Introduction
Greetings to all who have come here. My name is Jim Conzett. This is the future location of my Zentode© project. You will be able to see what all this is about soon. Analog circuit related design for now. That’s where I have the most resources available to me. Additionally, those of you with your own designs can share them here. I prefer to see audio related stuff posted here. That said, I will create a category for anything useful! Why cap the information here with my limited knowledge! I am providing this area to everyone interested in sharing their ideas.
So Jim, what’s up with all this and why?
OK, here’s a quick explanation; I started playing with electronics back in the late 60’s. My father worked for NCR (National Cash Register) up in Dayton Ohio. He was an engineer who was there as machines evolved from totally mechanical through the introduction of transistors and integrated circuits. I always had a plethora components and tools at my disposal. I also had the luxury of picking my dads brain when I had questions. Not a day went by that I didn’t make (or destroy) something. I was fascinated with electro mechanics and computers. Some of the computers at the time read data from reel to reel paper tape with perforations in it. Light from a bulb could shine through the perforations to transfer the data! Hard drives, floppy discs and memory chips were still being developed and cassette tape was the “holy grail” of data transfer. I still laugh when I think about that versus what I am typing this up with.
I was really into making things that either lit up or made noise. The instant gratification factor of those types of circuits was probably the reason I continued to experiment. To make a life story short, I ended up repairing items for people in the 70’s. I also made my own guitar effects and sonic gizmo’s like theremins. I have done this stuff all my life now. From my early years to real jobs like making anti chemical warfare personal protection devices, production manager of a military contractor, building satellite news gathering vehicles, designing electronic water purification units, designing high frequency pesticide alternatives, writing procedures and managing the component prep department of for ground fault circuit interrupter company, building up to 200 computers a week in a factory then finally becoming the lead man in a machine shop where I built (and designed components for) pneumatic robotic applicators and hand tools for Molex. Yeah, that’s the short version. There is much more.
Needless to say I never went to college, I was too busy making money. Sad part of all of that is, I have nothing to show for all my experience (including a bank account) except what I will bring to the table here. Mostly that is my fault for being too passive and trusting I guess. Additionally, I seem have a talent for being in the wrong place at the wrong time. I can also point a select finger to N.A.F.T.A. (North American Foreign Trade Agreement) for putting me out of work. I have served my time in corporate, this effort will be mine. Enough about all that. Time to move on.
Moving On
Tubes….how many configurations are there for 7,8 or 9 pins? Just as how many ways can you arrange a few notes to make a different piece of music? (Please, no-one reply with the answers!) Considering the use of solid state components in a tube amp, where does their use deem an amplifier as a hybrid? In the power supply? Short circuit protection? EQ or biasing? Do I really care? Nope… I have said this before and I will say it again: “Getting something to work is easy, making it applicable in the real world is the hard part.” Like writing code in PERL or PHP for example. It’s easy to write code for a form that returns a users entered word. It’s hard to write in all the possible variables of what the user could enter or “stray paths” around root routines. Not to mention the inevitable attempts to circumvent, server, O.S. and browser variables. Just like making a circuit, you must design around the factors that will cause undesirable behavior. Unlike code however, an electronic device, that you expect someone else to actually buy, should be reliable and designed around components that can be replaced. (Calm down you code heads, subroutines and modules I know.) The thing also must be idiot resistant. Yes, resistant, nothing is idiot proof.
My Attempts of Tangibility
After years of repairing audio gear, I have actually learned a little about what breaks and/or what doesn’t work well. Also, what ideas, components and designs seem to hang in there over time. I wanted to make my “products” unique in the fact that not only are they my designs but, they are efficient from board level to box. Efficient like: not just throwing huge expensive caps after some noisy diodes. Efficient like; using parts that are available. Efficient like; best means of using whatever power is available. Also efficient in how much bang you get for each buck. Great concept, right? I really thought so. However, after a few prototypes, “component balls” and years of research, I have found that there is really little I can do that hasn’t already been done. Maybe not “arranged” in the same manner but, I again ask; how many notes are there to compose with? I have searched and searched the net. I have viewed hundreds of schematics, DIY and websites containing info from some guys who are absolute geniuses. I have talked to many who are way better equipped with high end scopes and spectrum analyzers. That said, I have heard some great amps that were made before some of that stuff was even invented. My hat’s always off to the guys who can, and do, explain some of the math behind my madness. I beseech you. My zen resides in my creations. My meager knowledge, my 20Mhz scope and my desire to achieve my goals will hopefully produce something that many will enjoy. I do this because I like to, not to make a buck, obviously. I believe my commitment will open the door to what I’ll need to keep it going.
