DSL20H to AFD #36 mod

[Sparks910]

Hi guys,

I've just finished modding my DSL20H as close to the AFD #36 as I can and wanted to share. I'm pretty happy with it overall so here's the schematic and some sound clips.
The Green channel retains the built in tonestack but both cathodes have changed so it does get more distorted than stock.
The Red channel is reduced greatly in gain and tonality has changed now with the majority of mods to this channel to mirror the AFD #36/34 circuit.

The "inspiration" from the this mod comes from various iterations of the #36 schematic on the web and the preamp of the SL5/AFD100.
The good thing about the DSL20 is it has 4 gain stages and a plate driven tone stack as standard which means no drilling/mounting extra tubes to do the 36 mod! it can be put back to 100% stock easily.
Also with the design of this board I was stuck using a 1uf in the first gain stage as the cap is hard against the board and underneath is the tube socket for V1 so the cathode is a bit different to standard JCM800.
I've also added a switchable Cold clipper with a 10K and 39K option to control the overall gain - this is awesome!

If anyone is looking to do something similar feel free to use this as a base. By no means is it 100% accurate to the original #36 and is based on Santiago's amps that he made for Slash.
I also took inspiration from Jason over at Headfirst with his SC20H #36/34 mods as well.

Anyway this was definitely worth the effort as to buy a SC20H vs a DSL20 here in Aus is about $1000 extra for the SC20 and it doesn't have a loop or 2 channels.
You also cant find an SL5 or AFD100 anywhere so this was my next best option.

Recording chain is Les Paul Classic with PAF's >DSL20 red channel >JohnH attenuator/load box >Scarlett solo >Ableton Live >NadIR with Leon Todds Marshall 4x12 Greenback IR.
No other post processing or effects. Straight into the desk.

39K Cold Clipper




10K Cold Clipper



Schematic attached


Thanks,
Mark

 

[Jon Snell]

Might be me but the pages are blank re details.
I guess this is what you mean?

 

[Sparks910]

Not sure Jon, I've attached the Schematic to my original post. Hopefully it works now. Do the recordings work?

 

[Jon Snell]

Hi, your schematic is there, that's all.
Could be broken links.
Most upload to the cloud or youtube and post a link.
Hope that helps.

C74 150k any reason for that?

My R29 is a typo, should read R28.

 

[EndGame00]

Sounds way better than stock…It doesnt sound “plasticky” like a modern Marshall…it’s definitely close to AFD… im surprised you’re driving it with a CL80, i thought it was V30.

 

[2L man]

Have you measured or could you measure HT1 DC voltage on both power positions?

 

[Sparks910]

Hi all, updated my original post with Soundcloud clips and the current schematic. The cold clipper switch is a great mod and does wonders to the "ultra gain" channel. I'm considering going a 3 way with 100K as well.

Jon - the 150K off the gain pot is from the #34 mod. I included it because it lowers the overall gain and changes the pot taper. Made a big difference in usable gain ranges

2L man - no changes at all to the B+ so I havent measured any voltages. I also only use the 20W setting sometimes with a JohnH attenuator.

Any other thoughts go for it. This thing sounds awesome now, very happy at this point.

Cheers

 

[Sparks910]

Another update. This is now my idea of a "Hot Rodded 800". Essentially allows you to select from stock JCM800 preamp cathode values with varies "gain stages" to go from
standard 800 tones to modded 800 and then the AFD #36 style with the bypassed 10K cold clipper. Pretty cool overall - I'm sure this has been done before. A lot of these mods come
from Rob Robinette's website and other amps around the place.

If anyone else tries this please let me know what you think! I love the amount of gain stages I have available in this portable mini head now. It can literally cover anything you want.

 

[stickyfinger]

Sounds way better than any stock DSL 20 I've heard. Thanks for posting.

So I take it you figured out the original DSL20 schematic? Is it the same as the original DSL5?
I own one and thought about modding that little guy.

 

[Sparks910]

Thanks for the feedback mate. The DSL20 schematics are available here on the forums. It's is labelled DSL15 but has 2 EL34's. The schematic is pretty much bang on except for the 8k2 cathode resistor on the 3rd stage. It's actually 10k stock. I haven't looked at the DSL5 myself.

The DSL20 is a great mod platform. Its an easy 4 stage setup that you can do a lot with. I don't know why there aren't more documented mods out there for them. Especially given the price and wattage.

 

[PentodeLicious]

Sounds great!
Much better than the stock version which is underwhelming to say the least...

 

[RadRat]

Whoa, I was hoping to stumble across this very idea. How would you say the hot rodded 800 compares to the stock ultra gain channel?

 

[EJstrat&JVM]

Thank you for sharing. The AFD100 Santiago made, sounds much more nasal than your clips. That's why I love the AFD100, it's bloody nasal but in a pleasant way. When you play it you are not necessarily pleased, but when you hear it recorded (from a listener point of view) you go like "Wow, was it really me playing that amp?". All the AFD mods I heard they don't sound even close to what the AFD sounds like. Even the Headfirst mod, it doesn't sound right. The only mod that sounded almost identical was from a guy called Eddy Lentz.