Hoffman Amplifiers Tube Amplifier Forum
Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: TerryD on November 22, 2015, 12:46:03 pm
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Let me reveal my ignorance. Could I disengage the digital reverb and slap a spring tank into the same send and return r64 and r52?
If not could I do it with a few altercations? The head is really big enough with room to spare for a reverb tank. If it ends up too close to the transformer, say 3 inches, is there some kind of shield I could use?
http://distorqueaudio.com/hardware/mods/bugera-v22.html (http://distorqueaudio.com/hardware/mods/bugera-v22.html)
Thanks,
Terry
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... Could I disengage the digital reverb and slap a spring tank into the same send and return r64 and r52?
R51 would typically be 1MΩ-3.3MΩ in most tube reverb circuits.
You could do it, but you'd need a reverb driver circuit (12AT7, reverb transformer, associated parts), and a reverb recovery amp (a 12AX7 section, associated parts) to go between R64 & R52. Because of the board-mounted tube sockets & p.c. traces, you won't be able to easily re-purpose existing tubes to be part of the reverb circuit.
I'd consider this not worth pursuing (for me personally) without ripping out all of the existing circuit board and building a new amp from scratch with the existing chassis, PT & OT. The photos I've seen (if they are correct for your amp) show a p.c. board which covers almost all the open chassis space, precluding easily adding new sockets & parts off-board.
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Could I disengage the digital reverb and slap a spring tank into the same send and return r64 and r52?
No.
Because the existing digital reverb chip is self powered, as to operation and signal. As Hotblue says, a spring reverb unit needs a driver on the input side; and a gainststage on the output side.
You could put a reverb unit in the effects loop, or in front of the amp.
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OK Thanks. I've heard some purist just get rid of the digital reverb. Take it out of the circuit. Can I do that? Any advantage in that? will that get rid of all digital intrusions, which I abhor. Does just shutting it to 0 take it out of the circuit?
As always. Thanks.
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If you can't hear a problem now, I doubt you'll notice an improvement with it gone.
Most of the reverb in recordings you listen to is generated by digital rack units... I've been in studios with huge EMT reverb plates, but few places have the space for one of those.
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Maybe you could try one of these: http://surfybear.weebly.com/surfy-bear-fet-reverb-kit.html (http://surfybear.weebly.com/surfy-bear-fet-reverb-kit.html) , either stuck in the sides/bottom of the cab, or built as a standalone reverb.
Haven't personally bought or heard one, so not vouching for it. First heard about them in this thread: http://el34world.com/Forum/index.php?topic=16771.0 (http://el34world.com/Forum/index.php?topic=16771.0)
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I had some of my guitar buddies say they PREFER the digital in the bulgera over a short tank like the fender valve juniors have.
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Which is why I simply threw a larger tank in my blues jr. and it sounds fantastic. I just had to cut off the tabs.
My main point is that I don't want my signal path running trough a digital device, which to my ears always thins the sound and worse.
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Here is an interesting calculator for the cathode bypass cap and resistor.
https://www.ampbooks.com/mobile/amplifier-calculators/cathode-capacitor/calculator/ (https://www.ampbooks.com/mobile/amplifier-calculators/cathode-capacitor/calculator/)
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> slap a spring tank into the same send and return r64 and r52?
Spring reverb needs a small power amp, the spring, and a preamp.
Essentially you are building a Champ, but in two pieces, backward, with spring between.
That SurfyBear is the same idea except done without tubes. IIRC it may need adaptation to suit the Bugera reverb interface. It also needs a power supply, not like any power source found in most tube amps (though perhaps the digytal reverb chip's supply could be tapped).
The other, once common, plan is to do your Champ and spring in an external box, the Stand Alone reverb, patched between guitar and Bugera. A LOT of classic early 1960s records were done with that. You can buy kits. It is of course extra work for your roadies.
Digital gets some better every some years. And paying less sometimes gets you less. Even in the 1990s, a rack digital time-twister could be adjusted for very fine room-like reverberation (surf-spring was not something that one did).
While I agree that digital won't duplicate spring, I have observed that once the audience has the spirit (beer or prayer), fine distinctions of tone are overlooked.
> I don't want my signal path running trough a digital device
Only the reverb goes through the digi-thing. If not doing surf, that is 0% to 50% of your sound, all the rest is raw tubes. If not using reverb this song, the digi-bits signal is muted at the reverb knob. If you are very annoyed that digital exists, you could put a switch in the reverb signal return, and even a switch the digital chip, so it lays there dead when not wanted.
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me> not like any power source found in most tube amps
Looking at tube-town.de member "netbear"s back-trace, I now see that the Bugera has a full +/-15V op-amp supply of apparently good size.
Find the Rod Elliott audio site. He has well-thought-out basic op-amp reverb-spring designs (http://sound.westhost.com/project34.htm).
His Fig 2, make R1 220K and make C1 5nFd to match.
His Fig 3, you only need the U1B stage, the Bugera has the dry path and the mixing. VR2 should be an internal trimmer (possibly replaced with fixed resistor once trimmed). Set VR2 so with the Bugera's reverb knob on 10, the reverb is plenty, then dial-back in concert with the Bugera's knob. Take signal back to Bugera's Reverb pot from Rod's C4. You don't need the Mute switch because the Bugera has that after its reverb pot. (I suspect that T5 T7 are not connected as shown, but SMT is hard to trace, and I trust Bugera did it so it works.)
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Very interesting.
Thanks