Posts Tagged ‘amps’

I had just a few thoughts come to mind regarding modifying amps, modifying EQ, or creating your own.

It’s a fact that Mesa Engineering uses two modified forms of the Marshall tone stack for their Dual Rectifier series.  Compared to a classic Marshall tone stack, the Vintage/Raw tone stack moves the center of the “Mid” control down in frequency and has more attenuation.  This carves out some of the meatier part of the guitar frequency to make room for the massive lows and a high-mid emphasis.  The tone stack enabled for Channel 3 Modern has boosted upper-mids, but has a very similar, low-to-low-mid frequency response. (more…)

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Fuzz-Crunch-CleanI’ve been experimenting with making Channel 3 a fuzz tone for a long time, but recently got just the setting I wanted.  This kind of setting gets close to “Dazed And Confused” and sounds good with “Purple Haze”.  Being tube, instead of transistor, it’s a little softer, but the Presence  can dial in the edge a person needs for fuzz bliss.

Faux-Fuzz EQ Setting

Yellow is the Modern setting as described above with no treble and full mids. Green reduces Bass to 11:00.

The way that old, germanium transistor fuzzes would clip is awfully close to the way the cold clipping circuit works in these Marshall/Soldano types of circuits and the Recto has the bottom end to really sound huge.

I found this Channel 2 Raw setting to be a match for the fuzz tone.  It’s bright, with plenty of bottom, and crunches up quite nicely.  Both dirty channels get cleaner as guitar volume is rolled back, but, like a Tonebender, Channel 3 never gets “squeaky clean”, but it does make a nice half-clean sound, since the treble is flattened.

I hope this helps.  Enjoy.

I know I previously stated I would discontinue writing about mods, but this one has been in the back of my head for a long time.  A lot of the grind produced by the cold clipping stage is due to the presence of third harmonics (H3).  By forcing the idle point to be so close to grid current limiting, the amount of information loss from the distortion is going to produce it.

Yesterday, I was playing around with the Trioda load line program and found an interesting effect.  With the parameters set about where the resistances would be for V2b, the cold clipping stage, I was adjusting the cathode value.  As the cathode resistance moves from 39k to 10k, the amount of H3 falls to an amount which would become inaudible. (more…)

I already covered the input stage and clean channel.  I’m not going to repeat the information about the input, except for applications to the dirty tones.

The input stage is followed by a coupling cap and a 2.2 M load resistor in parallel with the voicing circuit and gain pot.  Most amps made prior to the Recto place the grid resistor between the coupling cap and the load.  The load is usually a potentiometer to control gain.  I think Mesa made this change to better enable the changes to the voicing circuit which control the load and blocking resistances. (more…)

(11/15/15: Edited information about the Presence and Treble)

Modern, high gain, guitar amplifiers generate much larger signals than vintage amps, hence high gain (high increase).  Compared to a vintage amp, modern amps can produce much more distortion and saturation.  In addition, the low frequency content of a Recto is fairly great.  Stages 1, 2, and 4 of the dirty channels are shunting the lows at about 88 Hz, -3 dB.  While the amp voicing is another topic, it’s important to have an idea of what is coming into the tone stack if you wish to shape it.  Since I own a Dual Rectifier, I’m using it as the example, but these concepts and this tone stack are applicable to many amplifiers.  I’m focusing on the Vintage mode of the Orange Channel.

Our topics for this discussion are: target frequencies, response of individual controls, the interaction of the controls, and dialing in useful tones more easily.  Some of the information is simplified for clarity.

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This is the result of testing equipment during a time when I was trying for vintage guitar tones.  I used an MXL condenser pencil mic.  It was about 6 inches back, straight on, pointed 3 inches left and one inch down from the cone.  I wanted to capture a balanced, smooth sound.

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Peavey XXX RewiredI rewired my cab to have top and bottom pairs, instead of left and right.  I run it 2×12 once in awhile and wanted to try it this way.  The top pair is a little tighter and the bottom is about like normal.  I thought this would be a good opportunity to explain the wiring and source impedances needed for this cabinet.  It is a 16 ohm mono and 8 ohms for each side in stereo.  The diagrams shown are actually the same as stock, since the pairs are only moved to different locations.

Ex:1 A single amp in stereo needs to use 4 ohm output jacks to have a safe match.  The amp adds the outputs together to make 8 ohms.

Ex 2: A single amp in mono needs to use a 16 ohm output jack, but an 8 ohm output would still be safe, if your tube amp can handle it..

Ex 3: Two amps into one stereo cabinet use one 8 ohm output jack from each.  Because the loads are being seen by separate amps, they don’t reduce to 4 ohms, like would happen with a single amp running parallel loads.  The cabinet is basically two 2x12s in one box when used this way.  If one source amp is removed from the third example, an 8 ohm connection into one pair of speakers is using the cab as an over sized 2×12.

I e-mailed Mesa Engineering awhile back about the loop mod for the 3 Channel DR parallel fx loop to make it serial.  I received the same schematic that I now know everyone else gets.  I can see the appeal for someone who doesn’t want their signal to be “tainted” by a pair of jfets, but they aren’t amplifying, only opening to allow the signal through.  It’s no different than having any other quality part in the path.

More recently, I saw that a company is advertising their bench fee for a different mod and the loop retains some of the functionality afterward.  I thought to myself, what would do that?  One thing that came to mind while off on one tangent is the idea to pinch the dry channel off. Then the light bulb flashed and blew up over the idea I’m writing.  This is not only easier than adding a part or bypassing the jfets, it is entirely reversible.  Here’s how to mod the fx loop and gain a killswitch:

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DR and H400aSo…  got bored and threw in a Harmony H400a to my setup.  When I would split my signal from the guitar and send it to both, the Recto would hum from a ground loop.  I expected the same here, but there was not any hum at all.  It won’t work for Metal, but for some good ol’ Classic Rock, Blues, or whatever isn’t brootuhl, it’s fun.  The Mesa EQ actually sounds pretty good through the Harmony, but it’s very “middy” from the lack of lowest lows and highest highs due to an 8 inch speaker.  At the right balance, it sounds great and provides some nice stereo sounds.  If I were to ever get around to making the doodad to run the Harmony to a speaker cabinet, this would be awesome.  If you have similar gear, it doesn’t hurt to try something and see if it makes a decent sound.

This is a pretty awesome video.  It lines up with some of the ideas I’ve been exploring and he is a very good guitar player.  Enjoy.

His cab is different from mine and his amp is the “Reborn” Recto, but most of our ideas are very similar.  For anyone trying to do the same kind of sound sculpting, remember to factor in the cab and don’t be too anal.