Gollmer 'The Blues'

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

Hey guys, I’ve been after this pedal for a while and managed to find a guy who sent me these gut shots, could anyone please trace the circuit from these? Many thanks!
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george giblet
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Post by george giblet »

You would need a better pic of the components. A clear shot from the top showing all the resistors and some close-in shots of the capacitors showing the part values.

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Post by george giblet »

I had a look this afternoon. This is about as good as can be done with those pics.

It would be really helpful to get a list of those cap values.

The pots values are also unknowns. The pedal doesn't have a heap of gain so they are likely to be 10k or 20k.
The tapers 10kA vs 10kB would be a worthwhile detail to add as well.

The zener isn't known either.

[Small bug on this schematic: U2A and U2B opamp sections should swap positions. ]
Gollmer - The Blues - sch V10.png

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Post by iambearface »

george giblet wrote: 04 May 2021, 00:35 You would need a better pic of the components. A clear shot from the top showing all the resistors and some close-in shots of the capacitors showing the part values.
Thanks so much George, I've messaged asking for better photos, will post when I get them.

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Post by george giblet »

Thanks so much George, I've messaged asking for better photos, will post when I get them.
No problem. Good luck with the pics. I can update the schematic. (I was going to post another schem just to fix the U2 swap bug.)

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Post by iambearface »

george giblet wrote: 09 May 2021, 01:41
Thanks so much George, I've messaged asking for better photos, will post when I get them.
No problem. Good luck with the pics. I can update the schematic. (I was going to post another schem just to fix the U2 swap bug.)
Hi George,

I've added some photos featuring some values, if there's any components you need more details of could you please circle them and let me know?

Many thanks!

J
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george giblet
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Post by george giblet »

Good stuff!

So the missing part values are:

- The six yellow caps.

For someone not used to reading the part numbers it's worth mentioning the part values
could be marked with the format 104, 472. There could be other numbers formatted differently
like 100V, and M5E, K6M those aren't the part values.

- The grey cap with the violet top. The part number will be marked like n47 or 1n0.

- See the arrow on my mark-up. There looks like a MKT box capacitor underneath the 22k resistor (red, red, orange).
Be good to confirm something is there and even better to get the part number. That's going to be in the format 472,
or 4.7n. I thought I could see that yellow part on your previous pics but wasn't sure if it was a sticker under the resistor.

I can make out the zener on your last pic as 2.7V as well as a few more resistors.

If you want to get the exact diode numbers of the black diode and the blue diode it's up to you.

I'll update the schematic. It's just long enough ago that I can't remember all the parts positions.
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Post by Manfred »

I made a layout clone with the component designators according to the schematic. I left out the component values,
I attach a component plan to enter the values known so far.
While tracing the PCB I found differences, I drew them in red color in the schematic.
GollmerCorretions.jpg
Gollmer The Blues PCB Layout.JPG
Gollmer The Blues Component Side Big.jpg
Ready to print PDF-files:
Gollmer The Blues Component Side.pdf
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Gollmer The Blues Solder Side.pdf
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SprintLayout6.0-file:
GollmerTheBlues.zip
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Post by george giblet »

I made a layout clone with the component designators according to the schematic. I left out the component values,
I attach a component plan to enter the values known so far.
While tracing the PCB I found differences, I drew them in red color in the schematic.
Thanks manfred. I made a comment about the opamp pin swap early on. I'll re-check the 1k + gain pot swap and the zener swap.

Note also, the last updated pic shows some more info,
- there are some 1uF electros. The first schematic showed all 10uF's.
- the zener is 2.7V. Blue case probably a 1W.

I haven't added those changes yet. I was trying to avoid posting another partially correct schematic since the OP
was hunting down the values for the ceramics caps.

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Post by Manfred »

. I made a comment about the opamp pin swap early on.
I am sorry, I overlooked that one in your post above,

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Post by george giblet »

I am sorry, I overlooked that one in your post above,
No problem. Thanks again for going over it. Another pair of eyes is a big help with these traces.
I agree with the 1k and zener flip.

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Post by iambearface »

Wow, thanks so much for helping me with this. Unfortunately the guy I've been trying to get more cap info from has gone off-grid so I don't have any more information.

To be honest, I'm in way over my head in here. How far are we from being able to try and make a clone?

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Post by iambearface »

I've managed to get hold of someone else who owns this pedal, looks like it's quite different though? Does this go any way to helping figure out the missing values while I try and get hold of them?

