New at runoffgroove.com: Matchbox

[B Tremblay]

The Matchbox is a FET emulation of the Matchless DC/30.  Check it out!

Article, schematic, and perfboard layout: http://runoffgroove.com/matchbox.html
Sound clips:  http://runoffgroove.com/salvo.html#matchbox

[Doug H]

Wow! Sounds nice! Gets a wide variety of sounds. I like it! I will have to try it on the breadboard.

Doug

[Bill Bergman]

Nice !!!!

[petemoore]

New At Runoff Groove...some of my favorite words to read.

[Marcos - Munky]

New At Runoff Groove...some of my favorite words to read.

I agree with you.

[Gary]

Many thanks to Doug Hammond for his ideas and help.

There are a broad array of sounds with this circuit.  The multiple combinations of the panel mounted controls yield several sounds.  It's useful for clean to fairly dirty sounds.  It doesn't sound exactly like a DC/30, but it doesn't carry the pricetag, either.  :wink:

[PB Wilson]

Nice! You guys are really doing your part to keep Smallbear busy!

Now how do I convince my wife that I need yet another overdrive pedal? :wink:

[Gary]

Now how do I convince my wife that I need yet another overdrive pedal? :wink:

Easy enough, try this:

"But this one sounds different!"

[PeterJ]

Or this:

"Whaddya mean, honey? I've had that one for years..."

[Ge_Whiz]

"But darling, this one saved me having to buy a new amp!"

[Ge_Whiz]

"But darling, this one saved me having to buy a new amp!"

[Ge_Whiz]

D'oh!

[will]

Hi Brian & Garry,

Another cool design to tryout! I’ve got to get more fets!

Just wondering if the 180pF cap at the bottom of the tone selector switch SWF is necessary?

Regards,
Will

[Gary]

Nope, not especially necessary.  This cap was on the schematic we were able to find.  According to the notes, this cap was added to make the total capacitance add up to the desired number.  We included it for nothing more than authenticity.  Feel free to remove it or modify cap values.  It's an interesting control and seems to be a little more flexible than a standard bass control, IMO.  It's not as interactive with other controls as a standard tone stack.  Let us know if you try this circuit.

[David]

Now how do I convince my wife that I need yet another overdrive pedal? :wink:

Why do you have to tell her?

My trick has been to tell my wife that I have to do maintenance on my pedalboard...

...frequently!   :twisted:  :twisted:  :twisted:

[Doug H]

Now how do I convince my wife that I need yet another overdrive pedal? :wink:

Why do you have to tell her?

My trick has been to tell my wife that I have to do maintenance on my pedalboard...

...frequently!   :twisted:  :twisted:  :twisted:

David,

This is your wife! Doug let me use his account to post...

Now put that soldering iron down and get back in here before I knock you over the head with this rolling pin!!!!!

Love ya, Honey,

Your loving wife....

[David]

Good one, Doug!

ROFL! :lol:   :lol:  :lol:  :lol:

[will]

Hi,

I just built a customized (hacked) version of the Matchbox. It sounds pretty good.  

Due to the selection of components I had on hand I made a few substitutions, so it’s definitely not authentic. However, I’m not into stompboxes to get authentic sound. My goal is superlative sound with my setup and an understanding what makes it tick.

The Input stage is essentially unchanged although I added an anti-pop 4.7M resistor at the input. I used a 2N7000 Mosfet. Since I don’t have a 6 position switch yet, I picked the middle value 2.2nF value as the output coupling cap for the 1st stage.

The biggest change was I raided another Fet circuit and used two 2N5457 Fet’s for Q2 & Q3. When biasing Q2 I realized the source resistor arrangement won’t work properly for this transistor. So I swapped the 4.7K and 1.2K transistors now the drain resistance is around 10K. Not much gain, so I bypassed the 4.7K with a 22uF cap.

This stage works quite well. I do have some overall questions/comments  related to Fet emulation of tube circuits.

I take the primary reason for the 4.7K resistor below the 1.2K Q2 source resistor was to limit the gain of this stage in the original tube circuit. I don’t fully understand why they do it that way. I understand it more in the Meteor and the ThunderChief it is used for feedback and a presence control can be added (or built in). Is it also to allow for bigger input swing (to resist input clipping), yet limit the output swing for more clipping/distortion? Any idea?

In the original Matchless they use a 100K plate resistor for Q2. This plate resistor is a direct part of the tone treble cut circuit. Fet’s will not get the same drain resistance. So I wonder if the value of the tone pot and tone cap value should be scaled to have similar response compared to the original.  

I’m wondering if may be easier to emulate tube designs with Mosfet’s as you can set the same plate/drain resistance and cathode/source resistance arrangement. The Mosfet equivalent to the grid leak resistor can be connected to a noiseless (decoupled) bias. To limit Mosfet gain to closer to a 12ax7 for tube circuit cathode bypass caps you can add resistors in series with the Mosfet source cap.

Regards,
Will