My question is further down in bold.
Hello everyone - I'm new to these forums and hope they'll prove to be useful as it seems to have helped a lot of you.
I'm also (relatively) new to electronics. While in high school I took some classes in electronics, so I have a basic understanding of it. And I'm also studying an engineering program with a pretty good amount of physics in it. So I have a theoretical understanding of what's going on in electrical circuits. Up until now I haven't really seen any benefit of knowing electronics.
What's different now?
I want to build myself a tube amp for guitar.
I'm trying to understand the design of the schematics I've read and how to alter them in a proper way for my own projects. I understand there's a certain level of complexity in these circuits - and I'm not here to learn how to develop similar circuits from scratch. I just want a working knowledge of how to alter them for my own needs.
Ultimately I want to build a guitar amplifier with a preamp based on channel 2 from a Mesa Boogie three channel Dual Rectifier, vintage model/gain/voicing setting with a solid state rectifier and "bold" power settings, paired with a ~5 watt, or so, preferably 6L6 power amp (based on the fact that I've had my best experience with 6L6 amps). The key to this is the word ultimately, as in "not next week, or month". I do not wish to do this to save money, but as a learning project.
Question: I've been studying power transformers. The primary 230 VAC, secondary lets say 190-0-190. I imagine three leads. Two with voltage peaks at 190 VAC, and one center with 0V. When rectifying the power transformer there are loads of schematics that measure ~300VDC (unsmoothed). How does that work? How can I get a higher DC voltage from a lower, but rectified, AC voltage?
Thanks
Hello everyone - I'm new to these forums and hope they'll prove to be useful as it seems to have helped a lot of you.
I'm also (relatively) new to electronics. While in high school I took some classes in electronics, so I have a basic understanding of it. And I'm also studying an engineering program with a pretty good amount of physics in it. So I have a theoretical understanding of what's going on in electrical circuits. Up until now I haven't really seen any benefit of knowing electronics.
What's different now?
I want to build myself a tube amp for guitar.
I'm trying to understand the design of the schematics I've read and how to alter them in a proper way for my own projects. I understand there's a certain level of complexity in these circuits - and I'm not here to learn how to develop similar circuits from scratch. I just want a working knowledge of how to alter them for my own needs.
Ultimately I want to build a guitar amplifier with a preamp based on channel 2 from a Mesa Boogie three channel Dual Rectifier, vintage model/gain/voicing setting with a solid state rectifier and "bold" power settings, paired with a ~5 watt, or so, preferably 6L6 power amp (based on the fact that I've had my best experience with 6L6 amps). The key to this is the word ultimately, as in "not next week, or month". I do not wish to do this to save money, but as a learning project.
Question: I've been studying power transformers. The primary 230 VAC, secondary lets say 190-0-190. I imagine three leads. Two with voltage peaks at 190 VAC, and one center with 0V. When rectifying the power transformer there are loads of schematics that measure ~300VDC (unsmoothed). How does that work? How can I get a higher DC voltage from a lower, but rectified, AC voltage?
Thanks
Is there a common practice in how many times you're supposed to smooth the DC voltage? I'm thinking RC smoothing (resistor-capacitor) , and that one RC stage is using one resistor and one capacitor. How stable does the voltage need to be?
I've seen four stages in most guitar amp power sections. Any comments on that?
I've seen four stages in most guitar amp power sections. Any comments on that?
vivid said:
One RC section will certainly smooth your rectified DC, and an LC section works even better if you want to spring for a choke. More RC or LC sections yield more smoothing, but drop volts and increase the output impedance of the supply. Some folks go for a low impedance output with a little more ripple, and some go for extra filtering sections to get the DC as flat as a pancake. If you add RC or LC sections for a given output B+, you'll need to start with more transformer volts.
BTW: 1.414=squareroot of 2
Download and play with Duncan amps power supply designer II (PSUDII) here:
http://www.duncanamps.com/psud2/index.html
It's free, easy to use, quite accurate and there are lots of people here to help you with PSUD. A great learning experience. It will show you what you will end up with as far as ripple, B+, etc. Use a current load instead of a resistive load.
Yes, good advice, use PSUD2. To get the best results, know and enter in the program the DC resistances of your power transformer primary and HT secondary windings. A lot depends on these values.
Put in a delay of a few seconds before reporting, because your filtering capacitors need time to charge up.
The 1.414 factor from AC RMS voltage to DC voltage assumes that the smoothing filter begins with a capacitor, by the way (e.g. C-L-C or C-R-C). The rectifier charges up the firct cap to the peak voltage (which is 1.414 x RMS voltage). The first cap slowly fall as it discharges into the load, until the next peak comes along and it gets charged up to the peak voltage once again. This happens 50 (or 60) times a second. So, the ripple has a 'sawtooth' waveform, which subsequent filtering stages help to smooth out.
Put in a delay of a few seconds before reporting, because your filtering capacitors need time to charge up.
The 1.414 factor from AC RMS voltage to DC voltage assumes that the smoothing filter begins with a capacitor, by the way (e.g. C-L-C or C-R-C). The rectifier charges up the firct cap to the peak voltage (which is 1.414 x RMS voltage). The first cap slowly fall as it discharges into the load, until the next peak comes along and it gets charged up to the peak voltage once again. This happens 50 (or 60) times a second. So, the ripple has a 'sawtooth' waveform, which subsequent filtering stages help to smooth out.
