To make a long story short, I'm planning to make a guitar amplifier by myself. I've (re)searched a lot over the internet, google, diyaudio and I lend some specific tube books from my father. (because nowadays those subjects aren't import any more on the study of physics 
). I also found this page, which is very useful: (TIP!)
http://www.pmillett.com/technical_books_online.htm
So I begin to understand how a lot of schematics are build that specific way. But there are still some questions left where I can't find the answer of on the internet or in books.
Now I know that guitar amplifiers are a very different kind of sport than most HIFI amplifiers. Reasons could be just production money, matter of taste or just some random choices because it was build that way.
One specific question to begin with is, why are most guitar amplifiers build PP?
Is that only because of the extra output power?
But why use two EL84 and not one SE EL34/KT77 ? That's almost the same price for the same power.
Besides, you need also an extra phase inverter for a PP amplifier.
For example, one idea was to make an KT77 SE amplifier. That must be enough for some 12-14W. Good enough to make the neighbours angry.
). I also found this page, which is very useful: (TIP!)http://www.pmillett.com/technical_books_online.htm
So I begin to understand how a lot of schematics are build that specific way. But there are still some questions left where I can't find the answer of on the internet or in books.
Now I know that guitar amplifiers are a very different kind of sport than most HIFI amplifiers. Reasons could be just production money, matter of taste or just some random choices because it was build that way.
One specific question to begin with is, why are most guitar amplifiers build PP?
Is that only because of the extra output power?
But why use two EL84 and not one SE EL34/KT77 ? That's almost the same price for the same power.
Besides, you need also an extra phase inverter for a PP amplifier.
For example, one idea was to make an KT77 SE amplifier. That must be enough for some 12-14W. Good enough to make the neighbours angry.
b_force said:
While I'm not a guitar person (anymore) I can say the answer is mostly because of the efficiency of PP output over SE. In patricular the output transformer requirments are much different. A PP transformer can be much smaller and lighter then SE and thus less expensive. Even if you include the extra tube (or tubes) and handful of small parts, the overall cost can be less. The shipping weight will also be less.
Something may also be said for the overload and distortion characteristics of PP verses SE when a certian sound is desired. But I think it's mostly the above.
b_force said:
What answer are you looking for? Commercial guitar amps went PP long ago for various reasons like cost, weight, and power. For yourself, there's nothing wrong with building a big SE guitar amp, and there are designs out there if you look for them. I'm building one right now with a super-6BG6GA tube.
The SE transformer has to carry a lot of current, and so it must have a heavier core and windings. That means that the SE transformer is a lot more expensive than the PP.
PP gets more efficiency out of each tube, so you can get more power with fewer tubes, or more power with a smaller power supply.
Two books that are very good for designing guitar amps are "Vacuum Tube Circuit Design: Guitar Amplifier Preamps" and "Vacuum Tube Circuit Design: Guitar Amplifier Power Amps" by Richard Kuehnel. These books will explain the details of how to design a guitar amp and what the benefits are of each type of design.
PP gets more efficiency out of each tube, so you can get more power with fewer tubes, or more power with a smaller power supply.
Two books that are very good for designing guitar amps are "Vacuum Tube Circuit Design: Guitar Amplifier Preamps" and "Vacuum Tube Circuit Design: Guitar Amplifier Power Amps" by Richard Kuehnel. These books will explain the details of how to design a guitar amp and what the benefits are of each type of design.
A guitar amplifier (as distinct from a H iFi Amplifier) is a musical instrument in its own right.
Keep researching and you will find plenty of tips and hints as to how to get the particular sound you prefer - have you defined what you want?
Aside: I'm an EE in the day job. The most common mistake I see in design is not defining your requirements specification before you start and then trying to design something that is "all things to all men." This is even more critical for software design where the "Feaping Creatures" (Creeping Features) syndrome sets in. The requirements spec is the only way you know when it is finished.
Perhaps counter intuitively the modern high gain overdrive guitar sound is generated practically entirely in the preamp section and it requires a HiFi-ish fast and tight power amp and power supply section.
The old 60's and early 70's Vintage Blues sound requires a fairly clean preamp section with a power amp section (often using cathode biased output tubes and concertina phase splitter) which can be overdriven and a soft power supply. This sound is best achieved using a push pull stage with a common cathode bias resistor without a bypass capacitor BUT then requires the use of matched output tubes OR a single ended output stage.
