Hello,
I am in the process of trying to build a guitar amp. I am currently going to school for EE, so I have a decent handle on electronics. Because of this, I was originally leaning towards a SS amp, but after reading more and more I think i finally convinced myself to go for a tube or at least hybrid amp. Since i am new to vacuum tubes, I have a few questions:
1. If I go for a hybrid design, what is more important: a tube preamp or a tube power amp? I have heard conflicting views on this but no real information to back it up. any ideas?
2. Are there any nuances to using tubes that I might not be aware of? ive read the geofex FAQ, but I want to make sure im not missing something.
3. does anyone have any fairly simple schematics for tube amps that have good tone? I'm not opposed to mixing and matching preamp and power amps from different places, and also plan on making some of my own alterations to the circuits (ie 10-band EQ and potentially other effects), I'm just looking for some good starting points.
I already have 2 12" 8ohm speakers... These to be exact:
Eminence Cannabis Rex 12" Guitar Speaker, 8 Ohm, 50 Watt#
I was planning on using these unless theres a good reason not to.
If you need any other info about my plans, please let me know. I am very excited to get this project underway!
Thanks,
Matt
I am in the process of trying to build a guitar amp. I am currently going to school for EE, so I have a decent handle on electronics. Because of this, I was originally leaning towards a SS amp, but after reading more and more I think i finally convinced myself to go for a tube or at least hybrid amp. Since i am new to vacuum tubes, I have a few questions:
1. If I go for a hybrid design, what is more important: a tube preamp or a tube power amp? I have heard conflicting views on this but no real information to back it up. any ideas?
2. Are there any nuances to using tubes that I might not be aware of? ive read the geofex FAQ, but I want to make sure im not missing something.
3. does anyone have any fairly simple schematics for tube amps that have good tone? I'm not opposed to mixing and matching preamp and power amps from different places, and also plan on making some of my own alterations to the circuits (ie 10-band EQ and potentially other effects), I'm just looking for some good starting points.
I already have 2 12" 8ohm speakers... These to be exact:
Eminence Cannabis Rex 12" Guitar Speaker, 8 Ohm, 50 Watt#
I was planning on using these unless theres a good reason not to.
If you need any other info about my plans, please let me know. I am very excited to get this project underway!
Thanks,
Matt
You will get the information you need to build your first tube guitar amp by studying what others have done. A fantastic resource is Schematic Heaven
Schematic Heaven. Where All Good Amp & Effect Designs Await Resurrection...
You need to decide on a topology, a power output goal, and output devices to achieve that power. Output transformer selection, and power supply are equaly important design blocks and somewhere in there the pre-amp selection. I always recomend a line of books called "the ultamite tone",. this will literally lead you through the process while providing more than a little background. (theory). For parts, I like Antique Electronics Supply, lots of variety. They can sell you everything you need with the possible exception of the enclosure. Those are my favorite picks and how I got started. Be patient, gather up ideas first, then gather up parts. You might consider some kind of breadboard first. This allows for the inevatable changes befor you get too far. This can actually save a lot of time in the long run. Test equipment need not be eleaborite, DMM, scope, audio source. Lastly--- beware high voltages.
Schematic Heaven. Where All Good Amp & Effect Designs Await Resurrection...
You need to decide on a topology, a power output goal, and output devices to achieve that power. Output transformer selection, and power supply are equaly important design blocks and somewhere in there the pre-amp selection. I always recomend a line of books called "the ultamite tone",. this will literally lead you through the process while providing more than a little background. (theory). For parts, I like Antique Electronics Supply, lots of variety. They can sell you everything you need with the possible exception of the enclosure. Those are my favorite picks and how I got started. Be patient, gather up ideas first, then gather up parts. You might consider some kind of breadboard first. This allows for the inevatable changes befor you get too far. This can actually save a lot of time in the long run. Test equipment need not be eleaborite, DMM, scope, audio source. Lastly--- beware high voltages.
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Hi Matt, Have you poked around Tales From The Tone Lounge; The Home Pages of Tone Lizard Amplifiers
Thanks guys! I am familiar with schematic heaven as I have used some stuff from there for pedals ive made. I have a few breadboards and plan to use them. do you know of any good resources that spell out the differences between different amp topologies? I know about A, AB and B somewhat in terms of resistors. Also, Im looking for something in the 60-100 watt range...im not too particular about wattage, more tone. thanks again!
