Lynch Mod for the SC JCM 800's

Ok, from the headfirst amplification downloads that Robert linked (very helpful regarding what's going on in an Origin, thanks Robert), the Hot Mod won't work with the Origin because somewhat surprisingly, it doesn't have what we think of as the typical Marshall type pre-amp circuit. V1a is a common gain stage (voltage amplifier) followed by the gain & tilt controls. From there on its not like most Marshall's in that V1b is another voltage amplifier driving a plate driven tone stack (as opposed to the typical Marshalls V2b cathode driven tone stack).
V2a is the cathode follower driven FX loop ("send") & V2b is the FX loop recovery voltage amplifier.
If he is to develop a Hot Mod plugin for the Origin amps it will (most likely) have to plug into V1.
Ok, onto what headfirst amplification has done in modifying that Origin.
It has been changed to a more typical modified Marshall.
V1a is your typical 1st stage with a 100k plate load resistor & a 2k7/0.68uf cathode.
V1b is again a 100k plate load resistor & the cathode is again 2k7, but this time "partially" bypassed with the 0.68uf capacitor by putting it in series with a 47k resistor. These two (V1a & V1b) add up to being along the lines of the added stage/1st stage on the bright channel of a Josse modded plexi.
V2 has been changed to a typical Marshall V2.
V2a is a voltage amplifier with typical values, 100k plate loaded resistor & 1k cathode resistor, but the cathode has an added 22uf "fat cap".
V2b is the typical Marshall cathode follower driving the (now moved) tone stack. Hope this helps guys. Cheers
 
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ivan H said:
Ok, from the headfirst amplification downloads that Robert linked (very helpful regarding what's going on in an Origin, thanks Robert), the Hot Mod won't work with the Origin because somewhat surprisingly, it doesn't have what we think of as the typical Marshall type pre-amp circuit. V1a is a common gain stage (voltage amplifier) followed by the gain & tilt controls. From there on its not like most Marshall's in that V1b is another voltage amplifier driving a plate driven tone stack (as opposed to the typical Marshalls V2b cathode driven tone stack).
V2a is the cathode follower driven FX loop ("send") & V2b is the FX loop recovery voltage amplifier.
If he is to develop a Hot Mod plugin for the Origin amps it will have to plug into V1.
Ok, onto what headfirst amplification has done in modifying that Origin.
It has been changed to a more typical modified Marshall.
V1a is your typical 1st stage with a 100k plate load resistor & a 2k7/0.68uf cathode.
V1b is again a 100k plate load resistor & the cathode is again 2k7, but this time "partially" bypassed with the 0.68uf capacitor by putting it in series with a 47k resistor. These two (V1a & V1b) add up to being along the lines of the added stage on the bright channel of a Josse modded plexi.
V2 has been changed to a typical Marshall V2.
V2a is a voltage amplifier with typical values, 100k plate loaded resistor & 1k cathode resistor, but the cathode has an added 22uf "fat cap".
V2b is the typical Marshall cathode follower driving the (now moved) tone stack. Hope this helps guys. Cheers
Click to expand...

Wow!!!!

You made my brain smoke!!!! Great work there!!!!
 
Latest from Dave:

Hi Rob,

Thanks for that. I shared diagrams with Andy Marshall before who was my co-designer and he said he didn't believe it would work regardless. Similar example of an amp with a cathode follower and tone stack that looks like it would work on paper but then doesn't is the JCM 2000 DSL 100. All that said, if we can get there with something, we will. It's certainly been a popular request and will take some time to fully go through. There are other considerations like the power supply that we have to look at as well. I am in touch with Marshall support regarding some inquiries so maybe we'll get there. But I don't want to state we have compatibility until and unless we get the full scope.

I do know that if something was to work in the origin, it would need to be a reverse-wired version according to Marshall.

