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Topics - RobA

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Open Discussion / Ge transistos in a muff
« on: March 28, 2015, 04:42:14 PM »
I've been doing some playing with Ge transistors in a Big Muff like circuit on breadboard. I like it. I just flipped the middle two transistors to PNP configuration and it works well. In the schematic below, I've added some switching in the clipping sections and changed the tone control to be what I used in the Scramjet tone control and then followed by what's essentially a Rat high cut control. The standard Muff TC works perfectly well too, I just wanted to do some playing with this idea.

The diode switching is fairly critical though and needs an on/off/on switch so that you can get a fuzz purely out of the Ge transistors overdriving. I've been playing with some AC125 transistors in the approximately 100 hfe range.

Before I start laying this out for a PCB, I was wondering if anyone had suggestions for improvement or had seen something similar that I should check out first.


Open Discussion / 2SK596S and J201
« on: February 13, 2015, 10:52:20 AM »
I'm getting ready to place a Mouser order, so I'm doing my standard run through the transistors to see if they have anything interesting and came across a couple of JFETs. The first is the 2SK596S from On Semi. It's an audio JFET. The only other thing I came across is that it looks to be a Sanyo part that On has now because they purchased Sanyo semiconductor. Anyone know anything about this one? The data sheet is here,

The second is that it looks like there is a new manufacturer of J201's. Totally overpriced especially compared to using SMD with an adapter board, but I figured I put up the link here anyway in case anyone really needed a PTH J201 and didn't want to risk the scammers.

Open Discussion / Arp Odyssey
« on: January 15, 2015, 07:44:05 AM »
Seems it's confirmed that Korg is bringing out the Arp Odyssey this month. I've wanted one of these for years.

Open Discussion / Morley Sapphire Flanger Box
« on: December 28, 2014, 02:46:08 PM »
While wandering around the web looking for other schematics, I happened on one for the Morley Sapphire Flanger Box -- never heard of it before. It uses an MN3207 with a CD4007 and CD4047 as the logic glue between the LFO and BBD with no weird IC's. So, I'm wondering if anyone's heard the thing.

Here's a link to the schematic,


Open Discussion / Projects with CV or expression pedal control?
« on: December 27, 2014, 09:32:59 PM »
I've been playing with the expression control of the Flintlock and the Stage Fright and I've been having a blast. So, I'm looking for pointers to other DIY projects with expression pedal control.

Open Discussion / NERF Darts
« on: December 15, 2014, 10:17:38 AM »
I was glancing around the house a couple of nights ago for housing material for roll-your-own LED/LDR combos when I spotted a NERF dart. Actually, that's not too hard around here as HvZ is currently a big deal in our house. So, I asked if I could chop one up and was allowed to, but only if I used one of the crappy originals that came with the blaster. End result, the fit is nearly perfect.

I was trying to get a bit of housing that would let me separate the LED from the LDR a bit and the dart let me do that pretty nicely. I just popped the leads through a bit of electrical tape so I could hold them where I wanted, pushed the LED in one end of the tube and the LDR in the other and then wrapped that tape up and put another bit of tape around the cylinder to hold it all together. I think the end result works better than what I was getting with using heat shrink.

It does only work well with 5mm LED's and the larger LDR's. I'm still looking for a cheap and easy housing for the smaller types. Any ideas?

Open Discussion / Heads up on more EoL transistors
« on: December 04, 2014, 12:48:59 PM »
Got an email alert from Mouser this morning about On Semi moving the J310 and 2n5089 PTH transistors to end-of-life. I checked a few others, including the 2n3904 from On Semi and they are listed as EoL too. Things must be getting serious if they are killing off the 2n3904.

Open Discussion / New course related to electronics
« on: November 14, 2014, 08:58:57 PM »
Not directly audio/music related, but it does look interesting. The focus of the course is on the interface between analog and digital -- sensors, transducers, actuators, etc. So there's some crossover to a lot of the stuff that's beginning to be more prevalent in effects.

The project for the course is supposed to be on building a robot. It's based on the MPS430 microcontroller which is the processor in the EHX expression pedal I just picked up. I think they said the parts kit for the robot would be about $50 US.

I'm thinking about using the processor in a non-audio project, so there's a pretty good chance that I'll try to do the class.

The pre-reqs for it are supposed to high school level algebra.

The link is at

Open Discussion / NTD
« on: November 07, 2014, 05:36:08 PM »
T is either for tool or for toy -- not sure which is more true at this point.

I finally got an oscilloscope. After waffling back and forth for months about which DSO to get, I went with analog  ;D. I got a GW-Instek GOS-630FC. It's relatively cheap, has a built in frequency counter in the LCD display, and reminds me of being in physics labs in school.

In the foreground of the pic is the Flintlock, which was the first patient.

Build Reports / Li-Po power supply for active pickups.
« on: October 21, 2014, 12:54:31 PM »
Well, it's not a pedal, but I'm happy with it, so here's a report anyway.

I've been working on this for some time now and I'm finally really happy with the results. This is a circuit I built to take the input from a Li-Po battery and outputs 9.6V of really clean power. Actually, according to my measurements, the output power is cleaner than a straight 9V battery. The other main advantage is that the power sits at 9.6V for the entire life of the charge -- and the charge lasts months.

