A brief explaination first (and overly simplified so sorry for all the EE's I'm going to annoy, I did Mech Eng so blame my training there). I'm going to refer to something called hFE as this is why I've made this call. hFe pretty much means gain... however that can be a bit vague because gain can mean either current, voltage or power gain. In our case with transistors, it actually refers to current gain. One of the nice things about gain is that it transfers into decibels, or dB with is a measurement of power but we also conveniently use for volume references. hFE itself doesn't have a unit but it is a relationship/ratio of current.
Anyway, the NTE102/NTE103 makes up a combination called a Sziklai pair, or compound pair. There is another pairing like this called a Darlington so it's worth adding that in now. These types of pairs use two transistors to create one larger transistor that has a significantly higher hFE, therefore higher gain/power. The maths is slightly different for a Darlington but for the Sziklai pair, we can get roughly what the hFE is. We will use β for hFE.
β = βQ1 * βQ2 + βQ1
For the NTE102 and NTE103, the hFE is approx 80. It varies more widely in germanium and we are assuming they are perfect, non-leaking, constant temperature and current loading but irrespective, we can get an idea of what the pair does by using the following formula.
β = 80 * 80 + 80 = 6480
In the original, the NTE102 and NTE103 pairing makes sense. Both of those transistors are marketed as being a complementary pair to perform medium-level switching applications. In fact, they are normally used for power applications purely because that is a hell of a lot of gain.
For the 2N5087/2N5088, on the ones I used, they normally measured around 400... You can see how this is going to get mighty big and why I actually had some oversight in suggesting this...
β = 400 * 400 + 400 = 160400
So basically, that is huge. Actually, what ends up happening is you get a limiting effect after a while of turning the trimpot up. It just simply gets incapable of using all of that. So if we're dealing with such a high amount of gain yet limiting it so much with the trimpot, there are a few ways around it.
- Use the original germanium pairing or something similar with low value silicon, or even a hybrid with a lower valued germanium paired with a modern silicon transistor. I currently run this in my first build purely because I managed to obtain some AC128's at a price that didn't require sawing a limb off.
- Use a dedicated darlington pair transistor. The MSPA13 is one of those, with a hFE of roughly 10,000, it might actually be a good candidate. When I breadboarded a Bazz Fuss, it was my favourite as it gave me enough power that introduced nice sustain and allowed me to do more switching of components like diodes without fearing drastic level drops that render it unusable.
- Lower the value you use by using one simple transistor with a decent gain, which is what I plan to do as a darlington/sziklai can easily be replaced by one transistor. The benefit I see here is that I can boost the level by simply turning the trimpot a bit louder, which is probably advisable considering the current setup normally has the trimpot barely turned up. The move to a lower noise transistor like a 2N5089 in a section of the circuit where I feel the most noise is being introduced makes sense. That section is subject to boosting higher frequencies which I feel the noise is most amplified. A 2N5089 will drive a boost/gain section in a lot of pedals already so it is worth trying. Of course, some values will need to be changed in order to optimise the setup but not many (might need to change the input cap to a larger value IIRC).
Again, there are so many ways you can go with this and right now I am just working on ways to make it *better* for bassists overall. Really, it's just another way someone looked at the Big Muff, a pedal that has been tinkered with thousands of times, most often by EHX. This one just happened to sound far more distinct from the rest and the sound seems like a good base to work from.
