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#11
Digital & DSP / Re: Question about PICs
Last post by Cybercow - Yesterday at 08:07:14 PM
Depends on the circuit IMO. In an instance where we wanted to exact the smallest number of foot-switches for a Rockman X100 rehouse project, we wanted to avoid depending on a programmable device and chose to go with a dedicated sequential logic switching circuit to achieve completed management of the X100's slide switches. We came up with this . . . .



No programming and it works well to access the 4 Modes and 3 Effects with an added 'Effect Bypass' option that the original X100 does not have.

In another version of our X100 rehouse project, we wanted one switch per mode for some clients and came up with this . . . . .



And TBH, we know nothing of how PICs even work. :icon_rolleyes:
#12
Building your own stompbox / Re: Distortion pedal with Fend...
Last post by Rob Strand - Yesterday at 07:45:04 PM
Something else, making the first stage variable gain via the emitter resistor isn't going to maintain a good/high input impedance.   At high gain settings the bootstrap probably won't be able keep the input impedance high.   Even if you raise the 10k base bias resistor the reflected impedance from the emitter through to the base is going to be low-ish.   Sometimes the devil is in the details of this stuff but RE*hFE = 1k * 300 = 300k looks borderline.

#13
Building your own stompbox / Re: Distortion pedal with Fend...
Last post by PRR - Yesterday at 07:09:02 PM
If this comes from the guitar, control of gain does more for noise than changing impedance or operating current. As you say, 1/10X impedance is a stupid low source impedance and only nets 10dB less hiss.
#14
Building your own stompbox / Re: Distortion pedal with Fend...
Last post by Rob Strand - Yesterday at 07:03:27 PM
Quote from: PRR on Yesterday at 06:50:39 PMThe thread says 5F6-A but people keep saying 60K.
You're right, it's the Bassman, low Z driving the tone stack.   In retrospect posting a link to the original schematic might might have helped.

The original 10k collector resistor might be OK.   

I definitely would not be dropping the collector load on the first stage to 1.2k  - that will make the first stage noisy when fed with a guitar pickup.   You might be able to squeeze it down to 4.7k.  However, if you *really* want to go so far as to drive the stack with a low impedance perhaps add a buffer after the first stage - just like the original circuit.

As far a noise goes you can tweak the current of the first stage transistor.  And you really should be using lower valued resistors on the tone stack.   Lower tone stack resistors and means using a buffer after the first stage.  If you dropped the tone stack resistor values by a factor of 10 then it technically needs to be fed by a 100 ohm impedance.


#15
Building your own stompbox / Re: Will this work?
Last post by Skruffyhound - Yesterday at 06:56:33 PM
I read the thread earlier before there were so many interesting answers, but I was going to say that I used to use my phone with a free signal generator app for this purpose. Now I have a hardware signal generator ... but  where's the fun in that when you can build something yourself.
#16
Building your own stompbox / Re: Distortion pedal with Fend...
Last post by PRR - Yesterday at 06:50:39 PM
The thread says 5F6-A but people keep saying 60K.

The 5F6-A specifically has a cathode follower and the Rsource is like 1.3k.

Most Fenders drive the tonestack from a 12AX7 plate with a 100k load resistor and the Rsource is about 40k (100k || 60k =~ 40k +/-20%).

But it is very unfussy. Mostly a loss of extreme treble. And there is a knob for that. It really is OK to just build it and ear it.

The prime tool for "noise" (hiss) here is having just enough gain (amplification, not fuzz) in front of the tonestack. Lower impedance throughout the tonestack helps but slowly, square-root of impedance. (Also the film caps get fat.)
#17
Building your own stompbox / Re: LTSpice and Micro-Cap
Last post by Rob Strand - Yesterday at 06:47:58 PM
The original is powered from ground and -14V so the collectors should swing a little under 0 to -14V.

Your oscilloscope needs to be DC coupled to see that, you might get +/-7V if the scope is AC coupled.

The point "I" needs to be fed by a voltage.   You should include resistors R78, R79,  R63, VR13 (set to say 25k) with R78 connecting to +14V and the opamp side of R79 connected to ground.

You can get instances where the oscillator doesn't start-up in the simulator and you have to force initial conditions.   Also you might need to set-up an initial condition voltage on C22 so the simulation doesn't take ages to stabilize.

I have simulated this circuit and in the back of my mind there was some quirky behavior with the simulation.  Off hand it might of been something to do with the voltages on C22.

#18
okay i so Via the build docs i have placed R1-14 Now i am just waiting on the reset of the parts and yeah i will need a helping hand next time as 2 toggle switches are off kilter. now the Big question does the pot orientation really matter, i'm talking with a dude that is also building and helping me with any questions i have. and so i have everything "internal facing the closed side of the pedal " face" he told me that the square solder pad is 1 and if i place facing side counter clockwise is*not loud* "up" and clockwise is *loud* "down"

the ** "is normal pedal orientation". i'm fine with the way i want it as it just makes me unique lol. i now Do know this is the "wrong way" to go about it but i do know the mistakes and i Do plan to do it right, as i am going to be building and gifting a 88 clone to a friend of mine.
#19
Building your own stompbox / Re: Octave Divider - only a di...
Last post by tuckster - Yesterday at 06:37:14 PM
Thanks for your kind words. Although I'm not good at electronics I think I'm not so shabby with tools :-)
#20
Ok, so I think there's little doubt it's the psychtar.  So far found one vero that isn't a precise match, but the parts match.  So I think I'm going to verify the board against the schematic and see if this sucker works!