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Post subject: Tremolo Explanation/Opinions
Posted: Sun Jun 05, 2011 1:28 am
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I was playing a silverface vibro champ recently and I really enjoyed the sound of its tremolo. Afterwards I was playing my DRRI and I found the trem very flat and unappealing. I heard that the champ uses bias modulation trem and the DRRI has optocoupler tremolo. I think I understand how the optocoupler works. Can someone here take a stab at explaining the bias modulating trem and why it has a richer sound?


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Post subject: Re: Tremolo Explanation/Opinions
Posted: Sun Jun 05, 2011 1:53 am
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The opto-isolator operates on the pre-amp signal while the bias-modulated type operates directly upon the output tube(s) at the power-amp stage. The latter effect is richer, more nuanced, and usually more intensified dependent upon the setting of the "depth" control. The gated-oscillator principle is the same for both types but the opto-isolator circuit is easier on power tube(s).

Arjay

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Post subject: Re: Tremolo Explanation/Opinions
Posted: Sun Jun 05, 2011 2:13 am
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Arjay is right-on. My 1962 Pro-amp runs three 12AX7 types to generate that phase-shift oscillation (no opti-roaches). It has vibrato/tremolo to die for. Just try a plain old BF or SF Vibro-Champ and you'll see what we mean ( I don't believe any VC had that opti-roach).

There are a bazillion mods and fix-its on the Net for opti-roach driven vibrato/tremolo improvements. One thing that is easy is to check to be sure the black covering is intact over the opti-resistor. Check this site for "whisker" (not whiskey--- though I wish) problem:


http://ampgarage.com/forum/viewtopic.php?t=4675


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Post subject: Re: Tremolo Explanation/Opinions
Posted: Sun Jun 05, 2011 2:38 am
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BMW2002Ti wrote:
My 1962 Pro-amp runs three 12AX7 types to generate that phase-shift oscillation (no opti-roaches). It has vibrato/tremolo to die for.


Correct. However the "harmonic tremolo" such as yours is inserted into the amp's circuit prior to the phase-shifter stage -- the "bias-wiggle" trem impinges directly upon the output tube(s) by modulating the bias voltage from the P/S. Of Leo's three trem circuit designs, the harmonic type was the most complex and best-sounding. However, the sheer number of tubes required for this type consumed a lot of "real estate" on a Fender chassis.

Arjay

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Post subject: Re: Tremolo Explanation/Opinions
Posted: Fri Jun 10, 2011 2:58 am
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You guys are great, thanks for the info.

Which model has the "best" reputation for its tremolo?


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Post subject: Re: Tremolo Explanation/Opinions
Posted: Fri Jun 10, 2011 5:05 am
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That's a toughie to answer. Let's just say there are a LOT of blackface and silverface (very little circuit differences, if any) out there. And for 6-8 watts it gives you vibrato/tremolo to die for. Really, studio quality stuff.

There are so few brownface Pro-Amps (with 6G5-A) circuits in good condition, that it took a long time for me to find mine. BUT, it's vibrato/tremolo is absolute killer. With wider range of control (IMHO). And if you use a Fender Reverb Unit with it... the sexiest, smoothest, tone you'll hear [oh yeah, the JBL D130F 15-incher doesn't hurt either].

Image


Versus this:


Image

Image


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