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Author Topic: Mosrite Fuzzrite (si version) build tips  (Read 11141 times)

LJN

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Mosrite Fuzzrite (si version) build tips
« on: December 04, 2014, 07:06:39 PM »
Hello. In the years since I've been on here, I've learned a little bit about building fuzz pedals. So, I thought I would post about the mosrite fuzzrite. This isn't the easiest circuit to build because there's not a whole lot of accurate information about it. I built one, and it took me over a year to get it straightened out. First, the pots should both be 500k log or audio taper. Second, transistor shouldn't be selected by hfe, but frequency as well. This is a very picky circuit. Select a transistor with a frequency around 110-140 MHz. Third, you'll have to experiment with smaller value collector resistors. I used 10k. There will be some radio static,  but don't worry. Just put a .002 uf cap on the board from input to ground. This is a very versatile fuzz, and is very underrated.  I use mine for everything I play. Make sure you put the 22k high pass resistor in there too. You may choose to put it on a switch. I did, but usually, I leave it connected. It's a very bright fuzz with only 14 seconds of sustain. It has become my favorite.  I hope this helps anyone who is having trouble building this great sounding fuzz. I used C1740 transistors in mine, by the way.
« Last Edit: December 04, 2014, 07:11:47 PM by LJN »
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Roly

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Re: Mosrite Fuzzrite (si version) build tips
« Reply #1 on: December 05, 2014, 02:07:59 PM »
Quote from: LJN
This isn't the easiest circuit to build

...and not made any easier by the lack of a circuit to refer to.


Quote from: LJN
Select a transistor with a frequency around 110-140 MHz.

Yawot?  Would you care to explain?   8|

(The datasheet typical fT of a 2SC1740 is 180MHz)
If you say theory and practice don't agree you haven't applied enough theory.

LJN

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Re: Mosrite Fuzzrite (si version) build tips
« Reply #2 on: December 05, 2014, 07:20:59 PM »
Okay. So there's not much in this circuit.  Two transistors, and not very much else. Some people will tell you that any transistor will work. That's wrong. The gain can be perfect, but if the frequency is too low, you get those weird decay sounds. If it's too high, it won't decay at all. The output will just cut off to dead silence as soon as the input signal drops. So what you have to do is find some middle number. Now, this circuit doesn't have much sustain. Only about 14 seconds. But it's more versatile than people think. Especially if you put the high pass resistor on a switch. With the transistors I used, the collector resistors had to be changed to 10k. This will cause radio static. To get rid of that, put a .002 uf on the board from input to ground. One last thing. The pots should both be 500k log taper. 33k and 350k are wrong.
If it sounds good, USE IT!

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J M Fahey

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Re: Mosrite Fuzzrite (si version) build tips
« Reply #3 on: December 06, 2014, 01:47:28 AM »
Still no schematic  ::)

Roly

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Re: Mosrite Fuzzrite (si version) build tips
« Reply #4 on: December 06, 2014, 01:58:04 AM »
Okay, let me put it another way - how did you measure the fT of the transistors you used?
If you say theory and practice don't agree you haven't applied enough theory.

LJN

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Re: Mosrite Fuzzrite (si version) build tips
« Reply #5 on: December 06, 2014, 04:11:52 PM »
I don't have anything to measure transistors with. I just looked up the data sheets of the ones I had tried and the typical frequencies of those were all between 80 and 90, which is a bit too low. I originally used the schematic from fuzzcentral, which does work, but has some errors. I kept tweaking it until I finally got a good sound out of it. Now, I'm not knocking fuzzcentral.  Their fuzz face schematic works perfectly. But, the fuzzrite is a different story. I have a schematic of mine, which I drew by hand. I'll post it for you later.
If it sounds good, USE IT!

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LJN

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Re: Mosrite Fuzzrite (si version) build tips
« Reply #6 on: December 06, 2014, 04:30:19 PM »
Okay. Here's my schematic. Transistors are C1740, collector resistors are 10k, pots are 500k log taper. The parts in red indicate all the changes that I made. It's a great sounding fuzz, but requires some getting used to. It's nothing like a fuzz face, or big muff. You'll be using the volume control on your guitar alot more, and your pickups will affect the sound quite a bit.
If it sounds good, USE IT!

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Roly

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Re: Mosrite Fuzzrite (si version) build tips
« Reply #7 on: December 07, 2014, 01:18:30 AM »
Well the 2SC1740 datasheet I have gives a figure of 180MHz.

At the risk of sounding a bit testy, let me pose the question a third and different way; what makes you think that the transition frequency of a transistor in the hundreds of megaherts would have any influence at all on its behaviour in the audio spectrum?

Do you understand what the fT of a transistor is?

You say;
Quote from: LJN
transistor shouldn't be selected by hfe, but frequency as well

Do you understand how the fT and hFE relate to the dominant pole in an audio circuit?

I want to know how you came to the idea that the fT of your transistors would be as, or more, important than their hFE (which I'll bet you didn't measure either).
If you say theory and practice don't agree you haven't applied enough theory.

LJN

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Re: Mosrite Fuzzrite (si version) build tips
« Reply #8 on: December 07, 2014, 05:07:51 AM »
Look. I can't really give you a scientific answer to this. All I know is that when I tried these, they worked. The data sheet showed a higher frequency, so it occurred to me that this is an important factor. Have you ever tried some transistors in a fuzz circuit that just didn't sound right even though the hfe was perfect? All I can say is try them and see if you like the way they sound. I wish I knew how to answer your question, but I'm just not that familiar with the scientific aspect of electronics. I can't do math, either. But the data sheets will tell you. Just look at some. What transistors have you tried? Look them up and compare the frequencies. It's worth it.
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LJN

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Re: Mosrite Fuzzrite (si version) build tips
« Reply #9 on: December 07, 2014, 05:22:22 AM »
By the way, did you even read what I wrote? If you had, you'd see where I said that I went by the numbers on the data sheets because I don't have anything to measure transistors with. Go back and read this thread very carefully. I tried to explain it as best I could. You're right. I didn't measure hfe. Because I don't have the equipment,as I previously stated. I can understand your frustration. Just read the thread again, and when you have, then you may understand. It's not always about measuring every little thing. It's about experimenting with different parts until you get the right sound.
If it sounds good, USE IT!

