Keeley 1962 Gut Shots  [traced]

General documentation, gut shot, schematic links, ongoing circuit tracing, deep thoughts ... all about boutique stompboxes.
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turdadactyl
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Post by turdadactyl »

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

turdadactyl
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Post by turdadactyl »

Here's that cap.
image.jpg

loylo
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Post by loylo »

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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Post by turdadactyl »

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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Post by okgb »

the W20K pot is a TS thing right?

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Post by FuzzMonkey »

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

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Post by Yogi B »

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.
This is what I think's going on in that area of the PCB, note the airwire for C3 to ground.
This is what I think's going on in that area of the PCB, note the airwire for C3 to ground.

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Dirk_Hendrik
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Post by Dirk_Hendrik »

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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Post by Yogi B »

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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Post by crazyhendrix »

Is there any layout of this? please, love the pedal!!

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Post by heyveno »

+1 any layout of this ?

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Post by storyboardist »

heyveno wrote:+1 any layout of this ?
I've got one coming soon. Perf, etch, and fab'd pcb!

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storyboardist
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Post by storyboardist »

Etchable/perf layout here:

Image

Fab'd board here:

Image

A couple notes. I used a 100p cap in the feedback loop of the second opamp stage and 10n caps for the other few that were in question. Sound just fine. I also changed the drain resistor on the output Katana stage to 22k. 47k wouldn't bias correctly (used smd 5457s). Also I didn't hear too much difference between the 1962 and 1962x clipping differences.

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Post by dv8r601 »

c6 could be 330pf According to conventional color labels. orange, orange, brown= 330(pf)

heyveno
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Post by heyveno »

storyboardist wrote:Etchable/perf layout here:

[ Image ]

Fab'd board here:

[ Image ]

A couple notes. I used a 100p cap in the feedback loop of the second opamp stage and 10n caps for the other few that were in question. Sound just fine. I also changed the drain resistor on the output Katana stage to 22k. 47k wouldn't bias correctly (used smd 5457s). Also I didn't hear too much difference between the 1962 and 1962x clipping differences.

how works this layout, only PCB print ?

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Post by heyveno »

heyveno wrote:
storyboardist wrote:Etchable/perf layout here:

[ Image ]

Fab'd board here:

[ Image ]

A couple notes. I used a 100p cap in the feedback loop of the second opamp stage and 10n caps for the other few that were in question. Sound just fine. I also changed the drain resistor on the output Katana stage to 22k. 47k wouldn't bias correctly (used smd 5457s). Also I didn't hear too much difference between the 1962 and 1962x clipping differences.

how works this layout, only PCB print ?
I made your 1962 x version and i have a original 1962x to compare.
Some notes before :
- I used mylar greeny for all cap ( just to try)
- I do it on prototype board



The TEST :

The clone sounds similar to original, but there are few diffences which made all the difference.

-lesser gain on clone
-lesser volume on clone
-no really difference with switch ( very easy to ear on original).

I will open the original i try to know, why.

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