Mixing board repair & sound system repair
We have been doing electronic repair on sound gear for over 35 years. We do electronic repair on analog and digital based systems. Mixing board repair, sound board repair and sound system repair is pretty basic stuff for us here.
Of course it gets a bit more interesting when you get into the repair of the automated digital mixing boards, but still no problem for us here. So whether it be a two channel microphone mixer, a larger 32 by by 8 mixing board, power amp, paging system or an automated digital mixing board that needs repair. We can get you up and running again.
Common problems seen on sound mixing boards
Noisy controls, crackling controls, controls cutting out on sound board
On most equipment correcting issues with dirty controls is usually a minor affair, but cleaning the controls on a large sound mixing board can turn into an all day affair depending on the design of the mixing board or console.
On some audio mixing boards all the control knobs nuts and washers need to first be removed, then all the circuit boards on the mixing board need to be pulled and then you can finally clean the controls. Then of course you have to reassemble the sound board and check it for proper operation.
On other mixing boards once you gain access to the circuit boards you can get to the controls to clean them without having to pull everything out, but even these mixing boards take some time to accomplish a thorough control cleaning.
Here at the shop and out in the field we generally clean each control on a mixing board twice, the reason for doing this is that if you have to spend several hours on cleaning the controls on a large 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 enough in your first attempt.
Mixing boards and sound consoles with one or more channels out
Generally speaking when your audio mixer has this type of repair issue it is usually a failed component in the circuitry most often a bad operational amplifier or a capacitor or two. However bad connections on the printed circuit boards in your mixing board can also be the cause of this type of issue.
Controls also sometimes do fail and most often if this is the case with a mixing board it will be a failed fader control. Lastly if a control is dirty enough it can cause no sound, though this is a little more rare that the other failures.
How difficult it is to find and correct these issues will depend on how well the board was designed for accessibility to service the repair issues on the mixing board.
Tube guitar amplifier repair and maintenance
The following section is for you tube amplifier owners out there
Tube guitar and bass amplifiers seem to have garnered a lot of mystique over the years. I hope to be able to sort from of the fact from fiction for you here.
Do tube amps sound better than solid state amplifiers?
In my opinion yes whether they are a guitar amp, a bass guitar amp, a home stereo amp, or the more rare tube power amp they have a warmer sound, great dynamics and a more pleasant breakup than a solid state amp. The downside of course is the generally higher repair and maintenance cost.
How often should I change my tubes?
If you are using your guitar amplifier or bass amplifier say 4 hours a day 5 days a week = 20 hours per week. Then you should change your tubes every 6 months if you want to maintain the best sound quality. A year ( approx 1000 hours ) should be the absolute maximum on a set of tubes. Yes, they may still light up and produce sound, but it will not be a very good sound.
What Brand of guitar amplifier tubes should I use?
This is a subject that seems to have a lot of misinformation associated with it.
There are some differences in sound between different brands of tubes you may choose to install in your amplifier. For instance as a general rule Groove tubes tend to provide a much harsher ( edgy ) sound particularly in guitar amplifiers, less so in bass amplifiers than say JJ tubes.
However aside from the harshness of groove tubes I find that most of the other main stream brands are similar in sound quality. The one place I find a big difference is reliability. The tubes we use here at the shop are all pre tested and burned in for maximum reliability and sound quality.
The JJ tubes that we used to prefer to use in repairs have recently dropped in reliability so we have switched to using tung-Sol tube. So far we have been having excellent results with them in all types of tube amplifiers.
There are of course NOS guitar amplifier tubes and other rare tubes that have a nice tone and a hefty price tag, but in most situations and for most people they are not worth the hefty price tag. When we do a repair we will of course use any tube that you desire for your tube amp repair, but in most situations find that our customers are very pleased with our choice of Tung-Sol tubes for their guitar amp repair.
My new tubes make my guitar amplifier sound so much better; surely this brand must be better than what I had.
