Building a Hybrid AX84 Guitar Amp with Reverb and Line-In Features

Question

Hello I slowly mature for the construction of a small, guitar tube amplifier. For now, I review the schematics and generally understand the topic. It will not be an independent project from scratch, but probably a hybrid based on AX84, because it is relatively not very complex and well...

jdubowski · Answer

No problem, only such an input is rarely needed in a guitar amplifier. Implementation - to receive a signal of the order of 0.1..0.5V you must have 1 degree of amplification before the final lamp. You insert AX84 by providing a signal from an external source to the 2nd triodode (switch), it is also worth doing a bypass for the color corrector which is strictly guitar in this system. As for matching the transformer to the anode - there is no problem, only that in a strictly guitar amplifier it can be smaller, and you can not afford such a luxury without losing bass. You have to replace something with a loudspeaker, so the load end (preferably on the loudspeaker socket, disconnected with its contact) + serial handpiece through which you plug your headphones. Note that there they added a cathode follower. Wisely used (shielding, cable length, etc.) will be OK. Remember about the capacitors for the right voltage and the appropriate power resistors. If you move your head, it will succeed even with the multimeter. Recommended reading:

t6ygfr5 · Answer

Hi

Thanks for the answer. I knew this page of Tom earlier, but only now did I begin to explore its resources. As I wrote earlier, I will probably design the project on AX84, although there are a few patents on the Tom website that I would like to use.
In general, I would like to make a 5W amplifier (SE, class A), with a reduction to 2 ... 3W - perhaps using a triode-pentode switch or another patent. The amplifier would have 2 channels: pure (typically Fender) and distorted, offering from crunch / overdrive to something like distortion (ie no hi-gain). I would like to have a separate tone and gain control for each channel, access to the effects loop and reverb. In addition, the switches enrich the sound: bright, boost, etc. Mandatory, headphones and unfortunate aux-in.

Contrary to what you have said, the aux-in input is relatively common in guitar amplifiers, but most often transistor - I did not find a tube amplifier with an aux-in input ... (maybe I was not looking for it).
If I understand correctly, then the way you gave (aux-in signal to the second triode grid) would result in another lamp between the preamp (also loop and reverb) and poweramp? Is there an alternative method? And if you could explain the issue of this cathodic follower just before the loop, I would be grateful, because somehow he did not pay attention to me.

Cramps, the more I read and review the patterns the more my enthusiasm falls and the doubts grow. Ehhh :cry:

Marcin_zam · Answer

From what I've understood, my colleague is talking about simultaneously using a guitar and player signal to have an exercise pad. Pozdr, Marvel

Futrzaczek · Answer

In that case, I do not understand the question of the author of the topic. It is enough to connect the aux-in socket with this triode grid using a capacitor with a capacity of 22nF to obtain sufficient mixing of signals. By the way, you get a free separation from the fixed component that players can spit out of the players.

t6ygfr5 · Answer

That's what it is - Marcin_zam hit the nail on the head, it's about simultaneous feeding of signals to the loudspeaker: from the guitar after passing the entire preamp string (and loops and reverb) and from mp3 (here without any adjustment and correction, only the volume in the player).

stolek_-92, or the signal from aux-in through the 22nF capacitor (which is ceramic, electrolyte or some other) is fed into the pentode power lamp grid (or triodes depending on the switch), right?

greetings

jdubowski · Answer

I also suggested an alternative which I accepted as a certainty. I am afraid a patent in the form of a single capacitor will not do the job - unfortunately, a large part of the players have a low-energy output and the effect of such an attachment will be annoying - the player's output will jumble to the ground (maybe not quite ...) signal from the preceding stage, because the same level usually has resistance output in the order of several hundred kilo- meters. Ergo - a cathode / emitter / source follower must be inserted before the mixing point. Foil capacitor - 22nF is not the capacity for electrolyte, and ceramics advise in the signal path to avoid because of this capacity are made of ferroelectric material with inadequate properties. Delete this switch (it refers to a system in which you alternatively release a mjuzik from the player or tear the wires). As for the place where the signal is plugged in, I would not set up the final pentode grid - there would be a voltage of several volts, which you will not get from the CD player.

t6ygfr5 · Answer

This pentode-triode switch in addition to the power reduction (what I want, despite the low power of the amplifier, because it may be that 5W to play at home is too much) is supposed to also provide a "different" sound when the tip is in triode. At least these are the opinions of people in forums. Unfortunately, I did not have the opportunity to verify these organoleptic theories - I never had my own lantern ...
Or maybe the solution will be a simple circuit inside the amplifier, based on transistors and amplifying the aux-in signal, and then give such a signal to the terminal grid?

If any of you would come across such a scheme of connecting the aux-in input to the rest of the amplifier, please post it. "One picture worth a thousand words" - it is easier for the layman to understand

pzodrawiam

Futrzaczek · Answer

The capacitor will present itself with a high reactance for the signal. In connection with the leakage resistor of the control grid, something like the voltage divider should be created. In addition, if the guitar signal is too damped, you have to work with the addition of a resistor between the capacitor and the lamp grid - this should cause additional suppression of the suggestion. Of course, the patent with the is more professional

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