Author Topic: Late Mark 2 Suitcase Preamp (all dials, no EQ sliders)  (Read 1881 times)

Offline goldphinga

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Late Mark 2 Suitcase Preamp (all dials, no EQ sliders)
« on: July 09, 2015, 02:10:30 PM »
Can anyone shed any light on these later preamps installed in the later MK2's? Is it the same circuitry/preamp as the Haigler preamp with eq sliders?

Thanks 8)

Offline Tim W

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Re: Late Mark 2 Suitcase Preamp (all dials, no EQ sliders)
« Reply #1 on: July 09, 2015, 04:08:25 PM »
On the SuperSite:

Check the bottom of the page.

http://www.fenderrhodes.com/service/manual.html


All the best
Tim
retrolinear.com

Offline pcola_rhodes

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Re: Late Mark 2 Suitcase Preamp (all dials, no EQ sliders)
« Reply #2 on: July 29, 2015, 12:53:03 PM »
I have one of these on a MK II name rail that is currently uninstalled on the piano.  I'd be happy to send you a photo if you wanna check it out.  It doesn't come in a "box" like the Haigler on my '79 Suitcase (hope that makes sense, preamps aren't my specialty).
1979 MK I Suitcase 73
1980 MK II Stage 73 w/Suitcase Preamp
Janus I Speaker
Fender Twin Reverb Reissue
BOSS CE-5
MXR Phase 90 (R28 modified)

Offline goldphinga

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Re: Late Mark 2 Suitcase Preamp (all dials, no EQ sliders)
« Reply #3 on: August 07, 2015, 05:47:16 AM »
Hey thanks man! Sorry i should have been clearer- i have one of these preamps already just wanted to find out more about who designed it and what made it tick.  8)

Offline Tim W

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Re: Late Mark 2 Suitcase Preamp (all dials, no EQ sliders)
« Reply #4 on: August 07, 2015, 11:37:20 AM »
The final suitcase preamp was designed by Paul Gagon.
He is now VP of Engineering at BBE Sound and G&L instruments.  A talented guy for sure.

The major difference in these versus the Haigler were the use of 5534s in the audio path for low noise. The stereo vibrato also has a unique feedback scheme using center tapped optos. In all earlier pres the intensity pot was in the audio path. In this design, the intensity pot directly varies the amplitude of the vibrato control signal. This then drives two opamp stages with feedback from the dual optos. One stage is inverting and the other isn't. With the feedback from the optos, the LED intensity is servoed in the LDRs to follow the vibrato lfo control voltage, controlling the amplitude of the two outputs. The entire circuit acts as a dual VCA of sorts, and its control voltage comes from the wiper of the intensity pot. It seemed Paul's goal was keeping as many pots out of the direct audio path as possible.


Best
Tim

Offline pnoboy

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Re: Late Mark 2 Suitcase Preamp (all dials, no EQ sliders)
« Reply #5 on: May 03, 2016, 06:42:00 AM »
It seems to me that the clever tremolo design was not intended to keep pots out of the audio path, but instead to effectively linearize and flatten the frequency response of the LED/LDR pair.