MK IV Lead Channel - Possible Problem

[Greystoke]

Hey Guys,

Hope someone can shed some light on what could be a problem I'm experiencing on the lead channel of a '91 short head MK IV.

The lead channel master has to be pretty high to equal the output level of the rhy 1 or rhy 2 channels. I'll use rhy2 and the lead channel as an example. With rhy2 gain on 8, lead gain on 8 and lead drive on 7 (bass, mid, treb all set identically), with rhy 2 master on 4, the lead master has to be at 7.5 to match the rhy2 volume.

Now the next part. If I turn the lead channel’s bass, mid, and treble to 0, the lead channel’s volume drops way, way down and becomes clean. By comparison, setting rhy2's bass, mid, treble to 0 doesn’t affect its volume much at all and keeps its drive.

Last thing. With the bass, mid, and treble on 0 on the lead channel, when turning up the the lead gain control from 0-9, it brings in a bit of volume - but then turning the lead gain from 9-10, the lead channel volume goes off.

I get these same results with two complete sets of pre-amp and output tubes.

Any info/suggestions will be greatly appreciated.

Greystoke

 

[Boogiebabies]

I think what is going on is normal. The R1 and R2 have way less compression than the lead channel. My MK IV is a 12/93 and reacts the same way. The tone stack or preamp tone controls on the MK IV are just like and old Fender. The come right after the first preamp stage and act not only as and EQ but sort of like a volume control as well. If you put them all to 0 I am surprised you get any signal out at all. The treble alone can act as an extra gain control as it dumps more high end into the mix. I have the same issue in the MK II's. When the Master is at 2 the clean is very loud. When the lead mode is engaged with the master on 3-4 the volume drop is
totally evident. In my travels, this is the norm for Mesa MK series amps and always has been. The same goes for the effectiveness of the reverb. It always seems more pronounced on the clean channels, or in a MK IV on the clean and R2.

If the difference in volume was crazy low, a good pot cleaning or replacement may repair the problem, but again yours sounds like a MK IV behaving normally.

Ed

 

[scottcrud]

bump

 

[screengrid]

Hi all,

so I have a MK IV from 01'91, here my most used settings for comparison:

R1 7-8
R2 8
tone R1 Treble 6, R1+R2 Bass 3, R1+R2 Mid 5, R2 Treble 5-6

Lead Gain 7-8, Treble 7, Bass 3, Mid 6-7, Lead Drive 4 - 8
Presence R1 5, R2 3 pushed, Lead 3 pulled
Masters R1 4, R2 3, Lead 2-2 1/2
Output Level 2-3

I never had problems with the loudness balance of the Lead Channel as you discribe.
Hmm, I would recommend to check the tube of the lead stage at first.
I agree with boogiebabies regarding your testwise settings of the tone controls.

 

[Greystoke]

Thanks for input, Boogiebabies and Screengrid. Now knowing that the tone controls are like an old Fenders, I'm not worried about the volume/gain drop when they're lowered.

But I am still concerned with the volume difference between the channel master settings. With drive and tone settings equal, the lead channel has to be set 3.5 numbers higher to equal the rhy 2 volume. If rhy 2 master is on 2.5, lead has to be on 6. This is my fourth MK IV and I don't remember ever coming across this.

If anyone here could take a quick volume check between your MK IV rhy2 and lead masters, I'd greatly appreciate it. Maybe set rhy 2 and lead tone controls the same and the gains/drive all on 8 and see how the volumes balance.

Thanks,

Greystoke

 

[kmanick]

I have this same issue with my Mark IV
if I run the output level at 3
I can run R2 channel volume at 2
but Lead channel volume needs to be at 5 or more to equal the volume of R2.
my R2 channel is crazy loud
nothing else seems to be off (plenty of gain etc) just the volume is much lower on the lead channel