G
Guest
Guest
explain how this works!
http://aronnelson.com/gallery/johan/Mini_my2
http://aronnelson.com/gallery/johan/Mini_my2
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NewYorkDave
Well-known member
Nothing complicated about it. The output signal is half-wave rectified and varies the grid bias for the first triode. It is indeed crude and probably sounds awful.
G
Guest
Guest
[quote author="NewYorkDave"]Nothing complicated about it. The output signal is half-wave rectified and varies the grid bias for the first triode. It is indeed crude and probably sounds awful.[/quote]
i think it is for more electric guitar type applications.....not hi-fi.
i would be interested to hear it...
i think it is for more electric guitar type applications.....not hi-fi.
i would be interested to hear it...
> output signal is half-wave rectified
Quasi-full-wave.
On sustained test tone, it will approach the peak-to-peak of the output wave.
On speech/music: it is unpredictable.
It will be 1.0-1.2V short due to Si diode drop. You need about a volt at the grid to get good GR. So the output will be a couple volts p-p while limiting, with nearly no GR for inputs up to 1 V p-p. That gives some threshold action.
0.7V RMS at the output needs about 10mV at the input at threshold, maybe 100mV in deep GR. Input level for SE 12AX7 has to be held to much less than 600mV for low distortion. It isn't in deep doo-doo, though it is too bent for "good" audio.
That assumes the rectifier pot is pretty full-up. If turned down, output level will be high, input level soon in excess of 600mV, signal grossly bent.
OTOH if pot is full up, the rectifier can be a heavy load on the cathode follower, clipping positive peaks.
Up to 1V of control voltage is applied to the grid which will amplify a thump. The cathode follower or a later stage will likely be thrown outside its linear range and clip for a while.
The attack is set both by the 5K/1uFd, and the 470K/0.1uFd in series with source impedance. If source is low-Z, it will be slow, OTOO 50mS. If source Z is much higher than 470K, it will be ~5mS but thump badly.
Oh: the 1.2V threshold is temperature sensitive, which might not be a problem though it is next to a hot bottle.
Build it, try it.
Quasi-full-wave.
On sustained test tone, it will approach the peak-to-peak of the output wave.
On speech/music: it is unpredictable.
It will be 1.0-1.2V short due to Si diode drop. You need about a volt at the grid to get good GR. So the output will be a couple volts p-p while limiting, with nearly no GR for inputs up to 1 V p-p. That gives some threshold action.
0.7V RMS at the output needs about 10mV at the input at threshold, maybe 100mV in deep GR. Input level for SE 12AX7 has to be held to much less than 600mV for low distortion. It isn't in deep doo-doo, though it is too bent for "good" audio.
That assumes the rectifier pot is pretty full-up. If turned down, output level will be high, input level soon in excess of 600mV, signal grossly bent.
OTOH if pot is full up, the rectifier can be a heavy load on the cathode follower, clipping positive peaks.
Up to 1V of control voltage is applied to the grid which will amplify a thump. The cathode follower or a later stage will likely be thrown outside its linear range and clip for a while.
The attack is set both by the 5K/1uFd, and the 470K/0.1uFd in series with source impedance. If source is low-Z, it will be slow, OTOO 50mS. If source Z is much higher than 470K, it will be ~5mS but thump badly.
Oh: the 1.2V threshold is temperature sensitive, which might not be a problem though it is next to a hot bottle.
Build it, try it.
thank's PRR..
this was just an exercice to see if I got the principle right and if so, how simplistic I could do it...the inputcap/resistor has since been replaced with a small 1:1 audiotransformer, wich improved things..deffinetly not HiFi, but quite allright when plugging an electric bass straight into it...crude but works..
johan
this was just an exercice to see if I got the principle right and if so, how simplistic I could do it...the inputcap/resistor has since been replaced with a small 1:1 audiotransformer, wich improved things..deffinetly not HiFi, but quite allright when plugging an electric bass straight into it...crude but works..
johan
Of course you could eliminate the DC thump by running two of them in push-pull, then it would be adviseable to improve the rec circuit and get the tube operating in a more linear area... then you could use a different tube type..... :shock:
But then.... maybe someone's done it before! :grin:
But then.... maybe someone's done it before! :grin:
Larrchild
Well-known member
In the realm of guitar amps, I've seen circuits that stole a little of the speaker signal to drive rectifiers and control the 1st preamp stage gain via bias,
Why not?, lol..you have but a half dozen components to add.
Why not?, lol..you have but a half dozen components to add.
..like I said..it was just an exercice to see if I got it..
..but after PRR's post, I pulled it out from the "never-finished-projects"-box ( its geting BIG ) and hooked it up with a signalgenerator and an oscilloscope..everything PRR prerdicted was true...big surprice huh.. :grin:
..so what I did last night was to separate the sidechain from the output with a simple FET sourcefollower, just to see...( learning, learning..thats the whole point..) and things got considerably better..still not HiFi...but give me a year or two...( I never seem to sustain interest long enough to ever finish these projects :sad: )
..but thanks for all the input..
johan
..but after PRR's post, I pulled it out from the "never-finished-projects"-box ( its geting BIG ) and hooked it up with a signalgenerator and an oscilloscope..everything PRR prerdicted was true...big surprice huh.. :grin:
..so what I did last night was to separate the sidechain from the output with a simple FET sourcefollower, just to see...( learning, learning..thats the whole point..) and things got considerably better..still not HiFi...but give me a year or two...( I never seem to sustain interest long enough to ever finish these projects :sad: )
..but thanks for all the input..
johan
clintrubber
Well-known member
[quote author="Larrchild"]In the realm of guitar amps, I've seen circuits that stole a little of the speaker signal to drive rectifiers and control the 1st preamp stage gain via bias,
Why not?, lol..you have but a half dozen components to add.[/quote]
Just curious: which types/brands do this ?
Thanks,
Peter
Why not?, lol..you have but a half dozen components to add.[/quote]
Just curious: which types/brands do this ?
Thanks,
Peter
Larrchild
Well-known member
I'm still looking for the link, but i meant that i saw a few DIY guitar amp circuits that did that.
clintrubber
Well-known member
[quote author="Larrchild"]I'm still looking for the link, but i meant that i saw a few DIY guitar amp circuits that did that.[/quote]
OK, I see. Was wondering - hadn't heard of any 'commercial ones' doing it, so I got curious.
Thanks,
Peter
OK, I see. Was wondering - hadn't heard of any 'commercial ones' doing it, so I got curious.
Thanks,
Peter
Larrchild
Well-known member
here we go, clintrubber, http://www.dogstar.dantimax.dk/tubestuf/4x4compr.htm
clintrubber
Well-known member
Thanks for finding that circuit ! Nice link. :thumb:
Control voltage to 4AU6 / 6AU6, just out of curiousity I saw the EF94 is a replacement for the latter, FWIW can't remember having seen such a tube so far.
Bye,
Peter
Control voltage to 4AU6 / 6AU6, just out of curiousity I saw the EF94 is a replacement for the latter, FWIW can't remember having seen such a tube so far.
Bye,
Peter
