IPaulC has been pretty open about the Timmy circuit and its history. But all the info on it is spread out between various threads on TGP and the DIY forums, and some circuit changes seem unaccounted for. So here is my attempt to make sense of it.
The earliest version of the Timmy is built on protoboard. The most commonly posted schematic seems to match this version.
This version has 6 visible diodes with two of them on a DIP switch and most of the parts from the schematic accounted for.
When PaulC switch to fabbed PCBs, he retained the same basic component layout. Let’s call this V2.
- The silver mica cap is now polystyrene
- where is the 6th diode?
- Standing resistors are all now flat, 2m2 drop resistor looks like it’s been moved onto the PCB instead of hanging between the 3PDT and sleeve of the input jack
Next, the layout changed. We’ll call this V3.
- Diodes are now on a SPDT toggle switch, 6th diode is still unaccounted for
- Additional 4n7 cap to right of IC
- Addition 33k resistor under 1uF cap
- This unit has an electrolytic 1uf instead of film
Using the same basic layout as V3, V4 adds more holes for components and some labeling.
- 33k resistor has been changed to 12k
- Two of the 3k3s have been changed to 10k
- 1k5 is now 1k
- 4n7 has now been changed to 2n2
Later V4s have…
- LM1458N op-amp
- Small cap from input to ground, Paul says this is 47pF (http://www.madbeanpedals.com/forum/index.php?topic=23478.0)
- Input cap changed from 47n to 39n
According to Paul:
“The brown cap is a 47pf to ground on the input. That was put in due to some guys getting radio. Small enough to not really effect the audible high end, but large enough to cut down on radio noise. The input cap was changed from 47nf to 39nf. That changes the low end roll off from -firstname.lastname@example.org to -3dB@8hz which really is no change. That was done years ago when there was a shortage of 47nf for a few weeks from all my vendors. Since it made no difference in performance I just stuck with the 39nf which I used in another spot. The output stage had it’s values changed from the stock 2x 3k3 w/4n7f setup to 2x 10k w/2n2f. This was done to get a little less loading on the 2nd stage to help the headroom a tiny bit with a weak battery. The 1k5 preset resistor in the treble control was changed to 1k to bring the brightest setting back to where it was with the 3k3 setup. You would have to squint your ears to really notice any of these changes. What can’t be seen is the treble control was changed to linear to cut back on the dead spot between 7-10 with the audio taper. That one had a big effect on knob settings. I’m not sure, but it probably has the volume pot tweak which had the resistor soldered on the pot, and then it was added later to the board which came after the version shown. I never promoted those pot changes because they don’t effect the sound – just smoother knob settings and I didn’t want it to look like I was trying to resell a new version to people.” (http://www.madbeanpedals.com/forum/index.php?topic=23478.0)
- So at some point in the V4s, the treble pot changes from 50kA to 50kB.
- I can’t account for the resistor he says was on the volume pot but moved to the PCB. It could be one of the 3k3s, if you have it connected after the 1uF output cap instead of before.
- Paul doesn’t mention the 33k that is added and then later changed to 12k. Maybe this is the one that was on the volume pot.
“Well – there’s even a newer version… For about the past year I changed the volume pot value and soldered a resistor on it to smooth it’s taper. In the old style unity gain was about 2 o’clock with all the volume boost going on in the small area between 2 and 5 o’clock. That always bugged me, but using a linear pot was worse – that would put unity at around 9 o’clock making it a useless control imho. With the gain at zero the pedal puts out 12dB, so changing the volume to 25ka and adding an 18k resistor from input to output fixed this for me. I calculated the 18k value to put the control -12dB at 12 o’clock making it unity at that setting. Like the treble pot change this was about smoothing the taper and not about changing the sound. It doesn’t sound different – the min and max settings are the same. Just the settings in the middle are tweaked to not be so touchy.
“About two pcb batches ago I added this resistor to the board because it was a pain to solder them on to the pot. I didn’t call this a new version because I don’t want people to think it sounds different enough to get them to buy it again. The sounds are all there – just at a little different knob setting. These are all pretty much mechanical tweaks and not tone tweaks
“Another change that ALWAYS happens is the resistor that feeds the LED. Those blue leds are all over the map when it comes to brightness, so in every pedal I have to adjust the value. I have a jig made with a dozen or so resistors in it. I plug in an LED and move it around to find the value that’s not to bright or to dark. Then I put that value on the pcb with that led. This does not effect the tone – just the brightness of the led.” (https://www.thegearpage.net/board/index.php?threads/timmy-version-question.1444785/)
- Based on the above, I would bet that the 33k/12k resistor in the photos is in the same place as the 18k Paul mentions here.