come and get some nice audio and test equipment
come and get some nice audio and test equipment
Join us for our first meetup. Meet Roger, Meserve and Matt and others interested in High End Audio. DIY welcome.
Thanks to Mark for a well organized event in an excellent venue. We were in an open floor plan office which also has many small rooms for demonstrations. His staff was well organized, friendly and very helpful. We had great food and interesting conversations. I highly recommend this event.
Here is the video of my talk. Thanks to Mike for doing a great job shooting the presentations and providing great sound. Here is the link to my talk which starts at 11.20 minutes on the time scale and goes into the beginning of Nelsons video. It looses sound near the end but I was pretty much done . Roger’s Talk
And here is Nelson Pass doing his thing Nelson’s talk Nelson talks a bit about Schade Feedback which I had read about in the 1938 paper from RCA when they announced the first beam tube, the 6L6. He cast a new light upon that information for me. He is using the concept in the amplifier he presented at the talk. As always, Nelson is discovering new devices and circuits.
Here is a link to Shade’s landmark paper of 1938, the invention of the Beam Power Tube (6L6, 6550, 6V6 and the KT series). See page 360 for the feedback. The earlier part of the paper is the design of the tube with the classic drawing of the beam forming on page 346. It’s a very technical paper so don’t let it bury you. Schade 1938 RCA
Explore Mike’s youTube for other video of the event.
At the sale I picked up a really clean SoundTech distortion analyzer for the school lab.
Hello Bay Area Audio Enthusiasts,
We are finally out of Santa Barbara and located in lovely El Cerrito. I am available for helping tune your system in your home or for repairs at the shop. You can also buy tubes in person. Write me at email@example.com to arrange a mail order or pick-up. Intern positions are available for both the business and school.
The Berkeley Hi Fi School will be offering classes in the late fall/early winter. We are working on a text book to accompany the classes. Every modern book I pick up has incorrect information about amplifiers and how they work. The internet is of course worse.
I am finding that many listeners do not know how to identify large amounts of simple distortion. They tend to think it’s something else like bloated bass or poor imaging. There isn’t much talk about distortion in the magazines and forums and most of what I read is not correctly stated. I have personally observed cases where a group of listeners were not able to identify distortion that was in excess of 20%.They were good listeners, just not trained in what distortion sounds like.
At the Hi Fi school we will listen to various levels of distortion from various sources. We will hear that second harmonic distortion is not benign and that small amounts of crossover distortion are very obvious. This whole story of high order harmonics is horribly misstated. When amplifiers create distortion they do it in specific ways. Speakers do it in entirely different ways. The way distortion is created is more important than its order or percentage.
Anyone who has time and interest to get involved with the school please contact me at the above email. We need some help in everything from organizing the space, updating the website, enrollments and special events. I am here to share my years of experience in audio but I can’t do everything. I have several new designs that I would like to see go into production. Help with producing and marketing those would be appreciated. Helpers will receive free classes and discounts on equipment.
I am also teaching Kinetics and Electronics at The Crucible in Oakland and an afterschool basic electronics and magnetism at Madera and Harding elementary schools in EL Cerrito. Let your friends in the area know about these classes.
We have a position available for a class enrollment manager who will coordinate enrollment activities including:
Compensation is free tuition toward any course offered and the opportunity to create a course of your own interest.
I am offering a small class of 2 or 3 students to teach to understand, make and fix amplifiers. Tuition is $50 per hour for 2 students or $40 per hour for 3 students. We will get a lot done in a small time. This will be customized to the students needs. You can bring amplifiers to repair or modify. I have two benches fully equipped.
We are having the first class on Sunday Feb 21 starting 10am-1pm for the lecture part of the class. That part will cover amplifier basics, reading schematics, learning typical voltages for troubleshooting. After Lunch break we will have the hands on class limited to 3 students working on the bench with my assistance.
Later in the spring we will be working on the amplifier described below. We are still waiting on delivery from China.
One of the students has ordered a Chinese amplifier kit that we can measure and improve in the class. This one will run $314 with shipping.
In my opinion this one is is a better deal at $200 with shipping. The output tube is similar a 6L6 and can use any 6L6 or 6V6. In the class you will learn about these tubes. This amp may be lighter hence the lower shipping cost.
Here is more information on the 6P3p amplifier including schematic. Being handwired this is an easy amp to modify and improve.
Here is the data for the input tube which is similar to a 6BQ7 and a close sub would be a 6922.
Here is the data for the output tube which appears to be close to a 6L6 and we can use a 6L6.
Please visit the new Music Reference forum on Dagogo. I have moved the Music Reference forum from Audio Circle to Dagogo as the fire got too hot for JonR over cables and fuses. Science went out the window. Your participation is appreciated.
Interesting article about the joy of fixing things.
