Solid State Guitar Amp Forum | DIY Guitar Amplifiers

Well, I am having a bit of trouble with my mini scope, but I did find something that seems odd to me.  I disconnected one of the speakers and attached the the dummy load, then fed a sine wave into the power amp.  I was surprised to find that I could hear the sound come from the still connected speaker.  It was quieter and not as clear as when you put it into the other input.  I also tried reversing it and got the same result.

Should the signal bleed to the other section?  I would have assumed it wouldn't.  But maybe it's normal?  It does cut out if I put a jack in the other power amp in. 

well good news bad news, good news i ordered the 2120D op amp i needed, bad news they are manufacturer discontinued and mouser and digikey were out of stock and not ordering any more of them bummer, all other outlets have a MOQ of at least 50 pieces o.O.  and to be honest im not even sure this will fix the issue with the amp but i have tried everything else i could think of. 

so i at least got the opamp i need on order before there were none left in the USA, i mean sure there are a lot of ones listed from chinese sellers but personal experience and word of mouth suggest a lot of those "china" sellers are selling fake op amp chips ( guess china has no shame in that they will even fake ICs.

Ok, looking closer at the schematic, the reverb thing doesn't matter.  The reverb gets it's input signal after the switching IC, so it shouldn't be able to bypass the clean vol.

But I'd still like to establish that this is the correct schematic.  You do get reverb on the clean channel, don't you?
Here's a pic as yours didn't show.  The black line above the OD ch. controls show which are for OD channel.  Reverb is not included, but is over to the right, as it is 'global' and supposed to work for both channels.  Is this pic like your unit?



If the schematic is correct and the volume pot is not the source of the bleed, the only other place I can see would be the 2120 switching IC.

thanks for the 2120 ic, i have also been messaging marshall about the issue to which i just now get a reply back from marshall:

Joanna Green <joanna.green@marshall.com>
To:
lordraptor1@yahoo.com

Feb 11 at 2:03 AM

Hello Fabian,

 

Regarding your question, it could be IC3 at fault as this is switching between the two channels.

 

Kind Regards

 

This email (including any attachments) may contain confidential information,
​privileged information, or constitute non-public information. Any use of this
​information by anyone other than the intended recipient is prohibited.
​If you have received this email in error, please inform the sender
​immediately and delete this information from your systems.

Marshall Amplification plc, registered in England, Registered number: 805676.
​Denbigh Road, Bletchley, Milton Keynes, MK1 1DQ, England.

JOANNA GREEN​
RETURNS/CUSTOMER SERVICES MANAGER
+44 (0)1908 375 411
DENBIGH ROAD, BLETCHLEY, ENGLAND, MK1 1DQ

 
This email (including any attachments) may contain confidential information,
​privileged information, or constitute non-public information. Any use of this
​information by anyone other than the intended recipient is prohibited.
​If you have received this email in error, please inform the sender
​immediately and delete this information from your systems.

Marshall Amplification plc, registered in England, Registered number: 805676.
​Denbigh Road, Bletchley, Milton Keynes, MK1 1DQ, England.

they to seem to think that IC3 ( this is the 2120 im assuming you were talking about in the schematic) COULD be at fault causing the issue. 

I have a Zoom G3 which I want to connect to a PC for recording. It originally came with Cubase LE but that doesn't seem to be available any longer.  Not sure if the G3 is even compatible with Windows 10.
Any ideas? https://www.zoom.co.jp/products/guitar/g5-guitar-effects-amp-simulator-pedal

Sent from my SM-A505FN using Tapatalk

Yes, that's correct.  I've got a bunch of resistors that will do the trick.  I also got a small portable scope that should do the trick.  I'm trying to get my hands on an old techtronix scope, but it might not be for a day or two.