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.

[Nathan]

Thread resurrection because I am considering this for my Blues Deville RI.


Anyone added V2b into a Blues Deluxe or Deville?   

[stratomaster]

That's a lot of work for an uncertain result.

What about the drive channel do you not like?

Just quickly looking at the stock schematic it looks like you can make a lot of improvement to the drive by making a few strategic tweaks.

The relay adds an aggressive high pass at about 415Hz (C4 and R8).  That is cutting a lot of the fullness in the lower mids and can lead to a harsh or raspy sounding overdrive.

I'd be inclined to replace C4 with a 2.2nF cap. I'd also experiment with 330k-470k for R8.  Together they will retain more of the low mids in this range, but also if R8 is reduced the next stage won't be driven as hard.  It's a mild reduction, but could be enough to help keep the added low mids from turning the drive to mush.

That may be all you need to get an overdrive tone that you're happier with.

Edit: In addition to the above, if you need more gain I'd try 220k in R6 and add a 1-2.2μF cap across R10. This will trim gain into V1b, but increase the gain out of it.  Should allow you to keep your sound clean at the lower ranges of the volume control on the clean channel but give you lots more gain in the drive channel.

[Nathan]

Thanks Stratomaster! This is helpful. What I don't like is how there is an unused triode hanging out doing jack squat. I have added the cathode follower in 2 Blues Jr's before and I came across NGW's link on my own, so it got me interested. With all of the Blues Dlx and Devilles out there I figured it would be a popular choice for the insatiable modders like us? 

[stratomaster]

If it weren't a PCB amp I'm sure there'd be more mods along these lines.  As you know from repurposing the triode on the Blues Jr, there's a lot that goes into it and a lot that can go wrong if you're not both careful and knowledgeable.  The end result even then is something with a lower degree of reliability vs stock unless heroic efforts are taken (custom board for the tube sockets, one off daughter boards, etc) or the installer is very experienced in PCB repair and how to properly cut traces and do "blue wire" work that can withstand the rigors of the road.

[tubeswell]

^what stratomaster said^


It’s challenging to try and optimise an amp into something that can do both scooped Fender cleans and mid-Freq boosted high gain using the same input stage without complex switching. The input stage usually needs to be configured for one type or the other. It’s a deep dive into iterative experimental changes testing and reworking on what physically is really a cheap mass produced amp with a crappy pcb and known reliability issues (especially in the power supply and channel switching). So you’ll be hauling the boards in and out constantly to tweak things, each time creating more physical wear  (leading to cracks in the traces etc which need patching up). It could be fun for a few days …


Or you could opt to gut the innards completely and either design a bespoke new amp yourself that enables the flexibility for tweaking that helps you achieve your aims, or opt for an off the shelf product which other people are already using and raving about (I.e. the Luigi dumblised board) which gives a decent clean and a great sounding overdrive, and probably an equal amount-if not greater- satisfaction with the end result)


Depends whether it’s about the journey or the destination.

[Nathan]

Understood guys!


I am leaning toward gutting and doing my own turret board for those reasons. The idea is to stick closer to 5F6A with a few tricks, I have most of the parts already. I even plan to add a tube rectifier with a 5VAC transformer. 


I thought for sure some folks here must have done the Andy Marshman mods. It should be a popular option IMO but I have not found examples anywhere of adding V2b in. This guy has a modified Deville with a great-soundign drive channel: https://www.youtube.com/watch?v=HA1SBZZJIo4
 but no mention of what was done to the circuit! I'd be pretty happy with that sound...
 

[stratomaster]

My point wasn't to go scorched earth and gut the thing, but that you can get to a much better sound with minimal modification that doesn't compromise the integrity of the amp. 

[tubeswell]

Yup - Hand on heart I'm a scorched earth guy when it comes to amps like this :-)