PAL Fx JCM 800 Emulator

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Re: PAL Fx JCM 800 Emulator

Postby Manfred » 12 Oct 2017, 19:30

J0K3RX wrote:Look here > http://www.uk-electronic.de/Download/Be ... JCM800.pdf

Most of the values will be the same...


Thanks, that looks good.
But there's one thing:
The middle pot wiring looks a little unfamiliar, but a traced the wiring on the shot and drew down the circuit as I had seen.
Maybe there was a wiring error.
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Re: PAL Fx JCM 800 Emulator

Postby J0K3RX » 12 Oct 2017, 22:01

Manfred wrote:
J0K3RX wrote:Look here > http://www.uk-electronic.de/Download/Be ... JCM800.pdf

Most of the values will be the same...


Thanks, that looks good.
But there's one thing:
The middle pot wiring looks a little unfamiliar, but a traced the wiring on the shot and drew down the circuit as I had seen.
Maybe there was a wiring error.


Take a closer look.. The wiper/lug 2 of the mid pot is going to the white connector gn2. Lug 3 of the mid pot is going to lug 1 on the bass pot. Lugs 2 and 3 of the bass pot are soldered together and then connecting to lug 1 of the treble pot...
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Re: PAL Fx JCM 800 Emulator

Postby J0K3RX » 12 Oct 2017, 22:03

The added tone adjustment trimmer is 10k
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Re: PAL Fx JCM 800 Emulator

Postby Manfred » 13 Oct 2017, 01:27

J0K3RX wrote:The added tone adjustment trimmer is 10k

Thanks, I going to revise the layout und the schematic.
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Re: PAL Fx JCM 800 Emulator

Postby Manfred » 16 Oct 2017, 00:14

I made test DC-circuits for each stage and alter the trim pot setting until I could read the anoted drain voltages of the PCB shot.
After that i measured the trim pot values.
Here the results:
RD1 = 34 Kiloohms
RD2 = 98 Kiloohms
RD3 = 18 Kiloohms
RD5 = 15 Kiloohms
RD6 = 20 Kiloohms

The measured forward conductanceof the applied J201 = 1.8 Milliamps/Volts.
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Re: PAL Fx JCM 800 Emulator

Postby Manfred » 16 Oct 2017, 22:30

The circuit simulation confirmed the measured trim pot values.
I am not entirely satisfied with the outcome.
All except one of the trim pot settings are in the range of a 47 Kiloohms.
The stage with the sources resistor value of 10 Kiloohms needs a trim pot setting of ~100 Kiloohms to achieve the noted drain voltage.
Where do the difference of the setting range of this stage come from?
Either the measured drain voltage is measured incorrectly or another JFET type id used.
Who knows, perhaps a trim pot with a value of 100 Kiloohm or more is installed in the origianl circuit.
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Re: PAL Fx JCM 800 Emulator

Postby Manfred » 16 Oct 2017, 22:39

Typos corrections.
Why is EDIT-button sometimes not displayed and therefore the function cannot apply?

Either the drain voltage is measured incorrectly or another JFET type is used.
Who knows, perhaps a trim pot with a value of 100 Kiloohm or more is installed in the original circuit.
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Re: PAL Fx JCM 800 Emulator

Postby Manfred » 18 Oct 2017, 03:51

Revised schematic and layout:

PAL800JCM_Layout_2.JPG


PAL_JCM800_Schematic_2.JPG


PAL_JCM800_PCB_ComponentSide_2.pdf


Zipped Sprint-Layout 6 file:
jcm2pcb.zip
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For this message the author Manfred has received thanks: 2
Intripped (18 Oct 2017, 20:54), peterc (18 Oct 2017, 12:51)
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Re: PAL Fx JCM 800 Emulator

Postby Optical » Yesterday, 06:26

Nice work. Based on this, you could modify the circuit slightly to achieve several other marshall variants such as the Freidman amps
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Re: PAL Fx JCM 800 Emulator

Postby roseblood11 » Yesterday, 18:39

It would be great to have a pcb with the option to build many different circuits that are based on Marshall designs.
Maybe uk-electronic.de could sell them?
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