The preference for push pull output stages was born out of the need for huge power output, before the days of big PA Systems.
Today, there is absolutely no reason why a single ended power amp section can not be used and in fact there are a number of amp manufacturers designing amplifiers with a "Body" control. This control basically allows one side of the push pull to be dialed anywhere between perfect balance and right off, effectively giving you a single ended sound. It is simply a pot between the phase splitter (one side only) and the output tube grid.
My own latest guitar amplifier (completed last weekend) has footswitchable Clean (2 stage) and Lead (4 stage) preamp using 6SL7 octal tubes driving a 6SL7 common cathode stage followed by a self biased concertina phase splitter driving Ultralinear connected Push Pull 6V6 Current Source biased output tubes. The Output stage is very HiFi-ish with a reasonably "tight" CLC power supply. That gives me all the sounds that I wanted from a guitar amp. Its a reasonably modern design but the use of 6SL7 gives it a vintage "bent". It won't do flat out full metal jacket shread and it won't do the early 60's flabby blues sound but it can do anything in between. In addition the use of a high mu tube (6SL7) for the concertina phase splitter emphasizes the concertina limitations and adds "warmth" as compared to the Stacked schmidt phase splitter which is used in 90+% of guitar amps.
Just one mans views/ideas.
Cheers,
Ian
Keep researching and you will find plenty of tips and hints as to how to get the particular sound you prefer - have you defined what you want?
Aside: I'm an EE in the day job. The most common mistake I see in design is not defining your requirements specification before you start and then trying to design something that is "all things to all men." This is even more critical for software design where the "Feaping Creatures" (Creeping Features) syndrome sets in. The requirements spec is the only way you know when it is finished.
Perhaps counter intuitively the modern high gain overdrive guitar sound is generated practically entirely in the preamp section and it requires a HiFi-ish fast and tight power amp and power supply section.
The old 60's and early 70's Vintage Blues sound requires a fairly clean preamp section with a power amp section (often using cathode biased output tubes and concertina phase splitter) which can be overdriven and a soft power supply. This sound is best achieved using a push pull stage with a common cathode bias resistor without a bypass capacitor BUT then requires the use of matched output tubes OR a single ended output stage.
The preference for push pull output stages was born out of the need for huge power output, before the days of big PA Systems.
Today, there is absolutely no reason why a single ended power amp section can not be used and in fact there are a number of amp manufacturers designing amplifiers with a "Body" control. This control basically allows one side of the push pull to be dialed anywhere between perfect balance and right off, effectively giving you a single ended sound. It is simply a pot between the phase splitter (one side only) and the output tube grid.
My own latest guitar amplifier (completed last weekend) has footswitchable Clean (2 stage) and Lead (4 stage) preamp using 6SL7 octal tubes driving a 6SL7 common cathode stage followed by a self biased concertina phase splitter driving Ultralinear connected Push Pull 6V6 Current Source biased output tubes. The Output stage is very HiFi-ish with a reasonably "tight" CLC power supply. That gives me all the sounds that I wanted from a guitar amp. Its a reasonably modern design but the use of 6SL7 gives it a vintage "bent". It won't do flat out full metal jacket shread and it won't do the early 60's flabby blues sound but it can do anything in between. In addition the use of a high mu tube (6SL7) for the concertina phase splitter emphasizes the concertina limitations and adds "warmth" as compared to the Stacked schmidt phase splitter which is used in 90+% of guitar amps.
Just one mans views/ideas.
Cheers,
Ian
G"Day Gingertube.
I am still living my tube building life vicariously at the moment. Moved house 6 months ago and still have not set up a workshop. Long story with some personal issues there so won't go in to it... Short story is I expect a mate of mine to purchase much of my woodworking machinery that is stored in an area that is too small for me to use them effectively. When they go I should have space enough to have a workbench and work area for handyman stuff and electronics projects...
Projects on my horizon are a pair of monoblock 7591 PP amps with Tamura output transformers (that is for another thread) and my son wants to learn electric guitar. My ex wife bought him a cheap guitar and (HORROR!!!) a cheap SS practice amp. I said we could research and build a tube amp for his guitar. From what I have gathered, he likes more of a classic rock style of music, but I am sure his tastes will change (he is 13). My hope is that we can build an amp with a reasonable power section that will last the distance for him. The amp you just describe sounds very interesting and something similar may well be suitable. Are you willing to share your design?
