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Transistors for Foxx Tone Machine?


 
10/14/1999 9:23 AM
Mark Abbott
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Transistors for Foxx Tone Machine?
Basically, the transistors mentioned for this device are for me (in Australia) unobtainable.  
 
What I can get is the following transistors; BC337  
BC338  
BC546  
BC547  
BC548  
BC549  
BC549C  
 
Okay, what out of that lot will do the job and sound pretty  
authentic?  
 
How well does the "swell" circuit?  
 
Much thanks  
 
 
Mark  
 
P.S. RG my friend Evan shall be forwarding you his credit card number. I shall be putting in another order, so don't worry about being paid. Thanks for sending the PCB out they are great!  
P.P.S. When will the Screamer PCB's be available?
 
10/14/1999 1:45 PM
R.G.
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Use the BC549's. They'll work just fine. In fact, any NPN silicon transistor with a gain of over 200 or so will work OK. The 549's will have low noise and even higher gain, so they should be dandy.  
 
For those of you worldwide where you can easily get the BC series, wherever I say "2N5088", just read that as "BC549".  
 
The swell circuit is poor. I did an article on that at GEO. The circuit is the same circuit as a fuzz box by A. Leo published in Popular Electronics in the late 60's or early 70's. It doesn't really do swell at all. It's just DC coupled, and the initial attack of a note makes it push the input stage of a tube amp to blocking, which it comes out of gradually, causing it to "swell" a little. It depends on having a fresh battery and a DC coupled tube amp input to work at all.  
 
Evan's already contacted me, all is cool.  
 
I'll push on the board house. It helps me feel better even if it doesn't make boards come out faster... 8-)
 
10/15/1999 4:23 AM
edwin
hi RG,  
 
i've build 2 FTM's recently and have tried quite a lot of transistors. Seems that Justin's recommendation on 2N3565 still sounded best to me but i can find 2N3565 anymore in this region(Singapore). The 2N5088 is not far off. 2N3904's sounded too trebly and harsh. Had some BC chips but can't remember their number BC583? with a gain of 500+ but sounded real mushy plus their pinouts are different. Have yet to try with BC109/c cos i've got some on hand. Gain is like 400+
 
10/15/1999 4:10 PM
R.G.
email

Original FTM's were built with one of two transistor types, 2N3565 and 2N5133. Neither is widely available any more.  
 
I've tried a lot of transistors in this thing as well, and for the life of me (and some other guitarists who I asked to sit in) I can't tell any significant differences in tone with only the transistors. This is consistent with the circuitry - the input amp is a feedback pair, the others are a phase splitter and a simple common emitter amp. The last transistor in common emitter has the best chance to "imprint" the sound with any transistor individuality, as the feedback in the input amp and phase splitter should wash any transistor quirks out. 2N5088 and BC549 are close, and I would expect BC109C's to be as well. All are high gain (350+, 400+, and 300+ respectively) low noise devices, with high linearity.  
 
I did not try the 2N3565 as I couldn't get any either. I did try the 2N3904's and they were slightly softer than the 2N5088's, which correlated well enough with my expectations based on their lower (200+) gain. It's odd that your 2N3904's went the other way, not what I'd expect at all.  
 
I think Mark would do fine with the BC549, or other high gain, low noise NPN's. I think he'd have an even harder time finding 2N3565's or 2N5133's.  
 
The Experience Pedal is a partial copy of the FTM and uses NTE123's, 2N3904's, and other devices as well.  
 
My personal opinion and experience is that there are places where individual transistors matter - the FF and its brothers, cousins, and derivatives being notable - but that effects where most of the devices are used in high feedback pairs, emitter followers, or simple CE gain stages are not such places. Even in circuits where individual transistor characteristics matter, such as the FF and the Rangemaster, my personal advice is to get it working with something now, and tune it in with the *perfect* devices when they become available.  
 
As in all matters of tone, your own personal ears are all that matters, and you should go with whatever they tell you is right, no matter what I or anyone else says. That's one of the beauties of building your own - you can put in what sounds good to you.
 
10/18/1999 4:31 AM
edwin
thanks for the explanation RG! i always learn a lot from reading your posts.  
 
i took the FTM out again and tested it with BC109/BC109C with hfe of 500-550. Again i could hear the difference and i did not even move the controls. Somehow I feel that the different transistors shows out more when the octave is kicked in.  
 
As you have said its all in the ears, tweak it till you like what you're hearing.  
 
regards,
 
10/18/1999 12:09 PM
MKB
email

Just another opinion... I built an FTM clone with 2N3904's and it seemed to match RG's findings, a bit soft sounding but nice. I really like it a lot. Put a footswitch to cut the octave in and out, what a great noise!
 
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