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June 29, 2022, 05:02:51 AM

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Marshall MG10 Switch

Started by dogbox, February 18, 2018, 10:25:30 PM

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dogbox

Hi Guys,
https://www.electrosmash.com/marshall-mg10
I bread boarded the first 2 stages of this and individually each channel sounds good. I changed it to suit a single 12v supply. Sounds Ok anywhere from 8v to 12v..with my AN7523 chip power amp. Eventually will make a good portable practice amp.

Just scratching my head about the switch found at the start of the gain stage.  I'm using a 3 leg, single pole double throw toggle. I put the centre leg at the output of the first stage, then the both outside legs just before the 10 uf decoupling caps of both clean and gain paths. The switch works, but I get some cross talk between the 2 channels, for instance turning the pot on the clean channel changes the the volume slightly on the gain channel, but in reverse. i have to reduce the clean channel to get the most volume from the other..you know what i mean..the signals aren't separated properly. Also I don't understand why in the schematic, the switch straddles the R9 1M resistor?? Before I put the switch in the 1M completely changed the the gain stage to "clean"..no nice fuzzy distortion. I left that out, but now thinking I need that in there.

I just can't get my brain around where to place the switch leg.
Here's the problem, If i put the 1M in the circuit as shown, and place the the switch after the 1M, i lose de-coupling from that stage. If I put the switch after the de-coupling cap, but before the 1M i lose distortion??? Can someone explain what I'm doing wrong here?? Am I using the wrong type of switch?? I have a bunch of the SPDT switches and a few 3PDT (effects pedal stomp switches)..would a DPDT switch be the correct type???
cheers
Steve


dogbox

just read the electrosmash page properly ..it says '4. Overdrive Channel - Clipping Amplifier.
The Clipping Amplifier is selected with the DPDT (Double Pole Double Throw) Switch1. The switch can also make the signal to bypass this part of the circuit resulting in a clean sound.'

OK so how can I make a 3PDT work here..I can't get access to many parts, due to living in a remote place. Any clues??

Enzo

The two 10uf are coupling caps, not decoupling caps.  C5,6.

Why did you wire a switch before C5,6, instead of where the schematic shows, after the two volume controls?   DO you currently have the two volume control wipers wired together?  That would explain the interaction.

Why would you place the one switch after the R9 1 meg?  The schematic shows the switch ACROSS R9, not after. In other words in Clean mode the 1 meg resistor is in the circuit, and in overdrive mode, the switch shorts across the resistor, thus removing its function.  If you put the switch AFTER the resistor, then it just opens the circuit, turning that signal path OFF.  The resistor is there to quiet that overdrive path when it is not selected.

The switch in the schematic is a DPDT - note the two switches are both parts of SW1.  To use a 3PDT, just leave one set of contacts unused.   Like asking how can I sit two people at a table with three chairs.

dogbox

#3
Seriously switch challenged here, I get dyslexia when it comes to switches... I can't figure them out.
A1 | A2  | A3
—————
B1 | B2 | B3
—————
C1 | C2 | C3

Does A and B row connect, when switch is one way...and then B and C??? If that is correct tell me where to connect on the schematic. I can't do it..I tried. The 1M resistor is doing my head in.?????
I appreciate your help with this Enzo.

Enzo

I don't know what you are calling A,B,C, your picture is 3x3.  Here is a DPDT


Enzo

The 1 meg resistor?  It is one million ohms in series with the signal to knock it down to almost nothing.  Note the 1 meg is only in the circuit during clean.  Clean is when the OTHER path is used.  When you want overdrive channel, the switch shorts across the 1 meg, thus removing it from the circuit.

phatt

If you have a meter then check which terminals are contacting in the 2 positions.
This edited circuit might help;
Phil.

dogbox

Thanks heaps Phatt. Had it sideways...yep soldered on 6 wires the wrong way. Switches are my Kryptonite  :duh :loco