diode help please!

does anyone no if i could substitute the diode in this schematic with silicon diodes, and what value. ?

thanks for any help on this

You *could* use silicon diodes (pretty much any ones would work), but you'd alter the sound produced. Germanium diodes have about a .3V drop when forward biased and silicon diodes have a .7V drop You wouldn't get nearly as much clipping with Ge diodes.

thanks for the reply .

i have this fuzz in a wah i use on my bass. the fuzz sounds great on the guitarists guitar and i want to build him one.

so what you are saying is ...if i build this with silicon diodes it will be filthier ?

plus, theres just that grit to Germanium thats just so different that Silicon diodes.

no, it wont be as filthy. germanium is "grittier" but less consistent then silicon

so should i bother making it ? or could i come out with something similar?

The GE's are also great for the way they turn from clean to dirty. They start to break up in a very pleasing way.

That said, GE will be gritty, silicon will be a tad more compressed, and LED would be loud and bright.

1n34A's are pretty cheap, on the 'bay.

Seems simple enough, but I'd put a pot where the tone switch is.

That's a variation on the Shin-ei fuzz wau. The fuzz circuit is an adaptation of the Shin-ei FY-6 "SuperFuzz". I'm pretty familiar with that circuit.

The input to the last driver stage usually runs between 45mV and 75mV peak-to-peak, depending on the setting of the first "Expander" pot. If you change to silicon diodes then you can probably expect this to double.

The output of the final driver stage normally runs between 360mV and 700mV peak-to-peak with the level pot maxed. If this also doubles then you'll be running between 720mV and 1.4V peak-to-peak. This is pretty hot for the front end of an amp. You can probably tame this a bit by changing the 47K resistor after the tone stack to a 100K. Otherwise, you might want to keep the level pot under the halfway point, unless you're also looking to overdrive the front end of the amp.

Frankly, I never liked this particular variation of the SuperFuzz circuit. In the original circuit the first stage was an NPN bipolar in a stablized bias configuration with the second stage. This provided some compression that reduced the radical tone differences between loud and soft notes. This FET input version cleans up better when you roll back the guitar volume, but at the cost of having the tone change along with your playing dynamics.

You might be able to get a 1N34 or 1N66 of the net.

There should be some GE diodes here you can use...

http://search.ebay.com/search/search.dll?sofocus=bs&sbrftog=1&dfsp=2&from=R40&satitle=germanium+diode*&sacat=-1%26catref%3DC6&sargn=-1%26saslc%3D2&sadis=200&fpos=22192&sabfmts=1&ftrt=1&ftrv=1&saprclo=&saprchi=&fsop=2%26fsoo%3D2

Stick with the original schematics... 0.3 to ~0.6 is quite the change in dirt characteristics... The Ge diodes should give you much more dirt/clipping since they only pass ~0.3V of the wave, as compared to ~0.6 which is more headroom for clean.

-D

If you need a source closer to home, Dick Smith carries a 1N34 compatible germanium diode. NZ$ 0.78

http://www.dse.co.nz/cgi-bin/dse.storefront/4835dc710c5254bc273fc0a87f3b06ec/Product/View/Z3040

awesome guys . thanks heaps for the help.

looks like i'm getting it from dick smith.

i looked at the store but couldn't find any. its not organized well. will have a better look. cheers

so i got some 1n60 germanium diodes would they do the trick?

like thishttp://store.americanmicrosemiconductor.com/1n60.html

Yep, looks like those will work fine. The 1N60 has a slighter higher peak inverse voltage than the 1N34, but you won't get anywhere close to that voltage in the fuzz wau circuit. It also has slightly higher inverse leakage current, but that won't make any difference in that circuit.

I'd say you're good to go!

Yep, looks like those will work fine. The 1N60 has a slighter higher peak inverse voltage than the 1N34, but you won't get anywhere close to that voltage in the fuzz wau circuit. It also has slightly higher inverse leakage current, but that won't make any difference in that circuit. I'd say you're good to go!

cool thanks for that amp-surgeon ,and everyone else who commented .

this is the largest schematic i have attempted , should be a good challenge .

now to work out my layout and i can fire up the soldering iron

I've been pretty intrigued by this schematic since I first saw it. Is there anyone who understands it's operation? It seems to me that the first NPN transistor on the left is biased in a very unstable manner. It looks like the base is being biased by the leakage current through the transistor - seems to me this could vary pretty wildly given different transistors and even temperature.

Also, I don't understand how the next two transistor stage works. It looks to me like they are being driven 180 degrees out of phase - I would expect the output to be zero.

In fact, that's exactly what's happening. The fundamentals are cancelled since they are equal in implitude (if the transistors are reasonably well matched), but opposite in phase. What are NOT opposite in phase are the first order harmonics produced by each transistor. They are in phase, and add up. The result is this circuit produces primarily the first order harmonics, which are an octave above the fundamental.

I'm not sure what you mean by the term "first order harmonics". My understanding of such a circuit is that it cancels out the even order harmonic distortion - second, fourth, etc. It is the second harmonic (the fundamental being the first) which is one octave above the fundamental. This looks as though it would completely eliminate the input signal, leaving only the odd order harmonics generated by the transistors in the differential amplifier.

Am I missing something?

Ooops! I meant the second harmonic. Once again the result of my fingers going to work before the coffee has hit my brain!

(Why don't we have an "embarassed" smiley?)

This isn't a conventional differential amplifier, where the emitters would be tied together but the collectors would have different loads, and each would provide a separate output signal. The collectors are tied together, so any signals which are equal and opposite in phase would cancel, and any signals which are in phase would add.

Normally, in a fully differential amplifier, the odd order terms keep their polarity, while the even order terms are always positive. When you take the differential between them, the even order terms would cancel out, leaving only the odd order.

In this case, we aren't taking the differential output, but the sum of the outputs. This means that the odd terms cancel, and the even terms add. The strongest of these is the second harmonic, or octave of the fundamental.

I don't have a fuzz wah, but I do have a Shin-ei FY-6, which uses the same octave amp.

The plot on the left is the signal at the base of one of the two transistors with a 100hz/200mV sine wave input, and the first "fuzz" or "expander" pot maxed. The plot on the right is the collector of the two transistors in the octave amp.

Looks interesting. I think some experimentation may be in order!

amp surgeon, what are you using for thoes waveform pictures?

a comp based oscilloscope?

A Tektronix TDS1001B. It's got a USB socket on the front which you can plug a thumb drive into. It'll dump captured waveforms as a CSV text file, which you can import into Excel or any other spreadsheet and play with the numbers. In this case, I just plotted line charts from them.

so i just finished soldering it up and its not working . sounds like a transistor round the wrong way. but i socketed them so i could switch round , and still no joy. i wounder if the trans i substituted bc548,from the original 2sc828.

or the fet vn10km from the orignial 2sk30a.

when i take the fet out of the socket then put it back in , it sounds like it works for a moment.

any idea? anyone.

cheers