Mark II preamp - Volume drop with vibtrato

[Electroharmony]

I've noticed on my new Mark II suitcase, blackface preamp with sliders and music stand (the one that has vibrato present a small bit even when off) , that there is a noticeable volume drop when vibrato is engaged.  About the same as a small stone pedal.  No mods have been done on the circuit.  Anyone else ever experience this problem, or have an explanation for this?  Also, would the VintageVibe fix for the vibrato problem take care of this?

[Ben Bove]

Depends on how severe the volume drop is - because a little is normal.

When vibrato is engaged, it switches to alternating mode, 2 speakers per channel.  So when you go from no vibrato and all 4 speakers going, it does reduce to 2 speakers on the first channel when initially engaged.

So the dropping of 2 speakers at onset is probably what you're hearing.

[Electroharmony]

Well, I can't verify if this is the normal condition... but comparing two suitcases side by side.  One with silverface (late 70's) and one with blackface (early 80's) , there was a noticable volume drop when engaging vibrato in the blackface suitcase, compared to the silverface, which was almost non-existent.  This was verified by two other people in the room.   Examined both pre-amp boards, and they are similar but not the same...

I know there is a problem with the vibrato on these late models, and wonder if this factors into it.  Has anyone studied the late model Suitcase's (mark II's) to find where and why this problem occurs ?

[Ben Bove]

Only thing I can say is that I've experienced trouble with vibrato circuits on the 5pin amps.  Usually the 4pin is either dead from lightbulbs or poweramp, but I've run into a number of 5pin problems.  So if you can shotgun side-by-side, then there's probably something wrong.