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Roly

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Re: Mosrite Fuzzrite (si version) build tips
« Reply #10 on: December 07, 2014, 01:05:44 PM »
The problem here is that I have read your posts carefully.

Some of your advice, such as;

Quote from: LJN
Select a transistor with a frequency around 110-140 MHz.

...has no actual factual basis, they are guesses, and not good ones.


Trust is an important issue.

Some sites such as Redcircuits and Runoffgrove post circuits and information that are simply bulldust, amplifiers that will always self-destruct at first power up for example.

This site has become trusted by many to give sound technical advice backed up by hundreds of man-years of collective experience, some fifty years in my case alone.  That trust must be carefully nurtured by making sure that incorrect or misleading information isn't posted without correction, and even members of the Brains Trust, the expert group, correct each other from time to time.

Sites such as R.G.Keen's geofex, Rod Elliot's ESP, or Steve Bench's DIY Audio Projects are trusted because they provide solid, accurate and tested information that people can hang their hats on, but that trust is hard to earn and easy to lose if they don't maintain high standards, and part of maintaining high standards is technical accuracy.

Your OP doesn't ask for help or information, rather it attempts to provide advice and information useful to anyone else attempting to build a Mosrite Fuzzrite clone, however some of the information you provide with a sound of authority is actually misleading.

It is trivial to measure hFE, and only slightly more difficult to measure fT, yet you make this very definite statement;

Quote from: LJN
Second, transistor shouldn't be selected by hfe, but frequency as well.

...when in a year you haven't measured either parameter of your particular individuals and therefore couldn't have any way of knowing which parameters were doing what to your circuit.  This is no small point when the 2SC1740 datasheet gives a production range of hFE from 120 to 560.

There is already a large amount of electronic mythology floating about in musicians circles, some of it imported from the world of know-nothing hyper-fi, and none of it is any practical use to musicians - it leads them astray and actually subtracts from the sum of human knowledge.


So, to a first approximation it would go like this:

Assume for a 2SC1740;
hFE = 100
fT = 200MHz

dB = 20 Log10 (Av)

therefore DC gain = 40dB

If we assume that the rolloff from the corner frequency fC is 6dB/octave or 20dB/decade, and work backwards remembering that fT is effectively the unity gain frequency, then the dominant pole fC is 40/20 = two decades below fT, or 2MHz for this device.



Put another way, this transistor is gain flat up to 2MHz which is itself two decades above the highest frequency you can possibly hear.  This means that hFE is an important parameter in an audio circuit, and that the effect of different fT would be entirely swamped by circuit strays, literally just breathing on your circuit will produce larger changes.

I have seen hundreds of circuits that must have wasted millions of hours of peoples time trying to get them to work as claimed, only to discover in the end that they are a total crock.  Your circuit isn't a total crock, but after saying;

Quote from: LJN
there's not a whole lot of accurate information about it.

...you added to the pile of inaccurate information about it, which is rather unfortunate given your intent.
If you say theory and practice don't agree you haven't applied enough theory.

g1

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Re: Mosrite Fuzzrite (si version) build tips
« Reply #11 on: December 07, 2014, 01:52:45 PM »
  You may well have found some transistors that sound better for this circuit than others.
  However, you can not jump to the conclusion that the frequency spec. is what is responsible for the difference.
  Roly has shown how this is the case.  There are many other aspects of transistors that could be responsible for the difference you hear.
  It could also just be a coincidence.  You would need to try many samples of each type of transistor to reach any kind of conclusion.

LJN

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Re: Mosrite Fuzzrite (si version) build tips
« Reply #12 on: December 07, 2014, 03:12:27 PM »
If my information seems misleading, I apologize. That wasn't my intention.  I merely wanted to point out that hfe isn't the only important factor. My circuit does, in fact work. I use it every day with no problems. Maybe I should try to learn more about electronic theory, but I'm no good with numbers. I found something that works great and I wanted to share it with people.  But if all you can trust is numbers, and say this is a coincidence, you're entitled to your opinion. I'm sorry that I'm not that familiar with these equations. I did try a number of different transistors. All of which I looked up the data sheets for. The hfe were all very similar according to the data sheets, but the frequency was different. If hfe was all that mattered, then wouldn't every fuzz circuit use the same ones? Further more, if that's the only thing that matters, wouldn't every circuit use the exact same transistor? Just think about that.
If it sounds good, USE IT!

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LJN

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Re: Mosrite Fuzzrite (si version) build tips
« Reply #13 on: December 07, 2014, 03:34:23 PM »
That being said, I'm curious. Have you ever built a fuzzrite? If so, what transistors did you use, and how did it sound? Surely, in your 50 years of experience, you've seen some odd things, haven't you? If I can find a way, I'll try to get you a video of mine. Then you can be the judge.
If it sounds good, USE IT!

 Epiphone Les Paul, Kasino U100- P, Sears 125-XL

LJN

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Re: Mosrite Fuzzrite (si version) build tips
« Reply #14 on: December 07, 2014, 05:03:58 PM »
The video wouldn't go through, so here's some pics.
If it sounds good, USE IT!

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