DSL 401 JCM 2000 diode bypass mode

[light_n_roses]

Hi there!

I own a Marshall JCM 2000 DSL 401 combo 40W amp and recently I have red a lot about how all tube non-diode sound should be better than distortion with diode ( of course maybe it's a just a non sense matter, I don't know but I'm curious). My amp has a clean channel, an overdrive channel 1 and an overdrive channel 2 ( which actually it seems to me just a gain boost and nothing more ). I would like to know if there is any way to install a switch to by bypass the diode distortion and have the all tube distortion from my amp. What do you think?

 

[Bloodrock]

Your amp has no diode clipping/Distortion. It's 100% tube overdrive.

 

[light_n_roses]

Are you sure about this?

 

[Blacque Jacque]

There are no diodes in the signal path for distortion.

There are zeners in the fx loop / reverb circuits for overload protection however.

 

[light_n_roses]

There are no diodes in the signal path for distortion.

There are zeners in the fx loop / reverb circuits for overload protection however.

sorry about the noob question but what does imply having zeners diode inside the fx loop / reverb circuits for overload protection? ( fx loop that I'm not using right now )

 

[Blacque Jacque]

They protect the opamps from excessive voltage in the signal path which would cause them to distort in a bad way or possibly even damage the opamps. Under normal signal conditions they will have no effect on the sound.

 

[iron broadsword]

Bottom line - you've got an all tube amp... So enjoy it. If it doesn't sound good to you, then that is just a matter of taste.

 

[light_n_roses]

They protect the opamps from excessive voltage in the signal path which would cause them to distort in a bad way or possibly even damage the opamps. Under normal signal conditions they will have no effect on the sound.

I see, actully I do not know what kind of situation could generate an excessive voltage signal imput.

Also this means that my overdrive chanell 1 it's all tubes distorsion, and even the overdrive channel 2 it's this way even if it doesn't seems because it's basically a boost of gain ( but I usualy play always on the OD1, not playing metal...).

 

[JohnH]

You are right about the od1 to od2 change. It is a 20db step in gain with no change of basic EQ

Do you like the tone that you get? If not, there ars several ways to change it either inside or outside the amp.

 

[Blacque Jacque]

I've never studied the circuit in that greater depth, 20dB ? Wow, that's a pretty big jump. I'd be happy with less gain & an independent MV for the red channel.

 

[light_n_roses]

and the boost gain of the OD2 is still obtained with all tubes distortions? No diode here too?

Anyway I'm preatty much happy with the OD1 tone.I don't use the OD2 that much as I usualy play classic rock and not metal. The claen channel isn't bad but it get distorted easily, expecially at low bedroom volume where you have to play with the combination of volume clean channel and master volume.

By the way, it would be better to have the presence control knob!

 

[JohnH]

Yep, no diode distortion. OD2 is actually the full amount of gain, and in its sibling the DSL201 it was the only OD channel.

In the DSL401, OD1 takes a point partway in the circuit and cuts the signal level by a factor of 10, hence reducing by 20db (its between V1 and V2, the signal is passing through a 470k resistor, and when OD1 is engaged it get dragged to ground via a JFET through a 47k resistor R100)

This amp has no presence knob because the way a presence control works is through negative feedback in the power-amp stage - and this amp hasn't got that (which adds to its tonal character)

But, if you want to tweak a few frequencies, this amp works well with EQ in the loop. Just dial in the extra frequencies you want and cut all the others, then fade up the extras with the FX knob. IMO, a bit of extra low end on OD1 is good this way.