Gollmer 'The Blues'

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george giblet
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Post by george giblet »

I'll have to come back later but a few comments:
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!
I can make out 222 = 2n2.
K5m fairly certain not a value
15 Mkk Not obvious. I have check which part that is on the schematic and think about it.

I made some points about the format of the markings in the post on 25 May 2021, 02:20 (with the circles)
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.

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Post by iambearface »

george giblet wrote: 17 Jun 2021, 00:45 I'll have to come back later but a few comments:
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!
I can make out 222 = 2n2.
K5m fairly certain not a value
15 Mkk Not obvious. I have check which part that is on the schematic and think about it.

I made some points about the format of the markings in the post on 25 May 2021, 02:20 (with the circles)
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.
Thanks George, the only problem I've got is that 1995 pedal man has disappeared on me.

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Post by Manfred »

15 Mkk Not obvious. I have check which part that is on the schematic and think about it.
That is C4 in the schematic, the value could be 15 pF.
As already mentioned the circuit of the new one is the same except for the OP-amp input buffer.
Here are the layouts with the filled in known component values as follows.
The corrected schematics will come later.
Old Version:
Gollmer The Blues layout old version.JPG
New Version:
Gollmer The Blues layout new version.JPG
The component values we should know.
Component values we should know..jpg
Component values we should know..jpg (97.34 KiB) Viewed 3946 times
Last edited by Manfred on 18 Jun 2021, 15:53, edited 1 time in total.

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Post by iambearface »

Manfred wrote: 18 Jun 2021, 09:37
15 Mkk Not obvious. I have check which part that is on the schematic and think about it.
That is C4 in the schematic, the value could be 15 pF.
As already mentioned the circuit of the new one is the same except for the OP-amp input buffer.
Here are the layouts with the filled in known component values as follows.
The corrected schematics will come later.
Old Version:
Gollmer The Blues layout old version.JPG
New Version:
Gollmer The Blues layout new version.JPG
The component values we should know.
Component values we should know..jpg
Thanks Manfred, I'm on it!

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Post by Manfred »

Thanks Iambearface , great.
Is your contact technically skilled, if so he could also read the resistance values of the potentiometers?

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Post by george giblet »

by iambearface » 17 Jun 2021, 14:54
Thanks George, the only problem I've got is that 1995 pedal man has disappeared on me.
What I meant was if you can get part values for the 1997 versions it would be a very a good indication of the missing part values for the 1995 version. Sure, values get changes from version to version but without any extra info they 1997 values are better than none. Also, if you can get values off the 1997 version it's a good idea to pass on the hints in my post to increase the chances of getting the correct values. If you aren't into electronics it's very easy to read off unrelated stuff printed on the part.
That is C4 in the schematic, the value could be 15 pF
Without any more info, that's probably the best estimate of the value.
Here are the layouts with the filled in known component values as follows.
I briefly scanned over that Q2 region and there's a good chance it's JFET buffer.
Unfortunately I haven't had a chance to go over any of the 1997 board in detail.
One thing I notice when looking at Q2 is the Vref dividers R2 & R3 and R10 & R11 don't
have any caps to ground. So that was thinking maybe some of the electrolytics
should connect to one or both of those Vrefs? I'm only mentioning it in passing
it could be there's not caps. I'd need to check over the tracing.

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Post by Manfred »

Hi Georg,
There is no elektrolyt on the bias voltage divider for Q2.
I attache screen shots of tracking with SprintLayout.
This test function is a great feature of Sprintlayout, with which the selected solder pads and traces which are connected to each other are highlighted.

