[IMG
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skyboltone
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figure this out Marshall 2555
Here's a wonderment for me. Apparently we are rectifying the signal and lighting led's with it. Anybody know why? Clearly the ground connection between the coupling caps at stage one is weird too. I've seen another scheme where it doesn't exist. The rest of it is pretty straight forward, but what's up with the leds?
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1101]http://i41.tinypic.com/2qnv4hl.gif[/img]
[IMG
1101]http://i41.tinypic.com/2qnv4hl.gif[/img]The Last of the World's Great Human Beings
Seek immediate medical attention if you suddenly go either deaf or blind.
If you put the Federal Government in charge of the Sahara Desert, in five years time there would be a shortage of sand.
Seek immediate medical attention if you suddenly go either deaf or blind.
If you put the Federal Government in charge of the Sahara Desert, in five years time there would be a shortage of sand.
Re: figure this out Marshall 2555
I believe they're lighting up the lead tone..diode clipping stage
Re: figure this out Marshall 2555
Dan
It's not the easiest schematic to read with ground connections all over the place. I know because I've built one of these!
The LEDs are used for diode clipping on the lead channel, much like how the diodes are used in a tube screamer.
Red LEDs rather than regular diodes were chosen for their forward voltage (i.e. the maximum signal they would pass versus the levels expected at this part of the circuit), but also the shape of the 'knee' as the forward voltage is reached.
Some types of diodes have a very sharp knee, and others a soft one, and this will significantly affect the resultant sound between overdrive and distortion characteristics.
This amp has a great lead channel (it works well enough for Joe B), although is quite different from most other Marshalls.
Paul
It's not the easiest schematic to read with ground connections all over the place. I know because I've built one of these!
The LEDs are used for diode clipping on the lead channel, much like how the diodes are used in a tube screamer.
Red LEDs rather than regular diodes were chosen for their forward voltage (i.e. the maximum signal they would pass versus the levels expected at this part of the circuit), but also the shape of the 'knee' as the forward voltage is reached.
Some types of diodes have a very sharp knee, and others a soft one, and this will significantly affect the resultant sound between overdrive and distortion characteristics.
This amp has a great lead channel (it works well enough for Joe B), although is quite different from most other Marshalls.
Paul
Re: figure this out Marshall 2555
I first saw these in a Silver Jubilee. diode clipping ala tube screamer. LED's clip differently than a Silicon or Germanium. Fender uses them as well in some of their amps, for distortion.
Just realized 2555 is a Silver Jubilee, oops.
Just realized 2555 is a Silver Jubilee, oops.
Re: figure this out Marshall 2555
In the late 80's I often did sound production for a band called "Vova Nova" . Their guitarist had a 2555 and I loved the sound he got our of it. I told myself if I ever was going to buy a Marshall, it would be one of those. Years later when I saw a schematic of one, I was astounded that some of the distortion was coming from diodes. That ended my predujice against SS. Used in the proper context, tubes and SS can coexist.
Heres a sample from one of Vova Nova's songs with Glenn using the Silver Jubilee (Hopefully they don't mind me posting this for educational purposes
):
Heres a sample from one of Vova Nova's songs with Glenn using the Silver Jubilee (Hopefully they don't mind me posting this for educational purposes
):You do not have the required permissions to view the files attached to this post.
Re: figure this out Marshall 2555
My JCM 900 has 4 LEDs in the feedback loop of an op-amp in the clean channel. I love the clean sound until the channel's pre-amp gain gets above "6" or so. I keep meaning to check & see how hard, if at all, those LEDs are being used (not enough current to actually make them light), but then I tell myself, "Hey - it sounds OK. Just shut up and play something".
W
W