Category Archives: Potential Project

Breadboards and prototyping pedals

As time goes on I become more and more addicted to futzing with pedals, which is a good thing I suppose. But it is tempting to just keep building kits without really knowing whats going on in there. I’ve made attempts to tweak the pedals I’ve built from DIY Effects but only to the extent of messing with clipping diodes. And to be honest they sound great already, so there isn’t much to be done. What I really want is to go back to basics and learn how different parts of the circuit work and also how they interact with others.

So I needed a way to, for example, build a simple transistor gain stage (like the SHO I did before) and perhaps chain it with another one, to see what happens. Or build a generic fuzz and then play with bias values or different transistors. You get the idea. All this is harder to do if you are constantly soldering/desoldering components, so it’s time for breadboards 🙂

This project is nothing magical, just some parts assembly, but it was a lot of fun. I based my version on the Beavis Audio board that you could once buy in kit form. Here’s the link to the Beavis site, and a photo of mine:

The prototyping board

The prototyping board in its first incarnation.

What’s going on?

Power comes in from a small bench supply I have (not shown) via a standard 2.1mm socket on the back of the breakout box. That goes into the 10k pot, which lets you simulate crappy batteries. ALso not visible are the two 1/4′ jacks that serve as guitar in and effect out signals. You can clearly see the 3PDT stomp switch and the smaller toggle. All these connections are present on the connection block which I bolted to the side.

I also added a board on the back with some handy holes drilled in it. These will hold whatever pots and/or switches the circuit might need. Shawn from DIY Effects had done this, and it looked like a great idea, so I stole it 🙂 Here’s his blog entry showing a massively complex circuit on his protoboard. One day I’ll get to this stage!

What’s next?

  • Build a reverb circuit, probably the ‘Box of Hall’ circuit featuring the BTDR-2H reverb module. It should be very simple.
  • Build a generic fuzz-face and then progressively mod the crap out of it to see how it works.
  • Try some cascading gain stages (based on the Z.Vex SHO) to see what following the tube amp topology achieves.
  • Arduino!!! (this is a potential can of worms that will end with a switchable rack system…mark my words)

UPDATE! Here’s the Box of Hall circuit on veroboard. I still used the breadboard rig to hook up to power and I/O. And with great joy I realized that my little Marshall practice amp (if you can even call it that) clips onto the the back quite nicely 🙂

The circuit on overboard, connected to my huge Marshall stack.

The circuit on overboard, connected to my huge Marshall stack.

UPDATE 2: I did a prototype of the classic Fuzz Face. Not much to see, but it’s proof that the breadboard has made it very very easy for me to experiment with different circuits.

Silicon Fuzz-face!

Silicon Fuzz-face!

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OD2 – final assembly

The Clay Jones circuit, plus layout

The Clay Jones circuit, plus layout. Click to see the big version.

In my previous post I was discussing a new project. Another distortion pedal based on a clone of a Landgraff Dynamic Overdrive. The circuit was drawn out (possibly from looking at the Landgraff device) a few years ago by someone called Clay Jones. See the picture on the right here. This circuit was made available to me, as a beautiful pre-built PCB, by the guys over at DIY Effects. They have a great OD circuit (currently at revision 2, I believe) that I had used previously, but this one is using their “revision one” board.

The clipping switch

The clipping switch. 3 diodes on the left, 2 LEDs on the right.

Clipping

The major difference between the revisions has to do with the clipping section of the circuit. Rev 2 has ample space for all kinds of options whereas Rev 1 is limited in terms of on board space. In this context that didn’t matter. I knew I wanted to mess around with clipping options and that meant it was easier to do that with a switch off the main board. I chose to try 3 diodes in one position and 2 LEDs in the other. The middle ‘off’ position is just the raw clipping of the circuit alone.

OD1 and OD2

OD1 refuses to make eye contact with the conspicuously naked OD2

Initial tests

I was able to wire up the board with power, pots and jacks very quickly, due to the great instructions, and had it plugged into my amp in no time at all. The goal here was to compare the clipping options and just make sure I wasn’t going down the wrong path. And I was not disappointed at all. The 3 diodes position has tons of gain, but in the lower positions sounds much like a cranked Marshall, but with a slightly softer attack. It doesn’t have the harsh bite of the typical Angus Young tone, which isn’t a bad thing. Then I switched it to the middle ‘off’ position, and it immediately got much louder, presumably because there aren’t any diodes clipping anything. Also for the same ‘drive’ position, the middle position had way less drive. Position 3, the 2 LED’s wasn’t a huge change from the middle position, but it softened the attack a little. Either way, I completely love this pedal!. So now to get it into a usable enclosure.

