To see if the circuit will produce the desired output, calculate the currents and voltages as done for the previous circuits. All london power power scaling amps are designed to provide smooth, sweet, clean sounds up to their limit of power. Tube power vs solid state power, how much is enoug audiogon. Build a wide range of tremolo circuit and an all tube reverb unit. It works by switching the circuit board to lower the voltage on the output transformer, totally transparency in tone at lower volumes. This is a high gain amplifier based on the jcm800 power amp platform. Nov 30, 2016 this is a high gain amplifier based on the jcm800 power amp platform. I have optimized the system for use in my own amps and call it opr. The steam amp 03 curated steampunk and dieselpunk gear madburner steam amp 4 industrial steampunk art and furnishings coppersteam. The preamp for this amp is completely different from the jcm800 with. Getting the pair moved into my listening room required. What amps are made with power scaling the gear page. Power supply schematic kt88 pushpull tube amp amplifier.
In general, i do not use them for the main amp because they are just too much of a pain for repair, tube sockets on the boards stress the traces and my customers dont like them. Next select the type of bias fixed or cathode and power supply dc or ac. Figure 324 is the schematic diagram of a scaling amplifier with the values calculated above. Readers of kevin oconnors the ultimate tone tut book series form a part of our population. The first screen in tubecad shows the schematic of the output stage. Its a deadsimple way of lowering power amp drive, yet compensating for loss of distortion at low volume and works like a charm.
Power scaling is a london power trade name rat is licensed to use this technology. But still, a tubed amp will sound somewhat better when driven to deliver power beyond its rating ie, at clipping than a ss amp will. Power scaling kits tube amp kits, tube amp books from london. The key to power scaling is that it is applied to the power output tube stage itself, and so comes before the output transformer. Set to full power, power scaling will not alter the clean sound of your amp. Btw, if you want to check out a cool master volume idea, go to the ax84 discussion forum and search poormans powerscaling. There is a computer program that comes with this page to help you. Note the size of this amp compared to the cigarette packet.
Power scaling reduces power, and thus volume, enabling the amp to produce power tube distortion at reduced volume levels, freeing you from the need for an attenuator. A warm welcome to tube amp modding fans and those interested in hifi audio. This is not a simulator, but a schematic capture and routing tool which i understand can integrate with spice. Great overdrive from the el34 when cranked, and not too loud at. A trio of software programs for the intrepid tubephile. Audio power amplifier circuit diagrams circuit schematics. Power supply for a tube amplifier schematic youtube. It can get mushy and soft at low levels if you scale the whole amp. Power scaling is a technology developed by london power, headed by renowned tube amp innovator and author kevin oconnor, that controls voltages inside the amplifier, allowing for continuously adjustable power output. Books about getting guitar sounds added latest amp tone books and videos, aug. If you set power scale to a lower setting, the amp now behaves as a lowerpower amplifier with a lower maximum loudness for clean sounds.
Although all the above methods attenuate the output signal, the units most commonly referred to as amp attenuators are the brute force methods of attenuating. Power scaling a london power trademark and vvr, which stands for. London power standard amp built into fender bassman 10 chassis. Below that you choose from a list of popular output transformers.
Initial power up checks were all fine guitar plugged in and sounds great. It is available as a head shown here, an 8 combo, and a 10 combo. For those of you who dont recognize it, this is a thermal relay in an octal socket. If you want to skip the build description and just hear the amplifier,just skip the article and jump to the sound clips a vox ac4 tvh is a small tubedriven practice amplifier release byvox in 2008. But the main voltage would have to dump a lot of heat and neither has a heat sink. The sv power scaling kits all use printed circuit boards with small boards for the pots to make wire connections. Without resorting to software modeling which actually produces fairly decent results. The experimenters power supply is excellent for tinkering with tube circuits, containing separate ac heater, dc heater plate and bias supplies. The following circuit operates at a mains voltage of 230 vac.
I thought the mosfets might have been one used to scale the main voltage and one to scale the bias voltage. At the same time i had a few voltage amplifiers breadboarded on the tubelab system for testing. The circuit is my own design built from scratch specifically for my needs instead of scaling down a big power amp. Jan 25, 2018 the power scaling used on the orgin is very different than anything marshall has done. I wanted to have a small but nice sounding tube power amp that i can use with my preamps and pedals. The basic deal is about half the tube watts vs ss watts for controlclipping on the speakers. Tube power vs solid state power, how much is enoug. Checked the amp over, added a wire id missed from my layout to the power tube cathode. London power standard circuit built into a late 70s fender bassman 10 chassis and transformer set. A functional steampunk tube amplifier, pumping out 8 beautiful watts of valve power. Output tranformer distortion with guitar amp attenuators and load boxes. A poorly biased tube can either be biased too cold making it sound dull and lifeless or biased too hot where the tube is destroying itself.