Consider the following scenario to illustrate why people think the tubes that they recently had installed in their amplifier whether it be for a guitar amplifier, a bass amplifier, or any other type of tube amplifier are so much better than the brand they had in there before. (In other words how tube rumors get started)
Most people do not change their tubes until they have a repair issue. We find that on an average most tube amplifiers we take in for repair have not had their tubes changed for 2-3 years ! After 2-3 years any set of tubes are not going to sound good in your amplifier. So pretty much no matter what tube is installed now will sound so much better that what you had that you will think the new amplifier tubes are best thing since sliced bread. In other words it is not so much the brand of tube that you installed, but the fact that you changed the tubes at all that made the amp sound so much better.
Where should I buy my amplifier tubes.
Beware! There are a lot of sources for guitar and bass amplifier tubes and name brand alone does not assure you are getting a quality tube.
You should as a general rule avoid the bargain internet tube warehouse type places because often the tubes they sell are seconds of inferior quality. The initial cost may be cheaper, but the repair bill when they take your amp down will not be. The old adage of you get what you pay for defiantly applies here!
Some but not all music stores that sell tubes usually sell what they can buy cheap, sell cheap and make a good profit on. Their choice of what to carry is often not based on careful research. For this reason most music stores are not a good source for tube purchases & information about tubes.
Even some repair shops unfortunately will sell cheap inferior tubes because they feel their customers will kick about the price if they don’t do this. What a good repair shop will do is sell the best quality most reliable tube they can obtain at a reasonable cost to the customer.
If this means sacrificing some business so be it, because a good repair shop will realize that quality and long term reliability will save the customer far more in the long run than the small amount of money they would save initially by using cheap inferior tubes!
Sorry if it sounds like I am a soap box here, but I am very passionate about providing quality service and reliable products to my customers.
I will never sell or use something at my shop that is not of good quality, poor quality parts make poor quality repairs, which makes for amplifiers failing in the middle of a gig ... and that is no good at all.
Don’t get me wrong I am not stumping for you to purchase your tubes from us, while we will gladly provide tubes for a guitar or bass amp repair that we are performing if you are looking to purchase tubes to replace on your own we actually prefer you purchase them from a reliable music store or online source .. Just be sure to do your homework and not base your decision on tube price alone.
Guitar amplifier, bass amplifier and power amplifier tube biasing
WARNING: THE CIRCUITS OF TUBE GUITAR AMPLIFIERS CONTAIN POTENTIALLY LETHAL VOLTAGES. IF YOU ARE NOT WELL ACQUAINTED WITH WORKING WITH HIGH VOLTAGE CIRCUITS YOU SHOULD NOT ATTEMPT TO PERFORM ANY OF THE FOLLOWING. THE FOLLOWING INFORMATION IS PROVIDED FOR INFORMATIONAL PURPOSES ONLY. IF YOU ATTEMPT TO PERFORM THE FOLLOWING PROCEDURES YOU DO SO AT YOUR OWN RISK!
The following method is a good method to use if you do not have a lot of test equipment.
Tube bias changes how much current the tube will pass, and since it is a given that all of this current leaves the power tube directly into the output transformer, you can simply shunt the output transformer with a milliammeter and measure the current directly.
Your negative lead on the milliammeter goes to the plate of the output tube (pin 3 on 6L6, EL34,6V6, 6550, and pin 7 for EL84 tubes) and the positive lead goes to the center-tap of the output transformer on your tube guitar amplifier. Now that you can measure the current flowing through the transformer, you can determine how much is going through the tube.
If it is a two output tube amp then the reading on the meter is what's going through the tube. If the amp has four output tubes, the reading must be divided in half. On four output tube amps, two tubes feed each side of the transformer. Since you are only shunting one side, then your reading would be for two of the output tubes and therefore must be divided in half to get an good idea of what one tube is drawing.
Since you now know how much current is flowing through the tubes, you will need to find the negative voltage supply for the control grids and increase or decrease that voltage to set the bias on your tube amplifier. You need to adjust that voltage so that the output tubes are idling at the proper current.
In most Fender amplifiers, there will be an adjustment pot. Marshall amplifiers also typically have an adjustment pot. Some tube amps such as Mesa Boogie do not have adjustment pots. A good number of silver face fender guitar amplifiers have an adjustment pot that looks like a standard bias control that is actually not an adjustment for bias, but is a balance for the output tubes. This circuit can be rewired to operate as a regular bias control.
