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Thread: Adding a solid state reverb to a tube amp.

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    Adding a solid state reverb to a tube amp.

    Hi all,
    Like many of you, I'm at home, not doing any gigs right now (not by my choice) so I'm in my shop working on some of those back-burnered projects. I'm building an amp for myself in a small cab (2x 6V6, dual rectifier, EF86 front end). I did an amp just like this for one of my buddies a couple of years ago and it's his favorite amp. I admit, that amp does sound good.

    But I'd like to have a built-in reverb with this amp. The amp is quite small and I'll most probably be bringing it to rehearsals and very small gigs. Having the convenience of a built-in, one knob reverb is appealing to me. Yes, there are better sounding reverbs via outboard, pedals, etc (some of which I already own) but that's what I'm trying for right now.

    I'd like to use an Accutronics (or other make) short reverb tank (the long one (17") won't fit in this small amp) and I want a circuit that is easy to integrate into an all-tube amp. I've looked at a couple circuits using the TL 072 IC (or another IC with the same pinout), one for drive and one for recovery and I'd like to pick a proven, good sounding circuit, if possible. Some people say discreet transistors are best for this sort of thing but others have written that ICs are ideal for this type of application, so it seems that there is no consensus.

    Can anyone recommend a solid state reverb driver/recovery circuit for such an application? And, yes, I want to build it myself.

    Also, I'm wondering if it's possible to power the ICs from the bias tap of my power transformer (stepped down and filtered, of course) or should I used a dedicated small transformer for this? Should I use a voltage regulator? I guess I hoping to converse with someone who has been down this path before and has some knowledge and experience about all this.

    Thanks for all your comments and advice, as usual,

    Bob M.

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    Supporting Member The Dude's Avatar
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    You could copy the reverb circuit from any number of amps with a SS reverb. The Fender Hot Rod Deville or similar might be a good reference.

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    Supporting Member loudthud's Avatar
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    Yes, you can use the bias tap as long as you don't need too much current. One problem is dealing with the Voltage that might be +/- 60V. Most solid state regulators can't deal with that. Zener diodes are a good choice, just be conservative with the power rating, no more than half the Watts with no load.

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    Don't forget the joker g1's Avatar
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    There are 2 of the most simple op amp types (with small tanks) on pg.7 of attached pdf.
    Personally I like the ones that drive the tank a little harder using 4 paralleled sections of a quad op amp but I can't recall the circuit. I think it was a Traynor/Yorkville but may have been Marshall. Maybe someone else will know it.
    Attached Files Attached Files

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    "Everything is better with a tube. I have a customer with an all-tube pacemaker. His heartbeat is steady, reassuring and dependable, not like a modern heartbeat. And if it goes wrong he can fix it himself. You can't do that with SMD." - Mick Bailey

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    Quote Originally Posted by The Dude View Post
    You could copy the reverb circuit from any number of amps with a SS reverb. The Fender Hot Rod Deville or similar might be a good reference.
    Personal preference, but I have had 4 or 5 HR amps and I hate the reverb on those. It seems like they overdrive the snot out of the tank and it has a very narrow range where it sounds good. IIRC they used the same circuit on the early Blues Deville/Deluxe but with a tank with lower imput impedance (BB tank instead of EB). Those to me sound much better. I've also put a parallel resistor with the tank input and that also helped smooth it out.

    Personally I like the ones that drive the tank a little harder using 4 paralleled sections of a quad op amp but I can't recall the circuit. I think it was a Traynor/Yorkville but may have been Marshall. Maybe someone else will know it.
    Vox did this on AC15C1/C2 but had 5 op amps.

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    Supporting Member The Dude's Avatar
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    Yep. I wasn't meaning specifically that design- just using it as an example. In other words, find a SS reverb circuit you like and copy it. There are plenty of examples out there.

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    Thanks for the replies,

    I thought I'd start with something like a Hot Rod Deville or Blues Deville/Deluxe solid state reverb circuit and tweak it from there. I only need about 5mA for 2x TL072 op amps so if I can design a dropping circuit from the bias supply and make it bi-polar, that would seem the easiest thing to do. I'm not sure if I have room for another transformer in this already crowded build.

    The reason I ask here is that someone must've tried this sometime before, with or without success, so I thought I'd inquire.

    Thanks for the participation,
    Bob M.

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    Lifetime Member Enzo's Avatar
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    And look at most any Peavey amp, they use a very similar circuit.

    What with the companies merging and such, I haven't been on Accutronics site in a long time, but they used to have a generic drive circuit, also very similar.

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    There's an add-on reverb for the Randall MTS amps that's interesting and works really well. The PCB is bolted underneath the tray in the centre with the component side uppermost an is the full width of the tray and about 4" long. A small add-on transformer sits on the amp chassis and connects the AC to a 2.1mm socket. The PCB has the rectifier and smoothing caps. The reverb signal is taken off the send/return and is controlled by the FX loop mix control. It's just an opamp drive and recovery. The design means no space is taken up inside the crammed amp for a PCB.

    This is the way I intend to build my next add-on SS reverb.

    EDIT; Maybe the Stage Center circuit would work OK - it's a proven standalone design.

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    Last edited by Mick Bailey; 03-27-2020 at 09:13 AM.

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