Matt
Matt
A PP pair of ElectroHarmonix (EH) KT88s will yield that sort of power. Edcor's CXPP50-4-3.4K O/P trafo seems suitable working into your speaker drivers, connected in parallel.
Do you really need that kind of power? Are you planning on filling Yankee Stadium, by yourself? With 102 dB. sensitive drivers, like those you have, 2 WPC would be quite adequate for HIFI purposes, in an "average" sized listening space. Be aware that PP KT88 "finals" will require about 475 V. of B+.
A mistake with that can easily get you killed.I sugguest you start off with the Fender Tweed Champ. It'll get you a long way both learning and tonewise. Once you get it working, maybe add a tonestack and you'll have weeks of fun fiddling around with that.
Then maybe build a Plexi 6V6 or something like that. Perhaps a 18 Watter, those things are great!
It's about trying out different things, and learning as you go on. Start small, it'll be much more rewarding.
Then maybe build a Plexi 6V6 or something like that. Perhaps a 18 Watter, those things are great!
It's about trying out different things, and learning as you go on. Start small, it'll be much more rewarding.
As per wattage; if you play just at home by yourself, anything past 1 or 2 watts is just extra pain in your ears (and neighbours). With a band, 20 watts will be plenty. You can get there with 6V6's or EL84's.
I play at home with amps that have EF80 power stages, for maybe 1 watt power. Still can't keep the buggers past maybe 3-4 on the (post PI) master volume. Sometimes I use a small attenuator to get the extra roar.
I play at home with amps that have EF80 power stages, for maybe 1 watt power. Still can't keep the buggers past maybe 3-4 on the (post PI) master volume. Sometimes I use a small attenuator to get the extra roar.
sorry. Those power ratings are definitely more then I need. I was basing that off of a few SS amps ive owned, but in reality I just need to play with a drummer, a bassist and maybe a couple brass instruments. It seems like I can get away with 20-30 or so watts. also, is there anywhere i can learn about the different kinds of tubes? for instance, I hear 6v6's mentioned alot. I know that these are tetrodes, but I dont really know much about what kind of performance I can expect from different tubes.
By asking for 60-100 watts in a tube amp you are limitted to a fairly small group of tubes.
There are more choices if you are willing to go to less avaiable NOS tubes, but Im thinking you should stick to devices that you can buy new. If you can start with something around 20-30 watts (or less) then there more options like 6L6 6V6 El84 ect. Lots and lots of designs out there and like folks are saying you can always "make it your own" with features, tone modifications. You should be able to keep the cost for your first cut prototype at around $200 not including fancy packaging. You already have the speakers!
There are more choices if you are willing to go to less avaiable NOS tubes, but Im thinking you should stick to devices that you can buy new. If you can start with something around 20-30 watts (or less) then there more options like 6L6 6V6 El84 ect. Lots and lots of designs out there and like folks are saying you can always "make it your own" with features, tone modifications. You should be able to keep the cost for your first cut prototype at around $200 not including fancy packaging. You already have the speakers!
also, how do you guys feel about using an SS preamp and a tube power amp? is there anything that I need to watch out for when mixing and matching like that? I like the idea of a SS preamp because I am much more comfortable with the theory, which would allow me to make some mods and actually understand the implications.
Using tubes in the pre-amp will produce a more noticable effect than tubes in the power amp.
Firstly, the questions I suggest you ask yourself before starting the project is:
-What kind of tone do you want (if you want to base it on something)
-What power level? (the others are right, tubes sound 12 dB louder than SS at the same power)
-What's your budget?
-How much gain do you need? (High gain amps are more complicated)
Additionally, the best beginner website for tube amps I've seen yet is AX84.com along with The Valve Wizard's site. Someone else already posted the tone lizard but his site is mostly for mods. I second the Schematic heaven website, that is a good one for educational purposes.
I urge you to stick to all tube if you do tubes. The simple (yet effective!) single ended tube power amp section requires only 2 resistors, a cap, a tube and an output transformer.
Firstly, the questions I suggest you ask yourself before starting the project is:
-What kind of tone do you want (if you want to base it on something)
-What power level? (the others are right, tubes sound 12 dB louder than SS at the same power)
-What's your budget?
-How much gain do you need? (High gain amps are more complicated)
Additionally, the best beginner website for tube amps I've seen yet is AX84.com along with The Valve Wizard's site. Someone else already posted the tone lizard but his site is mostly for mods. I second the Schematic heaven website, that is a good one for educational purposes.