Also, i wanted it to be able to be a standalone clean amp without a need for additional pedals to drive it. Power scaling is kevin oconnors london power term for the ability to variably reduce the output power of an amp. Fwiw, think of a tube amp with a passive line stage ahead of it. Assembly manual schematic parts list tubes and applications design simulations. Jul 11, 2007 btw, if you want to check out a cool master volume idea, go to the ax84 discussion forum and search poormans powerscaling.
The axefx ii does not model the power scaling circuit as there is no point in that. Because of rectification some of the components conduct dc voltage of more than 322 v. At the upper left you choose the tube type, and the number of tubes in parallel. The soft rectifier effect combined with solen polypropylene power supply caps completely eliminates diode noise effects. Power supply and power control circuit diagrams circuit schematics note that all these links are external and we cannot provide support on the circuits or offer any guarantees to their accuracy.
When using the terms cathode or fixed bias we are discussing the power tubes of an amp pre amp tubes are nearly always cathode bias or gridleak biased but that is a discussion for another time. If you do go for a different power amp, be aware that you cant use either of the marshallspec transformers, you need a power. This is a real swissknife of a 3 channel amp with lots of smart functions and at a really great price point. Apr 20, 2018 the power scaling switch wires go to the area between the second tube and the pi, not sure how they are doing the scaling, why it goes to this board area. This particular build does not include the power scaling or reverb in the london power. Power scaling is an excellent system and works well. Work has to be carried out only if the circuit is disconnected from the mains and deenergized. Even if you only own tube gear and have no ambitions at all of tinkering with any construction projects, youll find the tube manual to contain essential knowledge. Marshall origin series amplifiers page 9 marshall amp forum. Alternately, use a high power 80v zener to drop the plate voltage, one on each plate, and one on the screen supply as well. The ac20 model is based on the amp with the power scaling at maximum power which effectively disables it and sounds best imo. Nor, at 280lb in its flight case, is it likely to go walkin. This is a functioning 8 watt per channel valve amplifier that i built.
Kicad was made for modern electronics and doesnt come with any vacuum tube symbols built in. Birminghams laney amplification is often overlooked by the masses, even thought theyve been at it for decades and have some wonderful legendary amps to their name. Some circuits would be illegal to operate in most countries and others are dangerous to construct and should not be attempted by the inexperienced. The slides are pretty heavy on engineering design terms, but give a good feel for what it takes to construct and tune an audio amplifier using vacuum tube technology. Iive never seen a schematic for either a vvr kit or a power scalling kit. Power scaling allows you to live at that cusp or beyond, but at any loudness you need. Most speaker attenuators alter the tone before they reach 8db reduction. The device receives your amps output and fully clamps it down in the load box, where it derives from it a linelevel signal much like an amps di output which it sends along to its internal power amp. This is not a simulator, but a schematic capture and routing tool which i. Having a separate power amp is very flexible, since you can combine it with any preamp you want. Kevin oconnor is the creator of the popular power scaling methodology for amplifiers. If you are down with bode plots and circuit diagrams, though, it could serve as a nice introduction to. If you imagine a knob that goes to 10, with 10 being no scaling, the power scaled amp i spent the most time with sounded ok from 10 down to about 7. Guitar amp attenuators, power scaling, master volumes.
Demo is functional for 45 days, but will not save or print. This 20watt amp head is powered by a pair of el34 tubes with three 12ax7 preamp tubes. His library was last updated on 10262008, so its clearly not being maintained. Monoprice 5watt, 1x8 guitar combo tube amplifier with. Changes to the circuit are immediately reflected in the circuit schematic. The experimenters power supply is excellent for tinkering with tube circuits, containing separate ac. Each builder begins with traditional or original audio circuit ideas enhanced by. Marshall origin series amplifiers marshall amp forum. That s why many of us say that generally one can get away with a tubed amp of half the rated power compared with a ss amp. This article shows how i built a powerscaled tube guitar amplifier by making radical changes to a vox ac4 tvh amplifier head. Audio power amplifier circuit diagrams circuit schematics note that all these links are external and we cannot provide support on the circuits or offer any guarantees to their accuracy. I went through every tube in the tube cad library trying to get a voltage gain of 50 and a tube current of close to 10 ma. Power supply and power control circuit diagrams circuit.
