I believe Post # 1 had a request for the simplest EL84 push pull amplifier.
Additionally, the request was for a low power guitar amplifier, it was not for a world class Hi Fi / Stereo amplifier.
Some replies have circuits that were tested, and working.
Others replies may not have been tested or working.
Without knowing the status of tested and working, versus not tested . . .
Do a parts count of the amplifier, but not including the power supply:
Post # 1. 5 parts + preamp = 6 parts
Post # 2. 13 parts
Post # 5. 31 parts
Post # 12. 29 parts
Post # 27. 8 parts + preamp = 9 parts
Post # 31. 20 parts + preamp = 21 parts
Post # 32. 13 parts (including an auto transformer/phase splitter)
Post # 34. 20 parts + preamp = 21 parts
Post # 37. 23 parts
6 parts to 31 parts (plus power supply parts for each one).
. . . Just one look at simple
Additionally, the request was for a low power guitar amplifier, it was not for a world class Hi Fi / Stereo amplifier.
Some replies have circuits that were tested, and working.
Others replies may not have been tested or working.
Without knowing the status of tested and working, versus not tested . . .
Do a parts count of the amplifier, but not including the power supply:
Post # 1. 5 parts + preamp = 6 parts
Post # 2. 13 parts
Post # 5. 31 parts
Post # 12. 29 parts
Post # 27. 8 parts + preamp = 9 parts
Post # 31. 20 parts + preamp = 21 parts
Post # 32. 13 parts (including an auto transformer/phase splitter)
Post # 34. 20 parts + preamp = 21 parts
Post # 37. 23 parts
6 parts to 31 parts (plus power supply parts for each one).
. . . Just one look at simple
Regarding my Post #12, it's a Simple Ultralinear Design nevertheless that produces outstanding performance from a matched set of EL84's.
I'd compare it to those commercially manufactured $2000+ amps sold around some sites.
I'd compare it to those commercially manufactured $2000+ amps sold around some sites.
My opinion:
The best way to start is to make a simply test setup to verify the main functions of the circuit.
You need a good sound card, REW o Arta software; a dummy load and a attenautor to send the right signal to sound card (they accept max 2 Vrms in some cases)
After this, step by step you can check if each stage is working as designed; this helps you to manage the voltages with maximum care.
Then, with the first lisening session, you can change some points of the circuit ( p.e., bypass cap on a cathode) , re-measured and listen.
This is the best way to know where you are going with a project.
Saying about a project " I listen well" is nothing because it is a personal impression and, for this reason, is personal; in addition there is a installation in a room that is, of course, different from yours so the sound can't be comparable at all.
Your feeling is the most important aspect.
Hi rayma, I should have provided more info. 😳 It actually is a guitar amp: the Vox AC15. But, the reason I posted it is because the OP said, "I'm looking to build at first a guitar amp..."
These two don't seem to go together. One is the engineering way; control, test, work towards your measurable goal. The other is the more artistic side that accepts the personal perception, pride in craftsmanship or learning, and so forth.
They go together because one doesn't exclude the other.
We can't exclude that a fine test result can't show a good sound. or viceversa.
In every case, also for learning, can be a good way.
We can't exclude that a fine test result can't show a good sound. or viceversa.
In every case, also for learning, can be a good way.
Certainly true, ideally they should go together. Yet it is easy for a focus on either view to dominate.
coolox,
1. Does it really work and how does it sound? It is just two resistors in a power amp circuit.
Answer: . . . With only the output tubes, it will play very quietly from the bare bones signal from an electric guitar. With the input tube of post #2, it will be louder, and might have a little distortion at the louder level, but not that you would notice, probably most of the "distortion" (not distortion) would come from the natural harmonics of your guitar (and those are natural harmonics, not amplifier harmonics)
How something sounds is also different for different listeners.
Just read a few different threads, and see how many opinions you get for which amplifier sounds best.
"If you are not easily satisfied, you might be satisfied, or you might not be satisfied."
The worst amplifier ever is the one you never heard, and/or the one you never built.
1. Does it really work and how does it sound? It is just two resistors in a power amp circuit.
Answer: . . . With only the output tubes, it will play very quietly from the bare bones signal from an electric guitar. With the input tube of post #2, it will be louder, and might have a little distortion at the louder level, but not that you would notice, probably most of the "distortion" (not distortion) would come from the natural harmonics of your guitar (and those are natural harmonics, not amplifier harmonics)
- 2. can I plug a guitar in? how would it sound?
