BLUES DELUXE - Overdrive Mods (by Andy Marshman)

[ngw]

I have a Blues Deluxe on my bench that needs some repairs and the owner has asked me, to also do some mods to improve the distortion in "Drive" Mode.

I am considering doing the Andy Marshman Mods, as detailed on the Duncan Amps website (which uses the unused V2B Triode) -
www.duncanamps.com/technical/bluesdeluxe.html

Has anyone here done these Mods, or know how successful they are?
Due to the amount of work involved, I would welcome any info, advice, comments, or opinions, before committing to the Mods part of the job.
Attached are drawings of the Standard B.Dlx. Schematic and the B.Dlx. Preamp Schematic with the Mods.
The Schematics are shown in "Drive" Mode.

I have added a Shunt to the Output of V2B, to prevent any noise or stray signal, from the "Drive" Stage, getting to the grid of V1B, when in "Clean"/Bypass Mode.
Do you think this is necessary?

Thanks for any advice, suggestions, or comments.

Noel.

[pompeiisneaks]

I've debated doing that to mine, but never gotten around to it. I think I've only read that one as well, so I can't give more input other than

'any improvement to the blues deluxe drive channel is NEEDED, it sucks!'

I love the clean tone of that amp, but always hated drive. I had pedals for drive on it because it was so horrid. I bought mine somewhere around 94-96, first gen and still have it. Recapped it recently and debated doing that, but didn't.

~Phil

[ngw]

Well, it seems that no one has done these Mods, or no one is interested, apart from Phil.
Phil, I agree; the Drive is rubbish.

I will go ahead with doing the Mods and I should be able to make a good improvement to the Drive.
With the vital components mounted on an auxiliary board, I will be able to change values, if needed, without major disassembly.

Any comments/opinions on whether the Shunt on the output of V2B is necessary?

I will report back on whether it is a success, or not.

Noel

[M Fowler]

I have never heard of this mod so have no info.

Mark

[pompeiisneaks]

I'm probably just not aware of what the term 'shunt' means, do you mean the extra 1M grid stopper into the next stage or something else?

Ultimately since nobody's done the mod yet, I'm not sure anyone has experimented with it enough to know.

~Phil

[ngw]

The shunt, in the circuit above, is a ground/earth connection to the junction of RA5 & RA6 that is switched in by Relay 2 when in Clean Mode.
This is to shunt to ground, any signal or noise coming out of V2B (which is the added Drive stage) when V2B is bypassed by Relay 1, in Clean Mode.
I don't want any unwanted signal noise to make it to the grid of V1B and alter the original clean signal when in Clean/Bypass Mode. The owner loves his Clean sound.

Applying a Bypass to a still connected gain stage, as is done in these mods, is not something I have ever done. I usually isolate Stages or Channels that are not in use, so I am not sure what the risk is, of some noise getting to the V1B grid, if I do the Mods as described. Isolating the Drive stage is not feasible in this case.

I am just looking for some advice from anyone who has done something similar, to an amp, as to whether this shunt is necessary.
To apply the shunt requires cutting traces and swapping the connections on 9 & 13 at Relay 2B so that the ground is then on 13 and the Master is on 9, and the shunt gets connected to 11.
Then the ground will be connected to the Master in Drive and the Shunt in Clean.

These amps are a costly PITA to work on and I want to try and get it right, first time, rather than have to go back in to change something that I can't get to without pulling the PCB again. This saves me time and the client $$.

Noel