The photo below is of the battery and the boost installed in my Kramer "American" Forum II bass. The bass has active SD pickups in it and active electronics (bass & treble TC). (The "American" is in quotes because according to every thin I can find, the bass was made in Japan.) I've got the Li-Po circuit installed with EMG and Active Blackouts as well.

The boost PCB is sitting on the original battery clip tray and clipped in using a battery snap. The only other connection to the bass is an additional ground wire.

Note that in the photo the charge port isn't connected. I haven't decided yet if I should just drill the mounting hole in the bass' cover plate or not. I can't find any good info yet on if the bass actually has any value or not. I'm guessing no, but if it does, I'll cut a new plate out of plastic to keep the original intact.


Open Discussion / Red Pitaya Oscilloscope
« on: October 17, 2014, 07:55:49 AM »
I've been looking around trying to figure out which scope to buy and I came across this thing.

It looks really interesting. The software is open source and there's a dev environment for adding new programs. It comes with an oscilloscope, spectrum analyzer, and signal generator. One the blog, they've just released the source and application for an LCR measuring setup.

Does anyone know anything about this or seen it in action? The specs look good for what I need, but there are some (intriguing) differences between what you tend to see on other DSO. The max sample rate is lower (125MS/s versus more like 1GS/s) but the bit depth of the AD/DA is significantly higher (14bit versus 8bit) so the overall information rate is something like 8 times higher. I'm not sure how that's going to play out in the end. The specs mention a 50MHz bandwidth but that is low for the parts on it, so I;m guessing that it can actually go higher.

Oh yeah, it's a web connected device, so you run the software from a browser on any device you want. It'll work from any PC or tablet, phone, etc.

General Questions / Harbinger LDR specs
« on: October 13, 2014, 08:03:45 PM »
I'm getting the parts in line to build a Harbinger and I've got to place an order for some other parts at Allied, so I figured that I'd look at getting the LDR's there. But, they don't have an exact match for the Smallbear part. I looked at the part that is spec'd (but no loner available) in the Neo-Vibe article. That part had a 50k-200k light resistance at 10 Lux and a dark resistance of 20M with a wavelength of 550nm for the peak response. I can find LDR's at Allied for around seventy cents that are close to those specs. The NSL-5542 for example. So, the general is, do I need to look for anything else in the LDR or is that going to be good enough?

A related question is, is the hermetically sealed bit important?

Open Discussion / Rocking before mounting?
« on: October 03, 2014, 05:57:09 AM »
... Pots and switches.

I'd like to be able to test a build before soldering in the board mounted pots and switches. I tried doing it with header pins but the connections were just too unreliable. I've seen expensive automated machinery that'll do this, but that's just a tiny bit over the top for DIY (at least for my DIY).

Are there any good methods/tools to do this?

Open Discussion / Not really sure what to think of this
« on: September 05, 2014, 04:10:08 AM »
New pedal from Korg.

[ Invalid YouTube link ]

It sounds like it's based on the Vocaloid synth stuff. My son showed the vocaloid synth to me a few years ago and it's some pretty interesting tech. I'm not really sure about the translation to a stomp box though. Still, it could be fun to play with.

Tech Help - Projects Page / The Voltages Thread (Hopefully)
« on: August 27, 2014, 10:36:29 AM »
I brought up the idea a bit ago of having a dedicated thread for known good voltages for the projects. It seemed at least some folks thought it might help, but then I got sidetracked and it went to the back of my mind. Anyway, I still think it could be a useful resource and I just happen to have to voltages for my Stage Fright (which by-the-way, I love) sitting at hand, so here goes.

Stage Fright:

Supply voltage in: 9.4

IC1: (TL074)
1   4.67
2   4.67
3   4.25
4   9.33
5   4.64
6   4.65
7   4.65
8   4.67
9   4.64
10   4.55
11   0
12   4.62
13   4.65
14   4.64

IC2: (TL062)
1   Moving (.69 to 8.7)
2   4.65
3   2.8 to 6.5 or so
4   0
5   4.69
6   4.68
7   3 to 6 range
8   9.35

IC3: (NJM13700D)
1   1.16 to 1.27
2   0.291
3   4.57
4   4.57
5   5.72
6   0.31
7   5.6 to 5.78
8   4.58
9   4.59
10   5.64 to 5.7
11   9.16
12   5.63 to 5.73
13   4.58
14   4.58
15   0.38
16   1.13 to 1.27

1   1.12 to 1.3
2   0.286
3   4.61
4   4.61
5   5.72
6   0.3
7   5.61 to 5.78
8   4.58
9   4.56
10   5.66
11   9.15
12   5.58 to 5.69
13   4.58
14   4.58
15   0.317
16   1.14 to 1.28

1   1.11 to 1.3
2   0.29
3   4.63
4   4.61
5   5.64
6   0.4
7   5.68 to 5.75
8   4.58
9   4.60
10   5.75
11   9.23
12   5.60 to 5.76
13   4.62
14   4.61
15   0.363
16   1.14 to 1.28

Q1:  (2N3904)
E   3.90 to 3.98
B   4.56
C   9.14

Q2: (2N5457)
G   0
S   1.184
D   3.90 to 3.98

Q3: (2N3906)
E    4.56
B   3.90 to 3.98
C   1.13 to 1.38

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