JVM410H crunch channel vs 410HJS crunch channel

[maxxi]

Hi everyone

I have a question that I have been asking myself for a couple of years.

What's the difference between the crunch channel of the original JVM and the Satriani JVM schematic wise, and what would be needed to bring the OG JVM's crunch channel up to those specs?

I have done the following mods to my 410H: neg. feedback, plexi cap, compression reduction, 10H choke; but still the only channel I don't like is the crunch channel.
It seems the JS crunch channel is more "alive" and growls just the way I imagine a classic Marshall growls, the OG JVM's crunch channel seems to lack the punch that the JS has.

 

[spacerocker]

Hi everyone

I have a question that I have been asking myself for a couple of years.

What's the difference between the crunch channel of the original JVM and the Satriani JVM schematic wise, and what would be needed to bring the OG JVM's crunch channel up to those specs?

I have done the following mods to my 410H: neg. feedback, plexi cap, compression reduction, 10H choke; but still the only channel I don't like is the crunch channel.
It seems the JS crunch channel is more "alive" and growls just the way I imagine a classic Marshall growls, the OG JVM's crunch channel seems to lack the punch that the JS has.

I have been asking myself that question too...Now I have a JS Marshall (along with my modded JVM410H and 205C amps) so I can easily compare the two sound wise...

The answer is both simple and complicated:

It is almost impossible to modify the standard JVM crunch channel to be exactly the same as the JS model...This is because the gain structure is different in the JS model, with more gain stages used in the Crunch channel. This would be very difficult to change, as it would mean changing the way the switching logic works.

Also there is a simple circuit (sometimes called the treble peaker) which is similar to what is used on a 800/2203 which on the JS model is switched into the circuit ONLY on the crunch channel. This simple RC circuit is a high-pass filter, which shaves off some bass and enhances the mids/uppper mids

Finally, the two amps are voiced differently. The standard JVM is quite bright and "thin" sounding, whereas the JS is fatter and ballsier and has more of a mid-focus. My circuit analysis has shown that a lot of this is due to a capacitor across the channel volume pot on a JS model. This rolls off the top end considerably, and adds more mids to the tone circuit....



However, there is a simple mod called the "AFD mod" which can improve the standard JVM crunch channel considerably! it involves soldering a 100nF cap in series with a 1K0 resistor across R96 (at least that is my version of it) the result is that the crunch channel is brighter and has more gain than stock...The downside is that the OD channels are also affected, so you will need to decrease the gain/treble settings to compensate..This mod actually ISN'T on the JS model, but adding it to the stock model does improve the Crunch consideably!



Comparing the JS model crunch with the Standard model, the JS has much more gain in the crunch channel, and is much clearer and punchier....comparing the JS with my modded crunch channel, I'd say the gain is about the same, and the tonality is similar. The JS Still sounds better, but the difference is less than what it is with a stock JVM....

 

[maxxi]

I have been asking myself that question too...Now I have a JS Marshall (along with my modded JVM410H and 205C amps) so I can easily compare the two sound wise...

The answer is both simple and complicated:

It is almost impossible to modify the standard JVM crunch channel to be exactly the same as the JS model...This is because the gain structure is different in the JS model, with more gain stages used in the Crunch channel. This would be very difficult to change, as it would mean changing the way the switching logic works.

Also there is a simple circuit (sometimes called the treble peaker) which is similar to what is used on a 800/2203 which on the JS model is switched into the circuit ONLY on the crunch channel. This simple RC circuit is a high-pass filter, which shaves off some bass and enhances the mids/uppper mids

Finally, the two amps are voiced differently. The standard JVM is quite bright and "thin" sounding, whereas the JS is fatter and ballsier and has more of a mid-focus. My circuit analysis has shown that a lot of this is due to a capacitor across the channel volume pot on a JS model. This rolls off the top end considerably, and adds more mids to the tone circuit....



However, there is a simple mod called the "AFD mod" which can improve the standard JVM crunch channel considerably! it involves soldering a 100nF cap in series with a 1K0 resistor across R96 (at least that is my version of it) the result is that the crunch channel is brighter and has more gain than stock...The downside is that the OD channels are also affected, so you will need to decrease the gain/treble settings to compensate..This mod actually ISN'T on the JS model, but adding it to the stock model does improve the Crunch consideably!



Comparing the JS model crunch with the Standard model, the JS has much more gain in the crunch channel, and is much clearer and punchier....comparing the JS with my modded crunch channel, I'd say the gain is about the same, and the tonality is similar. The JS Still sounds better, but the difference is less than what it is with a stock JVM....

Thank you for the info! Really appreciatie it!
I did read about the AFD mod, but was thinking if it would be possible to limit it to the crunch channel, as the od channels have a huge amount of gain.

Are we talking a huge amount of extra gain on the od channels, or rather a difference thats's only noticable when you really listen for it?

would you have any sound clips of the AFD mod, preferably of the crunch and od1 channel?

Thanks!

 

[Kuga]

Also there is a simple circuit (sometimes called the treble peaker) which is similar to what is used on a 800/2203 which on the JS model is switched into the circuit ONLY on the crunch channel. This simple RC circuit is a high-pass filter, which shaves off some bass and enhances the mids/uppper mids

Is there a mod on the JVM HJS to get TSL100/122 presence?
Maybe I have an issue on this RC circuit. The crunch channel sounds so bassy lately. I play It with presence at 10 and resonance at 0.

 

[spacerocker]

Thank you for the info! Really appreciatie it!
I did read about the AFD mod, but was thinking if it would be possible to limit it to the crunch channel, as the od channels have a huge amount of gain.

Are we talking a huge amount of extra gain on the od channels, or rather a difference thats's only noticable when you really listen for it?

would you have any sound clips of the AFD mod, preferably of the crunch and od1 channel?

Thanks!

Unfortunately I don't have any clips of the AFD mod - But all I will say is it is well worth having! I have done this mod for a few people now, and everybody (so far) loves it! It is not possible to limit the mod to just the crunch channel, as that gain stage is also in use in the OD1/2 modes....but what you can do is reduce the gain of the OD1/2 Orange and Red modes. I see you have already done the "gain reduction mod", but you can reduce the gain further by adding a 100K resistor across R128 (gain reduction mod) to compensate for the added gain of the AFD mod. Alternatively if you fit an ECC823 in position V6 (instead of the standard ECC83) then this automatically reduces the gain in OD1/2 Orange and Red modes....

 

[maxxi]

Ok, seems the afd mod is worth a try. What voltage/wattage should the cap and resistor be rated at?

 

[spacerocker]

Ok, seems the afd mod is worth a try. What voltage/wattage should the cap and resistor be rated at?

Resistor: 0.5W Metal Film Type
Capacitor 100nF, 63V polyester/plastic