The following is just an idea, since I could not find a germanium transistor in the TO92 package.
I rember a earlier post with a germanium transistor stage.
Here was also no other connection to the base and the signal was also directly coupled via a capacitor.
The base bias voltage was generated by the emitter leakage current generated voltage drop at the emitter resistor.
ConnectionQ2UpperPin.jpg
ConnectionQ2MiddllePin.jpg
ConnectionQ2LowerPin.jpg

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Post by Manfred »

Preliminary schematics:
GollmerTheBluesVersion1_Schematic.JPG
GollmerTheBluesVersion2_Schematic.JPG

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Post by iambearface »

Hi guys, out of nowhere I have more details on the 1995 pedal! I hope these are helpful
Attachments
20210622_130556.jpg
20210622_130532.jpg
20210622_130352.jpg
20210622_130332.jpg
20210622_130303.jpg
20210622_125953.jpg
20210622_125858.jpg

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Post by Manfred »

Hi guys, out of nowhere I have more details on the 1995 pedal! I hope these are helpful
Hi Iambearface,
thanks a lot, great! :thumbsup

I will add the values to layout and schematic soon.

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Post by Manfred »

Except for the values of C14 and the potentiometers, the component values for the old version are now identified.
I ran a simulation of the second stage with different values for C14 and think that 390p could be the appropriate value, see picture of the frequency response.
Next I will try to use George's estimates to find the appropriate values for the potentiometers,
maybe we will soon get the values of the new version from the person who owns it.
Gollmer the blues 2nd Stage C14.jpg
Gollmer The Blues layout old version Rev2.JPG
GollmerTheBluesSchematicOldVersionRev2.JPG
Gollmer The Blues layout new version Rev2.JPG
GollmerTheBluesSchematicNewVersionRev2.JPG

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Post by iambearface »

Manfred wrote: 23 Jun 2021, 13:50 Except for the values of C14 and the potentiometers, the component values for the old version are now identified.
I ran a simulation of the second stage with different values for C14 and think that 390p could be the appropriate value, see picture of the frequency response.
Next I will try to use George's estimates to find the appropriate values for the potentiometers,
maybe we will soon get the values of the new version from the person who owns it.
Gollmer the blues 2nd Stage C14.jpg
Gollmer The Blues layout old version Rev2.JPG
GollmerTheBluesSchematicOldVersionRev2.JPG
Gollmer The Blues layout new version Rev2.JPG
GollmerTheBluesSchematicNewVersionRev2.JPG
Thanks Manfred,

Could you possibly circle on one of the photos the C14 so I can try and get a value for it? Perhaps also the potentiometers?

Still trying to get more info on the 1997 version, no luck as of yet

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Post by Manfred »

Could you possibly circle on one of the photos the C14 so I can try and get a value for it? Perhaps also the potentiometers?

Still trying to get more info on the 1997 version, no luck as of yet
Component values still missing.jpg
Component values still missing.jpg (96.43 KiB) Viewed 3687 times

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Post by iambearface »

Manfred wrote: 24 Jun 2021, 06:32
Could you possibly circle on one of the photos the C14 so I can try and get a value for it? Perhaps also the potentiometers?

Still trying to get more info on the 1997 version, no luck as of yet
Component values still missing.jpg
Just realized that this is the 1997 pedal, I've managed to get some more shots from the 1995 owner, but the parts circled unfortunately don't correspond with his circuitboard layout.
Attachments
20210625_144657.jpg
20210625_144525.jpg

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Post by Manfred »

Just realized that this is the 1997 pedal, I've managed to get some more shots from the 1995 owner, but the parts circled unfortunately don't correspond with his circuitboard layout.
Thank you, but these values were already identified.
Please ask your contact person about the circled values and the values of the potentiometers.
The values of the potentiometers should be printed on the opposite side of the pins.

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Post by Manfred »

I tried around to find the unknown component.
At first I thought of a voltage regulator, 78L05 or 79L05, as an audio amplifier but the pinout did not match the component on the PCB.
I then tried different FETs with the J201 working fine but the pinout didn't fit either.
Since most JFETs are symmetrical with respect to gate->source and gate-drain I swapped drain and source and it worked.
This JFET circuit acts as an attenuator with a factor of 20.
The output signal remains undistorted up to an input voltage of 2.8 volts peak to peak
I found this by simulation, whether this is the right circuit can only show the real circuit in the practical test.
GollmerTheBluesVersion2_Idea.JPG

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Post by Manfred »

Does anyone have any news regarding "Q2"?
I tried to shot a Gollmer The Blues at Ebay last month and was unfortunately outbid with 164 Euros and could not outbid this amount fast enough, too bad!

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