Common Mistakes, and How to Improve your Organ!

by John Smith

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Common Mistakes and Remedies
Building an organ requires a variety of skills and, as I have found myself, these require a little practice to make perfect. My Organ Building packages describe, as well as I can, how to achieve a working organ, as you would have seen there are test procedures throughout the building process which should ensure immediate success.

Unfortunately not all the organs built have been as good as others. This normally shows up when a builder who is happy with their organ hears another identical one playing much better. By the very nature of the project there are bound to be variations, but there is no reason why there should be wide differences.  Having now seen a lot of the organs that have been built, and helping those with problems, I have put together this list of common mistakes and causes of weakness:

First of all it is important to remember that the design as offered is a fully tested and proven one. Many of the problems I have seen are caused by modifications, in particular to the bellows and spill valves.  I can understand this as many of the builders are used to steam models and by their nature have practical enquiring minds.  Lets face it most of us are well practiced at using a different material or method if we can not put our hands on the specified part.  Unfortunately an organ is like a living thing and any one part not functioning correctly can upset everything else, hence the testing procedures. Also once the organ is assembled it is not at all easy to know where to start looking, especially if there is more than one problem. Remember that a small leak on its own is insignificant but many leaks are a disaster.

Remember that all wood is porous, some more so, and MDF can be dreadful. You cannot detect air leaking through a porous board so it is essential to seal it all just in case.  What I recommend is to dismantle your organ to its main components. You will now have a kit of all the ready-made parts, which can easily be reassembled after testing.

Start with the Bellows. Follow the testing procedure given, Check each individual feeder for air leaks, you may have to remove the reservoir to do this. Did you use clamping board when gluing on the cloth? Make sure the valves are built as shown and sealing fully. With the outlet holes blocked, each feeder should be totally airtight. If the reservoir does not stay up under pressure for a minimum of 5 seconds then find out why. Using blackout cloth I expect mine to stay up for at least 10 seconds, and they do. Some common causes of poor bellows performance I have seen are:

1. Cloth sticking out at corners, or not wrapped tightly around the hinge end corners.
2. Leather valves not lying flat, or fitted with springs or even with a ply backing stuck on them.
3. Rough surface on board under bellows.  If the ply is not smooth then glue a piece of smooth card on it.
4. Valves in reservoir catching on side of box.
5. Spill valve leaking.

When you are sure that the bellows are up to spec they can be reconnected to the pressure box. But for the time being with the outlet only feeding into the water gauge.  If you are fairly sure that your bellows were OK to start with then only carry out the following checks before dismantling:

With the spring in place you should now check for correct operation of the spill valve and spring tensions. The reservoir should only open the specified distance before the spill valve opens. It is essential to use a water gauge (a length of pvc tube stuck to the side of the organ will do). With everything airtight, the Busker organ can be run on 5 to 6 inches WG.

It is not enough to simply set the maximum output to this amount, but now spend time to make sure that pressure remains essentially stable over 90% of the reservoir travel. The length and tension in the spring affect this. Unfortunately my early plans showed a different size spring, or a large fold back paper clip, both of these gave good results in my prototypes, but I have now gained a little more experience. The correct spring should be made from 2.5 mm diameter piano wire, as sold in model shops. This is folded round a ½" bar one and a half times and with 3 ½" long arms. At rest there should be 5 ½" inches span. The block on which this rests on the bellows should be about 3 inches long and countersunk at ½" intervals for adjustment. Fit one block on the reservoir lid at the extreme opening end, and another under the pressure box.  The blocks should be made to give a gap between them of 3 1/4" with the reservoir closed.  Make sure that the spring is free to move in space over its total travel as you fix the blocks in place. This arrangement should give a virtually constant pressure over the range of the reservoir. Movement of the spring in the adjusting holes should give from about 4 to 6 inches WG. Check that the spill valve is not leaking and that the spring for it does not cause too much effect on the WG when the bellows are just spilling out, which is the normal running position of the reservoir. The bellows should provide a virtually constant pressure over the full span of the reservoir with the spill valve having no more than about ½" increase in this. Finally crank the bellows slowly, at about 18 turns per minute the reservoir should stay inflated and you should feel each bellow doing the same amount of work. It is only when the bellows are performing as described that the pipes can be properly voiced and tuned.  When you have connected the tubing make sure that the bellows still have full and free movement.

Now we can check the pressure box, seal the tracker bar holes with tape and make sure the box is fully airtight. When it is right it will have little if any noticeable effect on how long the bellows stays up. The turning-the-handle-slowly test should be about the same. When this is all in order the pipes can be checked.

When I recently built a Busker organ I did something I think for the first time. I had no pipes connected to the tracker bar but a roll of music was in place.  The interesting thing is that the bellows system just kept up as the roll was wound through, maybe this is a good thing to try but it is a very demanding test. And will vary with the music used.

If you left the pipes in position for the bellows testing then at this stage the organ may burst into full song. Do not be satisfied with anything other than 100% at this stage.

One area for obscure faults is the tracker bar.  Did you undercut the holes? It will work even if you didn't but not as it should. With the test roll check all the notes in turn. Are some pipes noticeably louder or softer than others? If so then something is wrong.

At this stage check that the top of the tracker bar is flat, run a length of unpunched paper through there should be no sound and no air being used. With the test roll check each note and see that only one pipe sounds at once, small leaks between the cells can be very difficult to find unless you specifically test for them. If there are leaks between notes it is actually quite easy to rectify them if you made the tracker bar as shown as you can perform keyhole surgery through the sidewalls.

Problems with pipes are usually due to air leaks, either obvious ones or porous bodies. For pipes that work but not at good volume I always suspect porosity and check by blowing into the top of the pipe.  If in doubt give it another internal seal with thinned PVA. Stoppers should be a good but not too tight fit. If the pipe still sounds weak then look at the mouth.  The airways should look clean and uniform, compare the mouth of the best pipe you have with one that is not as good. The 1/2mm gap is probably the most crucial measurement in the whole organ; use of thicker or thinner card will only detract from performance. The first thing I look at in any organ that has been brought to me is the airways.  If these are all clean and tidy then the organ will usually be a good one.

If you have to revoice the pipes it is quite acceptable to glue a little strip of wood to the upper shelf to cut a new angle on. Say a 3 x 5 mm strip.  I have done this before by using a bandsaw to slice off both lip and bottom cover re sanding flat and starting from scratch.

The other factor that affects the sound, of course, is the cut-up or position of the top lip. The only way to get this right for my organs is to position it when the organ is otherwise finished, using the test roll to position each top lip in turn. In a good organ this measurement will increase in a totally uniform way as the pipes get larger, if yours don't then something is not right.

If your organ only has one or two pipes slightly off then these should be checked and adjusted to sound as good as the rest. But if you find they are all over the place it is probably best to take them all out and remove stoppers and fronts and reseal and revoice. The advantage you now have is a proper wind supply to set them up on, blowing by mouth is a bit hit and miss. Connect a 10-inch length of tubing to the tracker bar and use this to test the pipes.

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