Short update

For nearly half a year, I couldn’t work on any electronics projects due to a renovation. Now that everything is back to normal, I can finally pick up work again!

In the mean time, my projects list only grew, of course…

My old tube amp (a philips AG9014) crapped out, an old signal generator has some issues (the sine wave wasn’t a sine wave anymore), the tube tester still isn’t finished and I had to do some other small repairs (cracked phone screen, a few broken guitar cables, etc.). That doesn’t even include any of my own circuits!

The old tube amp turned out to be an easy fix:A while ago, a tube went bad and took out a few resistors due to a wrong fuse. After replacing the resistors and tubes, the power tubes kept red plating. The schematic is easy to find online, but is quite hard to read. After a lot tests and inspections I finally noticed two trim pots hidden behind the power tube sockets inside the enclosure. Of course, these were for bias adjustment and after some trail and error I found a reasonable bais point. They’re probably running a bit cold, but close enough for rock ‘n roll ;). There are still some issues with the phono preamp and (probably) some of the pots, but it’s working again!

I’m currently running the fx-loop send of my guitar amp (Blackstar ht5-r) into the AG9014, which gives me a lot more headroom and really nice crunch at higher volumes. I’m really happy with the end result, especially considering that this is the amp that got me into both diy electronics and tube stuff.

Up next is finishing the tube tester, so I can test the tubes in the signal generator and hopefully find out which one is faulty. After that, I’ll probably go back to experimenting with strange tube preamps again :).

My wish list is a lot longer of course:

-Midi/arduino something

-trying something with diy analogue synth modules

-fixing/recapping another old tube amp (a philips AG9015)

-Some utillities, such as an A/B/Y, stereo to dual mono and back, etc…

-…

With some luck, I’ll post a bit more frequently over the coming months :).

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A headphone amp and the cold war

The cold war

In my previous post I mentioned a subminiature rod pentode, the 1sh24b. These tiny tubes were developed in sovjet russia, during the cold war. The point being that a vacuum tube would withstand an EMP, which would fry solid state circuits. Besides, communism didn’t exactly encourage factories to invest in expensive equipment to produce transistors and integrated circuits. As a result, the Russian army continued using vacuum tube technology well into the 90’s. Their remaining stock is widely available on many web shops, typically for a few euros each.

Choosing a project

Enough history, back to my own projects.
After finishing my dual EF86 preamp, I wanted to do another tube based project. The biggest issue with the EF86 is its price combined with the wildly varying quality of modern production tubes; it’s a bit of a waste to buy 6 tubes at 20 euros each, only to find that none of them are of sufficient quality. I therefore decided to look for a cheap alternative, with good characteristics. Of all the options, the 1sh24b seemed the best, by far: they’re the size of a pencil, have a lifetime of ~5000 hours, are intended for military use (meaning that they can take a fair amount of abuse), can be used at low plate voltages and are extremely efficient. At 1 euro a piece, they certainly won’t break the bank either.

Experimenting

Information and datasheet are hard to find, and mostly in Russian, but with some trail and error I had it amplifying sound without too many issues. Ok, so now I had a tube amplifying sound, now what… . This particular tube is not the best choice for an overdrive/distortion, as it is very linear. I tried to add buffers and a tone stack to make a nice boost, but that didn’t work out the way I wanted either. When digging through some components, I came across a small audio transformer. Although I didn’t have the tools to easily determine the output impedance of the tube (or a proper datasheet for that matter), a 7K primary and 4 ohm secondary seemed to be about right.

A working headphone amp!

After connecting the transformer to the plate, I connected my in ear headphones to the output and guitar to the input. At first there was no sound, loose connection. Then, nice warm, clean guitar sound! The volume was just high enough, so no level control needed. What it did need however, was some sort of low pass filter, in case I wanted to use a distortion pedal with it. In the end I  settled with a combination of negative feedback and a full pi filter.
Currently the whole circuit is still on the breadboard, as I haven’t had the time to build a proper power supply (I’m currently using a lab supply), or work on it at all. I’ll update this post when/if I’ve made any progress. No sound samples unfortunately, as all my recording gear is in my own apartment, and all my electronics stuff at my parents house.

To conclude, the 1sh24b is great to experiment with, and can definitely be used for a guitar effect. I am amazed by its efficiency (the whole circuit draws just ~15 mA @35V, including heater supply!) and specs. For a single euro, I highly recommend playing around with this piece of sovjet history.

Looking ahead

Of course, this is not my last project. When going through the same web shop from which I bought the 1sh24b, I also ordered a hand  full of 6sh2p-ev’s, which also originate from Russian military stocks. This is the same tube that is used in the ‘culture vulture’ distortion, so at 1 euro each I thought it should be worth a try. On the digital side of things, I have been trying to get several effects working in pure data, with varying success. Moreover, I intend to build an Arduino based midi controller in the near future, to control my HOG2 and pure data effects. The main advantage of creating effects in pure data, is that I don’t need any other test equipment or components, just a laptop. While I do have a small stock of components and some test equipment at my parents house, I do not have enough space in my own apartment for anything that isn’t already there. Therefore, working on analogue effects is currently limited to about two weekends per month, during which I also want to do other things. I am therefore looking forward to working on digital guitar effects and new ways to create noise through DSP.