I have a few Russian 6V6 equivalent tubes and a whole bunch of Russian 6SL7 and 6SN7 equivalents, a power transformer 290-240-0-240-290 150mA, 5.0 3A, 6.3 2A * 2. Just really need an output transformer (Edcore 15 watt guitar transformers look like good value), a speaker and a design.
Cheers,
Chris
I am still living my tube building life vicariously at the moment. Moved house 6 months ago and still have not set up a workshop. Long story with some personal issues there so won't go in to it... Short story is I expect a mate of mine to purchase much of my woodworking machinery that is stored in an area that is too small for me to use them effectively. When they go I should have space enough to have a workbench and work area for handyman stuff and electronics projects...
Projects on my horizon are a pair of monoblock 7591 PP amps with Tamura output transformers (that is for another thread) and my son wants to learn electric guitar. My ex wife bought him a cheap guitar and (HORROR!!!) a cheap SS practice amp. I said we could research and build a tube amp for his guitar. From what I have gathered, he likes more of a classic rock style of music, but I am sure his tastes will change (he is 13). My hope is that we can build an amp with a reasonable power section that will last the distance for him. The amp you just describe sounds very interesting and something similar may well be suitable. Are you willing to share your design?
I have a few Russian 6V6 equivalent tubes and a whole bunch of Russian 6SL7 and 6SN7 equivalents, a power transformer 290-240-0-240-290 150mA, 5.0 3A, 6.3 2A * 2. Just really need an output transformer (Edcore 15 watt guitar transformers look like good value), a speaker and a design.
Cheers,
Chris
Chris,
Look here:
http://www.powerscaling.com/community/index.php?topic=1017.0
Some off topic rave on the pro's and cons of concertina splitters and the problems of reverse grid current in vintage high mu tubes (like the 6SL7) but all then schematics I used are there (starting at page 3).
Acknowledgment:
The Preamp circuit is a (slightly) modified version of Kevin O'Connor's London Power Standard Preamp (LPSP). The mods are some resistor value changes to suit the 6SL7 and to make sure (reverse) grid current with vintage 6SL7 is not a problem.
I would make a couple of changes if I were building it again:
1) I used J201 for the channel switching JFETS. They caused me a little grief as their cut off voltage is too low (as low as -0.3 volts). I would use J202 or J203 instead if I were to build it again.
2) The negative supply is a bit more complicated than needed - I include the bias set resistors etc. for possible future conversion of the output tubes to fixed bias - probably wont ever be used, the "Baby Huey-ish" CCS biasing of the 6V6s shown works really well and I like the idea of no idle current adjustment ever required. It is what I'm running. Note that due to the required 24 Volts or so of bias these CCS's dissipate about 2x the power of the ones in the Baby Huey and require heatsinks. I used tiny 39 degree Cper watt heatsinks and they get hot to touch (not burned finger hot but uncomfortable to touch hot). Bigger heatsinks would not be a bad idea.
3) The LED current set resistors in the switching circuit are shown as 15K. With the LEDs I used these had to be dropped to 8K2 for a bit more brightness.
Also a comment:
The Power Amp schematic shows Pentode Mode/Ultralinear Mode Switching. One mode gives better guitar amp tone and I leave the switch in that possition all the time. I need to check the wiring to see which mode that is. Will advise tomorrow.
Cheers,
Ian
Look here:
http://www.powerscaling.com/community/index.php?topic=1017.0
Some off topic rave on the pro's and cons of concertina splitters and the problems of reverse grid current in vintage high mu tubes (like the 6SL7) but all then schematics I used are there (starting at page 3).
Acknowledgment:
The Preamp circuit is a (slightly) modified version of Kevin O'Connor's London Power Standard Preamp (LPSP). The mods are some resistor value changes to suit the 6SL7 and to make sure (reverse) grid current with vintage 6SL7 is not a problem.
I would make a couple of changes if I were building it again:
1) I used J201 for the channel switching JFETS. They caused me a little grief as their cut off voltage is too low (as low as -0.3 volts). I would use J202 or J203 instead if I were to build it again.