The enclosure

Measuring and drilling the enclosure holes

Measuring and drilling the enclosure holes

Based on a recommendation from DIY Effects I bought a box from Pedal Enclosures, specifically the YY type, in red hammer finish. All that remained was to drill some holes and start the assembly. This meant I had to think about how I wanted to lay things out inside the box as well as outside. But the basic dimensions of the box decided a lot of this for me. Here’s the basics:

  • The circuit requires Drive, Tone and Level pots.
  • I wanted to eventually add a switchable boost, so I need 2 foot switches. This will be like the “more” switch on Joe Satriani’s Vox distortion pedal.
  • I need a hole for my clipping switch.
  • LEDs for both the switches so I know where I am.
  • The usual 1/4′ jacks and power.
Making sure the parts fit as I go

Making sure the parts fit as I go

I covered the box with masking tape and found my old vernier calipers and a pen. With the box of components at hand, for dimensions, I was able to mark out the locations for the holes and punch them quite quickly. Then it was time for the drill press. After starting with an 1/8th ” bit for pilot holes, I layed into it with my El Cheapo “unibit” that I got from Harbor Freight Tools.

Assembly

Belly up, with new parts

Belly up, with new parts

Now for the fun part! As I had done most of the assembly work with parts I had laying around, I did have to replace the pots with smaller ones (16mm rather than 24mm), and also I had to wire up the full bypass switch (and the LED). But all of that was just busy work. This time, I purchased extra components from Small Bear Electronics.

I was lucky enough to have wired it correctly first time (as with the original OD pedal) so within the hour I had it plugged into my amp and was jamming away.

I am very, very satisfied with this pedal. I can get a wide variety of usable tones from it very quickly. I do need to replace the drive pot with something else as the range of “no drive” to “loads of drive” all happens in the first few degrees. Not sure if this is simply the difference between linear and logarithmic taper. Anyway, here’s another photo.

(Almost) finished in it's shiny red box

(Almost) finished in it's shiny red box. The toggle switch is for the clipping options. Forward is the 3 diodes, backwards is the 2 LEDs.

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New distortion pedal project, based on Landgraff Dynamic Overdrive

A few months ago I built a clone of a TS-808 Tubescreamer (based on a PCB and build instructions from DIY Effects) and that proved to be successful.

I recorded a sample of what it sounds like: Steinberger into P1 Extreme, with OD pedal

Now that pedal was built with the standard clipping circuit i.e. two diodes. Some would say this is dull, and indeed the DIY Effects build instructions contain other recommendations. These range from using three diodes instead of two, for a kind of asymmetric clipping, to using MOSFET devices.

So to try these out I bought a pre-populated board from DIY Effects.; one that had been wired up in the style of a Landgraff Dynamic Overdrive. I had no idea what this pedal actually sounded like but a quick trip on YouTube told me what I needed to know.

The clipping arrangement has been deliberately left up to me to configure. I plan to use a switch to allow for the different clipping methods. I think I’l do the following:

  • Two diodes: for the traditional TS-808 style.
  • Three LEDs: asymmetric clipping.
  • Two MOSFETs: I have no idea what it sounds like, but its worth a try.

SLW from DIY Effects sent me great instructions on how to do this, and recently posted about it. He uses a DPDT, but I might need 3 positions to do this. I’ll see if Radio Shack has some in stock. A nice cheap project if I can retrofit this into my existing grey enclosure.

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Tubescreamer transistor substitution

As part of the Tubscreamer clone project, I ordered parts from Mouser based on the list provided by the DIY Effects build documents.  They listed the MPSA18 as the transistor of choice, but at the time of my order Mouser had none, and I substituted a PN2222ATF. But, I realised much later that I didn’t have even the slightest clue as to whether this was a good thing.

