MESA Grid Slammer tracing (schematic and vero layout inside)  [schematic]

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Freppo
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Post by Freppo »

Hi there folks

I borrowed a Grid Slammer from a friend a few days ago and decided to trace it. It's a very good sounding overdrive IMO.
Guess what it's very closely based on? :P

Here's the schematic I ended up with:
Image

There are a few uncertain values. Impossible to see what they are, and i'm unsure about the measurements. Maybe you people could chime in here? ;)
C3 - A "large" ceramic cap that measures 5.7nF, could be a 51pF? It says SL51J (51pF would be more in line with the circuit it's based on)
C5 - Tantalum that measures 0.92uF (could be 910nF?).
C8 - Tantalum that measures 0.73uF (680nf? ). Seems large though.. a smaller value would be better here I think, like 220nF
Note: C2 and C9 are non-polarized electrolytics

Here's a few pics from the process:
Image
Image
Image
Image
Image
Image

I made a VERO layout from the schematic. It verified, kinda.. It works, but I don't have the right transistors so I used BC547B (had to twist the legs)
It doesn't have close to the same about of gain as the original (gonna order some C1815 to try, tayda has them cheap)
And it also sounds darker then the original, probably because C3 and C8 is wrong (used 5.6nF / 680nF)
Image
Image

Cheers
/ Freppo
Attachments
04.JPG
render.gif
Gridslammer trace btm.JPG
Gridslammer trace top.JPG
05.JPG
03.JPG
02.JPG
01.JPG
Gridslammer.png
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Bill_Mountain
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Post by Bill_Mountain »

I really don't see the point in building something like this in this day and age.

I guess it's just for Mesa fanboys.

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Post by Intripped »

seems to be, in the YATS realm, a clone of the Landgraff dynamic OD, with clippling diodes arranged ala Timmy

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Post by Intripped »

PS: NOT saying that the Timmy pedal is YATS, just to be clear

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Freppo
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Post by Freppo »

Intripped wrote:seems to be, in the YATS realm, a clone of the Landgraff dynamic OD, with clippling diodes arranged ala Timmy
Yup, what he said.. I desoldered and measured the few uncertain components today.. and that confirms it,
It's pretty much a clone of the Landgraff Dynamic Overdrive with a different fixed clipping arrangement.

My friend bought his for 99 euros, and I think it's a pretty good deal for a nice sounding TS type pedal..
I don't think a MESA fanboy would bother with anything else then a MESA "original" :P

It's the first pedal I've traced, so for me it was mostly about the challenge. I was super careful so I would get it right.
I exchanged the new values on my vero layout and now it sounds exactly like the original, so I dare say the schematic is correct now.
The vero layout is confirmed aswell (if anyone would care..) :)

Here's the updated schematic and vero
Image
Image

Cheers
/ Fredrik
Attachments
Grid Slammer.gif
Gridslammer schematic.png
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dai h.
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Post by dai h. »

pretty much just another Tube Screamer. Cool graphics. Kinda funny.

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Post by Güero 2.0 »

It seems there's a 3mm red led missing in the schematic
Top right in the original board.
I don't think that's for clipping purposes

Image
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andregarcia57
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Post by andregarcia57 »

There are only different diodes TS?
The remaining clone appears to be the TS

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Post by MerlynMetal »

What a lack of imagination! Just another TS.

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Freppo
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Post by Freppo »

Güero 2.0 wrote:It seems there's a 3mm red led missing in the schematic
Top right in the original board.
I don't think that's for clipping purposes
Yes, the 3mm led is not in the signalpath so I decided to exclude it (along with led resistors and switching). I don't understand the purpose of the 3mm led really.. It lights up when the pedal is in bypass.
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Güero 2.0
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Post by Güero 2.0 »

Freppo wrote:
Güero 2.0 wrote:It seems there's a 3mm red led missing in the schematic
Top right in the original board.
I don't think that's for clipping purposes
Yes, the 3mm led is not in the signalpath so I decided to exclude it (along with led resistors and switching). I don't understand the purpose of the 3mm led really.. It lights up when the pedal is in bypass.
Maybe for keep the current flowing to prevent switch clicks
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Post by commathe »

Has anyone figured out what diffrence connecting the middle of the two sets of clipping diodes (a la Timmy) has yet? I'm really curious about that choice as it seems pointless to me.

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Post by Blitz Krieg »

commathe wrote:Has anyone figured out what diffrence connecting the middle of the two sets of clipping diodes (a la Timmy) has yet? I'm really curious about that choice as it seems pointless to me.
Paul explained it here or at diysb. He agrees that it should have no effect, but he liked it better.