Thanks!
David
 
I'm really kinda surprised at how the designers have gone about the Origin pre-amp circuit. IMHO, they have wasted the V2 12AX7 by using it as the FX loop send/return buffer/amplifier. They could have used solid state devices for these purposes (like high voltage FET's). These have advantages like not needing a heater supply, not generating the tube's heat, having the signal "headroom" of a tube, being very small in size &, in a well designed loop, being totally transparent (can be left "in circuit" at all times). This would free up V2 to be used in the standard voltage amplifier/cathode follower arrangement, allowing the tone stack to be driven by the cathode follower & thus avoiding the loss associated with a plate driven tone stack.
V1 could have been arranged as in the "headfirst amplification" modified Origin, only with the ability to footswitch V1b in & out of circuit. This would result in the amp having a typical 4 hole Marshall "bright channel" along with a (footswitchable) higher gain OD channel. Just my 2 cents. Cheers
 
ivan H said:
I'm really kinda surprised at how the designers have gone about the Origin pre-amp circuit. IMHO, they have wasted the V2 12AX7 by using it as the FX loop send/return buffer/amplifier. They could have used solid state devices for these purposes (like high voltage FET's). These have advantages like not needing a heater supply, not generating the tube's heat, having the signal "headroom" of a tube, being very small in size &, in a well designed loop, being totally transparent (can be left "in circuit" at all times). This would free up V2 to be used in the standard voltage amplifier/cathode follower arrangement, allowing the tone stack to be driven by the cathode follower & thus avoiding the loss associated with a plate driven tone stack.
V1 could have been arranged as in the "headfirst amplification" modified Origin, only with the ability to footswitch V1b in & out of circuit. This would result in the amp having a typical 4 hole Marshall "bright channel" along with a (footswitchable) higher gain OD channel. Just my 2 cents. Cheers
Click to expand...

Question: how would you hotvrod the Origin???
 
Robert Herndon said:
Question: how would you hotvrod the Origin???
Click to expand...
Using the same principles as have been used in the headfirst amplification modified Origin, though this requires that the FX loop (if still used) becomes a "passive" loop rather than an active tube buffered loop.
There are type self contained, high voltage FET buffered FX loops available that can be added to many tube amps. The SMD designed Metroamp "zero loss" FX loop is one I've used & recommend. I believe this was the first of these types available (then everyone jumped on the bandwagon). Whether or not one can be fitted into the confines of the Origin chassis I couldn't say though. Cheers
Edit:
The type of V1 modifications done to the Origin by "headfirst amplification" are a very commonly used Marshall mod format, tried & proven long ago & used by many, including some well known production type amps. Cheers
 
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ivan H said:
Ok, from the headfirst amplification downloads that Robert linked (very helpful regarding what's going on in an Origin, thanks Robert), the Hot Mod won't work with the Origin because somewhat surprisingly, it doesn't have what we think of as the typical Marshall type pre-amp circuit. V1a is a common gain stage (voltage amplifier) followed by the gain & tilt controls. From there on its not like most Marshall's in that V1b is another voltage amplifier driving a plate driven tone stack (as opposed to the typical Marshalls V2b cathode driven tone stack).
V2a is the cathode follower driven FX loop ("send") & V2b is the FX loop recovery voltage amplifier.
If he is to develop a Hot Mod plugin for the Origin amps it will (most likely) have to plug into V1.
Ok, onto what headfirst amplification has done in modifying that Origin.
It has been changed to a more typical modified Marshall.
V1a is your typical 1st stage with a 100k plate load resistor & a 2k7/0.68uf cathode.
V1b is again a 100k plate load resistor & the cathode is again 2k7, but this time "partially" bypassed with the 0.68uf capacitor by putting it in series with a 47k resistor. These two (V1a & V1b) add up to being along the lines of the added stage/1st stage on the bright channel of a Josse modded plexi.
V2 has been changed to a typical Marshall V2.
V2a is a voltage amplifier with typical values, 100k plate loaded resistor & 1k cathode resistor, but the cathode has an added 22uf "fat cap".
V2b is the typical Marshall cathode follower driving the (now moved) tone stack. Hope this helps guys. Cheers
Click to expand...
e404e9583028f17f6319d74340f00ee7.jpg
 
Jethro Rocker said:
I saw your link, so you own one? Sweet!
Ypunleave rear grill off to adjust or just set n forget? Also, if one had to go cleanish to good dirt, does lowering preamp volume to like 6 still get cleanish even with gain up on Lynch?
Click to expand...

Yep. On all my amps. Back grill comes off and stays off. Want them light bulbs staying as cool as I can provide for. Especially for this module. Got to be able to reach it.

I've got the GL version which has a saturation pot. If you set it up right which I know you know what I'm talking about? Set it for as much as you want. Then roll guitar back for everything else. Seriously the roll back is that good and dynamic. Still smiling!
 
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