Inspiration
I have a Sears Silvertone 1484 tube amp. I bought it at a yard sale around 1983. I took it home, plugged it in and it didn’t work. I had no real means to get a schematic. I suspected a bad 6FQ7 tube being used as the phase inverter. It sounded OK, but not great. I boxed it up and put it on the “to do” shelf where it migrated into the “keepers” shed. I came across it again in 2005. I downloaded a schematic, did a cap job then tested each tube (all Silvertone!). That old 1484 sparked my interest in making my own amp….again.
Concept & Design
My first want was cool clean power. I had an idea inspired from a dead LED flashlight I once took apart. The efficient boost converter. Not only did the single 1.5 volt battery run the 2.5 volt LED, it ran it brightly and for a good while. I took apart some PC power supplies and dead monitors for some HV caps, resistors, coils, FET’s and stuff. I also pulled a PWM Pulse Width Modulator - TL494) IC from an old PC power supply and pulled its’ datasheet. I bread-boarded a simple boost converter running at about 50Khz initially. When the 12 volts provided 460v (@400ma load) right off, I pursued the idea. A couple tweaks later I had a PWM regulated 275 volts at .5amp boost converter that ran barely warm. (Except for the load resistor!) It was super efficient as well. Another possibly useful feature was built in shutdown. That chip was actually old news to everyone but, it guided my selection of features to consider. I needed to use a FET driver with that chip if I were to use it in my real world. I wanted the lowest component count and better efficiency than a HV transformer. (Or even using two transformers.) I did not want to sacrifice the dynamic sound of the tube amp in any way either. My tests proved to my ears that a tube based supply had no advantage over a solid state supply. The boost converter provided clean, quiet, cool and “safer” HV at less cost. I decided to use some variation of that idea for my tube plates. I made a note to overkill the relevant ratings of the single MOSFET used there to help assure decades of operation. After all, I won’t be powering 400 volt, current hungry power tubes, just pre and overdrive pentodes.
My second desire was clean power for everything else. I needed clean ac for a couple possible heaters as well as clean lower voltage dc for other areas. I like active filters in comparison to passive. Also bi/tri-amping instead of a tone/power stealing passive crossover. Got foot switch? Effects loop? Can’t stop playing to push a button so, I need to consider a zero crossing click free flip flop of some sort because; I want tube overdrive on command. I need power for that stuff, at least 1000ma.
My third wish is not playing through a mile of copper wire which is then magnetically transferred to another pile of windings through a chunk of metal. I also dislike the idea of matched quads and biasing issues. Ever plop a new $30 tube in an amp. Let it warm up a bit. Flip from standby and watch it glow red then implode before you could shut down? That really sucks. With FET and chip amp technology today, you can easily get to 100 Watts with minuscule distortion (the unwanted kind) in comparison to power tubes. Nowadays you can do that with lower voltages and way more efficiency. This allows you to pass your prized tube tone to the speakers without an expensive, inefficient output transformer. Do transformers contribute to, or hinder the tone? Well they are stepping on it by a few hundred volts so, I would assume that they suppress something. That’s my current opinion and I could be quite wrong. My attempt will not include an output transformer…..initially. Need power to run that block, about 35 volts per rail with a ton of current. The main limiting factor lies there.
Another basic requirement of mine is quality properly selected components. I can’t tell you how many things I have worked on that have used 1/4 or 1/2 watt carbon comp or film resistors far beyond their rated operating voltages. I have also seen mixers and amps made by supposedly high end manufactures that use filter caps with their maximum voltage run very close to the supply voltage, very close. I have also seen that same company push linear regulators at their maximum rating while bolted to a huge heatsink. I won’t even go into proper diode selection. That’s pretty poor design/manufacturing especially in audio gear.
I have seen allot of poor component selection over the years. No design is perfect though. I know a guy who bought a $1500 tube amp and it returned it the next day due to a ridiculously poor quality footswitch. There are always areas open to interpretation and many ways to perform the same task. However, blatant rule of thumb basic electronics violations are ridiculous. There is no excuse. You should feel secure that a $500 or more piece of gear uses the right parts. Where does the breakdown and blame begin? Did the engineer(s) use the wrong component? I find that unlikely. Was it drawn up and/or procedures written incorrectly? Possibly. Did purchasing buy the wrong parts due to lack of adequate information? I have seen that happen as well. Yes, it would seem that quality gets diluted between the original design and shipping. ISO, MIL or whatever paper trail does not seem to help although, I have seen less in MIL spec due to complete accountability all the way back to the source. So……. whatever I make, whether it has two components or two thousand, there will be no blatant component violations. If what I do here gets adopted by some machine, I will do everything in my power to make sure component selection is very specific. There will be a big red “No Substitutes” stamped on all drawings. Quality and continuous improvement is embedded in my thought process. Should I need four op-amps, I will spend an extra $6 per unit to improve quality. I will choose, to my best ability, the best part for each individual duty, not the least expensive.
