Tag Archives: capacitors

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.


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.


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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Building a TS Overdrive – from DIY Effects

Adhoc workstation

Here's the board with the instructions on the left. All the components were in neatly labelled baggies.

After my initial trepidation about which transistor to use (and with some patient guidance from Shawn at DIY Effects) I was ready to build the TS Overdrive guitar effects pedal. I’d read the build document many times as I learned from building my AX84 P1 eXtreme that you can never go over this stuff too much.


So step one was to start installing components and get soldering.  I had my less powerful 15W iron this time as it has a smaller tip and will be less likely to cook any components. I also brought out my very handy clip stand device, which helped me hold components as I assembled them. It also has a magnifying glass attached…very handy. I began with resistors, then moved onto capacitors (electrolytic first). Then it was the IC socket and transistors.

Standard TS 808 clipping diodes

Standard TS 808 clipping diodes. There are many options available here.

Clipping options and transistors

There are several options included with the board design that allow for different clipping methods. You can use the stock diodes, or MOSFETs or even LEDs. I went for the original method (which is regular diodes in position D1 and D3. D2 gets jumpered) because I wanted to hear what the original TS 808 circuit sounds like. These things are legend and I’d never had one in my arsenal before. As mentioned in the previous post, I had an issue getting hold of the prescribed MPSA18 transistors and in the end found an assortment of general purpose ones at Radio Shack. So this build used a pair of 2N3904 transistors.

Heat shrink on the pot terminals

Heat shrink on the pot terminals

The remainder of the build went very well. It really was a case of following the build notes, and carefully marking off each component (or indeed wire) as I assembled it. I knew that the board had to mount on top of the pots so I was careful to heat-shrink the wires coming off the pots themselves; I didn’t want any random wires to short out parts of the circuit.

Final assembly

This was tricky for a few reasons:

  • I used solid-core 20AWG wire. This mean that while the wires stayed where I put them, it also meant it was harder to orient the board. See next point.
  • Rats nest of wires

    Rats nest of wires, but it's physically sound and ready to go!

    The holes in the pre-drilled enclosure from Pedals Parts were such that I had to choose between having the tone pot right near the top of the pedal (which looked crap) or the tone pot near the stomp switch. I opted for the latter, but that meant the board had to be oriented the other way round, which then meant the wires I had already soldered in were about an inch too short. Coupled with them being sold core and the result was physically sound, but looked really messy.

Fire it up!

Almost done

Almost done. The view through the looking glass!

So all that remained was to solder in the LED, and put the knobs on. I’d failed to order a bezel for the LED, so right now it’s just kind of floating there. The knobs went on easily, and look good. After using a mix of Alpha and CTS pots on my amp build, I must say I like the action on these Alphas. The CTS pots I used on the amp were nylon shaft whereas these are solid aluminium which feels so much better.

Next step was to plug in a battery, screw on the back, and fire it up. And I must say it sounds excellent! I dialed my amp to be as clean as it gets…i.e. no pre-amp distortion/saturation, and dialed the TS OD to be a clean boost (no Distortion, Level just a bit louder). Harder to  dial in was the Tone. The documents are correct when they say that most of the range is at the end of the knob’s travel, so there’s a kind of sweet spot where you get some good “bite, but it’s not harsh. With the tone on maximum it can be a bit “fizzy”.


From here on I jammed for quite some time, punctuated by twiddling with the knobs on the pedal. It was hard to make it sound bad, to be honest. It’s definitely not a high gain machine, but I wasn’t expecting one (and that’s why I got the Boss DS-1). It’s a fantastic blues overdrive that works well with single-coils as well as humbuckers or P90s. If my SM57 wasn’t broken (might be the cable) I’d record some samples.

I plan to do a number of things from here:

  • Try different clipping options.
  • Try different transistors.
  • Re-finish the enclosure. This Hammerite stuff isn’t pretty. It’s been a week and it hasn’t dried properly, so I think I sprayed it on too thick. I’d probably go for green enamel as a nod to the original Ibanez TS 808 that started all this.
  • Record some samples.
  • Minor adjustments such as mount the pots lower so the knobs don’t stick up so much. Also, buy and install the bezel for the LED (which I might change to blue, just cuz).


An older version of the DIY Effects board, but with a different/better design.


A new enclosure, different clipping method, and a sound sample.

Final assembly of the TS OD

Final assembly of the TS OD from DIY Effects

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Cap job

Discharging the old Davy capacitors

Discharging the old Davy capacitors with my new tool. Note the horrible quality soldering, courtesy of Marshall.

This past weekend I was able to replace the larger 50-50 caps in my amp. It meant I got to use my capacitor discharge tool which I’d been toying with for a while. Soldered between two alligator clips, I have a 5W 5k Ohm wire-wound resistor. I left them clipped on each positive cap terminal for a few minutes. That seemed to do the trick; my test was to do “the screwdriver trick” and short them to ground. There was no “loud pop and sparks” so my tool was successful.

Original Davy 50-50 cap being removed

Original Davy 50-50 cap being removed

So I de-soldered the old wiring and removed the old clamps. It was easy to put the new ones in and re-attach the wiring. I had taken pictures along the way,so it was trivial to get the wiring back in the right place. History has shown that my memory is close to useless, so I didn’t even attempt to hold it all in my head.