Thanks for the answers. I'll make sure to play around with PSUD.
I've got another question on the B+ voltages. There are several B+ voltages in the power supply (B+1, B+2, B+3, etc). I understand that the voltages are different after more stages of filtering, but what deciedes which B+ voltage is used in a certain gain stage?
I've got another question on the B+ voltages. There are several B+ voltages in the power supply (B+1, B+2, B+3, etc). I understand that the voltages are different after more stages of filtering, but what deciedes which B+ voltage is used in a certain gain stage?
Any ripple in early stages will be amplified by subsequent stages. Therefore the supply for early stages must be the most filtered, and therefore will be of the lowest voltage, assuming the usual sequential arrangement of filters.
In other words, lowest voltage for the first input stage, highest voltage for the final output stage.
vivid said:
Ripple will be low level hum at your mains frequency X2 so either 100Hz or 120Hz depending on where you live.
Your required B+ depends on your tube choice, operating mode (triode, pentode, UL) etc etc. Do you have a schematic that you can post?
It may be worthwhile for you to find an appropriate schematic of a 6L6 based guitar amp circuit, build that, and then modify as you gain experience. There are loads of 6L6 based designs around, I'm sure. Since you only need one output channel (mono for guitar), costs should be very reasonable since you only need one output transformer, etc. The schematic will drive your requirements for B+ for each stage.
Build it as a breadboard on a chunk of plywood, that makes it easy to modify and if you decide you want a different topology, just unsolder and start over. The tubes, sockets, transformers are completely recyclable for different 6L6 based designs, although you'll probably need different R and C values for different topologies.
I will second the AX84 link, loads of useful designs. Everything from low watt single ended to high output push pull. I am in the middle of a 6V6 push pull design from this web page now for my son (the 6V6 PP power amp with lead pre-amp). Designs are presented with schematic, chassis layout templates and turret board templates. Makes it much easier for a new builder to get a good result.
Chris
Chris
Thanks for the tip. I've already been surfing that site for a couple of weeks now, studying schematics and other info they have there. Unfortunately I think their forum/BBS is in a terrifyingly bad format, so I'd rather post questions here.
I'm trying to understand how to alter the circuits. I think I would be able to change the output tube only without touching the preamp circuit. But when adding removing gain stages I'm not sure how this affects the circuit.
That's why I want to know how to determine what B+ voltage to use for a SE one-tube power amp working in triode mode with a preamp section containing 5 gain stages and a cathode follower.
The big thing isn't to just build it - I want to have a certain degree of understanding of what happens in there aswell.
I'm trying to understand how to alter the circuits. I think I would be able to change the output tube only without touching the preamp circuit. But when adding removing gain stages I'm not sure how this affects the circuit.
That's why I want to know how to determine what B+ voltage to use for a SE one-tube power amp working in triode mode with a preamp section containing 5 gain stages and a cathode follower.
The big thing isn't to just build it - I want to have a certain degree of understanding of what happens in there aswell.
vivid said:
To determine B+, you need to look at loadlines for the tube in question, which are on the datasheets. Most datasheets also have typical operating conditions (and component values) for triode, pentode, cathode bias, fixed bias topologies, etc.
To find datasheets, go to Duncan's amp pages, TDSL tab, enter your tube, and look at the bottom of the page for links to datasheets. It sometimes pays to look at several data sheets (mullard, philips, etc)
Building an amp with 5 gain stages from scratch as a first attempt is potentially setting yourself up for disappointment, as you will likely have stability problems. Pick up a copy of Morgan Jones' "Valve Amplifiers" 3rd edition if you haven't already, and read, read, read. My copy is falling apart from me reading it about 5 times, and I haven't considered a "from scratch" design yet. I have built several amp projects posted here, and have learned a boatload doing it.
There really is no substitute for building something for quick learning; it's the difference between reading about how to ride a bicycle, and riding one.
I guess you're right. I just don't want to be stuck with a power transformer that is insufficient for what I may want to expand a simpler amp into. Also I don't want a too powerful transformer which will give me unnecessarily high voltage, higher cost and more weight.
What would be appropriate for powering 5x12AX7 and one SE 6L6?
What would be appropriate for powering 5x12AX7 and one SE 6L6?
Did you look at the "core" projects at AX84? There are a bunch of separate pre amp projects that connect to a bunch of different power amp projects. Just marry the two. Loads of SE and PP choices. I would start with something proven, learn while building, then modify or build something different as experience grows. You must learn to walk before you run...
The HT used for the preamp is not critical. Once you get over 200V you can voice the preamp for whatever tone you want, you don't need to worry about it that much.vivid said:
It's the power valve/s that really determine what power supply you need. Single ended amps usually require somewhat lower voltages than push-pull amps using the same valves. (SE around 250V to 350V, occasionally more with bigger bottles). Once you have that sorted then the preamp voltage will follow on naturally and will ultimately be a bit lower in value. See also: http://www.freewebs.com/valvewizard1/smoothing.html
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