I urge you to stick to all tube if you do tubes. The simple (yet effective!) single ended tube power amp section requires only 2 resistors, a cap, a tube and an output transformer.
RTF671 - I don't have any specific tone in mind. really, I want the tone to be somewhat dynamic, I play anything from clean jazz to bluesy stuff to metal depending on who im playing with, hence the desire for dynamicness (if i need different amps for these purposes then so be it, but I was hoping to play around with it to see what i could get). as far as power level, taking into account the efficiency of the speakers i have, im think around 20-25 W or so my budget is pretty flexible. I was hoping to get all parts (not including resistors and common caps) for around $200-$300 and I dont need extremely high gain, Im not sure of an exact number. I was looking at the Mark Huss's Plexi schematic and i'm thinking about starting with that. at least as a basis for what I want to do.
Matt,
A PP pair of EL84s or 6V6s will yield 12 to 15 W. That's what I strongly suggest you use, for financial and safety reasons. Risk grows exponentially with increasing voltage and you will be under 375 V., using those types. Edcor's GXPP15-4-8K looks like it could be suitable, as the O/P trafo.
Sagging B+, when the amp is cranked, is part of the tube "magic". You get that sag by vacuum rectifying the B+. It seems the economical way to get the B+ is by Greinacher voltage doubling the O/P of a Triad N-68X isolation trafo with a 6BY5 dual damper diode. A pair of 47μF./250 WVDC 'lytics should be satisfactory in the doubler stack.
A PP pair of EL84s or 6V6s will yield 12 to 15 W. That's what I strongly suggest you use, for financial and safety reasons. Risk grows exponentially with increasing voltage and you will be under 375 V., using those types. Edcor's GXPP15-4-8K looks like it could be suitable, as the O/P trafo.
Sagging B+, when the amp is cranked, is part of the tube "magic". You get that sag by vacuum rectifying the B+. It seems the economical way to get the B+ is by Greinacher voltage doubling the O/P of a Triad N-68X isolation trafo with a 6BY5 dual damper diode. A pair of 47μF./250 WVDC 'lytics should be satisfactory in the doubler stack.
Eli is right, a pair of tubes arranged in a push/pull out section will yield a good amount of power. Using a tube recto will create some sag (because each anode has resistance thus mild current limiting effect). As a beginner I would recommend against although you could always add it later.
You should be able to get the tones you like with a pair of power tubes and 3 pre amp tubes. To give you an idea of what you are working with tubes, each small signal (e.g. pre-amp) tube has two sections. The output only have one each. Generally common layouts use 3 gain stages and an impedance buffer to feed tone controls and 2 sections (1 tube) as a phase inverter.
By using tubes you will not need a bi-polar power supply (in fact I recommend against it, it makes things... weird). However because the output section runs off of DC you will need an output transformer to feed an AC signal to the speaker. Tubes behave differently than transistors because they are mainly voltage amplifiers.
I could go on but I don't want to overload you
What are your thoughts so far?
You should be able to get the tones you like with a pair of power tubes and 3 pre amp tubes. To give you an idea of what you are working with tubes, each small signal (e.g. pre-amp) tube has two sections. The output only have one each. Generally common layouts use 3 gain stages and an impedance buffer to feed tone controls and 2 sections (1 tube) as a phase inverter.
By using tubes you will not need a bi-polar power supply (in fact I recommend against it, it makes things... weird). However because the output section runs off of DC you will need an output transformer to feed an AC signal to the speaker. Tubes behave differently than transistors because they are mainly voltage amplifiers.
I could go on but I don't want to overload you
What are your thoughts so far?
One point I would like to make is that you shouldn't confuse output power with volume. They do not travel in lockstep. 15 watts is plenty for most club gig situations provided you have reasonably efficient speaker. The other advantage of low-wattage amps is that it is easier to get output-stage distortion (clipping) without resorting to kludgey solutions such as power soaks.
Tone is a function of a number of factors including (but not limited to):
Power-supply voltage sag
Speaker efficiency
Speaker breakup characteristics
Preamp distortion
Power amp distortion
Speaker power compression (as voice coils heat up, their impedance increases)
I second the suggestion to check out AX84.com. There's a lot of good stuff there. Also, don't expect to get it perfectly right the first time. Get your hands dirty and learn as much as you can from the experience.
A more complete explanation of the role of the output transformer is that it converts a high-voltage, low-current, high-impedance signal into a low-voltage, high-current, low-impedance signal.