That would optimally be the same as a tube amp with solid state preamp, except for with the solid state preamp you would have gain. Power scaling is kevin oconnors london power term for the ability to. A key trick is to scale just the power valves and that way you do not lose the edge on the preamp. If your speakers clip at 100w with a strong ss ampnot cheezy piece, you can figure clipping at about the same output with a 50watt tube amp, or thereabouts. Power supply schematic kt88 pushpull tube amp amplifier, tube.
Jul 25, 2019 the device receives your amps output and fully clamps it down in the load box, where it derives from it a linelevel signal much like an amps di output which it sends along to its internal power amp. Does anyone have schematics for the power scaling circuit as employed by kevin oconnorlondon power. Also contains some vacuum tube models which drop straight on, and an example of a vacuum tube power amp. Apr 10, 2010 the slides are pretty heavy on engineering design terms, but give a good feel for what it takes to construct and tune an audio amplifier using vacuum tube technology. Ive got an actual london power amp with the power scaling. Oddblocks 12sl7 srpp kt88 pushpull tube amp schematic. Its all the good things that people get a tube amp for except for the brand name. The power scaling switch wires go to the area between the second tube and the pi, not sure how they are doing the scaling, why it goes to this board area. Power scaling allows a dynamic power range over 40db. London power amps use proper grounding to eliminate hum and buzz. The power scaling used on the orgin is very different than anything marshall has done. Construct a 15w tube power amp or a true classa solid state amp. This effect can be some clipping, heavy clipping, or just that cusp of compression you get in a tube power amp approaching clipping. If you find that the whole 20 watts are a little too powerful for what you need, the builtin power reduction circuit cuts the power to just 5 watts.
Or, a combination of a less efficient rectifier tube and zeners. At the right you set up choice of fixed or cathode bias. Posted on july 27, 2011 by jwk ive been scaling my radio collecting back a bit, as i need to work through the backlog of ones i already have, but one caught my eye. If you want to build a tube amplifier and you dont want to just copy someone elses circuit it might be a good idea to learn how to design it. That allows some interesting solutions that may not cheap or practical for bigger amps but fit great here. The power amp then sends a signal to the units speaker outputwith volumelevel and tone controls for the user interfacewhich can be. Power scaling reduces power, and thus volume, enabling the amp to produce power tube distortion at reduced volume levels.
Note that all these links are external and we cannot provide support on the circuits or offer any guarantees to their accuracy. The pre amp for this amp is completely different from the jcm800 with added gain stages. If i could only choose one combo it would be ss pre tube amp. When using the terms cathode or fixed bias we are discussing the power tubes of an amp preamp tubes are nearly always cathode bias or gridleak biased but that is a discussion for another time. New build single ended el34 with power scaling 10w. Youll find that it can create perfectly saturated blues tones and soaring leads with ease. Part of diy is that you can do things that manufacturers wont. You do get to preserve the effects of preamp, power amp and output transformer distortion.
By trying out several different sets of operating conditions in the computer i could eliminate hundreds of possibilities without playing with electricity. Select an output transformer and a power tube from the builtin libraries. It is a tube amp with a 12ax7 preamp tube and a 6v6 power tube. Vvr schematic and pcb layout for cathode biased amps for more. I implemented it on an amp i just built and like it a lot. If you are down with bode plots and circuit diagrams, though, it could serve as a nice introduction to building a class ab amplifier circuit. You could build a plexi preamp into a 1w power amp, but dont be too disappointed if you dont achieve the cranked plexi sound from a most likely at that wattage singleended power section with the wrong tube. The 12at7 amplifier below is the best that i could do. Fellow radio enthusiast n9god has developed the n9godvalves library of tube symbols and references but theyre mostly industrial and audio tubes. Build a wide range of tremolo circuit and an alltube reverb unit. That would optimally be the same as a tube amp with solid state pre amp, except for with the solid state pre amp you would have gain. Power scaling for tube guitar amplifiers a technology by london power. Stephenson amplification lj15 ext power scaling, 2channel power amp.
I tried several tube types to see if i could improve the tone and i went back to the stock preamp tube. Hello, all you highpowered tube amp maniacs out there. At first i tried scaling just the power amp, but have just reverted to whole amp scaling. In my online travels i have discovered london power scaling and other similar. Power scaling is the best solution for those players who incorporate some amount of output stage effect in their sound. In the amp that came through here that had power scaling of the whole amp, it seemed to me to have a very narrow range of acceptable tone. Mv, powerscaling in 50w, 100w amps music electronics forum.
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