2) The negative supply is a bit more complicated than needed - I include the bias set resistors etc. for possible future conversion of the output tubes to fixed bias - probably wont ever be used, the "Baby Huey-ish" CCS biasing of the 6V6s shown works really well and I like the idea of no idle current adjustment ever required. It is what I'm running. Note that due to the required 24 Volts or so of bias these CCS's dissipate about 2x the power of the ones in the Baby Huey and require heatsinks. I used tiny 39 degree Cper watt heatsinks and they get hot to touch (not burned finger hot but uncomfortable to touch hot). Bigger heatsinks would not be a bad idea.
3) The LED current set resistors in the switching circuit are shown as 15K. With the LEDs I used these had to be dropped to 8K2 for a bit more brightness.
Also a comment:
The Power Amp schematic shows Pentode Mode/Ultralinear Mode Switching. One mode gives better guitar amp tone and I leave the switch in that possition all the time. I need to check the wiring to see which mode that is. Will advise tomorrow.
Cheers,
Ian
Thanks Ian. Just tried to look at that site, but would not allow viewing without registration and then would not allow registration with a gmail account Will have to find a workaround later as I am just stepping out the door...
I thought the output sounded a little "baby huey" ish
Regards,
Chris
Will have to find a workaround later as I am just stepping out the door...I thought the output sounded a little "baby huey" ish
Regards,
Chris
"One specific question to begin with is, why are most guitar amplifiers build PP?
Is that only because of the extra output power?"
I think it's mainly because push-pull is required to operate in class AB
for high output power and/or anode efficiency. Guitar amps are heavy
as it is... Cheaper for mass production also, as already pointed out.
But it's not just PP, it's class AB that is the big win in efficiency.
SE output stages do have inherent 2nd harmonic production, but
typical guitar amp circuits have SE front ends and somewhat
asymmetric phase splitters that generate a lot of 2nd harmonic.
Having said that, there are a lot of very popular class A botique guitar
amps on the market and it is a popular mod for class AB amps to run
in class A.
IT would be interesting to explore SE guitar amps. One may get away
with a limited bandwidth OPT, which could help with the weight issue.
I would think a 20 watt SE amp could be built without going to
heroics. Just think, no phase splitter to design ;-)
Is that only because of the extra output power?"
I think it's mainly because push-pull is required to operate in class AB
for high output power and/or anode efficiency. Guitar amps are heavy
as it is... Cheaper for mass production also, as already pointed out.
But it's not just PP, it's class AB that is the big win in efficiency.
SE output stages do have inherent 2nd harmonic production, but
typical guitar amp circuits have SE front ends and somewhat
asymmetric phase splitters that generate a lot of 2nd harmonic.
Having said that, there are a lot of very popular class A botique guitar
amps on the market and it is a popular mod for class AB amps to run
in class A.
IT would be interesting to explore SE guitar amps. One may get away
with a limited bandwidth OPT, which could help with the weight issue.
I would think a 20 watt SE amp could be built without going to
heroics. Just think, no phase splitter to design ;-)
As mentioned the reason for PP amps owning the guitar amp market is most bang for buck. The amps out there get 60watts out of a pair of 6L6s, and you don't get that with tubes running in anything but class-B. The main reason is buyers always look at specs first, and everything else second. Besides in the old days they did not use miked cabs and huge PAs like today. But time they are a changing...a bit... Small class-A guitar amps are coming out of the woodwork like there's no tomorrow. Some music styles actually work best with PP class-B amps, so class-A is not always the best for guitarists.
I started building guitar amps some 8 years ago, and at first I was confident my amps would blow those old textbook designs out of the water. hehe...I can tell you right now if you build a guitar amp with the same design specs as a HiFi amp it will sound like crap. I did that mistake and made sure all details in the amp was high-end HiFi quality. The fun part regarding guitar amps is they are just like an instrument and should have it's own character and personality, which it wont have if made like HiFi amps. I finally got the tone right when a guitarist friend of mine told me to make it so bright it hurts. The trick is getting the brightness without the harshness.
Anyhow, good luck and have fun trying crazy ideas. I desided to offer something different and therefore build OTL guitar amps. you can see some here, tho this website is old and I havent had time to update anything for about a year...www.devildogamps.com
I started building guitar amps some 8 years ago, and at first I was confident my amps would blow those old textbook designs out of the water. hehe...I can tell you right now if you build a guitar amp with the same design specs as a HiFi amp it will sound like crap. I did that mistake and made sure all details in the amp was high-end HiFi quality. The fun part regarding guitar amps is they are just like an instrument and should have it's own character and personality, which it wont have if made like HiFi amps. I finally got the tone right when a guitarist friend of mine told me to make it so bright it hurts. The trick is getting the brightness without the harshness.