If your guitar amplifier does not have an adjustment control you will need to locate the voltage divider resistors in the negative voltage grid supply. The circuit will most often have a wire going from a tap on the power transformer to the cathode of a rectifier and then will most likley go to a couple resistors in series.
If the first of these resistors is decreased in resistance, the negative grid voltage will increase making the tube current decrease and if the second of these resistors is decreased, the negative grid voltage will go down, making the current go up. Decide which resistor must decrease and temporarily connect a large value pot somewhere in the range 250K to 500K across that resistor.
Start with the potentiometer at its highest resistance setting. While monitoring the current on your meter, adjust the pot until the appropriate current is reached. Then turn the amp off and disconnect that pot. Next measure the pot with an ohmmeter, then find a resistor of that value and solder it across where the pot was connected. Re-check the tube current after you install the resistor.
What is the amount of idle current is correct for the output tubes ?
There is no one correct set in stone setting. There are only upper and lower current limits. A general recommendation is not less than 10 mA and not more than 50 mA as a good rule of thumb. Some tubes such as (6550, EL34) may like to see up to 75 mA.
Generally most 6L6 style amps sound best around 35 mA. Any setting that gives you the tone you like within those limits is correct.. The above method will work in most amplifiers out there .
A technicians view on Fender reissue guitar and bass amplifiers.
According to some people the new Fender reissue amps and the originals do not sound the same I am personally in that group.
As of this writing Fender Offer the following reissue amplifiers: Fender 65 deluxe reissue, Blues deluxe reissue, Blues deville reissue, 59 Bassman reissue, 63 Fender reverb reissue, 65 Super reverb reissue, 65 Twin reverb reissue.
I have not had one of each and every one of these amplifiers in the shop for repair at the same time to compare them side by side. I have however worked on and heard a great many of the Fender vintage guitar amps over the years so I know what they should sound like. Here are some probable reasons for some tonal differences.
These are my thoughts derived from my experience as an electronic repair shop providing tube amp repair service over the years. In the course of providing tube amp repair on both the originals and the reissues here is what I have come up with.
First of all let me state that I think Fender has done everything possible to make them as close to the originals as is possible and to my knowledge the schematic matches between the new and the old units.
Production methods and component quality have changed over the years. Resistors for example are much closer to their stated value than they used to be. Which could account for some of the reason on older amps one amp simply sounded better than the same model from the same year.
In other words while the circuits were the same the tolerance factor in early component design meant the circuits operated slightly differently from amp to amp. For example a 100,000 ohm resistor with a 10% tolerance meant the resistor could be anywhere between 90,000 and 110,000 that's a 20,000 ohm window.
Capacitors fall into the same category in regards to tolerance. However before you go out searching for old carbon composition resistors and old style capacitors .... the type of resistor is not the issue it is the fact that the values varied. Carbon comp resistors are also much nosier than the new film resistors.
As far as capacitors go you do not want old capacitors as they go bad just sitting on the shelf. The electrolyte in them dries up. Other possible differences may include the manufacturing process and materials used in the transformers. As well as materials and processes used to manufacture the speakers.
So in summation The new reissue amps are going to all pretty much sound the same from unit to unit. The old original amps are going to have tonal variations due to looser component and manufacturing tolerances.
If you want a Fender 65 deluxe , Blues deluxe , Blues deville, 59 Bassman , 63 Fender reverb, 65 Super reverb, 65 Twin reverb or any one of the other many fine amplifiers that fender has produced. Even if you buy an original it will not necessarily sound as good as your buddies down the street does.
Can you tweak the new ones .. of course you can. There are after market transformers, speakers and different tubes that are all going to change the way it sounds.
However if you want one to sound the same as your buddies original down the street. You are going to have to get your buddies and yours and bring them both in to the shop.
Then every resistor and capacitor will have to be measured in his and the ones in yours that are a different value due to tolerance will need to be changed to match. This of course is an impractical situation for most people as you would have to have some pretty deep pockets to go this route
If after that the sound is still not where you want it. Then it would be time for the after-market output transformer, then a different speaker, and possibly different tubes.
Then if it still did not sound as good as the original we would know it was just the magic from the 60's that made them sound so darned good .