- Answer: read answer to question 1 above.
- 3. what happens when tubes aren't matched? how does it sound?
- Answer: if the mis-matched plate currents are different enough, the output transformer could be saturated,
- if noticeable, would first be on the bass notes.
- 4. if I gradually add improvements, how does it sound?
- What improvements? The answer to that is as many as the number of improvements that you do, and the variety of those improvements.
How something sounds is also different for different listeners.
Just read a few different threads, and see how many opinions you get for which amplifier sounds best.
"If you are not easily satisfied, you might be satisfied, or you might not be satisfied."
The worst amplifier ever is the one you never heard, and/or the one you never built.
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Not I.
Oh, this is for a guitar amp? That's something completely different.
I guess transformer core saturation won't matter much then. Use a small OPT with biggish output tubes to get that swampy saturated tone thing happening.
I don't think there's anything simpler than following the good old Fender Deluxe Reverb output stage (12AT7 LTP, 6V6 pentode outputs) which could easily be adapted to 12AT7 and EL84, or even 12AX7 and EL84.
Indicentally, that Fender Deluxe output stage is really close to the Vox AC15 output stage. So if you like the AC15, I say that's a good way to go too.
Within reason, yes, any guitar preamp should be able to drive such an output stage. The LTP will have high input impedance. You may have a problem with too much gain (depending on your guitar tone tastes) but that can be dealt with by applying a bit of NFB around the output stage, Fender Deluxe-style.
I believe the original poster is looking for something SIMPLE.
I do not think he wants to modify or re-engineer an existing design.
What is simple to many of you is not simple to many others.
I also believe the intent was to build something that works, but it does not need to be the best guitar amplifier ever.
We are at Post # 51, and still there is no amplifier built by the original poster, and I am beginning to think he is discourcaged enough to give up the idea of building one.
Be helpful, do not complicate the issue.
Just my opinions.
I do not think he wants to modify or re-engineer an existing design.
What is simple to many of you is not simple to many others.
I also believe the intent was to build something that works, but it does not need to be the best guitar amplifier ever.
We are at Post # 51, and still there is no amplifier built by the original poster, and I am beginning to think he is discourcaged enough to give up the idea of building one.
Be helpful, do not complicate the issue.
Just my opinions.
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Well, in an effort to be helpful and to conform to your opinion on the matter, I'd say that the originally posted schematic is about as simple as it can get, and it will work with a minimum of tweaking.
I'd also say that triode-wiring the EL84s will be more likely to result in success than UL operation, as it will not absolutely need negative feedback to sound pleasant. In my experience, running a UL stage with no global NFB results in a kind of raw-edged sound (in my opinion).
Here's something that I think is as simple as can be done, and should be easy to get working well. Power supply not shown, which will be important too.
I'd also say that triode-wiring the EL84s will be more likely to result in success than UL operation, as it will not absolutely need negative feedback to sound pleasant. In my experience, running a UL stage with no global NFB results in a kind of raw-edged sound (in my opinion).
Here's something that I think is as simple as can be done, and should be easy to get working well. Power supply not shown, which will be important too.
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OP is building a guitar amp. Triode operation and CCS tail are not ideal for guitar.
It may look asymmetric, but that’s probably just because of where the taps were on the schematic symbol. Looks like bog standard ultralinear to me based on how it’s connected. I’ll be the taps on the trafo are really just at 40% on either side of CT.
As far as the simplest possible solution go back to post #5. Triode stage-concertina-EL84 pair. Doesn’t get much simpler or foolproof than that. Use the UL or not - user’s choice.
As far as the simplest possible solution go back to post #5. Triode stage-concertina-EL84 pair. Doesn’t get much simpler or foolproof than that. Use the UL or not - user’s choice.
Its simple: Tubelabs Simple PP....well tested and designed, and with cathode bias for simple user service....I have build one myself and it delivers!
Is not bog-standard output stage. Л3 g1 is grounded, they may have been playing with the output transformer.
It will be interesting to measure it.
The output pair is being run as an LTP with a common cathode resistor to do the phase inversion but there isn’t anything unusual going on with the output transformer.
Exactly, which is unusual for an output stage. I hope @cooloox will measure the output transformer, then we will know for sure.