From the Geofex site, there are some recommendations on choosing components:

6. Transistors: When in doubt, use a 2N5088. Or a 2N3904 – or a 2N4401 – or a BC549 – or… find cheap, available NPN and PNP devices that you can get easily and use them.

From a Tonepad customer on a forum:

Tonepad site indicates using a 2N3904. This is certainly acceptable, but you may have a little more oomph on the output with a 2N5089 or an MPSA18. 2N3904 are fine units for a lot of purposes, but in this case not so much. You’ll likely be more satisfied with MPSA18 or 2N5088/5089. Stock TS9s come with 2SC1815 transistors which tend to be higher hfe than 3904s, though not quite as high as the A18s or 508Xs.

So it’s all quite ambiguous as these all come across as “opinions” rather than an objective assessment. Time to learn something about transistors, as right now all I know is:

  • They’re all black plastic things on 3 legs
  • See previous point.

Now of course I know that tubes aren’t readily substitutable without knowing more about the application. You can’t blindly replace a 12AX7 with a 12AT7, even though they’re both 9-pin glass bottles, without knowing that the AX has a gain of 100 but the AT is more like 20. Searching around for answers led me to a document that has been plagiarised all over the inter-tubes:

Understanding the transistor data will definitely helps you to find the right and correct part number for substitution.

So, comparing the various parameter’s ratings as written in the “official” Fairchild PDF documents linked above, I see that the PN2222A is actually a pretty good fit for the MPSA18 in terms of VCEO, VCBO, IC etc. But when I look at HFE, the DC current gain, I see:

  • MPSA18  (VCE = 5.0 V, IC = 1.0 mA ) = Min 500
  • PN2222A (VCE = 10V, IC = 1.0mA) = Min 50

This seems to be off by an order of magnitude (even if you adjust for the current difference), almost like the 12AX7/12AT7 tube swap I hinted at before. So it seems the PN2222 is NOT a good fit. I’m going to ask a very knowledgeable friend about this to confirm my guesstimate.

Until I find a good answer, RadioShack has 2N3904 and 2N4401 transistors on their website, so I’m going to wander over to their store at lunchtime and buy a few of each.

UPDATE: RadioShack has little packets of 15 “assorted transistors” for about $2.50. Guess what’s in there? 2N4401, 2N2222 and 2N3904. So I bought a pack each of NPN and PNP. On the back of the pack it describes the NPN types as:

  • Typical HFE: 200
  • VCE 30V
  • IC 800mA
  • Power dissipation: 1.8W
  • …designed for high-speed, medium-power switching and general-purpose applications.

UPDATE AGAIN: Here’s the post with all the details of the final build.

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Bias adjust for my P1 eXtreme

Variable cathode bias option for P1 variant amplifiers

Variable cathode bias option for P1 variant amplifiers

As my P1eX is pretty much done (I have to revisit the grounding scheme as there’s a fair amount of hum when cranked) I’ve been meaning to get around to trying different output tubes to see what differences I get in tone. Initially I chose the 6V6 tube which should give me a “Fendery” tone…whatever that means. Admittedly it does sound “Fendery” when it’s doing “light crunch” with a Strat in position 2 or 4, but when it’s cranked it gets “Marshally” very quickly. Not that I’m complaining.

So here’s some tubes I can try , with their recommended cathode resistor values:

  • 200R / 5W – KT88, 6550
  • 330R / 5W – EL34/6L6
  • 400R / 5W – KT66
  • 600R / 5W – 6V6

Right now the amp is cathode biased, so I must also add the fixed bias modification. This will allow me to measure voltage across a 1 Ohm resistor going from the cathode pin to ground (therefore giving me current). See the diagram to the right for the circuit. It’s quite simple really.

UPDATE

I was having difficulty finding a 1kOhm/2 watt potentiometer, but I have located a part here on the Newark site.

I can get “bias tip jacks” from the Hoffman site with no problems.

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Boss DS-1 – The Keeley Modification

Boss DS-1

Boss DS-1, innocently waiting to be torn apart. The controls in this configuration sound terrible, by the way.

