I was asked to design a SE amplifier above 10 W power level.
The customer let me suggest him new ideas, but the main target was to create a relatively "clean" amplifier. I planned to try something new for the tone stack and I also wanted to try something else than conventional EL34 as an output tube.
One design goal was to keep all supply voltages adjustable to find the best possible result.
The prototype has no been built and is under initial tests.
Output power exceeds 15 W.
Since this is my first guitar amp, all comments are welcome.
The customer let me suggest him new ideas, but the main target was to create a relatively "clean" amplifier. I planned to try something new for the tone stack and I also wanted to try something else than conventional EL34 as an output tube.
One design goal was to keep all supply voltages adjustable to find the best possible result.
The prototype has no been built and is under initial tests.
Output power exceeds 15 W.
Since this is my first guitar amp, all comments are welcome.
An externally hosted image should be here but it was not working when we last tested it.
An externally hosted image should be here but it was not working when we last tested it.
I can't read the main schem values either, and I've got my "extra powerful" reading glasses on.
jeff
Imageshack seems to decreased the resolution too much.
I try to get better pictures tomorrow.
http://img845.imageshack.us/img845/5307/vahv2.gif
I try to get better pictures tomorrow.
http://img845.imageshack.us/img845/5307/vahv2.gif
6F12P (6Ф12П) is Soviet triode-pentode with two very efficient tube halves.
Both pentode and triode have very high Gm (~19,5 mA/V) and the triode part has µ = 100.
The reason why not an other 6N1P is that a pentode was wanted as a voltage amplifying stage.
OPT impedance is 2k5, but it could also be up to 3k5 with essentially similar performance. There will only be slight difference between the level of 2nd and 3rd harmonic.
The anode (to cathode) voltage is some 120 V, because there is R5 (22k) as cathode resistor. This means that the DC-voltage at the cathode is some 130 V.
R4 forms local negative feedback at the output tube only and thus improves the linearity of whole amplifier, as does the global negative feedback due to R24 as well, but with different way.
The total NFB can be adjusted with P6 at the output trafo.
The tests will show which supply voltages should be left user-adjustable.
I do not know yet.
Won't this exceed the maximum filament to cathode potential?
The idea with 2 levels of feedback is interesting, but isn't that potentially counterproductive in a SE guitar amp that is likely to be driven out of its linear range? Guess only listening can tell.
I do not know this.
Can you give an example of such circuit ?
Now the pentode goes distorted when the signal form guitar is at maximum.
And the distortion threshold can be adjusted to lower level by biasing the pentode a bit different way.
The manufacturer has specified max. Ukh as +120 V...-150V.
Typically there is a lot of safety margin too. I am not concerned about this.
No, these two feedback loops are working fine together and both improve the linearity, alone and together.
I have used this system with Hifi-amplifiers and it seems to work with guitar amplifier as well.
If only the global NFB is used, then the overall stability of the amplifier could be a problem in some cases. In other words; the use of local NFB at the output tube makes a "good" amplifier easier to build.
a while ago I found this passive compressor curcuit
I dont know if its any good
distortion control I guess is only a matter of overdriving one gain stage
and I suppose it means one more attenuation pot
one to cranck up the gain, and one more after the overdriven tube, to attenuate it again
hmm, and maybe additional adjustment pot or switch, to bring the overdriven tube in a state where its easily overdriven
Attachments
hi Arto, is this a country fellow man to you ?
Guitar Effects Projects - Richardo's Pages
and theres is a lttle bit here too
http://www.261.gr/limiters.html
dont if if its of any use to you
Guitar Effects Projects - Richardo's Pages
and theres is a lttle bit here too
http://www.261.gr/limiters.html
dont if if its of any use to you
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