My K-20X

[joecool85]

I've been playing guitar for 12 years now and the whole time I've owned this amp - Dean Markley K-20X.  It's been through a lot.  Over the years I have added a line out (just like the K-20, not sure why they got rid of it on the K-20X), added a speaker out jack and removed the rear wooden "bar" on the back side of the amp.  I now have replaced the permanently attached power cord with an IEC jack w/fuse.  Not only does this allow for quick cord replacement, but also easier storage, the use of a 90 degree cord so you can put the amp closer to other devices, and it puts the fuse in an easily accessible area (back panel).  The old fuse location being on the PCB was not only inconvient, but arguably unsafe (putting mains current and voltage to the PCB).  The mains wiring now bypasses the PCB completely making the amp safer and easier to service.

As a side effect, I needed to relocate the power transformer to have room for the back side of the IEC jack.  It is now directly under where it use to be, same mounting holes and all.  This puts the transformer outside of the metal enclosure.  This potentially removes some noise (though so far I haven’t noticed a difference).

Now the pics!

**EDIT**
Attached schematic as it currently stands, minus speaker cutout switch which is spst inline with speaker + lead (2/24/2020)

[joecool85]

Of note, I added those little wooden "brackets" at the bottom of the amp.  They allow me to put a cord in there and not have it fall out.  This is what it looked like without them. 

[mexicanyella]

Nice work, and nicely documented! I like your Squier Tele too...that's a neat orangey vintage finish.

This is an inspiring thread, because I've got a pre-X K-20 that's working but pretty ratty, with paint spills on the tolex and a cracked MDF baffle board. Not sure if I just want to keep it around as an extra flavor of small amp, or if I want to get creative with it.

I've considered removing the chassis and making it into a pedalboard-mounted amp, so I could just carry my pedalboard and a small cabinet for low-volume stuff.

I've also thought about swapping in a 4-ohm 8" midbass/PA-type driver and enclosing the back (below the chassis) with some cleats and panels screwed/glued in place, and using it as a bass practice amp. Not sure I want to get that non-reversible with it, but at very low volumes, it sounds excellent with a P-bass (drive channel set with gain very low--1-1/2 or 2--and the output vol halfway or more). Even with the stock speaker and open-back cab, I bet it'd be a great bass recording amp, miked up for some low-volume grunt and twang and combined with a clean, maybe compressed, DI for lows... 

[joecool85]

I've thought about cutting down the existing cab and turning it into a small head. It drives a 10" wonderfully BTW.

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[mexicanyella]

Mine did a pretty good job of driving a 2 x 10 cab I sold recently, loaded with a pair of 50-watt SLM speakers. Wish I still had a 4 x 12 sitting around to try it with!

The X models might be different, but to my ear the pre-X K-20 has a pretty lazy transient response, and I'm not sure if that's a power supply limitation, or a specific attempt to emulate a saggy tube rectifier, or what. My early 80s Peavey Audition 20 seems to have a lot more clean headroom and feels a lot "faster" in terms of transient response.

On the other hand, I recently discovered that if I put a compressor pedal in front of the K-20 and set the amp's input gain about halfway, the bass about 1/4 of the way up, and dime everything else, the K-20 goes nuts with sparkly upper mids and loose, wild-ass lows...kind of like Joe Walsh's James Gang-era tones. It makes me think of cranked tweed Fender, sort of. I'm happy to discover something that amp can do that my other amps cannot.

[teemuk]

I see the PC board is used for other, more feature packed, amps of that series as well. Have you thought about building those unpopulated areas in the printed circuit board? What's omitted by the way? I reckon at least spring reverb driver and recovery stages...?

[joecool85]

Teemu, it is a reverb circuit. The K-30RX shares a PCB. It has reverb, a slightly larger cab and a 10" speaker. Same output power though despite being a "30" vs a "20".

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[joecool85]

Added a "kick stand" to the little guy. I used a brass rod, a cable clamp and two screws. All stuff I had laying around. The bar is from our bed's headboard, our Son dismantled it when he was about a year old lol.

[joecool85]

More pics

[Bill Moore]

Thanks for the info! I lost my K-20 to my wife's sister, but if it ever comes back home, I have a few more ideas, (reverb would be cool!)

[galaxiex]

Hi Joe, Hope you don't mind me putting this here.

Thought we could compare our K-20 amps.
I opened it up to install a speaker jack and was mildly surprised at the differences to yours.

Mine was made 1993, which probably accounts for the differences.
Any idea what year yours is?

The layout and circuit board are obviously different.
Mine has the line out on the front panel and a fuse holder on back.

I was hoping to find the same circuit board as yours with the un-populated areas for the reverb.

Oh well, I'll just use a reverb pedal.

A minor feature I like is the slanted speaker baffle.

Cheers!

Edit; looks like it would be easy to make the drive switch, foot switchable. 

[joecool85]

Hi Joe, Hope you don't mind me putting this here.

Thought we could compare our K-20 amps.
I opened it up to install a speaker jack and was mildly surprised at the differences to yours.

Mine was made 1993, which probably accounts for the differences.
Any idea what year yours is?

The layout and circuit board are obviously different.
Mine has the line out on the front panel and a fuse holder on back.

I was hoping to find the same circuit board as yours with the un-populated areas for the reverb.

Oh well, I'll just use a reverb pedal.

A minor feature I like is the slanted speaker baffle.

Cheers!

Edit; looks like it would be easy to make the drive switch, foot switchable. 

Yours is a K-20, mine is a K-20X. Almost identical circuit, but there are differences especially in the PCB. I'm not sure of the year on mine because it isn't stamped. But I bought it around 2000.

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[galaxiex]

Well I'm done tinkering with this amp.

I installed a speaker jack (not much to show there, so no pics) on the bottom of the chassis.

I noticed a huge difference between the volume of the drive and clean sounds.
eg; if I get the clean setup to where I like it, and then switch in the drive, there is a huge volume jump that doesn't work for me.
I prefer just a modest vol increase + the distortion.

The culprit seems to be the 2 resistors, R5 and R6 in the attached schematic.

BTW this schem part numbering does not match my board, but no matter... the circuit seems to be the same.

Anyways.... after some experimenting I left R6 alone and changed R5 to a 22K.
Now the clean sound dials in at much lower settings, but that's ok, cuz switching in the drive gives me the slight vol boost + dist that I want.

Down side is... if I crank the clean setting too much, it starts sounding just like the drive is switched in, and very little difference when the drive is actually switched in.

Oh well... its still better than the huge jump in volume from before. 

[Bill Moore]

I have posted before on my little K-20, and had intended to experiment some with it.
Our (only) grandson was down a month ago, and likes an amp with OD, but most I have at the house need to really be loud for that. I showed him the Dean Markley, and he played through it a little, and said it was OK. For several days he would go into the music room, and play, always choosing the little K-20. When we were getting ready to take him back to the airport, I found a bag that would fit the little amp in, and told him to take it home. (I had to pay to check his other bag, but I was happy to do so). It now resides in Alaska, and his mom said he is really proud of it!

[J M Fahey]