Archive for the ‘DIY’ Category

Update: This is the final version of the DR Booster:

Dr Booster final

The R10 is actually a pot, not a resistor.  With R10 at 10k, the boost is 19.1 dB; At 0 it is 3.5 dB.  The frequency band is 33 Hz – 2.9 kHz, with 330 Hz as the center. (more…)

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The McBooster

Posted: June 29, 2016 in DIY, Effects, Ideas To Be Developed

I breadboarded a simple and basic booster which began as a MXR Microamp clone.  I was looking for something to push the amp into a certain sweet spot and the Microamp wasn’t quite right.  I thought it was too farty, frizzy, and prone to clipping for what I wanted.  I changed many of the part values, moved the pot to the feedback loop, and adjusted frequencies a couple of times to have a wide-band-pass filter which increasingly loses treble as the gain is increased.  The gain of the booster is also decreased to 8 (18 dB), versus a gain of 20 (26 dB).  This is to prevent clipping the op amp to an extreme with modern humbuckers.  If a person is using vintage pickups, the values can be changed to get greater gain, but it isn’t really necessary.  I used it with my humbuckers in pseudo-single coil, parallel wiring and it made them pop right out, adding clarity and girth. (more…)

This week, I’ve come across two great sources of information, ideas, and inspiration: (more…)

I have a LTD AX-2E, which was a model available for only one year.  Despite the funky body shape, it’s a beautiful guitar and the U shaped neck profile is nice.  The jumbo fret size makes the strings appear to stand at a gargantuan height from the ebony fretboard, but the point of tall frets is to enable very little pressure to fret a note.  It’s almost a scalloped sort of feel.  Kung-Fu action grip will make notes sharp. (more…)

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…)

GE7signalflow

Basics of the Signal Path

The input to the Boss GE-7 Graphic EQ has a buffer which is active at all times.  There is a slight emphasis around 2 kHz to help the guitar sound stand out.  Immediately after the buffer is the amplifier for the level control.  It’s a differential type with only one source voltage split with the level’s sliding potentiometer.  This slider will either boost or cut the whole signal when it is moved from the zero line.  From here, the signal is split; one path goes to the EQ section and one part goes to the positive input of another differential amp.  The EQ section feeds the negative input of the differential amp. (more…)

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…)

Awhile back, I found this page while doing research for building effects pedals or amplifiers.  Jack Orman has some really great information and ideas on his site for many different circuits, modifications, and adaptations.  I’ve found it to be quite inspiring and I encourage anyone who is interested in guitar or effects technology to check out his site. (more…)

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…)

Wow.  After most of one year devoted to my favorite amplifier, I don’t have a regular topic to cover, now.  Toward the end of 2015, my health declined pretty dramatically.  I ended the Dual Rectifier analysis early, because it was taking too long to put the articles together.  Aside from helping people understand the amp or tweak it, my intention was to assist DIY circuit designers, by highlighting interactions between the preamp stages and the key changes Mesa made to the basic design as established by Marshall and Soldano.

Since this version is now obsolete, I felt there would be little harm in sharing an analysis.  I haven’t done this for people to copy the design in whole.  Since the schematic is available in dozens of places, that could already be done by anyone who would want to.  I want people who are making their own amplifiers to see what this example does and decide if anything from it should, or should not, be a part of their own design, or if a modified form could be used.

When my health became even worse than it already was, I was stopped dead in my tracks.  By the time I could sit at the computer again, the inspiration was waning; not by lack of my want to write it out, but by the effects of the disorders I have to contend with.  It’s a very difficult hobby and I don’t want to make mistakes if I’m trying to help others.

Left Undone

I had not originally planned to write about the power amp, but some of it was relevant to analyzing the preamp modes.  I put that into the “Overview” article, but there is more that could be said.  I’m not sure I’m going to be able to do it.  In particular, the negative feedback could use a more detailed analysis to determine exactly how much stability is being added.

The other thing is the power supply.  The effects from combinations of different settings of the power and rectifiers would help with understanding the compression and headroom designed into the stages.  In fact, with only a very quick look, I noticed that V1 and V2 are probably more compressed and act like a limiter compared to tubes upstream, but it would need an analysis to be sure of that and also the extent of it.

So….

I’ve had a request to analyze the Mesa Boogie Mark V.  I might analyze select parts of it.  At this time, I don’t have the energy to go into massive detail and I don’t own a Mark to test the results.  I could post it as “just hypothesis”.

If I run into my own problems or cool, quirky tones, I’ll post about solutions or tweaks.  I also have one my old pedal designs to tinker with and some DIY ideas to look through, but I am not able to be in a hurry with any of it.