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FAQ


From time to time, we get the same kinds of questions asked of us about various things. We've assembled some of the most common questions and our answers, for your convenience. We hope this saves time and phone calls.

1. Do you service car amplifiers?

A. Mostly no. The cost of troubleshooting and repair of many class D can run as high as $500 in labor. This is due to the sophistication of these amplifiers and their switching power supplies and the necessity of purchasing large batches of HEXFETs and other devices, for selecting matching groups out of, for replacement of an output stage. Often it will require two dozen devices purchased in order to find four that have a close enough transconductance match. This process is time consuming and expensive, in addition to the initial troubleshooting. On top of this, many car audio manufacturers won't share their schematic diagrams--it's proprietary, which raises the difficulty level of repair tenfold. So no, rather than jump into that quagmire, we've decided to make it policy that we do not service automotive audio amplifiers.

2. How do I troubleshoot my audio system to isolate the problem I'm having?

A. If it's a stereo amplifier, and you're getting sound out of only one speaker, first try swapping speakers and speaker cables between left and right channels. If the problem remains in the same channel, then try swapping the input cables from the source. If the problem remains, then there's a good chance it's in the amplifier. Be sure to wiggle the plugs at the RCA input jacks, as some may not be making good contact and may be responsible for no signal getting to the amplifier. If the amplifier has a rotary selector switch, try turning it slightly to see if the 'dead' channel comes to life--this is a problem with a lot of Sansui amplifiers from the 1970s--the selector switch may be worn or dirty. If the amplifier is blowing fuses, then it definitely is in need of servicing--keep damage minimal and do not attempt to power it on anymore.

3. Do you recone speakers?

A. Not presently. That requires special materials and ovens to do properly. At this time, we're focusing on being the best darned amplifier repair business and focusing strictly on amplifiers, tape decks and tuners. That's not to say that we might not invest in the tools to do this job properly in the future. At present, we don't recone speakers.

4. Can you fix my electronic musical instrument?

A. Often, yes. Especially older electric pianos and organs that use discreet circuitry. We have successfully repaired a number of electronic keyboards, pre-1980.

5. My amp has been stored for five or more years. Is it safe to power it up?

A. No! When an amplifier has been stored for a long time without being power cycled, the electrolytic capacitors in the power supply can develop a condition wherein the DC leakage increases dramatically. When capacitors are made, the manufacturer places a voltage across the terminals to form the oxide film on the plates. The oxide film is semi-permanent, but if the cap sits unused for a long period of time, the oxide film can degrade. This makes the capacitor vulnerable to shorting out the first time power is applied after a long period of non-use. The correct way to "re form" capacitors is to connect a series resistor and an ammeter in series with the capacitor being re formed, and slowly raise the voltage, while observing that the charging current stays within a certain value specific to that type of capacitor. Often, you can 'get away' with just ramping up the voltage slowly on a Variac connected to the amplifier, raising it up and down starting at 10% of nominal line voltage and adding 10 volts with each successive ramp up. This certainly is safer than slamming the power supply with 120V immediately!

6. My amp blew a fuse. Is it okay to jumper across it until I can get a new fuse?

A. Absolutely NOT!! The fuse is there as a 'safety valve' to prevent more catastrophic damage, or even FIRE, should the equipment be allowed to sink the full line current into what may be a shorted diode rectifier or a shorted output transistor. Doing so will garantee greatly increased damage to the amplifier, most likely destroying the power transformer in the process. Bypassing the line fuse can convert what may have been a $80 repair into a $500 or higher repair. Here's a hint about fuses and discerning the failure mode: with glass fuses, it is possible to see the fuse 'wire' inside. There are two ways a fuse can fail: from fatigue due to underrating, and catastrophic. A fatigued fuse will generally not have blackened carbon deposits on the inside of the glass cylinder. Often, you can replace this fuse and give the amp a try. If the fuse turned black inside, that means a lot of current went through it, as in, it tried to supply current into a dead short. When you see a blackened fuse, it is highly probably that the amp has a serious problem with the power supply or output transistors. You can try replacing the fuse, but it's nearly certain that it will fail again. The amplifier needs to be serviced.

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We buy large batches of transistors, from which we grade on curve tracers to find matching sets. Matching is important both for lower distortion as well as longer lifespan.

 
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Some quadraphonic receivers feature a hall acoustics simulator. When this is engaged, you won't hear an accurate replica of the program from the rear channels.

 
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Older tuners need alignment. Often, a good realignment can restore sensitivity, selectivity and reduce distortion for better FM listening. We do this with a spectrum analyzer.

 
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Did you know that the thermal paste on vintage amplifiers often dries out and becomes less effective? Replacing the thermal paste is one of the steps to restoring.

 
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Vacuum tubes are the foundation of classic audio systems. Many people believe that they provide a smoother, mellower sound, that is less harsh and irritating, producing less listener fatigue over many hours of listening.

 
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Checking the square wave response of an amplifier provides an "at a glance" look at overall performance in the frequency domain. Any rounding indicates poor high frequency response. Downward tilt indicates poor low frequency response.

 
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Single-ended triode amplifiers can be susceptible to magnetic interference from transformers and electric power lines nearby. The directly heated cathode is free to vibrate like a guitar string and since the plates are made of steel, alternating magnetic fields can affect it.

 
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What are those strange noises I hear in the background when I call you? That is Yuki-bird, our African Grey Parrot. A prolific talker and sound effect maker, she often hangs out in the shop and critiques our work.