Reverb in amp circuit

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Reverb in amp circuit

Post by apaclin »

Hi, just wanna make sure where are the reverb and tremolo in the circuit of the amp, let's say Deluxe Reverb? Is it before the amp or in between the amp and cab? And is it generally the same way for all amps or does it differ?
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Re: Reverb in amp circuit

Post by Hugh Robjohns »

They are in the preamp stage, before the power amp.
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Re: Reverb in amp circuit

Post by Wonks »

Except when it's a power tube bias tremolo circuit, when its the bias of the power amp output valves that are affected, but driven by a circuit in the preamp. In this case it's both the preamp and the power amp that create the tremolo effect.

The valves in this type of circuit can't be biassed too hot when the tremolo isn't engaged due to the big ± variation in the bias setting from 'normal' otherwise the power valves could easily burn out very quickly.
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Re: Reverb in amp circuit

Post by ef37a »

Tremelo Wonks? Where did that come from? Apaclin was asking about reverb and yes, as Hugh says it is in the pre amp section. In older amp, like the big Fenders it was a separate stage with a double triode* with one section arranged like a mini power amp with a transformer in the anode circuit which allowed the low impedance of the reverb 'tank' coil to be "matched" to the valve's anode impedance. The other triode is used as 'recovery' amplifying the relatively feeble tank coil's output and feeding that into the signal path. The output of that valve is then injected into the previous stages to sustain the reverb. With CARE of course! Otherwise the whole lot goes screaming mad.

A great many 'modern' valve amps have used an op amp to drive the tank as a cost cutting measure. Would not be so bad but they chose the WORSE possible op amp to do it with! The TL072 which has very poor load driving capacity. An NE5532 with both sections paralleled would have been a far better choice and a headphone chip even better because reverb tanks need to be hit pretty hard otherwise you get a poor signal to noise ratio.

I modded a Blackstar A100 to take a reverb tank for a famous guitarist. I often wonder what happened to it? Only one in the world AFAIK.

*Often the 12AT7/ECC81 as that has good power to drive the tank combined with medium gain for recovery.(otherwise it is a bloody awful audio valve!)

Actually (been a long time since looking at schems!) the two triode sections were often strapped together to increase power output and the output coil injected elsewhere. I have a book of old Fender circuits if anyone wants chap&verse?

Dave.
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Re: Reverb in amp circuit

Post by Wonks »

apaclin wrote: Wed May 31, 2023 9:36 pm Hi, just wanna make sure where are the reverb and tremolo in the circuit of the amp,

That’s where it says tremolo. :headbang:
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Re: Reverb in amp circuit

Post by ef37a »

Wonks wrote: Thu Jun 01, 2023 7:26 am
apaclin wrote: Wed May 31, 2023 9:36 pm Hi, just wanna make sure where are the reverb and tremolo in the circuit of the amp,

That’s where it says tremolo. :headbang:

'King eye! Sorry Mr W. While were are at it, tremolo circuits were often built around the PI stage (WEM) and used a large, for the day, electrolytic capacitor of 500mfd and low voltage, 25V. Capacitor technology was not as good back then and that cap had to only drop in value a few% and the oscillator would not start.

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