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Tech tips and blog post page





This page discusses items related to Keyboards, Digital Pianos, Organs (church, band and home), Sound Systems, Intercoms, Recorders, Amps, Home Stereos, Entertainment Systems, Jukeboxes, and Commercial Sound Systems.







Speaker Phasing

This is a simple, but important topic.

12 inch loud speaker

All speakers as most of you know have a positive and a negative terminal.

If these terminals are hooked up backwards the speaker will still work, and if only one speaker is used you will probably not even notice the speaker is out of phase.

The problem comes into play when using more than one speaker cabinet, or multiple speakers within one cabinet.

If one of the two speakers is hooked up backwards then the two speakers will be out of phase and when played together they will sound very thin as they are essentially canceling each other out. This is because one cone is moving out while at the same instant the other is moving in.

In cabinets with multiple speakers it is also important if you have to replace a speaker that you match it up as closely as possible to the original, or replace both at the same time. The reason is if the two speakers have different efficiencies and cone materials then the cones will move at different rates which creates another type of phasing issue.

When hooking speakers up you cannot always rely on the markings on the speakers. I have seen many speakers over the years that the positive & negative leads were labeled backwards.

The good news is that it is extremely easy to check for phasing issues and proper speaker polarity, all it takes is a 9 volt battery.

With nothing else hooked up to the speaker touch the positive lead of the battery to the positive lead of the speaker, and touch the negative lead of the battery to the negative lead of speaker. As you are looking straight into the front of the speaker it should move towards you.

The direction of motion when you hook up the battery is what you are looking for.Be sure not leave the battery hooked up for more than a few seconds at a time.

When doing this with a cabinet you can simply use the input terminals of the cabinet to perform this test.




Mam … Step away from the super glue.

Tube of Super Glue

Do yourself a favor and please think at least twice before you reach for the Super Glue.

I just spent and extra 30 minutes time carefully extricating a jack from a circuit board so as not to damage the board because someone attempted to glue the plastic jack back together and ended up instead gluing the bad jack to the circuit board.

If something breaks on your gear, Super Glue may sound like a good idea at the time, but 99.9% of the time it is not. Most of the time it just makes things 10 times worse than they already were as it is very thin and tends to up everywhere except where you really want it.




Cleaning controls or “pots”

Rotary control and slide control from music gear

Almost every piece of equipment be it a keyboard, a mixing board, a guitar amplifier, or an effect unit has some good old fashioned potentiometers (Pots) that at some time in its life will need to be cleaned.

Cleaning controls is a pretty simple process; it is the getting to the controls to clean them that can sometimes be complicated.

First a warning about faders or slide controls. Do not clean them unless the absolutely need it, and then only use special fader only cleaner. Then finish the job up with some fader lube. If you use anything else the controls will become so stiff you will barely be able to operate them. Even when you use the proper products on them they will still be stiffer than they were before they were cleaned. That is why I advise not cleaning them unless it is necessary.

Fader controls unlike rotary controls can be cleaned without taking the equipment apart. You just spray the fader cleaner in the slot that shaft rides in that the knob attaches to. Then work it back and forth over its entire sweep several times, apply some fader lube in the same way, and you are done.

Cleaning rotary controls requires disassembly of the unit being worked on. Once you have accesses to the controls the process is pretty simple. Most, but not all rotary controls have a slot or other opening on the back or side that you can spray your preferred brand of control cleaner into.

Clean the controls one at a time, do not spray them all first and then go back and rotate them as it is not nearly as effective as spraying the cleaner into the control and then immediately rotating it vigorously several times over its entire sweep.

Here at the shop we generally clean each control twice, the reason we do this is if you have to spend several hours on cleaning the controls on say a mixing board that you had to pull all the circuit boards on to get to the controls you sure as heck don’t want to have to pull it all back apart because you were not thorough in your first attempt.

A few additional notes on control cleaning.

When cleaning controls on keyboards, and synthesizers be careful not to get any control cleaner in the area of the keyboard display, or the keyboard contacts.

When cleaning controls on guitar amplifiers try not to get any cleaner on the tubes or any of the power resistors.

When cleaning controls on mixing boards there will generally be a lot of cleaner run off after cleaning the controls. Put the board on some old newspapers or something else absorbent and let the cleaner drain off before you put the cover back on it. It generally helps to do this with the mixing board left sitting in a variety of positions to facilitate draining of the excess cleaner out of the mixing board controls.




Roland Juno 106 voice IC’S

Roland Juno 106 keyboard

Roland stopped making the replacement Ics some years ago. However there is a guy over in Europe who is making a good quality reproduction.

So if you have an old Juno laying around that you thought was beyond hope due to bad voice IC’s this is good news.

I have installed this new part in several Juno keyboards to date, they work great and even after several years I have yet to have had one fail.

I do not recommend attempting this one yourself, but if you do be very careful as the traces on those old boards are pretty touchy and they can be destroyed pretty easily.




Buyer Beware!

The Internet is like the old Wild West, pretty much wild and untamed in many respects.

If you are buying new musical gear on the Internet please check to see that who you are buying it from is an actual authorized dealer for the product. If they are not there are two possible problems.

One of them being is the product could actually be counterfeit. Yes it is true counterfeiting is not just limited to Gucci handbags any more.

