Interesting Observation Regarding My Mark II Graphic EQ

[Rick Mark2A]

Recently I picked up a nice EQ/Spectrum Analyzer (TC Electronic 1128) to use in the loop of my Mark II. While playing around with it, I dialed in a preset which basically set everything flat with the exception of a mid cut in the 600hz and 800hz ranges. As an experiment I set the five band EQ on my Mark II to exactly mid point, which I assumed would be a flat setting. I then proceeded to observe the spectrum analyzer on the TC unit and switched the onboard eq in and out of the circuit. When I switched the Mesa 5 band EQ into the circuit I noticed that my mid cut disappears on the spectrum analyzer. In order to get my mid cut back I had to pretty much drop the 750hz slider on the amp all the way down. This seems odd to me. Is this a normal feature on the Mesa five band EQ, to provide an actual 750hz boost when set to the flat position? Or perhaps, was this a feature found on the earlier Mark II's (mine was built 12/78). Would love to hear from Authorized Boogie, or anyone else who notices this on their Mark amps.

 

[caphead]

Technically, the basic design of the graphic EQ circuit hasn't changed much since it's introduction until very recently. Those results you shared are very interesting though; it would explain why the normal inclination for most people is to turn down the 750Hz, though there are notable exceptions.

 

[Snottyboy]

Call Boogie for an explanation. Then report back here! Interesting.

 

[Rick Mark2A]

Call Boogie for an explanation. Then report back here! Interesting.

Nah. Long ago I tried the phone thing with them a few times to inquire about having my amp serviced. I was told someone would call me back, and so I got tired of waiting for the callback and had my amp serviced locally. No way I'm going to bother calling them for something like this. I could just imagine how that would work out. :roll:

 

[Snottyboy]

Call Boogie for an explanation. Then report back here! Interesting.

Nah. Long ago I tried the phone thing with them a few times to inquire about having my amp serviced. I was told someone would call me back, and so I got tired of waiting for the callback and had my amp serviced locally. No way I'm going to bother calling them for something like this. I could just imagine how that would work out. :roll:

I only have one experience calling Boogie, about 3 years ago. It was for a similiar type of question as yours regarding my IIA and ended up talking with Mike B. for about 45 minutes. I got more of an explanation than I ever could have hoped for.

 

[user 21540]

In the Blue Angel amp there is an actual GEQ module in the circuit that is inside the amp. It is filled with epoxy and its settings -- which are presumably flat -- can't be changed. It is alway engaged in the circuit. I've heard it referred to as a mojo module. So, the GEQ circuit was known by Mesa to add something extra even when it was engaged with flat settings.