The Organ Forum

In a post by Lajko, he wrote:

At least in the 651, the Tibia channel has a cross over so the highs go through the Leslie and the low do not because (as the service manual says) the low frequencies have a wave length too long to have any effect by the rotating Leslie.

I did not know this- can I assume then that the lower frequencies go to the 15' speaker?

How would I add a subwoofer? Can it be a powered subwoofer or does it need to be passive?

A side note.  There is only so much power available from an amp so if the power is being used to drive low frequencies, it takes away from the mid, etc.  The idea is to balance the highs and lows...

A powered subwoofer INCLUDING the necessary isolation to avoid ground loop hum would be best.

Hint:  There are many low-end subwoofers that show up at thrift stores... while they are not the best for instrument music, they can be used to test the proof of concept... Even some of the subwoofers for computers can be used to test as well as those for home entertainment systems..

Fred,I noted your comment about ground loops. I just replaced an older organ with a new one and immediately my external speakers developed a hum/buzz. The organ guys said it was a ground loop but I am wondering why my old organ (connected in exactly the same way) did not have it? They suggested a cheater plug (3 to 2, sans ground) but no way would I do that. I've ordered a couple Hum X devices to use to isolate the organ from the external amplifier and powered subwoofer. Any other suggestions? Thanks.

An absolute thing is ALL your equipment MUST be serviced from the same receptacle. 

Not having the schematics of your equipment it is hard for me to venture a guess as to the problem or potential fix.  As a starting point you could connect a heavy wire, say #12 between the chassis of the units and NOTE if there is any change in hum level...

One fellow I went to help had connected a Leslie and the problem was traced to a modification someone had made... the cure was to lower the impedance of the connection... they had a high impedance as well as lower impedance settings on a switch... Just change that and fixed the modification ground solved the problem.

If you have schematics or can let me know what models you have maybe I can find them online/.

Fred,

I believe your first sentence "serviced from the same receptacle" is the key to the first place I will start.

The two units (organ and amplifier) are connected to two different receptacles. Plus, the amplifier also amps my stereo system and satellite TV system. They were fine with the old organ but I'll check out your suggestions.

I really appreciate your taking the time, Fred.

Lots of ground loop possibilities there...

And an IMPORTANT thing... you mention the amp is part of your stereo system... MANY stereo speakers have been blown by connecting to musical instruments... BECAUSE the consumer speakers in most are rated as "Music Power" which is just inflated specifications to sell to consumers... our numbers are "bigger" than the competion... The power so rated depends on the normal "duty cycle" of music from CD's etc.

Organs and other music instruments are capable of continuous waveform which will overheat and destroy common stereo speakers...

So if you use your stereo system to amplify, play "softly" through it... The typical inflation of the ratings are a factor of about four...

I would recommend you find a set of speakers and amplifiers that are designed for use with instruments...

Fred,

As usual, you've provided useful, important info. I seem to have removed 90% of the hum using two Hum X filters on the two separate outlets powering the organ and amplifier/stereo/home theatre systems. Basically, plugged the Hum X into the outlet, then a multiple outlet strip into the Hum X unit. This is a temp solution until I can isolate the real culprit and make some better changes.

Regarding the advisability of using stereo system and regular speakers on the organ, that's also a good point. I built my speakers using fairly good components (see URL that follows) but I'm still careful to avoid playing loudly or clipping. I do play loudly rarely but most of the time, my playing is soft, background style.

I have a total of six, rather large, home made, 9-11 cu ft speakers. Here is the speaker link:

http://www.greatplainsaudio.com/downloads/604_8H_II.pdf

My two newest speakers use the 604's, while the older ones use classic Altec Lansing separate midrange and hi freq horns. They're not A7 (Voice of the Theatre) but of that same ilk. I'd love some A7's but they are too huge, even for me.

Best regards, Fred, and thanks. 

John

You can put a good grade audio transformer at each end, back to back with a low impedance link between to de-couple any ground loops.  Use twisted shield pair between and let the ground shield "float" at one end.  This balanced line is best bet...

The transformers would need to be rated for the low frequency end which means having enough iron in the cores to not saturate... You could try a pair of audio output transformers, one at the organ Hi to Lo and the mate at the amp Lo to Hi...