Tone is a function of a number of factors including (but not limited to):
Power-supply voltage sag
Speaker efficiency
Speaker breakup characteristics
Preamp distortion
Power amp distortion
Speaker power compression (as voice coils heat up, their impedance increases)
I second the suggestion to check out AX84.com. There's a lot of good stuff there. Also, don't expect to get it perfectly right the first time. Get your hands dirty and learn as much as you can from the experience.
A more complete explanation of the role of the output transformer is that it converts a high-voltage, low-current, high-impedance signal into a low-voltage, high-current, low-impedance signal.
Eli and RTF, thanks for your help. after looking aroun dbased on what you guys are saying, I think i agree. do you guys have any schematics as examples of what i might be trying to do? also, if i have a tube preamp, what kind off tubes do i want for those?
bunkie, thank you, i am starting to realize that the speakers im used to for judging power were way less efficient than the ones ill be using for this project. the the transformer essentially makes the low impedance speaker look a lot bigger to the amplifier circuit correct?
also, do you guys think I need a 2 x 12 cab or will 1x 12 be good for what im trying to do? thanks for all of your help!
bunkie, thank you, i am starting to realize that the speakers im used to for judging power were way less efficient than the ones ill be using for this project. the the transformer essentially makes the low impedance speaker look a lot bigger to the amplifier circuit correct?
also, do you guys think I need a 2 x 12 cab or will 1x 12 be good for what im trying to do? thanks for all of your help!
By far the most typical guitar pre-amp tube is going to be the 12AX7. It provides good gain and is easy to design around. There are others that can be used but they are less common and less typical and less widely available.
Here is one of the best beginner amps to example, the AX84 P1. It is a simple and small (but full tube) amp.
AX84 P1
Here is a chapter from an easy to understand book on designing guitar tube amps:
The common cathode triode gain stage
Here is an design of a push pull amp:
Daisycutter 18W
So far what do you know about tubes? I do suggest you pour over the Valve wizard site, I learned a lot of what I know from there.
Here is one of the best beginner amps to example, the AX84 P1. It is a simple and small (but full tube) amp.
AX84 P1
Here is a chapter from an easy to understand book on designing guitar tube amps:
The common cathode triode gain stage
Here is an design of a push pull amp:
Daisycutter 18W
So far what do you know about tubes? I do suggest you pour over the Valve wizard site, I learned a lot of what I know from there.
lynchy,
Speaker efficiency is not directly linked to impedance. It's a function of many factors and a high-impedance speaker can be high-efficiency and vice-versa. So, a less efficient speaker does not automatically present a different impedance. It is important to match the speaker impedance with the output transformer impedance, too high an impedance causes problems for output tubes.
The factors that define speaker efficiency are cone mass, the size of the gap between the voice coil and the magnet pole, the strength of the magnetic field, the compliance of the surround and spider and the relative stiffness of the cone, to name a few.
Speaker efficiency is measured by measuring the loudness with a one-watt signal at a distance of one meter. Most manufacturers supply this measurement. 93db is pretty efficient, 89db is pretty inefficient to give you some ballpark numbers.
Speaker efficiency is not directly linked to impedance. It's a function of many factors and a high-impedance speaker can be high-efficiency and vice-versa. So, a less efficient speaker does not automatically present a different impedance. It is important to match the speaker impedance with the output transformer impedance, too high an impedance causes problems for output tubes.
The factors that define speaker efficiency are cone mass, the size of the gap between the voice coil and the magnet pole, the strength of the magnetic field, the compliance of the surround and spider and the relative stiffness of the cone, to name a few.
Speaker efficiency is measured by measuring the loudness with a one-watt signal at a distance of one meter. Most manufacturers supply this measurement. 93db is pretty efficient, 89db is pretty inefficient to give you some ballpark numbers.
Yea I know. I just meant that the 4-16 ohms of the speaker load is fairly small compared to the high impedacnes in the rest of the amp, so the output transformer makes a multiplier that makes those 4 ohms look a lot bigger right? and the speakers I have are 102 dB, so theyre pretty efficient. I was just overlooking this when deciding the wattage I needed.
Thanks RTF! those were really useful. I think im ready to start designing this puppy once I get some free time. Ill be sure to get ideas up ASAP to make sure im headed in the right direction
Thanks RTF! those were really useful. I think im ready to start designing this puppy once I get some free time. Ill be sure to get ideas up ASAP to make sure im headed in the right direction
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