Monthly Archives: May 2010

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.

Components

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”.

Result!

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).

UPDATE!

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

UPDATE AGAIN!

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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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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Finally, a functioning AX84 P1eX tube amp

Board installed in chassis

Board installed in chassis, transformer wires trimmed, heaters wired, switches wired.

Final components

The last post left off with me needing to order some missing components. I had genuinely screwed up the order, and wasn’t going to order 2 components online, so I ran over to Radio Shack during the week for a missing resistor, and a capacitor for the tone-stack. It took mere minutes to solder these in place.

I was worried that I had the wrong kind of capacitors in place for the 12AX7 cathode bypass caps. The schematic implied they should be polarised electrolytic, but the layout diagram specified both types. So it was a little ambiguous. Forum members on the Hoffman site confirmed that in that location it didn’t matter.

Wiring

By this point I was ready to install the circuit board into the amp and start wiring it up, but I wasn’t quite ready. The output and power transformer’s wires needed to be trimmed and wired in where appropriate. The guide recommends NOT wiring up the secondaries to the circuit just yet, this is all part of the power-up sequence. In-line with the AX84 build guide, I made sure I had the layout diagram and the schematic to hand at all times. This meant I could use my trusty green hi-lighter to mark progress as each connection was made.

This is where I made my first mistake. The layout diagram and the schematic wanted the black pair of wires from the power transformer primary to be connected to the mains switch. You can see, in the picture above, the white wire neatly capped and sitting there all smug in its incorrectness. My transformer, while being the correct model, had 3 wires (black, white and grey). I made a guess based on the diagram stuck to the side of the box the transformer came in, and went with black and grey. This is because Hammond made a “running change” to the primaries to accommodate the so-called modern line voltage of ~120V (as opposed to “traditional” 115V). Here’s the details on the Hammond site.

For those customers who are seeing too high a secondary voltage due to higher primary line voltages – use the White & Black wire and tape the gray wire…

Of course, I didn’t discover this until AFTER I had attempted to power it on. More on that later.

Wiring progress

Wiring progress. Preamp section and tone-stack.

Meanwhile, mistakes continued. In this picture you can see progress being made on wiring. All looks good, and I was trying so hard to be diligent and follow the layout (and schematic) but see if you can spot the mistake on the input jack. I didn’t until much later on. I put this down to never having worked with Cliff jacks (the shorting kind). More on that later too.

As I progressed through I realized something else. The layout diagram was in conflict with the schematic, or at least I had misread it. What looked like ground bus connections between turrets proved to actually be shield connections (the fat grey wires you can see in the picture to the left). So I had to remove some connections to fix that one. This was just down to me reading the layout incorrectly.

Initial power-on

Ready to try again, PT primaries corrected

Ready to try again, the PT primary wires have now been correctly wired with white and black.

Once I had wired up as much as I thought I could, (layout + hi-lighter = best practice), I proceeded to work my way through the Paul Ruby first power on sequence. All previous work had been done on my dining room table which gave me lots of space to spread out, but now I needed much more room and decent power as it really was time to fire this thing up. This of course meant I needed to use my one and only speaker cabinet, the 2×12 I built years ago. I moved everything down into my workshop in the basement.

So when it came to powering it up with no tubes or secondaries connected, it kept blowing fuses. I’d see a all too brief flash of pilot light and then nothing, so clearly it was drawing power, but too much. This was due to the PT primary issue mentioned above. I thought about it and decided to check the wiring again, which led to discovering the “running change”. The picture to the right shows the correct white and black wires, with the grey tied off and capped. Now I got a solid glowing pilot light, and good voltages at the PT secondary. Ok, cool. Turn it off.

At this point I got over (stupidly) confident, so I turned all the knobs to zero, plugged in the tubes and the speakers, and turned it on in standby for a couple of seconds. I did see the heaters glow, so I left it sat there for a minute or so. I got even more cocky, so I plugged in a guitar cord (I hadn’t been so bold as to have brought a guitar downstairs to my workshop), and flicked the standby switch into ‘play mode’. No fuses blew, and the tubes did not explode or melt.

With confidence surging, I plug everything in

With confidence surging, I plug everything in. That's an ECC83S and a 6V6, both from JJ via Eurotubes

Then I gently turn up the two volume knobs, just creeping each one up a little bit at a time, hoping for some sound. I suppose I was hoping for silence as this would imply to me that it was working. What I in fact got was crackling/hissing and even squealing when the knobs were turned right off. So after 20 seconds of this, I turned it off again in disappointment.

The time had come to stop. I’d done well that day to get this far, and I was definitely tired. So to stop myself from making any more mistakes I decided to call it a day.