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A previous rendition of the headphone amp. A few days after this picture I condensed the  circuit to a quarter of a breadboard. The tube is in the middle of the right breadboard.

Low voltage tube preamps

Like most guitarists I love the sound of a good tube amplifier. I first got into tubes when my uncle brought a broken hifi tube amp for us to work on. He had been building radios since he was a small child, while I couldn’t tell the difference between a resistor and a capacitor at the time. We slowly worked on the amp in the weekends (although he did most of the work and I was just watching and asking questions). When some of the tubes had to be replaced, he tried to find some spares in the basement at his job (he worked at a university). When he came back for a few more, they proposed that he would simply take all of them, since no one would ever use them again. As a result, I now have a decent stock of tubes.

Rather then just leaving them collecting dust, I wanted to do something with them. The most logical step would be to build my own tube amplifier. However, the complexity and cost were a bit too much.  After some online research I found the valve caster, a ECC83 (12AX7) preamp, with 12 Volts on the plates. To my surprise, the schematic was dead simple and I had it running on the breadboard without too much trouble. Although it sounds fine, it didn’t give me the sound I wanted.

When looking through the stock of tubes I came across a number of EF86’s. On the internet I also found a schematic of a starved plate EF86 boost/overdrive. To keep the heater supply simple I just added a second EF86, running the whole circuit on 12 Volts, without the need of any regulators or large resistors. The result was a very touch sensitive, warm boost or overdrive, exactly what I was looking for! I did have some issues with ‘ghost noting’, although I’m not entirely sure if that’s the proper term. It appears that at certain settings there was a 120Hz amplitude modulation. Although some hum is not a huge issue, too much ghost noting is, basically you hear both the fundamental, as well as the fundamental plus 120Hz, which is out of tune. When used less extremely, it can actually be used as an effect by it self, adding some eerie ambiance (giving the feeling something’s wrong, but you can’t really tell what). The song below illustrate this, although it’s very subtle.

After found what caused the issue (a few missing capacitors), I fixed it and made the ghost noting switchable. The pedal has been on my board ever since and is always on when I’m playing, regardless of the genre.

I can’t find the schematic I used, but here is a layout of a similar project, although this one only uses a single EF86. There are few problems with this project though. Mainly because the EF86 is not intended to work at such a low plate voltage. Most good new old stock (NOS) tubes will work, but only the best will give a good result. I’ve tried several new production EF86’s, but they didn’t give any audible output at all. So unless you happen to have a few EF86’s laying around, this project is probably not worth it (unless you don’t mind spending a ton of money finding the right tube).  A more realistic consideration would be to use the special quality version (E80F) of the tube instead. The downside is that they’re even more expensive and quite a bit larger too.

In my next post I will explore the incredible 1sh24b subminiature rod pentode as the only active active component in a headphone amplifier.

 

Noise

Staying true to the title of this blog, I’ll first share the ideas behind two of my most experimental ‘songs’. The first track I’ll discuss was recorded several years ago. Back then, I didn’t have much fancy equipment, so I had to be creative. At my disposal were an electric guitar (an Epiphone LP black beauty), a Boss HM-2, a Boss FZ-2 and a 5 watt Blackstar amp. I simply put the guitar in front of my amp and let it feedback. With the controls on the guitar, effects and amp, I had some basic control over the color and pitch of the sound. It turned out to be quite an interesting exercise, as the sound responded both instantaneously, but also on a much longer timescale. Balancing between uncontrollable ringing and no sound at all proved to be difficult, but not impossible. It’s also worth noting that the distance between the guitar and the speaker are crucial if you feel like trying this.

The second track I would like to discuss was recorded much more recently, last week actually.

After buying a HOG2, one of the first things I wanted to try was to manipulate (white) noise and hum into music using additive synthesis (i.e. by adding harmonics to the fundamental). The noise mainly comes from a hyper fuzz, with no input signal and high gain settings. This method proved to relatively easy compared to my first attempt at harsh noise, as the signal is always in a stable state (it won’t change, unless you turn a knob). The down side is that it’s harder to create a slowly, organically, evolving sound. Some delay and reverb help, but it’s not the same.

Who knows, maybe I’ll combine to two methods to get the best of both worlds.

 

Creating noisy creations

Hi there, I’m Pieter. Currently, I am finishing a masters in paleoclimatology (meaning that I study Earth’s climate in the geological past). I’ve been playing the guitar for about six years and bass guitar for 3 years. At some point, I wanted to play more experimental music, with strange effects. In search for the ‘sound in my head’ I had a hard time finding the right effects, so I decided to try to make some of them my self. I already knew the basics and had most of the necessary equipment (a story for another post), making for an easy start.

Lately, I felt the need to document, and share, musical ideas and creation. Although I’ve been posting updates on my personal Facebook, I don’t want to bother all my Facebook friends with in depth posts on starved plate tube amplifier schematics and such. That’s were this blog comes in; here I’ll share all my diy guitar effect projects (whether finished or just a concept), musical creations and probably some DSP and MIDI stuff as well.

At this point, I’m not sure how much time I can and want to spend writing blog entries, but I’ll try to post frequently, as I’ve got plenty ideas.

That’s enough for now,

Pieter