Thanks again guys
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Post by george giblet »

Unfortunately the guy I've been trying to get more cap info from has gone off-grid so I don't have any more information.
These things happen. It does make cloning more difficult though.
To be honest, I'm in way over my head in here. How far are we from being able to try and make a clone?
My feeling is a clone is only a true clone when the circuit is know exactly.

Having traced many circuits there's been many cases where some parts have been left unknown for years until new information shows up. That hasn't stopped people building pedals though, however, it does propagate wrongness over time. The usual story is someone gets an original and the clone sounds different.

For some parts it's possible come up with reasonable estimates for the values. However you have to treat these as estimates not as the real thing. In some cases the estimates might be very close to the real pedal and in others they can be way off. Logic can can only take you so far. The values in the "real" pedals are what they are. There's even cases where the real values are technically wrong.

I put a few estimates on the schematic already and if I did it again there's a good chance I'd put down different values. I estimated the C11 and C12 from this video. However, C6 can have a similar effect to C11 and it's not possible to know the quality of the recording.


I've managed to get hold of someone else who owns this pedal, looks like it's quite different though? Does this go any way to helping figure out the missing values while I try and get hold of them?
Yes, I can see the pedal is different. The PCB is dated 1997 whereas the previous version was dated 1995.

Without tracing the pedal my guess is the first stage, U1 on the schematic, has been replaced with a transistor or JFET buffer. That would result in a more economical circuit. Superficially the rest of the circuit looks similar. It also brings up the question which circuit to build. Sometimes you find people like one version more than another! That can be because other values have been changed.

Interestingly I cannot see the yellow capacitor underneath the 22k resistor (R9 on the schematic). As far as cloning goes I was thinking the value of C5 and C6 could make a big impact on the voicing of the pedal. Not knowing those values would mean it would be hard to come-up with a representative clone. The new simpler circuit might let us strip things back and it could turn out those parts aren't significant.

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Post by Manfred »

I've managed to get hold of someone else who owns this pedal, looks like it's quite different though? Does this go any way to helping figure out the missing values while I try and get hold of them?
:thumbsup

Thank you Iambearface, that would be great.
Can you ask the person to take good photos of both sides in flat position, then I can make a PCB clone layout for tracing.

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Post by Manfred »

I was able to generate an image template for SprintLayout6.0 from the photo image of the newer version from above to create a PCB clone.
Next I will start the trace and use the results to create the schematic from it.
Gollmer The Blues Version2.JPG

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Post by iambearface »

So I managed to get some values from the newer version, I'm not sure if this helps? The man who's got these for me is super busy and I don't want to annoy him too much!
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Post by Manfred »

iambearface wrote: 15 Jun 2021, 09:35 So I managed to get some values from the newer version, I'm not sure if this helps? The man who's got these for me is super busy and I don't want to annoy him too much!
Thank you for your efforts, it would be important that this man could look at it again or take a few photos where you can see the component values better.
I understand that he has no time when he is very busy with other things, but maybe he will have more time at a later time.
For now I can say that the circuit is the same except for the input buffer.
With the input buffer I have the following problem.
The upper pin of Q2 is connected through a resistor to a bias voltage generated by a voltage divider.
The middle pin is connected to the operating voltage via a resistor.
The lower pin is directly connected to the input voltage via a capacitor, there is no further connection via another component to ground or to the operating voltage.
There it would be particularly important to know which type this component is.
GollmerNewVersionDetail.jpg
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Post by iambearface »

Manfred wrote: 15 Jun 2021, 10:44
iambearface wrote: 15 Jun 2021, 09:35 So I managed to get some values from the newer version, I'm not sure if this helps? The man who's got these for me is super busy and I don't want to annoy him too much!
Thank you for your efforts, it would be important that this man could look at it again or take a few photos where you can see the component values better.
I understand that he has no time when he is very busy with other things, but maybe he will have more time at a later time.
For now I can say that the circuit is the same except for the input buffer.
With the input buffer I have the following problem.
The upper pin of Q2 is connected through a resistor to a bias voltage generated by a voltage divider.
The middle pin is connected to the operating voltage via a resistor.
The lower pin is directly connected to the input voltage via a capacitor, there is no further connection via another component to ground or to the operating voltage.
There it would be particularly important to know which type this component is.
GollmerNewVersionDetail.jpg
Thanks Manfred, is there a tl;dr way I can ask him what we need specifically? Perhaps circling components for values for again?

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Post by Manfred »

Perhaps circling components for values for again?
Yes, that is how we will do it
I need a little more time.

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