Mark IIC+ pull deep question.

[theroan]

When this knob is pulled, what frequency or frequency range is being boosted?

The reason I ask is it seems the pull deep is the one thing that prevents the Mark V from really copping the IIC+ sound. What if one were to put a vario boost in the loop at the frequency that the pull deep handles.

Just a thought.

 

[Boogiebabies]

Since the IIC+ V2A cathode on that circuit is already bypassed with a .47uf cap, switching in the 15uf cap does not add more gain
per se but voices the cathode circuit to pass much more lows through the stage. The frequency should be centered around
17.75Hz with a 1K cathode resistor and 15uf (14.53uf in parallel with .47uf) bypass cap. The standard 1K/.47uf circuit frequency
should be centered around 548 Hz.

 

[>Photi G<]

I thought that the Pull Deep affected the Power Amp response?

 

[Boogiebabies]

I thought that the Pull Deep affected the Power Amp response?

It does, but it's a preamp function. If you look at the circuits position in the preamp it's pumping
17.75Hz at the stage that feeds the master volume. The .047 coupling cap off the V2A allows
most of that bass response through to continue to the GEQ or phase inverter which then sends the signal to the
power amp. The only power amp functions that are specific are the presence and slave.

 

[chipaudette]

As BB said, the "Pull Deep" affects the frequency response of one of the tube stages in the preamp. For the IIC+, it affects the response of the tube stage that is right after the effects loop before the signal heads off to the GEQ and the power amp.

Here's the change in frequency response of this last tube stage with and without the Pull Deep...

http://www.flickr.com/photos/50442673@N03/4629417552/

So, it's interesting to note that, when "Pull Deep" is not engaged (ie, the knob is pushed) that last gain stage actually boosts the treble frequencies more than the bass frequencies. Then, when you engage the "pull deep", the low frequency response of the stage is restored, which makes it feel like the bass has been boosted. But really, the "Pull Deep" simply restores the naturally flat response of that gain stage.

It's also important to note that the boost by the "Pull Deep" isn't actually that large. To recreate the "Pull Deep" you only need to boost the low frequencies about 5.5 dB. Your graphic eq pedal might do +/- 15 dB. Therefore, you don't need to go rail-to-rail with your EQ pedal to simulate "Pull Deep"...unless you really dig the sound!

Chip

 

[ryjan]

Guessing by that graph I would say use a parametric eq, set it to around 50hz and boost 5.5db, then fiddle with the q setting until it sounds right.

 

[theroan]

That's very cool info. I'll let you know if it works.

 

[chipaudette]

Or, if you've got a common Graphic Eq Pedal like the Boss GE-7, you could try something like...

100Hz: +5.5 dB (ie. up to the first of its three tick marks)
200Hz: +4 dB (up to just shy of the first tick mark)
400Hz: +2 dB (just above the center)
800Hz and Above: Zero.

Chip