The Official Marshall DSL40c Information Thread

[MarshallDog]

Well, I decided to modify my foot switch. Since it is such a big housing for basically a single SPDT foot switch for channel switching, with the reverb switch being mostly useless if you're running a reverb pedal like many people, and since I needed a buffer for my board but have mostly run out of space without some serious reworking, I decided to build some goodies into the original housing. Has taken me longer than expected, but finally got it done tonight. Works great! Little bit of switch pop, which I need to fix, and the gain pot for the boost is wired up backwards (CCW increases volume, CW decreases volume) so I need to fix that. Will dig into it tomorrow and fine tune it, but overall very happy with the mods.

1) Installed dual LED (Red/Green) on channel switch, with green being the green/clean channel, and red the lead channel.
2) Removed the reverb footswitch and moved it to a SPDT toggle switch on the back since I had one handy, and doesn't hurt to be able to use onboard reverb if need be.
3) Built and installed "half" of an AMZ Super Buffer circuit (using a single TI RC4558P dual op-amp, his design calls out 2 dual op-amps but didn't find it necessary) with a true bypass DPDT toggle switch on the back.
4) Built and installed a DIY MXR CAE MC-401 boost/buffer circuit (using another TI RC4558P instead of the spec'd LF442 since I had it handy) with a gain pot, LED indicator, true bypass 3PDT switch, and a switch to toggle between buffer and boost mode. The toggle only needs to be an SPDT but I used a DPDT since I had it handy. It basically is the equivalent of turning the pot down to zero, which on the MC-401 circuit turns it into a unity gain buffer. When you start turning the pot it begins to boost the signal. This is an independent circuit from the AMZ Super Buffer circuit, and has its own input and output jacks, so basically 2 pedals in one housing. So I can have a buffer and a boost or two independent buffers anywhere in the chain (4 jacks).

The boost and buffer circuits are of course not my own designs, got the schematics from other sites and soldered together on bread board. Not the prettiest thing, but gets the job done and is obviously not seen. The board is insulated with a piece of thin plastic on the back and is secured with a couple stick-on stand-offs (not pictured). I was barely able to squeeze this thing closed, super cramped in there with all the cables. I was just barely able to make it all fit with a little poking and finessing.

So to recap, the left foot switch is channel switching, right foot switch is MC-401 boost/buffer on/off, the top left toggle is reverb on/off, the next toggle is MC-401 boost/buffer toggle, and the last toggle is AMZ buffer on/off.

Some pics attached. Disregard the patch cable going from the output of the buffer into the input of the boost. This was just taken a few minutes ago during my initial testing, and have not yet integrated it into my chain.

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Very cool and nice. The only thing I did was put LEDs on my pedal...

 

[c00lkatz]

Very cool and nice. The only thing I did was put LEDs on my pedal...

Thanks! It just seemed like such a waste to have that huge pedal on my board with basically only one usable footswitch, and it only switches between 2 channels without any LED indicator. Seemed like a prime candidate for a custom pedal project. Turned out just about how I imagined. Sure wish they made the chassis out of aluminum though...that steel was a pain to drill and is quite heavy after adding all the components.

This was my 3rd DIY pedal project. The first was a simple JFET buffer I put into a plastic box with the intent of mounting under my board, but after getting a Fuzz Face, I found I needed the ability to turn the buffer on and off easily (the Fuzz Face doesn't play well with buffers). The second build was a dual input/output JFET buffer in a typical 1590B enclosure that I did for a friend. Decided to try the AMZ Super Buffer this go around, as it seems to be well received and is unity gain (the JFET buffers are slightly less than unity). Have also wanted to try a clean boost, and seeing as I have a CAE wah pedal, the CAE boost seemed appropriate and easy enough to try.

If anyone wants the schematics for this specific project, just let me know. I drew everything up in Orcad Capture, including all the switching.

 

[c00lkatz]

Well tore it open, rewired the MC-401 pot properly so that it increases gain CW, and rewired the AMZ buffer DPDT switch to the same method I used on the MC-401 3PDT switch and the pops went away (don't know why I did it differently...brain fart!), everything works great! All the switching is working, boost has a ton of clean gain, buffer is working and can tell a big difference with it off (loss of depth and treble), MC-401 boost/buffer toggle working. Really digging this thing, much better use of that huge chunk of steel!

