Keeley 1962 Gut Shots  [traced]

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Keeley 1962 Gut Shots

Postby turdadactyl » 27 Nov 2016, 06:29

Looks like a Tube Screamer type overdrive with an NE5532p op amp.

Capacitors are:
C1 - not present
C2 - 10nj(illegible)
C3 - 10nj(illegible)
C4 - .1J63
C5 - 1nk100
C6 - [Some funky tropical guy, as pictured]
C7 - Illegible
C8 - Illegible
C9 - .1J63
C10 - Not present
C11 - 10nj100
C12 - 100uF/25V
C13 - .1J63
C14 - .1J63
C15 - 10nj100
C16 - 47uF/16V
C17 - 10uF/25V

Pots are:
Gain - B100K
Tone - W20K
Level - A100K

I'm not motivated enough this late at night to go through the resistors, but I think they are all visible.

IMG_6272.JPG

IMG_6273.JPG

IMG_6274.JPG

IMG_6275.JPG

IMG_6276.JPG

IMG_6277.JPG

IMG_6278.JPG

IMG_6279.JPG

IMG_6280.JPG

IMG_6281.JPG

IMG_6283.JPG
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Re: Keeley 1962 Gut Shots

Postby turdadactyl » 27 Nov 2016, 06:46

Here's that cap.
image.jpg
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Re: Keeley 1962 Gut Shots

Postby loylo » 27 Nov 2016, 10:14

It looks a bit different from the circuit board pics on Keeley website. Specially in between the 2 jacks, where there are shorts and Q1 unpopulated.
Image

turdadactyl wrote:Looks like a Tube Screamer type overdrive with an NE5532p op amp.

According to Keeley's description, it is a a Katana split in half (Q5 and Q6) and a marshall bluesbreaker in between.
This should sound gainier than a tubescreamer.
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Re: Keeley 1962 Gut Shots

Postby turdadactyl » 27 Nov 2016, 15:02

Yes, sound wise it is definitely more gain. I was just theorizing its a dual diode in the feedback loop op amp overdrive setup like the TS. I snapped the pics and that was about as far as my brain went after midnight.
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Re: Keeley 1962 Gut Shots

Postby okgb » 28 Nov 2016, 00:59

the W20K pot is a TS thing right?
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Re: Keeley 1962 Gut Shots

Postby FuzzMonkey » 28 Nov 2016, 01:59

okgb wrote:the W20K pot is a TS thing right?


Indeed.
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Re: Keeley 1962 Gut Shots  [traced]

Postby Yogi B » 14 May 2017, 13:44

loylo wrote:It looks a bit different from the circuit board pics on Keeley's website. Specially in between the 2 jacks, where there are shorts and Q1 unpopulated.

In fact that seems to be the only real change to the PCB, and it appears that as a compromise for removing the additional LED clippers the series resistor (R7) has been upped.

As for Q1, the board looks to be the same as is used in the 1962x version that adds in a MOSFET clipper for "KT88 mode", that's your Q1. On that subject, I'm guessing that in the "x" version D2 is still jumpered and it's pads are only present on the board for backwards compatibility. Also, from the one image that I've seen of the reverse of a 1962x, C1 was added but C10 was left unpopulated.

loylo wrote:According to Keeley's description, it is a Katana split in half (Q5 and Q6) and a Marshall Bluesbreaker in between.

This is indeed correct, and might serve as a useful starting point for determining the unknown capacitor values.

Anyway, here's my crack at a schematic:
1962x_sch.png

Though the values I have for the resistors seem reasonable, they're probably still worth checking.

However a thing that's left me scratching my head is the presence of R3, R4, C2 & C3 which appear to be in the (negative) feedback loop of the first opamp. Conventional thinking would dictate that they are responsible for forming a high pass filter, thus would be connected to ground as in the regular Bluesbreaker, however there is no ground pour on that area of the PCB and I can't see any traces going to ground (or otherwise). Although the traces in that section of the board are not clearly visible in any of the photos, they must still join up elsewhere where they should be visible and AFAIK I've not missed half a trace somewhere...
... so that begs the question am I going blind, mad, or otherwise? :hmmm: As for the schematic, I've just assumed that it is as per the Bluesbreaker.
1962x_brd_.png
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Re: Keeley 1962 Gut Shots

Postby Dirk_Hendrik » 15 May 2017, 16:52

The net where the + of C16 (and many others) are connected to is your virtual ground at half the supply voltage. Removal of the line and using labels instead, treating it as a supply voltage. Makes reading a lot easier. Furthermore virtual ground can be seen as a ground connection (or supply voltage, to make things difficult) from an AC perspective. In essence a node that will bleed off any ac signal to silence. Meaning that, for instance, that capacitor on the tone control is, soundwise, connected to "ground" .
Look at a Tubescreamer schematic (a real one, not some spin-off by someone else) and see how the cold lug if the volum control does not connect to ground but to the virtual ground. Still, there's no sugnal when the control is fully CCW. Since the virtual ground is a silent node. That principle.
Sorry. Plain out of planes.

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Re: Keeley 1962 Gut Shots

Postby Yogi B » 15 May 2017, 18:45

Dirk_Hendrik wrote:Look at a Tubescreamer schematic
Or indeed some Bluesbreaker schematics which demonstrate the same concept!

Dirk_Hendrik wrote:Furthermore virtual ground can be seen as a ground connection (or supply voltage, to make things difficult) from an AC perspective.
Yeah, I'm aware of that principle and although I might have been thinking "AC ground" when writing "ground", I was also thinking of actual ground because previously I had the ground plane spanning the entire board, thus it was the obvious place to attach C3.

So that airwire that's jumping out of the image desperately seeking ground, should in fact be making the ever so long journey of about 2mm directly downwards to join the trace that originates from R2. However although unessential, it still doesn't explain the whereabouts of the 'real' trace that's without a trace in the photos.

Dirk_Hendrik wrote:Removal of the line and using labels instead, treating it as a supply voltage. Makes reading a lot easier.
I may do on a 'final' schematic, but in a working version where things might be changing I generally find it easier to keep everything connected with actual lines (within reason).
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