And now for the world’s most famous IC – the 555 Timer
This Signetics – Hans Camenzend IC was not just a best seller but for electronics specialists possibly the most versatile chips of it’s time. Possibly still is. What was most intriguing was that for any youngster just starting out in electronics, this was an experimenter’s dream. It was low cost and with just a handful of components one could learn one helluva lot about oscillators (astable or free-running), bistables and monostables. Of course it could be used for a lot more than just a police siren.
If you read the previous article on how quickly we can become deaf through negligence or just plain stupidity (like this scribe) I have managed to get some gems together for the DIY types.
Firstly, for those wanting to repair car amplifiers, Perry Babin has done an incredible job in keeping to the facts and make his tutorials available for free or chargeable as a download. There has been a lot of time and effort going into this so full marks to the author for doing such an amazing job. I guess the best way to get started is from this link: Basic Car Audio Electronics. Continue reading “Car Audio – More on amplifiers and SMPSU”
Some scientific types believe that the walls of Jericho fell because of resonance. In a few years from now we are going to be seeing a lot of hearing loss amongst generation-Y and Millenials. Generation Baby Boomer may well be exempt except for the musician variety. Many musicians today suffer from tinnitus. The frightening aspect to all of this is that it can happen to anyone, especially those subject to loud music on a day to day basis. When wearing headphones on a day to day basis one would think that a feedback system would warn the user when dangerous SPLs are being generated but no.
Above: If this is what the Yellow Pages looks like after a few seconds imagine the guy’s cochlea.
The problem with headphones is that we do have a tendency to use them at a level which may not seem uncomfortable at first but will cause damage over a prolonged period. And one doesn’t know until one day you find yourself asking someone to repeat what they have said. Over and over again.
I touched on the subject of Jericho specifically because of the ease at which large structures can be made to resonate and cause untold damage. The human body can be broken down to various sub-parts each with it’s own resonance and the chest and surrounds are believed to be at that very frequency where our modern car audio culture is aiming – deep high powered bass. Okay, this is opinion only, I am not a scientist neither the most knowledgeable about the human anatomy. There has been research done in this field and it seems credible that high powered audio will not only damage your hearing but other parts of the body as well. In fact disintegration is highly likely.
Audio Outputs for auto sound
In the 70s car audio would in all likelihood be working around powers of about 4.5W RMS into a 4 Ohm load using our wonderful formula (Vcc * Vcc) / 8RL. Supply rails at 12V. At 13.8V we are looking at about 6W, 12W into a 2 Ohm load and 48W bridge tied into 2 Ohms. The thing is I don’t really recall many car audio systems being bridge tied until the 80s. 20W into 4 Ohms was more or less the norm and this was loud enough. Why then ramping the supply rails up to +40/-40V and into a 2 Ohm load? Marketing is a fairly reasonable assumption. Youngsters of today compare sound systems and the likelihood that they are making comparisons based on quality rather than raw power is negligible. Power is king.
Upholstery sound killer
Upholstery kills the high notes. We do not have a pre-emphasis feedback system which will crank these registers whilst applying attentuation to the bass. Listening to rap music at the traffic intersection is a case in point. Loud belching, farting, burping like sounds emanating from the car next to you is not uncommon. The thing is, and I mean this in all sincerity, what is it doing to you listening to that hellfire and brimstone spitting sound system? Having good acoustics is the first point of action.
Insane power levels
To Mom and Pop 10W per channel was more than sufficient and when they hit their 70s and if they were in good health their hearing mechanisms were usually intact.
New York band Manowar hit the SPL charts a few years back when they reportedly spewed out enough power to push dB meters to nearly 130dB. This is insane. Car audio enthusiasts see this as small puppy. Pushing levels to nearly 140dB at a few hundred Hz is common. And they drive playing at this level?
Our conversation level is usually at around 60dB, jackhammer at around 105dB and explosive power tools at around 120dB (nail guns). Ford Bronco with a 48kW sound system generating an SPL of 175dB? Utter madness.
Marketing the stuff
Ironically the best audio is found in luxury vehicles. Money spent on quality and not quantity.
Using the first article to get our creative juices flowing I found some more well written well designed amplifiers using tubes and semiconductors.
The design link below shows various permutations to feed a high voltage swing with little distortion to an emitter follower output stage. This circuit, titled Hi-End Hybrid Amplifier 100W uses a high end K&K solid state current generator (source) in series with a pentode voltage amplifier. The tube in this case can be a Siemens D3A or Russian 6C45.
OK, so what is our pitch here?
High safety margin, for a 100W amplifier using 4 x MJE15032 and 4 x MJE15033 output transistors in the output, the input to the current amplification circuit is through a capacitor (DC block) from the voltage amplifying pentode and an LM308 op amp for stabilising the DC offset at the output, removing the need to apply manual adjustment.
The MJE15032/MJE15033 can be obtained at a good price from Mantech (Communica advertise only the PNP at R17 each excl).