This weekend I finally got to play more with my new tube amp, and that included plugging in my Boss DS-1. I have to admit, it was somewhat disappointing:

  • It won’t do “clean boost” or even “slightly dirty boost”, which means its not so hot at driving a tube amp cleanly.
  • The tone control is close to useless. It has a really narrow usable range at about 8 o’clock on the dial. Anything above sounds fizzy and thin, anything below sounds muddy.
  • When you get it in the sweet spot though, it does sound good for lead tones.

So I thought I’d look around for modification ideas. I’d read about plenty of them, but never with a mind to actually performing them myself. I’d read about the Analogman modded DS-1, which apparently gets good reviews from Steve Vai (among others), whom I admire.

Also there’s the Robert Keeley modifications (a review). Now remember I am lazy and new to this, so it’s not like I’m going to analyise the circuits myself and come up with anything just yet, so I searched around for practical guides to these modifications, and found this Instructable on doing the Keeley Mod which seemed nice and easy.

The next step is to get the parts lined up, so I used the Instructable documentation to create a project on the Mouser web site. Try this link to my Keeley DS-1 mod “project” which is just a parts list really, but it makes ordering easy. Anyway, parts are on their way, so I’ll post more when I actually perform the mod 🙂

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The quest for tone

Further to the Tub-screamer pedal project (I’m waiting for a few final parts), I found a great article on the Geofex site all about the original Tubescreamer internals. Here’s a quote I found amusing:

The best thing to do, I believe, if you’re hunting the Tube Screamer Holy Grail is to stick in an 8 pin socket on the board, noting the orientation of the original chip carefully, and then just plug in various dual opamps until you find one that conjures up images of your own personal guitar deity.

In this world of tube amplifiers and guitars/effects there are snake-oil salesman around every corner trying to get us to spend hundreds (if not thousands) of dollars on all kinds of gadgets that’ll bring us closer to “that tone”. They recognise that at the heart of it we (guitarists in general) are star-struck wannabes that have a very simple desire to be “as good as that guy”. And “that guy” may be Clapton or Vaughan or whomever. In quiet moments when we’re listening to our favourite music we think “if only I could sound like that”. I don’t care who you are, you do it. I bet even Clapton does when he’s listening to Buddy Guy, or Freddie King.

For me it’s Eric’s tone on the studio version of “Spoonful”. It’s clearly some kind of Gibson, probably a Les Paul. It’s also certain to be a 100 watt Marshall cranked pretty high so it’s “alive” and on the brink of feedback. In my view that’s the sweet spot for any rig. In the mix there’s an ocean of reverb on the track which adds to the haunting sound she creates. You can hear him playing with a variety of pick strength…sometimes he’e gentle, other times he’s really digging in. Never does his guitar sound harsh; it’s always creamy smooth and very, very musical. Now for me to get that tone I simply use my 50w 2204 Marshall and either my mid-70’s Les Paul or my Tokai copy. That’s all I need to fulfill that particular dream; especially as I realise I’d never truly be able to recreate that sound as I’m not Eric.

However, if I were more susceptible to the snake-oil salesman I could do the following:

So the question is, how much closer to that tone will I get by spending > $200k? Maybe 1% closer. I can get 95% of it with my so-called cheap rig. The other 5% is all about Eric.

Back to Tubescreamers. The aura surrounding them is due to people like Stevie Ray Vaughan. He used a TS-808 in his rig, so naturally everyone wants one. Conversely, nobody wants the TS-9 or any kind of reissue as folklore would have it that they “aren’t the same”. The fact is, the pretty much are the same. The Geofex article linked above proves that beyond doubt. So why is it that people will pay $350 for a handwired TS-808 from Ibanez? Why is it that sellers on eBay think they can get $600 for an old one? It’s all snake-oil.

I’m going to build my $37 clone from the circuitboard I got at DIY Effects, and the parts in got from Small Bear Electronics/Pedal Parts Plus, and be 95% there. 🙂

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Tubescreamer clone

While browsing the Hoffman Forum I clicked on a new member’s profile link, and it took me to this product page of a PCB for a Tubescreamer clone. I have been wanting to build one of these for a while now, and once I finish my P1eX, I’m going to do just that. So here’s the plan:

I can do a funky paint job (or even a boring one..who cares) without too much difficulty, so this looks like a pretty cheap project at $37. Talk about bang-for-buck!

PS Originally I typed TUB-screamer. I think I prefer that name 🙂