Mark IV lead gain

[Tyrant]

I've been running through a bunch of settings on this "new to me" Rev. A compact combo and I notice the amp is real quiet until right at 4.5 on the lead gain alot of hiss is introduced. It does not come on gradually and it is significant. Master between 2-3. Just wondering if this is the norm.

I must say it is impressive. This thing is a tonal monster, it's beyond versatile. R2 is sweet. I was able to find quite a few bubbly crunch tones in short order. The thiele w/c90 should be here today and I'll be looking to swap the speakers more than likely. I assume it's a straight forward swap. All I can say is Turn it UP!

 

[srf399]

There is manageble hiss with my MKIV as I turn up the lead gain. I mean it's definately there but it comes on gradually and it's not that bad. Try switching preamp tubes one at a time using the spare preamp tube that is located inside the amp enclosure.

 

[holdsworth]

Here is my thoughts on the Mark IV lead channel hiss...

When I was using a gold Ei 12ax7 in v1 position, I recieved absolutely no hiss whatsoever, no matter how loud I turned up the amp. The only down side to this, besides the fact that is was extremely dynamic and articulate, was that it didn't have a lot of gain. The high gain JJ tubes on the other hand, inserted in the v2 abd v3 positions, gave me all the gain I would ever need. However, they significantly increased the hiss, especially on lead channels. The original Mesa tubes were somewhere in between, louder than the Ei but quieter than the high gain JJs.

My point being I suspect the preamp tubes have alot to do with the hiss factor in the Mark IV, as I have experienced first hand. Try tapping on your tubes and testing for microphonics, making sure none of your tubes are running hot ect. If there isn't a problem there, just try changing your preamp tubes for something less hot or which are known to have less microphonics or noise.

 

[twally]

holdsworth is absolutely right about the preamp tubes. When I first got my (floor model but a great buy) Mark IV I had the same problem with hiss in the LEad Channel. In fact, I could hardly sit in front of my computer while playing in Lead Mode, due to the hiss and "noise". I replaced all of the tubers and now everything is fine. Well, except I am thinking of going to "hotter" tubes.

 

[twally]

holdsworth is absolutely right about the preamp tubes. When I first got my (floor model but a great buy) Mark IV I had the same problem with hiss in the LEad Channel. In fact, I could hardly sit in front of my computer while playing in Lead Mode, due to the hiss and "noise". I replaced all of the tubers and now everything is fine. Well, except I am thinking of going to "hotter" tubes.