An auto-bias heater filament Mosfet load headphone amplifier
Quite a mouthful but nice clean design pulls all the stops in hybrid design. Design found here.
Hybrid vacuum tube/solid-state audio power amplifier
Nice design which will break the bank amplifier found here – this amplifier uses an 6AN8, a pentode-triode combo. The output devices are BUZ900 and BUZ905. The 6AN8 may not be that easily available in South Africa but the good news is that Mr. Valve lists this valve for R150.00. Based in Pretoria, excellent service.
The BUZ900 and 905 are expensive, TO3 equivalents include the Hitachi 2SK134 and 2SJ49. Available (no price given) at Mantech otherwise Yebo listed as ECF20N20 and ECF20P20 going for over R300 per pop. Ouch! Note that these are lateral type MOS devices and because of the TO3 can this amplifier is ideal for experimenters wishing to modify the output stage with cheaper alternatives. After all, we are looking at the voltage gain devices, chiefly pentodes driving Mosfets.
Tube and Semiconductor Combos – the best of both worlds
An interesting project on the web is that of a 6SN7 Mosfet audio amplifier capable of delivering 50W per channel. The article, written by Simon Brown is called Amplifier War and Peace – An Hybrid Amp
I am not a big believer in that tube amplifiers are so much better than that of solid state but I do believe a properly designed amplifier using both devices can address problems, both in sound reproduction and ease of build.
What I DO like about tubes is the almost ease at which one can build a pre-amp or power amp by simple point to point wiring. This type of wiring is also notoriously the best way to build these amplifiers – easy to change layout, reduce noise, unnecessary oscillation and to modify at a later stage.
The project, found at Audio Xpress features two 6SN7s in a current source configuration driving a complementary pair of Mosfets, IRFP140 and IRFP9140. All aspects to the design are covered but the author does warn that it’s not for inexperienced builders. Here of course we must also make mention that the V2 is running at 300V on the anode. The power supply is well thought out. The entire project can be built on prototyping board.
Another project which caught my eye and also under Audio Xpress is that written by Stephen Moore – A Hybrid Valve MOSFET SE Amp – Complete Project. With a smidgen of Nelson Pass in the constant current source and gate bias circuitry we, like the above circuit, have two 6SN7s or similar acting as the voltage gain stage to drive the source follower IRFP2907Z. (using the John Broskie Aikido amplifier approach).
Both these articles are very well written with a lot of insight and explanation as to the shortcomings of Mosfet output devices, work arounds and just as important, driving these devices with high voltage swings from tube devices.
The Taga HTA700B V2 SE Hybrid amplifier boasts the following:
Power Output: 2x45W RMS / 4ohm; 2x35W RMS / 6ohm; 2x26W RMS / 8ohm Class A/B
Vacuum Tubes: 2 x 12AX7B
THD: Less or equal 0.1% (at rated power) Signal/Noise ratio: =>88dB
Frequency Response: 20Hz – 28kHz
Inputs: RCA stereo CD, USB (for computer)
Outputs: Stereo RCA with variable volume control
Connectivity Wireless: Bluetooth® v4.0
Bluetooth® Profiles: Advanced Audio Distribution Profile A2DP
Headphone Impedance: 32-320Ω
Headphone Output Power: 1W 160Ω
USB Supported Data: Asynchronous 24bit / 192kHz
True high-speed audio processor CM6631A
DAC Cirrus Logic CS4344 chip
Included Accessories: Bluetooth® antenna, USB cable,
As an addendum to our previous article “Alternatives to Tube Output Transformers” we thought it pertinent to add a bit of local flavour, Mars Amps in Paarl to the mix. No, I have not met the gent but Karel Mars is a well known tube guru in the country and lends his expertise to the DIY community either through workshops or on the local avforums website, found here. (OPT winding).
Mars Amps has a variety of tube pre- and power amplifiers available in kit form, shipping both locally and internationally.
Output transformer alternatives – the long and the short
This is a topic often coming up in audio circles and yes, we can use a mains transformer to drive a speaker and no, it’s not a drop in replacement.
Getting down to the basics, a tube audio amplifier comes in two flavours – high fidelity, getting the best out of vinyl and secondly, dedicated guitar amplifiers which serve one purpose – distortion. I am of the brigade which believes that one gets what one pays for, a good quality audio amplifier relies on an exceptional output transformer. Tube amplifiers designed for distortion do not rely on huge, bass performing quality transformers. They do however need to be reliable. Continue reading “Alternatives to Tube Output Transformers”
As mentioned in a prior article, Class D amplification is nothing new, modern switching components and topologies paving the way to resilient and high quality amplification circuits.
We can also draw a parallel between modern switched mode power supply design, H-Bridge motor control and that of Class D, all benefiting from newer ultra fast switching transistors, the bug-bear of the first class D and switching power supplies. Continue reading “Class D Chips”