Anyhow, good luck and have fun trying crazy ideas. I desided to offer something different and therefore build OTL guitar amps. you can see some here, tho this website is old and I havent had time to update anything for about a year...www.devildogamps.com
Hi Michael,
As parttime/longtime producer of boutique amps, www.revintage.se , I have been there. Can not understand the SE hype. The really nice sounding solution is selfsplit PP( reVintage Prince). No splitter needed, always Class-A and better sound for guitar.
My next track to explore is 6B4G PP for guitar, maybe with triode/antitriode, selfsplit with 6B4G and 6V6........
I can recommend 7591 as output tubes together with custom wound Heyboer OPTs. And don´t forget to use rectifier tube.
b_force said:
You pay for the iron. Lowest note in guitar, E at 41Hz doesn't require an output transformer to be designed any lower than this,saving weight and copper so you will find a HiFi amp transformer designed for 20Hz cutoff double the size, better quality often quadruple the cost. In saying this there are quitar amps used for HiFi. SOme are astoundingly good. I use a HiFi amp for trumpet as sound levels can be awesome high requiring higher power without clipping distortion caused by power/ B+ sag.
My other 807 p-p amp I use for guitar is also a near HiFi amp. It sounds too clean. To make it sound rough I use zener diodes with a double pot across the grid leak resistors in the output stage with series caps so clipping can be gradual and a very loose global nfb loop, perhaps 6dB NFB. That tactic is an old one not seen anymore. It isn't a quality arrangement, and alot of quitar amps were/are fudged around surplus WW2 /TV tubes and forced into work. 1-10% thd was quite the norm, whereas a true HiFi amp is looking at less than 0.1% 3rd harmonic thd at rated output and masses of global nfb to keep it quiet. BIG difference.
richy
This site has a LOT of info, including fully spec'd instructions, layout etc. for several of the mythical (?) Dumble and Trainwreck amps..
You'd have to register here too, though, to get to the nuggets.....
www.ampgarage.com
This one , www.hoffmanamps.com , also have a lot of info and projects.
www.ax84.com also have a lot of projects, mainly on the slightly less ambitious side, but still lots of good info.
As for SE vs PP, I don't think I'd bother with SE for guitar, except maybe for smaller practice amps of say 2-5 W, but then I'm no guitar guru....
You'd have to register here too, though, to get to the nuggets.....
www.ampgarage.com
This one , www.hoffmanamps.com , also have a lot of info and projects.
www.ax84.com also have a lot of projects, mainly on the slightly less ambitious side, but still lots of good info.
As for SE vs PP, I don't think I'd bother with SE for guitar, except maybe for smaller practice amps of say 2-5 W, but then I'm no guitar guru....
b_force said:
When a string decay we expect to hear softer sound than when it is loud and bright. It is natural.
PP may produce harder sound on low levels, while SE amp sound the softer the softer is the sound. Well made PP amps may behave the same, but it is easier to get wrong, artificial, sound from PP than from SE amp.
I still remember sound of a small German amp called Regent - 30. It was PP, in class A. Fantastic sound.
Edit: hum was the biggest minus, but the sound was fantastically musical. Here is the info: http://www.el-me-se.de/pdf_files/Regent 30 H.pdf
What a reply's 
But keep discussing, I think it would be very interesting to talk about difference tastes and how they can be accomplished.
No time to reply now, but I'm already thinking of a specific tube guitar book.
The problem is that there are many books and my opinion is that they are not al that great. Mostly I'm missing the deep story's and theoretical side.
Does anyone know if "O´Connor, Kevin - Principles of Power" is a good book to have?
But keep discussing, I think it would be very interesting to talk about difference tastes and how they can be accomplished.
No time to reply now, but I'm already thinking of a specific tube guitar book.
The problem is that there are many books and my opinion is that they are not al that great. Mostly I'm missing the deep story's and theoretical side.
Does anyone know if "O´Connor, Kevin - Principles of Power" is a good book to have?
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