Marshall 2205 Extra Gain

[lovetone]

I good friend of mine loves the boost overdrive channel on his 2205

He runs the gain on full but would like a little more overdrive. Looking at the schematic it uses a diode bridge for the clipping so not just a case of changing the gain on that stage.

Anyone here had any experience getting any more gain?

[oj]

I good friend of mine loves the boost overdrive channel on his 2205

He runs the gain on full but would like a little more overdrive. Looking at the schematic it uses a diode bridge for the clipping so not just a case of changing the gain on that stage.

Anyone here had any experience getting any more gain?

Bypass the 10 K katod whit a 1uF.

[lovetone]

Okay i'll give that a go, do you leave the diode in or remove it?

Cheers

[lovetone]

Okay i'll give that a go, do you leave the diode in or remove it?

Cheers

[d95err]

There are two different versions of the 2205, which are completely different amps with different topology.

I assume you have the later 2205 (the type used by e.g. Schenker and Norum). In this version, the boost channel has a 10k with a diode in parallell. This stage is diode biased and is already at max gain. Bypassing it with a cap makes no difference. I’m guessing the previous responder was thinking of the classic 2204 preamp which is a different circuit.

The amp should have a ton of gain on tap. Are you sure it’s working correctly?

[lovetone]

Yes its working as it should, my friend who owns the amp use's it on full gain, it does sound great but he would like a little more.

He rides the guitar volume, full on is for his solo's. We have tried boost pedals in front which does help but at the same time addes to the compression.

[JD0x0]

Leave diodes if he wants more distortion. You could modify the diodes, too. The fV will affect headroom and compression, and making the clipping more 'asymmetrical' can make it sound more edgy and aggressive.

I'd bypass R16 before I tried bypassing the 10k cathode resistor, as it's more likely to become unstable or cause blocking distortion, when bypassing the cold clipper. Bypassing the following gain stage may work a bit better, for that reason, IMO.

[JD0x0]

There are two different versions of the 2205, which are completely different amps with different topology.

I assume you have the later 2205 (the type used by e.g. Schenker and Norum). In this version, the boost channel has a 10k with a diode in parallell. This stage is diode biased and is already at max gain. Bypassing it with a cap makes no difference. I’m guessing the previous responder was thinking of the classic 2204 preamp which is a different circuit.

The amp should have a ton of gain on tap. Are you sure it’s working correctly?

If I'm not mistaken, there's an earlier stage using an unbypassed 10k cathode. Followed by a 1.5k/100k stage, followed by the stage you mentioned, which has the 10k bypassed with a diode. The first 10k could probably be bypassed, but I'd suggest bypassing the 1.5k cathode, instead.

[pdf64]

It may be useful to identify which the appropriate schematic is for the amp in question
https://drtube.com/schematics/marshall/4210.gif
https://drtube.com/schematics/marshall/2205prem.gif https://drtube.com/schematics/marshall/2205pwrm.gif

[lovetone]

This is the correct schematic for 2205 i have been talking about.

https://drtube.com/schematics/marshall/2205prem.gif

[pdf64]

Ok, so the input stage V1a is common to both channels, V2 circuits relate to the normal channel, V1b and V3a circuits relate to the boost channel.
Apologies if these queries seem obvious, but to avoid possibly incorrect assumptions being made, for suggestions to better align with the user’s objective, it may be helpful to clarify -
1 Are both channels typically being used?
2 What are the typical settings of all controls (the normal channel controls may affect the boost channel a little)?

[JD0x0]

This is the correct schematic for 2205 i have been talking about.

https://drtube.com/schematics/marshall/2205prem.gif

Yep, that's the one I was looking at when I made my previous remarks

[pdf64]

This is the correct schematic for 2205 i have been talking about.

https://drtube.com/schematics/marshall/2205prem.gif

Yep, that's the one I was looking at when I made my previous remarks

But R16 looks to be a V2 cathode resistor, and V2 is exclusive to the normal channel signal path, rather than the boost channel which is the one that requires more gain.

I good friend of mine loves the boost overdrive channel on his 2205...He runs the gain on full but would like a little more overdrive...

[lovetone]

This is the correct schematic for 2205 i have been talking about.

https://drtube.com/schematics/marshall/2205prem.gif

Yep, that's the one I was looking at when I made my previous remarks

But R16 looks to be a V2 cathode resistor, and V2 is exclusive to the normal channel signal path, rather than the boost channel which is the one that requires more gain.

I good friend of mine loves the boost overdrive channel on his 2205...He runs the gain on full but would like a little more overdrive...

The normal channel is not used, the levels are normally all at zero

On the boost channel, Gain 10, level 7.5, Bass 2.5, Mid 6, Treble 5, Master 4.5, Presence 4

[pdf64]

The manual advises that for max overdrive, the boost channel volume control be turned up full, see p3 https://drtube.com/schematics/marshall/ ... manual.pdf
That makes sense, as it will result in V3a, the stage after the diode clipper, being overdriven.

Additionally, I suggest that all the normal channel controls be turned up full, as their circuits act to load the input stage when they're set low (in the upper registers at least). It may not make much difference, but for the want of a moment's twiddling, it's certainly worth trying

See if those changes are enough, before diving into mods. The downside is that compared to those currently used, the control adjustments might change the boost's overdriven tone a bit.