I’ve taken some time to go over the photos of the Rev 2 Centaur the Nik degooped and gone over his schematic in greater detail.
First, Nik’s schematic using the exact same component numbering as Martin Chittum’s, except for the LED and clipping diodes which are mixed up. For comparison:
From the photos, the real numbering on the Rev 2 PCB matches up exactly with the numbering on the KTR and the visible labels on all Centaurs I’ve been able to see (with the exception of the few parts added onto those boards). R1B from the KTR and Rev 3 of the Centaur is also R1B here on this Rev 2:
Even though none of the photos show the underside of the PCB, the light shines through it enough to see that there is no ground pour. This confirms that Bill added it between Rev 2 and 3.
In the above photo, you can clearly see no ground pour on the opposite side of the board.
There is also no serial number. It’s not that it’s unclear, instead it appears as if it was never written. Not even a smudge. It should be in the lower left corner on the top side of the PCB. This is consistent even in the earliest Centaurs. Either Nik or torg removed in before these photos were taken, or it was never there. Torg mentioned, ‘Serial is unclear – it’s #200+ region ‘).
In the degooping, most of the electrolytic caps’ labels came off. The build doc says the two 4u7s were 1uF on this unit. I have to assume the 47uF caps stayed the same, so if we take Nik at his word, we have two 47uFs and eight 1uFs. The 1uF tantalum looks like it got removed in the degooping, but the space for it looks like Bill intended for tantalum to go there.
As Nik stated, R11 is missing (R14B on the Centaur PCB). There are no solder pads for it. This comfirms it was added between Rev 2 and Rev 3, along with the ground pour.
There appears to be an extra jumper beneath the middle IC. This is not present on the Rev 3 board. It’s not clear which portions of the circuit it’s connecting. Also, this is the section of the PCB where R26, R27, and R28 (R29, R30, and R1C on the Centaur/KTR) should be on Rev 3.
Nik removed C4 (officially C13). This is where it should go. The Centura build doc calls for 27nF for the early circuit. I have my doubt, as this was not one of the changes mentioned by Bill and I suspect it was removed for measurement, as the goop usually leaves the labels illegible.
The 422k resistor is called for in both sets of the Centura specs, but the one in the photos does not look like 422k (yellow-red-red-orange-brown). Actually, never mind. It kind of looks like the yellow was scratched off, and then it’s red-red-orange-brown. The lighting makes it difficult to distinguish between red and brown. So this could easily be 422k.
Here is where things get shaken up. Compare this unit with S698 (the one Chittum degooped).
In the Rev 2, we have 392k, 100k, 100k, 27k, 47k. The corresponding row on S698 has 100k, 392k, 100k, 27k, 47k. The 392k switched places with one of the 100ks. On the bottom row, this Rev 2 has 27k, 100k, 1k5, 680R(?). S698 has 100k, 27k, 1k5, 1k. The 100k resistor moved again, this time switching with the 27k. We have to assume that they were simply rearranged due to the addition of the extra 100k and two 68ks in Rev 3 and that they are still located in the same parts of the circuit.
The 680R resistor is another thing Bill never mentioned. If Nik’s specs are correct, Bill went from a 680R metal film to a 1k carbon film between Rev 2 and 3. A 680R metal film resistor should read blue-grey-black-black-brown. The one in the photos is too damaged to read, but it does appear to have a black band. Not that that tells us much. A 1k metal film would also have two black bands (brown-black-black-brown-brown). With so much damage to the resistor bands and capacitor labels, Nik would likely have to measure the values of the parts.
Here’s a quick chart of the difference between Klon versions.
If we assume Nik’s values are correct for Rev 2, those values can be filled in for the missing values in Rev 1. If we take Nik’s Rev 2 to be anomalous, we can fill them in with the values from Rev 3 and should assume Rev 3 values for Rev 2 where, at the very least, Rev 2 has spots on the PCB for them.
If all of this just makes you more confused about the different revisions of the Klon, it probably should. There’s just too much BS out there and not enough degooping to confirm. We really need more degoopings.
What we know for sure, as of 2017:
- Rev 1 lacked solder pad W7. This connects to the clipping diodes. The top right lug of the stomp switch runs under the PCB instead.
- Rev 1 connects the stomp switch’s output lug (middle bottom) directly to the output jack.
- Rev 1 has no ground pour.
- Rev 2 adds R1B and W7. The stomp switch output lug still connects directly to the output jack, but the top right lug connects to W7.
- Rev 2 lacks the ground pour, R1C, R14B, R29, and R30.
- Rev 3 adds the ground pour, R1C, and R14B. Also R29 and R30.
- The KTR ups R1 to 2M and adds R1D (2M) to maintain input impedance when in true bypass mode.
- The KTR’s polarity protection diode is 133ZHW and the charge pump diodes are S1AQ3. These are just SMD parts functionally equivalent to 1n4742 and 1n4001.
I still have the following things that I’m unsure about:
- Should Rev 1 and 2 have all 1uF electros? Nik’s Rev 2 has the labels damaged.
- Should C13 be 68nF or 27nF in Rev 1 and 2? If Nik’s unit is typical, we can assume Rev 1 also had 27nF. Unless Bill started with 68nF, changed it 27nF, then changed it back. If it’s not typical, 68nF should be correct for all versions.
- Should R6 be 680R or 1k? Just like C13, if Nik’s unit is typical, that means Bill either went back and forth on the values, or both Rev 1 and 2 had 680R. Otherwise, 1k is the correct value for all.
- Did Rev 1 have R29 and R30? It likely didn’t, but the different approaches in adding new part numbers makes me wonder if Bill had these in Rev 1 and took them off for Rev 2 before adding them back. Maybe they were on the schematic at some point before he started adding letters.
Not that I’m trying to accuse Nik of anything. I’m just wary due to false claims of alternate Klon specs that have surfaced in the past. That, combined with Bill mentioning some very specific changes (R14B, R1B, and the ground pour) but not mentioning the new values seen in Nik’s unit. And then there’s always the possibility that Nik’s unit was a custom job or just Bill messing around with different component values. Who knows? The lack of a serial number doesn’t inspire confidence in the idea that this Centaur is representative of all Rev 2s.
Ok, I’m really burned out on Klons.