So, my brother and I wanted to build a Marshall 2022 20 watt amplifier but it's our first time building an amp so we had a few questions:
Is the attached picture of the schematic correct? (Will anything blow up?) Hahahaha
How do we measure the output impedance so we can match it with the correct speakers?
How and where in the schematic should we put and fx loop? (We know it's between the preamp section and power amp section but how can you tell where it's located?)
Any additional advice for us as it's our first time building an amp?
Thank you
Is the attached picture of the schematic correct? (Will anything blow up?) Hahahaha
How do we measure the output impedance so we can match it with the correct speakers?
How and where in the schematic should we put and fx loop? (We know it's between the preamp section and power amp section but how can you tell where it's located?)
Any additional advice for us as it's our first time building an amp?
Thank you
Attachments
The 50uF (that is in parallel with the 125R) should have its positive terminal
connected to the cathodes of the EL84s.
Two EL-84 output tubes in push/pull configuration like your schematic has will have a nominal output impedance of around 8K ohms. They will be able to output 15 clean watts of power, and somewhere near 20 watts of distorted power when the amp is cranked. For reliability sake, you'll want to look for an output transformer that has a power capacity of at least 20 or hopefully 25 watts (or more), with an 8K ohm primary to a 4 / 8 / 16 ohm secondary. That way you can run it cranked all the way up without worrying about burning it up. The bigger the power capacity of the transformer, the more reserve strength the transformer will have as the amp is played loudly.
Dave
Dave
Hi Dave,
It's a guitar amp, not a hifi amplifier. Guitar amplifiers often use undersized output transformers and do just fine. It wouldn't have the same overdrive sound with a larger output. Power transformers are sometimes undersized, by design. That's for attack and decay while you're playing.
-Chris
It's a guitar amp, not a hifi amplifier. Guitar amplifiers often use undersized output transformers and do just fine. It wouldn't have the same overdrive sound with a larger output. Power transformers are sometimes undersized, by design. That's for attack and decay while you're playing.
-Chris
Read what Rob Robinette has to say about safety and how to build a tube amp etc etc.
Kits are the easy way in. The amp you've listed is basically the same as any number of kits, e.g. a 5e3
Use a light bulb tester.
Stay safe and have fun!
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Anatech / Chris, you are right! I stand corrected. I had my head stuck in the "Fender 50's" and this is a Marshall schematic.
Nah091000, what Chris and I just discussed is part of a deeper story that surfaces when you take an existing design or schematic and build an amp with it. Not only do you have to successfully interpret the schematic in front of you, but you also have to be aware of its history, not only from an engineer's perspective, but also the player's perspective. Playing styles have changed dramatically in the last 70 years, and changing your playing style can directly influence how the amp should be designed and what components you should use during a build.
Back in the 50's when guitar amps were relatively new, amp manufacturers had the same goal as the companies that built High Fidelity equipment. Guitar amps were meant to be played clean, and the manufacturer's job was to create amps with as little distortion to the signal as possible. To that aim, cranking an amp into its distortion voice was considered abterrent behavior and a misuse of the amp.
The clean-only mindset influenced not only the player's behavior, but also the engineer who designed the amp itself. For example, the EL-84 tubes in your schematic are capable of generating approximately 15 watts of undistorted output, so the engineer generally selected a transformer where the wires inside the transformer and the size of the transformer core could handle 15 watts of clean power.
What happened over the years is that players discovered that an amp is actually half of a system, and its purpose is to generate the electronic voice of the guitar, but not necessarily faithfully reproduce the output of the pickups. Over the years, players discovered that the guitar sounded better and was more playable as the amp was turned up.
As Chris pointed out, one of the reasons "turning it up" was so good was that the increased power effectively saturated the transformer core with magnetism, and it simply couldn't generate a larger magnetic field. That's where a large part of a tube amp's natural compression comes from and why players love a cranked tube amp.