You can see the underside of the main PCB through the hole in the chassis (see left). I left this cap, the one sitting next to the choke,  sitting quite high in its clamp (see the picture at the end of this post) as I was paranoid about shorting the wires against the PCB.

Two of the new caps in place

Two of the new caps in place.

You can also see in the above pictures that Marshall wasn’t too picky about employing people that could solder particularly well. Their preparation seemed to be the key…i.e. when they stripped insulation off wires they did not bother to spend half a second to twist the strands together before tinning it. I had to replace a few wires as the original wire was not going to hold up too well.

Once completed, I fired her up and checked the bias. All was normal, and it appeared to have greatly reduced the amount of hum…especially when cranked. Success!

Next step will be replacing the electrolytic caps in the grid bias circuit.

New filter caps installed

New filter caps installed

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Bias adjustment prior to replacing capacitors

This last weekend I was able to begin the process of restoring the innards of my 2204. The very first thing I did (after discharging the filter caps properly) was solder a 1 Ohm resistor between the cathode and ground of the EL34 output tubes. Once complete I was able to check the bias of the existing setup by measuring voltage across that resistor. Ohms law provides that he voltage I measured was equivalent to amps. It was way down at 19 mA.

So I referred to this Eurotubes biasing page which told me:

The formula for calculating the bias is the dissipation of the tube divided by the plate voltage which gives you 100% and then you can bias anywhere between 65% up to 85% of this.

The bias components on the 2204

The bias components on the 2204 board. They’ll need replacing soon.

My plate voltage is 400 so using 25 watts as a basis, 25 / 400 = 0.062. 70% of that is 0.062 x 0.7 = 0.043 = 43 mA. Tweaking the bias trimmer gave me 39mA on one tube and 41mA on the other. A reasonable match.

This didn’t seem to affect the tone using the original tubes and filter caps. I recorded the resulting ‘tone’ at a known setting that gives me the Marshall sweet-spot tone.

Two things I noticed that will need investigation:

  • The bias adjustment trimmer was almost at the end of its travel to give me the value I wanted. This may mean the trimmer is close to death?
  • Why was it set at 19mA in the first place? Is this also an indication that my plan to replace the bias components really must be done soon?

UPDATE from the future! March 2015

I replaced the output tubes recently and biased it the same way as above. When playing the amp in anger at a rehearsal, I found that the amp breaks up into quite pleasing distortion much earlier than I expected. It is indeed a great sound, but I’ve lost the strident clean tone I would normally get. There’s one song we do that needs that…for my Telecaster and a tremelo effect. I now suspect that the new tubes were simply born this way, and that I need to change the bias so the amp is running a little colder.

Look at this post: http://www.mylespaul.com/forums/squawk-box/31210-getting-jmp-2204-bias-within-range.html

FWIW my rule of thumb for JMPs is 28-32 mA for EL34s, 34-36 mA for 6550s. I sometimes go a little hotter, but to my ears there’s generally no sound improvement for the shorter tube life. I generally shoot for something like 15 watt plate dissipation.

Most tube dealers recommend you bias really hot. I wonder why?

This implies I biased it REALLY hot at 41mA. We are going into the studio tomorrow, so I’m going to rebias first thing, and see if I get my ultra clear ‘barking’ clean tone back.

UPDATE again: Dec 2015

It is worth stating that I was indeed able to get my loud and clear tone back. My amp was indeed biased way too hot. I can still get good 2004 grinding tones by using lots of pre-amp (I might put it on halfway) and dial the master volume to suit the loudness I need. But mostly I run mine with the master all the way, and adjust the pre-amp knob to suit loudness. There’s a sweetspot where I get a great strident clean tone that takes pedals very well.

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More components to replace

After some discussion on the Hoffman/EL34 forum, it seems that as I am going to replace the filter caps in my Marshall 2204, it’d be a good idea to replace the “bias components”. This basically means that I should replace all components between the power supply and pin 5 (grid) of each EL34. This little circuit includes a couple of electrolytic capacitors, so the same rules apply…if they’re old, replace them. I’m going to replace the resistors in the circuit with metal film resistors. I don’t see any harm in doing so, and it’ll be good practice.

Master Model 50w Mk 2. Lead - my amp

The schematic I’m using appears accurate when compared to photos of my board. That in itself is giving me practice in identifying the right components, and tracing the circuit visually. There’s a cognitive leap from schematic to physical layout that takes getting used to…like translating a UML diagram to actual source code.

You’ll see a section above the power transformer that is sort of labelled ‘BIAS’. Note the labels by some of the resistors, RG, RB1 and RB2. These seem to be variants for the European market. This initially confused me, as the parts on the actual board didn’t map to the schematic. That was until I remembered I’m British so my board has ‘all’ in ‘all but USA’ component values (see the little box above V4/V5 in the heater wiring section?). I was seeing 150k on the schematic, but finding 200k on the board.

Luckily I made this discovery before I ordered all the remaining parts from Hoffman.

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