Does size really matter?
That really depends what you are talking about doesn’t it? I’ve heard a tiny tube produce a fat sound. I have heard a 4 watt tube amp sound “better” than a 30 watt solid state amp. I have in front of me my one pound regulated HV power supply that replaces a 5 pound un-regulated transformer. I have heard a DIY $14 chip paired with a $10 tube sound better than many new name brand amps. That said, my old Silvertone 1484 sounds sweet to me. I guess it matters where your basis for comparison lies and what you play. However, frequency is frequency. That gourmet dish may taste great to some, like crap to others. You can’t please everyone no matter how good you think it is. When it comes to live instrument or vocal reproduction, producing a universally pleasing amplifier is difficult if not impossible. There exists a shotgun approach any designer must address no matter how specific the application. Accuracy may vary!
Pull!
There is a tube I wish to use for this. I have always liked the 5654 pentode. That tube is consistent, long lived, rugged and flexible (with leftovers). This is actually one of the few times where my preference was not the most expensive! These little tubes are available for less than a more “popular” tube too. In my opinion, they have more to offer to the big picture of the design. The Jack Russell Terrier of tubes. Now, A, B, AB, push pull, auto, fixed…… what!!! How much power do I have again? I will put one or two of these tubes somewhere in the middle. Yeah, that’s the ticket. This is where I will get my actual tube “air”. Hopefully.
Want Gyration?
Although using a single transistor gyrator circuit as a power supply filter for higher current applications grossly inefficient, I had an idea. The single transistor gyrator needs a good load to work. So much power being dissipated as heat. I have a couple tube filaments that would make a nice load and use the heat. Super clean power rails for my preamp/tone stage and my glass has clean DC on the heater. Could also supply a boost converter should I need one. Small parts count, small caps, better results but greater cost. I will experiment.
Update: I won’t be using gyration for filtering. The recovery speed at various audio frequency load levels directly changes the amount of “filtration”. The nine support components to compensate for that take up space and add cost. Although, the circuit I designed to work for this is still quite useful, the time and costs actually outweigh the effect on the end result. A result which proved too be barely measurable.
Final Stage
I don’t want an output transformer. FETS or a chip amp? Cost versus features. Oh yeah, the most important…sound. I am not relying on the amount of power to be a huge contributor to the “tone” so, the cleaner I can boost the output wattage the better. I will try a couple chip amps first due to the great convenient features they sport and their very minimal distortion. The old bang for the buck theory rears it’s head here. But how to they sound? How well will they pass my tone at ~50 times more power? Where is their supply power coming from again?
The Limiting Factor
My amps main limitations and cost can be summed up in two words: “power transformer”.
The bigger the boat, the bigger the boat anchor. Off the shelf or custom? How much at what voltages? Center tapped or separate windings? There must be a happy medium between how many secondary windings and buck/boost conversion options. Can I even get a transformer winder to consider working with me at such low initial quantities and budget? Tooling and engineering fees? Shipping costs? I have huge concerns here. It’s a make or break point. My regulated power supply circuit is very adaptable to many input voltages. Basically, just hook it up to the transformer capable of the amount you want in the power amp stage then add a generous 2 amps. Should be able to find an inexpensive tranny right?
Update!
Ya know, this really sucks. I have to go to Chicago or China to get my transformers made. Out off all the places that wrap wire around laminated metal, there are none who want my money locally. (Kind of like buying homeowners insurance. (I live in Florida.)) Got the cash, want some product, what?? Kiss my a–. Two grand for engineering fees? I’ll buy a surplus winder thank you. It’s not like I have not wound thousands myself, written procedures for, made fixtures and parts for them and ran the line before… No not me. I suggest a rockwell rating of 43 on the Heller die. Do I have to tell you where to set the oven, “draw down” times & temp/(anneal) quench procedure or is that a different department you dweeb. Go draw a box or yell at a poor minimum wager who has to sit there and take it. Ahhh, sensing a little hostility there? Passion to my cause.. Hopefully to a result dempt acceptable.
Closure
I am working on it!
Sincerely,
James Conzett
Founder, Zentode LLC.