The problem is when you reach transformer saturation, that extra energy has to go somewhere, and it ends up doing mischief by heating up the transformer core and the wires inside the transformer. Additionally, as the amp is over-driven and starts clipping, the signal from the tubes looks more and more like a square wave, and contains a lot more energy than it did when the amp was playing clean.
If the wire in the transformer is too small for that kind of electrical abuse, it eventually burns open, thereby ruining the transformer.
Here is where the engineer and the player diverge in their thinking (and what I inadvertently did in my advice to you). The engineer would solve the problem by fitting a larger transformer that contains thicker wire. Not only does that solve the saturation problem, but keeps the tranny from burning up.
On the other hand, the player is now unhappy, because the amp doesn't sound nearly as good. The solution (as pioneered by companies like Marshall and then carried forward by many botique amp builders) was to keep the same small transformer core and increase the size of the wiring. That way the core would still saturate but the tranny wouldn't burn up because the wiring was more robust.
One way to think of it is that the '50s Fender engineer would design a tranny for 15 clean watts. The Marshall engineer would design the tranny for 15 distorted watts (meaning the amp was really slamming the tranny with 20-25 watts of energy, but the Marshall tranny could easily handle being cranked). Most guitar amp transformer builders today know the amp will be cranked, and build transformers accordingly, so you should be fine.
Dave
Nah091000, what Chris and I just discussed is part of a deeper story that surfaces when you take an existing design or schematic and build an amp with it. Not only do you have to successfully interpret the schematic in front of you, but you also have to be aware of its history, not only from an engineer's perspective, but also the player's perspective. Playing styles have changed dramatically in the last 70 years, and changing your playing style can directly influence how the amp should be designed and what components you should use during a build.
Back in the 50's when guitar amps were relatively new, amp manufacturers had the same goal as the companies that built High Fidelity equipment. Guitar amps were meant to be played clean, and the manufacturer's job was to create amps with as little distortion to the signal as possible. To that aim, cranking an amp into its distortion voice was considered abterrent behavior and a misuse of the amp.
The clean-only mindset influenced not only the player's behavior, but also the engineer who designed the amp itself. For example, the EL-84 tubes in your schematic are capable of generating approximately 15 watts of undistorted output, so the engineer generally selected a transformer where the wires inside the transformer and the size of the transformer core could handle 15 watts of clean power.
What happened over the years is that players discovered that an amp is actually half of a system, and its purpose is to generate the electronic voice of the guitar, but not necessarily faithfully reproduce the output of the pickups. Over the years, players discovered that the guitar sounded better and was more playable as the amp was turned up.
As Chris pointed out, one of the reasons "turning it up" was so good was that the increased power effectively saturated the transformer core with magnetism, and it simply couldn't generate a larger magnetic field. That's where a large part of a tube amp's natural compression comes from and why players love a cranked tube amp.
The problem is when you reach transformer saturation, that extra energy has to go somewhere, and it ends up doing mischief by heating up the transformer core and the wires inside the transformer. Additionally, as the amp is over-driven and starts clipping, the signal from the tubes looks more and more like a square wave, and contains a lot more energy than it did when the amp was playing clean.
If the wire in the transformer is too small for that kind of electrical abuse, it eventually burns open, thereby ruining the transformer.
Here is where the engineer and the player diverge in their thinking (and what I inadvertently did in my advice to you). The engineer would solve the problem by fitting a larger transformer that contains thicker wire. Not only does that solve the saturation problem, but keeps the tranny from burning up.
On the other hand, the player is now unhappy, because the amp doesn't sound nearly as good. The solution (as pioneered by companies like Marshall and then carried forward by many botique amp builders) was to keep the same small transformer core and increase the size of the wiring. That way the core would still saturate but the tranny wouldn't burn up because the wiring was more robust.
One way to think of it is that the '50s Fender engineer would design a tranny for 15 clean watts. The Marshall engineer would design the tranny for 15 distorted watts (meaning the amp was really slamming the tranny with 20-25 watts of energy, but the Marshall tranny could easily handle being cranked). Most guitar amp transformer builders today know the amp will be cranked, and build transformers accordingly, so you should be fine.
Dave
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