Things With Strings

Having already modelled the preamp stage of the  Vox Pathfinder 10, 15 and 15R  respectively, and noted the similarities circuit-wise between the PF10 and the PF15, I discovered another much-loved practice amp with a similar preamp stage - the Marshall Lead 12. I should say, before going any further, that there are huge differences between the power amp stages. The PF10 uses a TDA2030A chip amp whereas the Lead 12 uses discrete components. The chip amp power stage on the PF10 shouldn't colour the tone much, but the discrete one in the Lead 12 most likely does contribute to the overall tone of the amplifier. A simulation of the preamp stage with the Treble, Bass and Mid controls at 50% and the Gain control at 0%-100% gave this Marshall Lead 12 Preamp Simulation Marshall Lead 12 preamp simulation, Gain 0%-100%, TMB @ 50% Vox Pathfinder 10 preamp simulation (overdrive engaged) Vov Pathfinder 10 preamp simulation, Gain 0%-100%, T+B @ 50% Comparing the two, the Marsha

I've got a Vox Pathfinder 10 amplifier that I bought a couple of years ago, and I love it. It's a great little amplifier, but I don't care for the distortion channel, it just sounds harsh to my ears. There are quite simple modifications that can be done to this amplifier to remove the clipping LED's and increase the boost of the clean channel (check out Ben Craven's mods  for details). I'd been considering doing some of these, but whilst researching the subject, I discovered that the currently out of production (as at Nov '18)  Pathfinder 15/15R generally receives a lot more love than the Pathfinder 10. I found schematics for both the PF15 and the PF15R online, and saw that there were a lot of similarities between the PF10 and the PF15, particularly the earlier non-reverb PF15. The PF15R (with reverb) is quite a bit different after the first two opamp stages. I thought I'd model both the PF10 and PF15 pre-amp stages in LTspice  to see how they compar

It's coming up to Christmas, and what to buy for your daughters boyfriend? Hmm, how about making him a pedal for his guitar. After much deliberation I decided on Tim Escobedo's Duende (MOSFET version) and drew up a super-compact perfboard layout... I went straight into soldering without breadboarding, as the circuit is pretty simple, and luckily it worked straight away. Here's a picture after adding all the components to the board. And here's a shot of the completed unit In use, I found that I needed the volume control at about 1 o'clock before I could hear any difference, and I was expecting to hear something a bit earlier on the dial, but once above 1 o-clock, there is plenty of volume to be had. Switching the device on does brighten the signal somewhat even at unity gain, and the device is very quiet in operation, No hiss, hum or buzz. I wish I'd had a girlfriend whose dad made pedals when I was his age!

I'm planning on building a bass drum module, and I will need a pulse generator to test it, so I knocked up a circuit based on a 555 timer in ASTABLE mode and put it in an Altoids™ tin. You can easily find a circuit for this just googling around. I drew one up in Kicad like this. As I wanted this to be a pulse generator for triggering a drum circuit, I wanted the frequency range to fall within a range that would be useful for music, which is calculated by a combination of R1, P1 and C1 in the circuit diagram above. There are plenty of on-line calculators that will help here. I used this one  http://www.ohmslawcalculator.com/555-astable-calculator  (P1=R2 in the calculation). I found that a combination of R1=3K3, P2=1M and C1 as 2µ2 gave the best range for my purposes (approximately 0.327Hz to 198.761Hz). I had a small piece of perfboard offcut that I tried to squeeze it onto, and here is the layout. For the output jack, I used a 3.5mm jack I salvaged from an old PC sou

After the success of Pete's Bazz Fuss  I figured it was my own turn. I've only ever used stripboard in the past, but wanted to have a go at building a circuit on perfboard instead, so wanted to choose something relatively simple for a first go. The circuit I chose was the EHX™Muff Fuzz™ which despite it's name os more of an overdrive than a fuzz type effect. I drew up my own perfboard layout as below, taking care to make sure the components could be connected easily when soldering. Soldering up was relatively painless, and I was quite please with the neatness. You can see from the pic below that it is a mirror image of the layout above. I used 2N5088's for the transistors and 1N60P for the diodes. The picture below shows the component side of the board prior to shortening the transistor legs.  It worked pretty much straight away to my relief, and sounded OK, so I boxed it up in a 1590A sized box (always a painful process) and here is the f

It's been ages since I built an effects pedal, so to get my soldering chops back up to speed, I decided I'd build a simple fuzz pedal for my long-time friend Pete as a surprise present for his impending birthday. The circuit I chose was the Bazz Fuss (yes that's the correct name)  which you can read about here if you care to. I went for the basic v1.0 of the circuit and used a 2N3904 for the transistor, and boxed everything in a 1590A sized enclosure. Despite a number of stupid mistakes that I had to rectify, I got it all done and boxed within a day, complete with lo-fi graphics. Here's a gut-shot. gut-shot And here is the finished item. lo-fi graphic It sounded OK when I played it although it needed the volume knob maxxed out to get the best out of it. Maybe a higher gain transistor would have been better still. I'm pretty sure Pete will like it though.