We are looking for students for a Saturday morning (9-12) and afternoon (1-4) class (6 hours with 1 hour lunch break) to learn hands on repair of guitar and HiFi amplifiers. Students will learn how to analyze circuits, make measurements, substitute components. Tentative start date February 28, but negotiable once the students apply. Cost is $40 per hour. You can bring something to fix and do it yourself for less than having someone else do it. Space is limited to 4 students. This is a very special opportunity to learn from a EE with over 45 years of continuous experience in all areas of electronic and electric appliance repair. Roger taught this course in Santa Barbara to a larger class for 5 years with great success. The class is intentionally small so that your specific needs and interests can be addressed.
For the Audiophile there will be an 8 week class, Saturday 9-12,write for start date. Each class will take an in depth look at each part of the system from source to speakers. Students will have an opportunity to take test equipment home to check their system response. Cost $240
Recently added to Resources:
Teaching electronics to a group with a widely mixed background is a challenging job. What I have written below, and will in the future, contains material that addresses this wide range of interest and background. Some students may understand all of it and some may be happy to get just a few bits of wisdom. I encourage you to read all of it and not get hung up on the deeper technical points. If you are a beginner all you might learn is that a speaker’s impedance can be all over the place and that some amplifiers don’t like that but some do.
Impedance is just like resistance except it includes a frequency factor. We use the term resistance for DC measurements or for things like resistors that do not change with frequency. Things like light bulbs, space heaters and wire are usually used at DC or low frequencies where the resistance is constant and can be measured with an Ohm Meter. Ohm Meters use a battery to force a current through the resistance, measure the resulting voltage drop and use Ohm’s law to calculate the resistance. This is a very simple thing for an analog or digital meter to do. However to measure impedance we need to provide an AC current. This is not so easy. By now you have probably realized that unlike mechanical things where we can watch them work, move levers and wheels, with electronics there is nothing to see. We use meters, oscilloscopes, generators etc to measure things and some things are easier to measure than others.
DC measurements are easy. AC measurements are a bit harder and complicated by the fact that the resistance may vary with frequency, this is when we call it IMPEDANCE. The first problem with measuring impedance should be obvious. At what frequency do we measure it? Once we know that is varies with frequency we have to ask at what frequency or range of frequency are we going to measure?
If the device we are measuring is going to be plugged into the wall we would simply measure it at the line frequency of 60 Hz as that is our power in this country. It would not be too difficult to make a meter that did that. It would be just like a DC ohm meter but have a 60 Hz sine wave generator in place of the battery.
A more interesting example is a speaker. Since we use a speaker over the audio band of 20 Hz to 20 KHz we might want to know its impedance so that we can connect it to an appropriate amplifier or tap on a tube amp. Because the impedance is not constant we might want to know how high and high low the impedance goes. A typical 4 ohm speaker’s impedance might be as high as 50 ohms and as low as 2 ohms. While an amplifier is not bothered by high impedances, as they draw less current, it may be very unhappy and distort when the impedance gets very low as now it has to provide more current than it can. In your home when you try to draw too much current from the wall it trips a circuit breaker. In an amplifier it may blow a fuse or simply limit the current using its internal electronic protection. Unlike a circuit breaker that has to be reset, electronic protection does not and often does not indicate that it is active, however you will hear it as distortion, or in some designs, a relay disconnects the speaker but usually resets itself automatically in a few seconds. Load line protection just clips the signal and there is no indication other than what you might hear.
Modern Home Theater amplifiers do not like low impedance loads and will usually indicate a fault on their menu screen. Sometimes this fault says “check speaker wires for shorts” because it thinks you load is a short!. These amplifiers are very sensitive to low impedances as they have rather weak power amplifiers that need a lot of protection. Even though they may be rated at 100 watts they may protect way below that level into difficult loads like electrostatic speakers making them useless for that application. When we are driving a device with a voltage we typically call it a load because energy is being expended and work is being done. The work of a speaker is to make sound, the work of a heater is to warm air, the work of a light bulb is to provide light. All these things convert electricity to something else.
Now how do we measure the impedance of a speaker or some other load whose impedance varies with frequency? We have to set up a test circuit using a variable frequency oscillator, an AC volt meter and AC amp meter. We then measure the voltage and current at frequencies of interest and use Ohm’s law to calculate the result. With a speaker we may just want the high and low impedances. With modern automated equipment we usually run a sweep from 20 to 20 Khz. and plot the result. Here is an example of a speaker impedance curve.
The solid dark line is the impedance (read on the left side) which goes off the chart below 100 Hz. The dashed line is the phase (read on the right side) which almost goes to 90 degrees indicating the load is a capacitor at high frequencies. This phase angle looks like a short to electronic limiters and will cause severe distortion with most transistor amps. Tube amps do not have limiters and will play this load. This is one reason that tube amps are preferred with electrostatic speakers.
Note that this Electrostatic speaker goes below 1 ohm at 20 Khz and is only 2 ohms at 8 Khz where trumpet music may cause the amplifier considerable distress. This will be covered in depth in the complete course on power amplifiers.
Part Two will address impedance matching… a very popular and poorly understood topic on the forums.