They are not looking for this speaker to be a powerhouse and used passively will be just fine. Maybe the drive level in the trek preamp needs to be turned down. If I must rewire this to match the 6W standard to make it work correctly then I must. However, I am not looking forward to it.

**jdoc** · 06-24-2012, 09:43 PM

what were you trying to drive the 120 with, a C2 has no amp and a 120 has no amp, either way where is the watts coming from?
A stock 120 speaker is too small for a C2 pedal output, it is only a full range 12" suited for spinets in a living room.
Something is missing here?

**Satman3** · 06-24-2012, 11:20 PM

Thanks for the quick response, jdoc. I was aware that the trek preamp in the C2 would not drive the speaker directly but went on the fact that the stock AO-28 preamp in my C-3 drove the leslie loud enough to be heard in a small church with halfway decent pedal tone, although it was not the greatest bass. I scoured ebay for a vintage amp to interface with the speaker but could find none; hence the reason for an inexpensive amp recommendation. Is there a 12 inch speaker out there with better bass response than what is in this leslie. The church would be well satisfied with this speaker if I could get it to play like it did on my C3 with no distortion and a quality sound. I have a 122 that is loud enough to hear down the street but the pastor said they dont need that. Your approach and suggestions are well appreciated.

**jdoc** · 06-24-2012, 11:51 PM

maybe drive it with a small guitar amp($30 at a pawn shop), back off the preamp signal to start and adjust as required, feed into the amp and disconnect the onboard amps speaker and connect to the Leslie speaker, if you had decent sound with the stock 12" fine...different quality speakers were used
this will give eq to adjust treble up and bass down if required, my one Leslie kit is built into a small Fender amp so I can plug anything into the Leslie
I use a small ss Fender Bass amp for this contraption and like it.

**Satman3** · 07-24-2012, 03:01 AM

Sorry I did not have a chance to give you guys an update as I got busy doing other things and also took a 2 week vacation. I went by the other day and found that they had already ordered a lepai 20 watt stereo amp with rca inputs. I did not have a chance to secure a small guitar amp as mentioned previously by JDOC. Is the lepai amp a viable way to hook this up as I tried to hook it up but never got consistent volume from it. Once or twice I did get it to sound pretty loud after wiggling the rca connection which was a solderless deal from radio shack. I purchased some solder type today to see if that would make a difference. Now that I think about it I should have checked the plug for continuity. I have already soldered a connection onto a new plug and we will see how that goes. The distortion I mentioned seems to be prominent when the higher drawbars are pulled out and the vibrato knob is turned.

**Hammond101** · 07-24-2012, 03:44 PM

I wonder if the issue is in the C2 or Trek II and the Leslie 720 is OK.

Interesting that the 1W or so off your C3's AO-28 would drive the 125 to a suitable level. Never tried that one.

**Satman3** · 07-24-2012, 07:25 PM

Thanks for the response Hammond 101. The output transformer in the 720 was gone and hard to find.It looks like the majority of the problem is in the C2 now but I still have not ruled the trek II out. As I was looking at the trek schematic left in the organ there is a resistor rated at 22K that is in the vibrato line box. As I stated it really distorts when the vibrato knob is turned. Is this a major concern with the solid state preamp or should I be looking elsewhere. I need some of you hammond gurus to help me figure this out as well as a devise a course to troubleshoot. You did mention the power output of the AO-28 as being small. I was also surprised that it had enough volume to sound decent. Being that this is a very small church they desire not to blow the walls down or be heard the next block over. They are after a good organ sound.

**geoelectro** · 07-25-2012, 01:23 AM

In the Trek II preamp there is a built in 122 type switching "kit" whose output is on the G G terminals. In your application you do not want to connect there. Instead, connect to the G3 and G4 terminals. This is ahead of the "kit" and more comparable to the direct GG output of a Hammond.

The "kit" in the Trek II uses capacitors instead of the usual matching transformer. In the transformer version, there is some step-up in power do to the 1:1.1 winding and a solid low impedance output. Same when driving it direct from the GG terminals as far as impedance goes. In a capacitor type switching circuit the output impedance is much higher making it unable to drive low impedance loads.

Another problem with this kind of capacitor circuit compared to the transformer version is since the impedance is higher it is more susceptible to noise, especially on long cable runs.

All that said, I've never heard of anyone driving a speaker directly off the preamp...

Geo

**Satman3** · 07-25-2012, 01:07 PM

That was a well explained technical application. I talked to a tech at Hammond that said the ao 28 puts out more power than most people realize but did not take the time to explain the mechanics. It may seem uncommon but I realize that I could never drive the speaker at a decent volume level directly from the preamp. It was only done on the c3 to test the speaker for sound. After the Leslie was connected, it sounded pretty good without the amp. The consensus was if I could get by with the 1147 kit and the trek ii preamp I would be fine with the size of the church. Do you see problems with the 1147 kit often or does the problem resemble more of a problem with the trek ii preamp. I know many churches that have solid stated their organ with the trek ii and see few problems. I also inquired about the possibility of using the small stereo amp to insert amplification into the equation. I assume that the 120 wants to see an unbalanced signal from the preamp so I am intercepting the wires going to the Leslie and running them into an RCA input on the amp and the output back to the Leslie speaker. Am I correct in assuming this will work. Thanks for the help.