Since I'm more of a tube guy, I don't even begin to know where to start fixing this amp. Download Free Microxp V0 82 Experience Isotope on this page. I have a Marshall Lead 12 combo. I bought it used a few years ago to gut and build into something else, but it sounds pretty good as is and makes a nice light practice amp.

The stock speaker really sucks and makes the amp sound crappy. When the crappy stock speaker is replaced with a good Celestion or similar, it really opens up the amp's tone and makes it sound much better.

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The mini stack head was used by a lot of the LA guys in the mid to late 80s in rack setups as the tone generating machine, IIRC. It has never really worked right.

When I got it the low input channel was intermittent, it would cut in and out while playing the amp. The high input is fine. I tried reflowing the solder on the low input jack, but this made the problem worse.

Now it squeals when the gain is dimed and the volume is turned up. Any suggestions where to begin? Autocad Activation Code Generator 2014. There aren't that many parts connected to the low gain input: a jack, a resistor and an opamp.

Any ideas where to start to fix this thing? Schematic is here: The combo is model# 5005, the mini stack is model# 3005. Steve, If it were my amp, I would replace both input jacks. There's a muting function on the op-amp output being performed by the 'low' input jack, and a voltage-divider function by the 'high' jack; I don't know precisely what's going wrong in your amp - possibly some kind of positive feedback or the op-amp + input ground reference disappearing - but I'm pretty sure that replacing both jacks will make it go away. I would also recommend resoldering all the component connections around IC1, and in my Lead 12 I pulled the 1458 and put in a socket and LF353 op-amp, which improved the overdrive quite a bit IMO. You could also try cleaning and retensioning the jack contacts; IME the effect of this will last anywhere from a week to 3 months, but YMMV. Update: I got three new Cliff jacks from AES.