The other is they are second sourcing the product which makes them the original purchaser and you are considered as far as the manufacturer is concerned to be buying it 2nd hand from the Internet seller.

In either of these cases the manufacturer will not honor the warranty on the product. In the case of counterfeit products many times the manufacture will require a serial number to order repair parts and if the serial number is not in their system the will not sell the parts to repair it.




Broken USB ports

Musical instrument USB port

Many pieces of gear these days have USB ports of this style.

Keyboards use them, DJ mixers Use them, DJ control surfaces use them, some standard mixing boards use them, some effects use them, Digital recorders use them … On and on the list goes.

The problem is the connectors were really designed to be plugged in and left alone. The music industry really needs to come up with better connector to use. The big problem is about 25% of the time when these break off the circuit board they also damage that circuit board.

When these break it is best to take them to a well-equipped and experienced shop. Trying to change these yourself, or having an ill equipped shop try it will only end in your having to replace the entire circuit board... This in most cases is the Main PCB. This is a most definite do not try this at home situation.

My best advice of course is to be as careful and as gentle as you can with these USB ports. As I said they are a poor design choice for this gear and break easily.




BUYING USED MUSICAL EQUIPMENT

In this tech tip I am going to talk about some things to look for when buying used electronic musical equipment.

Buying used equipment can save you big bucks or provide you with big problems if you are not careful.

The first rule is plug it in make it works and test all the functions. If the person you are buying the equipment from does not have the needed equipment on hand to test whatever you are buying, (such as a guitar & cable for and amp, an amplifier and cable for a keyboard, etc.). Bring your own! When you test a piece of used musical equipment you are thinking about buying don’t just turn it on play through it and say yea it works I’ll take it. Leave the equipment on for as long as possible as many problems take an extended warm up period to show up.

Lightly wiggle all the jacks (including the ac adapter jack if it has one) on the unit while it is operating to check for intermittent connections. Lightly tap on the unit in different places while it is running again to check for any obvious bad connections. If a unit is capable of running on batteries and ac power, check to see that it does indeed work with both. Rotate all the controls while operating the unit, if they are audio controls there should be no erratic behavior or crackling from them if there is, while this is usually not a serious problem it will mean an additional repair expense.

If the controls operate a function as on a keyboard or an effects unit the same applies only the problem will show up in the way the display that indicates that function changes. If a unit has an external fuse check it to see that it matches the value written on the unit. If the fuse that is in the unit is of a substantially higher value or worse yet has foil on it. Insist that the proper value fuse be installed to make sure the unit will operate and is not drawing too much current which could indicate expensive repairs.

If the unit is fairly complicated make sure you get an owners manual with it. If the person selling the unit does not have an owners manual figure on spending an average of $15.00 to $25.00 to get one if it is not available as a free download, as many are these days. Many private parties sell things as is with no warranty, but it never hurts to ask for some kind of warranty (don’t expect too much and don’t be mad if you don’t get it.) If you are buying from a music store expect some kind of warranty. In either case be sure you get the warranty in writing so you are both clear on it. Last but not least get a written bill of sale with the model and serial number of the unit on it.




Series Parallel Speaker Wiring

Series Parallel Speaker Cabinet Wiring

Assuming That all the speakers are of the same impedance and wattage (as they should be). The impedance of this cabinet will be the same as one of the individual speakers used. So if you are using 8 ohm speakers the impedance for the this set up would be 8 ohms. The wattage of the speaker cabinet will be two times the wattage of an individual speaker. So if we are using 25 watt speakers in the example the total wattage for the speaker cabinet will be 50 watts.




Series Speaker Wiring

Series Speaker Cabinet Wiring

For speakers in series you simply add the impedances of the speakers together. The wattage of the combination will be that of the lowest wattage speaker that you are using. It is highly recommended to use identical speakers whenever possible.

Series speaker wiring is usually the least favorable way to wire a speaker cabinet as you are limited to the wattage of one speaker as far as power handling capability goes. However sometimes it is the only way to wire the speakers to get the impedance you need for the amplifier you are using.




Parallel Speaker Wiring

Parallel Speaker Cabinet Wiring

With parallel speakers of equal impedances you divide the impedance value by the number of speakers. If you were using 16 ohm speakers the impedance of the circuit below would be four ohms. To determine the wattage you add the wattage of the speakers together if you were using 25 watt speakers in the circuit below the power handling capability would be 100 watts.




Mono mode

Proper hook up for most power amps.

We get a lot of power amps in for repair because they have been switched into mono (bridged) mode and were not properly hooked up to run in this mode.
Mono mode in most power amps configures the amp so that 1/2 of the wave form is amplified by each side of the power amp.
As a general rule once the unit is switched into mono mode you must use the two red binding posts only to hook up your speakers some amplifiers will have a dedicated output for mono mode and this output will be marked as such.
Also as a general rule a power amp ran in mono mode does not want to see a total load below 8 ohms. Unless the amp is marked otherwise running a speaker load below 8 ohms will either drastically shorten the life of the amp or outright fry it.


The information provided here is for informational purposes only. We are not advocating or suggesting that you work on your own equipment as there are potentially lethal voltages in almost any piece of electronic gear.