Posts Tagged ‘Tube amp’

The purpose of the article about changing the anode resistor value was to improve the clean channel and smooth the dirty channels.  That is exactly what it will do, but I wanted to talk about conceptual ideas regarding this change.  I’m going to use pedals for illustration and then translate that over to tube amplifiers.

Analogy

I used to build guitar pedals and I’ve spent a lot of time cascading circuits into each other.  While transistors and op amps react differently than tubes, the overall result on dynamics is similar from one component to another. (more…)

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I ran across this article about Sovteks and how the rating charts for several tube brands compare.  I am needing tube replacements and this seems pretty handy for finding tubes that fall into Mesa’s bias range for their 6L6GC.

I’ve been using Ruby 6L6GCMSTR, which is an excellent tube, and I will likely stick with it, but these others have piqued my interest in differences between the sub-types. (more…)

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…)

Tonight, I tried some different setups between my Recto and a Line 6 Pod X3 Live.  I was trying to get a good headphone mix for silent playing.  The “Slave Out” was making noise and I switched to using a send from my Nova System to the X3.  I found the similarities between the modes to be quite minimal.  It was striking, really. (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…)

Mission Improbable

There are a few reasons I’ve been spending so much time exploring the Dual Rectifier.  Those reasons include: misinformation, biases and myths, and helping others.

The misinformation takes many forms.  Sometimes, it’s just reading about the DR having “active EQ” (false), that it isn’t a “solo” amp (false), or other equally dubious claims about the design that are ridiculous.  Biases and myths also fit in with the misinformation, but are just as much about the insecurities of the users as any misunderstanding of the amplifier.  Claims about early revisions being “superior” or the utility of the 2001 3 Channel version are as ridiculous as the circuit misinformation, because it’s all subjective.  If I was a little more cynical, I’d even think the second hand market is involved in promoting and spreading this kind of bias to increase, and retain the increases on, the obsolete designs.  Seeing as how Mesa designs them, builds them, markets them, receives feedback, and profits most from the sales, if the old amps were superior, they’d swap directly back to it due to customer demands and complaints. (more…)

Classic RockBefore the mass application of  post-preamp master volume controls, old amps had to be cranked up to get distortion.  The distortion of the power amp is what gave those old amps their defining overdrive characteristics.  Modern, master volume, amps rely on preamp distortion more than the power amp to create crunch and chunk without a person’s ears bleeding from the high SPL.

The 3 Channel Dual Rectifier (non-multiwatt) has an extremely cold biased power amp at full power.  This allows it to amplify the preamp distortion with a minimum of additional overdrive being created, if any is created at all.

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The pdf opens in this window.  Open it in another tab if you want to see it and follow along.

Table Dancing Double Multiplier Warmonger

This is an approximation for the preamp of an amp I love.  It has multiple channels, wazoos, doo-dads, and what-nots.  This is a bit different from the original.  It’s only one channel.  I moved a couple grid stop resistors to attenuate with the grid leak resistors.  Their values are different than the original, but are scaled to do the same functions.  I changed the value of parts of it to reduce noise, but have approximately the same frequency and performance responses in most cases.  I changed some of the cathode resistors to a more common value, but it’s close to tolerances and barely shifts it into a colder bias that makes little difference.  Some of these changes are also because it doesn’t need to have all the extra stuff in the overall circuit if it’s only one channel.

This is NOT an exact clone.  I think of it as a distillation of godliness into a smaller package with some wiggle room for my own preferences.  I didn’t include the tone stack, PI, or output.  I’ll leave that up to anyone who would like to further tweak it, in case they want to have a feature or omit a feature.  It’s about flexibility.

Some notes about the schematic:

  1. My software barely supports tubes and the pins are all labeled for 6,7, and 8.  This obviously is wrong on some of the tubes, but I couldn’t change it.  V2 and V4 would be 1,2 and 3.
  2. It doesn’t have a model for a regular mono jack or a cliff jack.  The stereo jack works fine enough for demonstration and I’m sure a person would be able to figure out what to do.
  3. You can change the input grid stop resistor to taste.  The original uses an alternate way of attenuating radio frequencies and I chose a small value to prevent attenuating the guitar if it’s volume knob is turned down a bit.
  4. You might consider lowering the value of V4’s cathode bypass cap if the bass response is too mushy.  Removing it altogether along with it’s series resistor might not be a bad idea, but will also attenuate the highs by a great amount and greatly reduce the gain of that stage.
  5. A somewhat smaller value on V3’s anode bypass cap will brighten the sound a little.  That’s there mainly to prevent oscillation, but it’s cutting a huge chunk of frequencies right out of the stage that aren’t going to oscillate.
  6. I made the grid stop resistor for V4 56k.  This is pretty low, but is partially to offer less attenuation and lends some brightness after some of the larger values upstream and to offset some of the attenuation in v3’s circuit.

I welcome any comments, questions, suggestions, or cease and desist letters anyone has.

Diode in Tube Amp larger

I am building an amp and I wanted the ability to add another stage for distortion.  Unfortunately, I have some issues which will prevent me from using another 12ax7 stage.  Looking at some high gain amp examples, I noticed that a great many of them contain one stage that is biased so cold and at such a low amperage/high voltage, they go into severely hard clipping that is a square wave with rounded edges.  Because of the bias point, one side of the signal is going to clip much more than the other; this is called asymmetrical clipping and tubes do it naturally and very well.

Diodes are a low cost way to add distortion.  If designed with some foresight, it can be designed to be “tube-like”, but really doesn’t sound exactly like a tube on it’s own.  Placed between stages, it will get enough filtering through the tubes to not sound cold, hard, or whatever the purists like to say as they push their amps with solid state pedals.

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