 

[Snow and Steel]

Well my parts came in and are finally assembled. I'm hoping to get these put in next week.

I've got a matched set of Ruby EL34BSTR power tubes, a tung-sol for V1, a Ruby for V2 and V3, and a sovtek LPS for V4, and I've got a 16 ohm Celestion V30 to drop in it. Looking forward to it!

 

[Patrick1959]

Hi Guys, I have a bias issue and could use some advice. I recently replaced the tubes in my 40 c with the ultimate package from the tube store. 2 winged "C" (SED) EL34's and four JAN-GE 12AX7WA tubes. Biased at 38. I let the amp warm up for 20 to 30 minutes before biasing. After putting the amp together and playing it initially, it sounds great. after a day or so, the bias changes and the amp sounds bad. I have repeated the bias procedure twice with the same result. Any ideas?

 

[MarshallDog]

Hi Guys, I have a bias issue and could use some advice. I recently replaced the tubes in my 40 c with the ultimate package from the tube store. 2 winged "C" (SED) EL34's and four JAN-GE 12AX7WA tubes. Biased at 38. I let the amp warm up for 20 to 30 minutes before biasing. After putting the amp together and playing it initially, it sounds great. after a day or so, the bias changes and the amp sounds bad. I have repeated the bias procedure twice with the same result. Any ideas?

It may be bad tubes. I would call The Tube Store immediately and tell them, they may send out new tubes at no charge. They have excellent customer service.

 

[Patrick1959]

Thanks, I'll try that.

 

[Patrick1959]

.

 

[Snow and Steel]

how old is your DSL40c?

weren't there some first run amps that had a drifting bias issue? if that is the case you would be covered by Marshall, and would either get the amp fixed [with new tubes and bias] for free, or potentially a new amp.

 

[Screamin Willie]

I think that was the JCM2000 DSLs that had the bias drift problems.

Sounds like bad tubes. From what I've read there were some Winged C seconds in the last runs that made it to market. I would put the old power tubes back in and see if the drift problem still exists.

Willie

 

[Snow and Steel]

A LOT of problems with winged C's it seems. Even people that et "good ones" say they sound good but burn up too quick. I skipped them and went right to the Ruby EL34BSTR on a recommendation form Doug @ Doug's tubes.

 

[Patrick1959]

I bought the amp about a year ago. It's a bedroom amp. Has not been played hard at all. I contacted the tube store, they said to burn the tubes in for 20 hrs. That has been done. I'll have time to bias the amp early next week and see what happens. So, if it drifts again I should go for the Ruby EL34BSTR power tubes? The reason I changed the tubes is because the Marshall stock set had drifted . I did not try to bias those because they had bad reviews on this forum, and I thought since I'd have to bias anyway I would kill two birds at one time.

 

[Screamin Willie]

Let us know how it goes with the re-bias.

Willie

 

[SlickTide1]

I just replaced my power tubes with a matched pair of Electro Hamonix EL34's and EH 12ax7's in all four of the other slots. Biased to 38.4 and now my dirty channel sounds awesome, but my clean channel is not as clean as it was before. Have read 90% of this thread and was wondering if this was normal? Not getting the cleans I use to....

 

[ken361]

Bias it a little cooler

 

[SlickTide1]

Bias it a little cooler

I thought about that...How much cooler?

 

[Micky]

I thought about that...How much cooler?

Not knowing your B+ voltage, but 32-36 may help...

 

[MarshallDog]

I just replaced my power tubes with a matched pair of Electro Hamonix EL34's and EH 12ax7's in all four of the other slots. Biased to 38.4 and now my dirty channel sounds awesome, but my clean channel is not as clean as it was before. Have read 90% of this thread and was wondering if this was normal? Not getting the cleans I use to....

EH tubes are a bit darker sounding...try a brighter tube in V1 BUT that will affect the Other channels a bit.

 

[ken361]

Or use less gain

 

[Bownse]

Or use less gain

Be careful about Gain. "you may be the subject of random sniffings."

http://bit.ly/2aZLqHH