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Author Topic: Ultra Chorus/Ultimate Chorus mod  (Read 1594 times)

fallingfrog

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Ultra Chorus/Ultimate Chorus mod
« on: January 22, 2021, 12:08:35 PM »
So I bought one of those solid state fender amps from the 90’s- an Ultra Chorus.  It’s a really solid amp, an independent 65 watt power amp for each 12 inch speaker, really nice stereo chorus effect and real spring reverb.

But, I didn’t think that the clean channel took overdrive pedals well.  It was way too fizzy.  I looked at the schematic, and I found two simple modifications that you can do that I thought I might pass along to save time for anyone else who wants to try them.

They are:
1) the ultra chorus/ultimate chorus has a bright cap.  It’s C6 on the schematic.  I clipped it out and a lot of the fizz went away.

2) the ultra chorus has a standard fender tone stack, but being solid state all the resistor values are smaller and the capacitor values are bigger than in, say a fender twin.  However, the treble capacitor is way smaller than it should be in that circuit, and consequently, if you turn up the treble enough to give you the emphasis you want at around 2khz, you get way too much emphasis around 8 or 9 kHz.  The solution is to increase the value of C7 from 470pf to 1250pf.

Do these two things and the amp sounds just like a proper Fender should!

fallingfrog

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Re: Ultra Chorus/Ultimate Chorus mod
« Reply #1 on: January 24, 2021, 11:26:11 PM »
Edit:  the treble capacitor should be 1440pf, not 1250.  Then it has the same tonal fingerprint as the 250pf treble cap in a tube fender amp tone stack.

Stefan

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Re: Ultra Chorus/Ultimate Chorus mod
« Reply #2 on: February 12, 2021, 06:46:45 PM »
Bookmarked, I have one these excellent amps.