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Post by Dirk_Hendrik »

Güero 2.0 wrote:
Freppo wrote:
Güero 2.0 wrote:It seems there's a 3mm red led missing in the schematic
Top right in the original board.
I don't think that's for clipping purposes
Yes, the 3mm led is not in the signalpath so I decided to exclude it (along with led resistors and switching). I don't understand the purpose of the 3mm led really.. It lights up when the pedal is in bypass.
Maybe for keep the current flowing to prevent switch clicks
Or something similar.
As much as I like this thread and all the work done I consider a "I did not understand the function of the corcuit and therefore excluded in from the traced schematic" rather odd. That part may be what sets this circuit apart from others and someone else may see the function straight away.
Sorry. Plain out of planes.

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Freppo
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Post by Freppo »

Dirk_Hendrik wrote: Or something similar.
As much as I like this thread and all the work done I consider a "I did not understand the function of the corcuit and therefore excluded in from the traced schematic" rather odd. That part may be what sets this circuit apart from others and someone else may see the function straight away.
I don't see what's odd about my decision to exclude the 3mm led.

Fair enough, it's true that I don't know exactly what function of the 3mm led is for, but I know for sure that it's not in the signal path.
If I even had the slightest suspicon that it could effects the sound somehow I would not have excluded it from the schematic.
What Guero wrote about keeping the current flowing to prevent clicks makes sense.. if one one else has a better explanation?
My vero sounds exactly like the original without it, so I very much doubt that "it's what sets the circuit apart from others".

I'll make a schematic with the leds, led resistors and switching included if anyone else think that it's important.
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Freppo
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Post by Freppo »

I can also mention that I excluded a diode from the schematic aswell.
The circuit has both an 1N4001 and a 1N5817 in parallell between +9v and ground.
Seems a bit overkill for polarity protection IMO

Just thought I'd add that before anyone comments further on "missing" parts in the schematic. ;)

Cheers
/ Freppo
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Post by Sweetalk »

Boring... YATS!!!!!

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Post by Dirk_Hendrik »

I guess there's a difference of opinion in the concept of tracing here :wink: That's no problem.

When I trace a pedal I tend to make the trace as close as possible to how the pedal is built. That means, as an example, that if there's 2 PCB's interconnected I will also add the connector pinnumbers. That, in turn, helps when i have to repair a pedal. I can look at the connector pinnumbers and measure.
No, these connectors do not add to the signal path indeed.

When I did the tracing of the Cornish G2 I took a similar approach. The quality of a Cornish G2 is not in the circuit. That's a Muff. The quality of a Cornish effect is in the way it's built. Therefore tracing a Cornish meant documenting the way it was built as well. That did, indeed, change nothing to the signal path.

Difference of perspective that is. What do you target your trace to be used for? From experince I know that incomplete schematics are a horror when doing a repair.

So, that was my perspective.
Guiro's suggestion about constant current is a fine one. But when the circuit containing that LED is not traced that will remain a guess. I "could" easily come up with the suggestion that this LED is used in a current limiter circuit, providing a sagging behaviour tonewise. We'll never know since it was ommitted from tracing project that's otherwise pretty good.

And therefore in a similar manner I question that 1N5817 straight away. No, you are right that it does not make sense to have 2 diodes in parallel. However, if that 2nd diode happened to be a zener it would make sense.
Sorry. Plain out of planes.

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Post by MoonWatcher »

Blitz Krieg wrote:
commathe wrote:Has anyone figured out what diffrence connecting the middle of the two sets of clipping diodes (a la Timmy) has yet? I'm really curious about that choice as it seems pointless to me.
Paul explained it here or at diysb. He agrees that it should have no effect, but he liked it better.
He said the difference was very subtle, I think. Something about there being a kink in the sinewave visible on a scope when the short is NOT there. I guess it could be defined as crossover distortion, but I don't think that's what it is.

I think Paul also pointed out that it’s not something he came up with. It's apparently sort of common with other forms of audio that have to deal with distortion.

My friend and I tried out an overdrive pedal with and without the short. I couldn't notice a difference but my friend liked the setup without the short better. Go figure.

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Freppo
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Post by Freppo »

I hear you Dirk and I don't disagree with anything you wrote. :thumbsup
The tracing in this case was done purely as a personal challenge and not for anyone to see.
But I'm happy I even got through it, as it's my first tracing ever, so I wanted to share.

You made a few strong points on how a tracing should be done,
so I felt the need to go back again and have a second look and eliminate all guessing.

So, I quickly drew up how the LED's are wired (except that it's connected to 9v before the 100ohm (r8) resistor)
Image
The 3mm LED does stay lit (only weaker/dimmed) when the pedal is engaged and in bypass it lights up fully.

Furthermore, you were right about the second diode between 9v and ground. It's a 1N4739 Zener. :roll:
It's about a 0.5 volt drop at the 9v rail compared to my powersupply.

What do you make of that?

Thanks
/ Fredrik
Attachments
Gridslammer (2).png
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