Switchable 1986/1987/2204-clone problem - help needed!

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Bluesbenny
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Switchable 1986/1987/2204-clone problem - help needed!

Post by Bluesbenny » Mon Mar 14, 2016 2:52 am

I build a Marshall clone with includes all original layout paths of the Marshall 1986, 1987 and 2204 amps. I used the Ceriatone layouts of (a) the Plexi 50 1969 Bass, (b) the Plexi 50 1968 Lead and (c) the 2204.

I use four switches mounted on the backside of the chassis :
• Switch 1 : 3 pole/4 position-switch to change the cathodes, for shared and split cathodes, V1a-cathode changes from 820R/220uF to 10K and parallel wiring of a 0.68uF cap to the 820R resistor after V2a
• Switch 2 : 4 pole/3 position-switch to change the tonestack between 56K/250pF to 33K/500pF, parallel wiring of a 0.022uF cap to the 0.0022uF cap after V1b.
• Switch 3 : 4 pole/3 position-switch for parallel wiring of a 0.068uF cap to the 0.022uF output caps and changes of the negative feedback.
• Switch 4: 6 pole/2 position-switch to change between 1986/1987-layout and 2204-cascade layout.

It was a hell of a work. For this reason I was a little bit disappointed that the amp is not working. There is no real sound from the amp, no matter which switch position you are using.

• The Power is working and output transformer seems to work as well.
• You can hear the turning of the presence knob, bass knob, middle knob and the treble knob (especially with high presence). So the problem seems to be before the tone controls. But you cannot hear the turning of the volume controls (after pulling V1 on my JTM45-clone, the JTM45-clone showed the same symptoms).
• Position changes of switches 3 and 4 produce light pops, the others not.

I checked all connections for all switches and everything seems to be done according to my layout. I measured between the poles and behind the next capacitor rsp. the next resistor and get the expected value in every position.

Switches 1, 2 and 3 do not seem to be the problem. For this reason I think I have to focus on the cascade switch 4 which is responsible for the change of the signal path between 1986/1987 and 2204.

Here are the connections I did on the cascade switch 4:

• Pole 1 (red): 0.022uF coupling cap after V1a --- position 1987 : to normal volume pot right lug --- position 2204 : to 470K/500pF mixer
• Pole 2 (purple): bright volume pot mid lug --- position 1987 : to 470K/500pF mixer --- position 2204 : to 0.022uF coupling cap before V3a
• Pole 3 (black): treble pot mid lug --- position 1987 : to 0.022uF coupling cap before V3a --- position 2204 : bright volume pot right lug
• Pole 4 (brown): 0.022uF cap after V1b --- position 1987 : to bright volume right lug --- position 2204 : wiring a 470K resistor in series to normal volume right lug
• Pole 5 (blue): Normal volume pot mid lug --- position 1987 : to 470K mixer resistor --- position 2204 : pole 2 of V1
• Pole 6 (green): 470K mixer resistor --- position 1987 : to normal volume pot mid lug --- position 2204 : to ground.

Here is my layout with all poles and junctions for a better understanding:

http://s1077.photobucket.com/user/Benny ... v.jpg.html

Here are the original Ceriatone layouts:

http://www.ceriatone.com/images/layoutP ... iatone.jpg
http://www.ceriatone.com/images/layoutP ... 0-Lead.jpg

Any ideas what is wrong? Do I have a design bug?

danman
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Re: Switchable 1986/1987/2204-clone problem - help needed!

Post by danman » Mon Mar 14, 2016 3:28 pm

Welcome to the forum. We will probably need several good clear pics of everything to be able to help out. With so much going on in the amp it will be hard to troubleshoot. I would suggest disabling everything but the basic circuit and try to get that working properly. Once you get that working, then you can start to add in each of your switched channels and get them working properly.

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neikeel
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Re: Switchable 1986/1987/2204-clone problem - help needed!

Post by neikeel » Wed May 25, 2016 11:42 am

danman wrote:Welcome to the forum. We will probably need several good clear pics of everything to be able to help out. With so much going on in the amp it will be hard to troubleshoot. I would suggest disabling everything but the basic circuit and try to get that working properly. Once you get that working, then you can start to add in each of your switched channels and get them working properly.
Absolutely!
Neil

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