The next day

I had a chance to poke at the amp some more the following day, so I went downstairs determined to get this damned thing working. I decided to re-check the power supply, and measure voltages at the tube pins. The schematic was good enough to specify what they might be, so it was easy to measure each one and write them down in pencil on the schematic. Good news, the voltages were all within 15% of the schematic. Cool, I did something right!

Input jack wiring

First noise

The amp all hooked up to my speaker cabinet and resting on a sophisticated cradle.

Hoffman forum members had suggested I check and recheck the jack wiring, both in and out. Their experience, and my sonic description, told them it was probably a grounded grid. And sure enough it was. The 1Meg load resistor was wired incorrectly, and also the shield on the wire going from the jack to the grid was soldered to the tip. Nice job Simon.

I made the corrections and prepared to power it up again. This time I had a guitar with me, so I plugged it in and left it leaning against the side of the cabinet on the bench. I hadn’t planned on playing it yet.

Ok, so I power it back on in standby….wait 25 seconds or so…and flick standby off.

Silence. Ok, good. Turn up the volume knobs a little…..more silence. Turn them both up about half-way….more silence, but a bit of hiss. I’m thinking this is odd, so I reached over to the guitar and strummed the open strings. CLAAAANNNNGGGGG! It made noise!!! Oh my god!!

So at this point I grab the guitar and strap it on. It’s a Tele-like guitar I built years ago, with a set of EMG pickups that allow for lots of flexibility. It has an 89-SA-85 with a 5 way switch, so I can dial in Strat and Les Paul tones easily, and there’s quite a range of signal strength coming out of the guitar so I can see how different amps behave. A great testing guitar.

A functioning "P1 eXtreme" amplifier

A functioning "P1 eXtreme" amplifier

Man this thing sounds good. At low volumes it’s very clean. Not too inspiring, but jazzy I suppose. Go about half way and it starts to come alive. The tonestack starts to have some influence on the signal so there’s different tones to be had. A very useful tonestack actually. I was expecting the same useless range that my 2204 has, but no.

And with everything on 10 it grinds and burns as well as my Marshall 2204 does. In fact thats a great way to describe this amp; when it’s cranked all the way, it sounds like my Marshall does in it’s sweet spot (which in itself takes a while to find, and is ridiculously loud). With the P1eX I just have to turn everything all the way up….what a dream! Induced feedback is present in copious amounts and is tweakable by simply adjusting one’s proximity to the speakers. The guitar feels incredibly “alive”..it’s the real thing. Don’t for a minute imagine that this amp is somehow a toy, or the very nature of it is a compromise. Far from it. This thing has tone…loads and loads of it. I’d be so bold as to say that I’d gig this amp now, in its current state. This is an exceptional blues amp. You could even do AC-DC with this. At low volumes, but with the preamp gain on about 80% it’s still got lots of sustain, but without the harsh fizz of 100%.

I’m clearly new to this amp so I will be playing it much more in the coming days. I have a variety of guitars that I can plug into it, so I hope to report later with some recordings to demonstrate.

What a day! 🙂

Lessons learned

  • It doesn’t matter how much you study the drawings beforehand; mistakes will be made. Plan to fail etc. I should know this from almost 15 years in software, but there ya go. My mistake with the input jack wiring was because I was rushing at the end of a long day of soldering.
  • Read all the instructions and build guides that you can find. The “official” guide is great, but others have gone through builds just like me and they are posted all over the internet.
  • Don’t be in such a hurry. I don’t know why but I kept wanting to “just get it done”. Why would I choose to hurry this experience away? The point of a journey is not to arrive, right?
  • When you’re a newbie like me, don’t guess. I could’ve destroyed a $50 power transformer by doing what I did with the PT primary wires. I was lucky.
  • I have a very patient wife and family. They put up with me taking over the entire dining room table, stinking up the place with solder flux fumes and leaving tiny pieces of copper all over the place, for two whole days. They didn’t complain once.
  • I have a great workshop, with lots of tools. It lets me do a lot of things I was previously not capable. I should appreciate that more.

Future plans

  • Make some recordings. Every time I turn it on and play, it surprises me. I must record it properly.
  • See if I can make it less noisy at high volumes. While it sounds good cranked, it’s noisy. I will revisit the grounding approach after checking against layouts and studying “the Merlin documents“.
  • Try different output tubes. I have some Groovetube EL34M tubes waiting to go into my 2204, so I can try one of them.
  • Build the cabinet to go with the amp. I can’t take it anywhere without that.
  • Take it to a local jam night and see what others think.
  • Modifications. Once I get to know its capabilities more I will know if I want to tweak it.

UPDATE! Here’s a post including some recordings of the amp.

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