SLuckley's Revibe. un buffered FX loop

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norburybrook
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SLuckley's Revibe. un buffered FX loop

Post by norburybrook »

I'm wanting to build one of SLukleys revibe's he kindly has posted on his web site, a design taken from Doug Hoffman.
revibe.pdf

I was wondering if it would work through a Dumble amp FX loop without using a Dumbleator?

I know it's designed to work with the guitars going straight in and then out into an amp but I was hoping there might be a simple way of having the option to run it through an unbuffered loop.


thoughts?



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martin manning
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Re: SLuckley's Revibe. un buffered FX loop

Post by martin manning »

You don't need a buffer stage to drive the Revibe's high impedance input, but there is an extra gain stage or two in the chain that you probably don't need. I think it will still work fine in the ODS FX loop, just dial the send signal level down with the amp's master volume. The Revibe output shouldn't have any problem driving the PI input (which is also high Z), and the level controls will then function as separate reverb/vibrato volume controls.
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norburybrook
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Re: SLuckley's Revibe. un buffered FX loop

Post by norburybrook »

Thanks Martin that's good news. I'm going to start getting some parts together. I'll start a thread when I eventually get started.

I've always wanted a separate fender reverb and trem and I think now's the time to actually make one.

Should work great with my Rocket/Z-wreck too as I've seen Brad Paisley using his stand alone reverb like this


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Re: SLuckley's Revibe. un buffered FX loop

Post by sluckey »

norburybrook wrote: Thu Dec 28, 2017 2:24 pm I know it's designed to work with the guitars going straight in and then out into an amp...
Keep that in mind. The signal levels from a passive FX loop will be much hotter than the instrument signal levels the Revibe expects. You can probably use the DWELL and LEVEL pots to compensate on the input. But you may need another pot to control the output level of the normal/vibrato signal. Follow the blue signal path down from the output jack through a 220K mixing resistor. You will find a 10:1 voltage divider consisting of a 220K and 22K. I would replace that 220K/22K divider with a 250K pot. Then you will be able to adjust the output signal up to a level that should drive your amp's PI.

If this doesn't work well for you then just put the Revibe between the guitar and your amp input as it was intended.
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martin manning
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Re: SLuckley's Revibe. un buffered FX loop

Post by martin manning »

If the outputs are more-or-less balanced correctly now, perhaps it would be better to put a 1M output level control right at the output jack?
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Re: SLuckley's Revibe. un buffered FX loop

Post by sluckey »

The reverb and normal/vibrato outputs are balanced now with that 10:1 divider added in the nor/vib path. There's no problem getting enough nor/vib signal to drive the PI if you just remove that 10:1 divider. Afterall, the 6G12 circuit fed directly into a LTP PI without a divider.

The problem is the reverb recovery circuit. There's only one triode just like the original 6G15 reverb unit. The low level reverb signal is meant to be mixed with a guitar level dry signal. That works fine with the 10:1 divider knocking the nor/vib signal back down to an instrument level. I'm sure there will be enough gain in the reverb recovery to do a low level reverb sound but will probably need an additional triode (like the AB763 amps) to get to Dick Dale reverb level. That's the iffy part.

I'd try it without any mods at first. It may just work good enough for you. If not, keep the iron hot and start modding. But I believe once you hear this unit connected as it was intended, you'll forget about wanting to put it in an FX loop.
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norburybrook
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Re: SLuckley's Revibe. un buffered FX loop

Post by norburybrook »

Steve ,

thanks for chiming in. I've heard demos of fender type units and I like how they sound, It will be interesting to see how it works in a loop. Obviously the sounds I've heard aren't overdriven and of course that's when things start to get a bit squirely if it's not in a loop.


Thanks again for your drawings etc, your site is a valuable tool for builders. I just need to find the right transformers now this side of the pond...

Oh, quick question: what was the bridge rectifier unit you used in your build? I can see it's one of those 'all in one' types.

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Re: SLuckley's Revibe. un buffered FX loop

Post by sluckey »

I used the 1000 volt - 3 amp bridge rectifier available from Hoffman Amps for $2.01. Four cheap 1N4007s will work nicely too.
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didit
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Re: SLuckley's Revibe. un buffered FX loop

Post by didit »

Pleased to see Steve & Martin commenting. I resisted. All my theory would inevitably be less helpful than their actual experience.

However, now will add a few thoughts. Wonder if, in place of the 1M fixed, putting a 1M potentiometer at the Revibe input with wiper to the triodes would provide useful flexibility? Also a question about the Revibe design -- would it not be improved if the reverb could, with switchable control, cascade into the vibrato versus having the two purely in parallel?

Best .. Ian
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Re: SLuckley's Revibe. un buffered FX loop

Post by pompeiisneaks »

didit wrote: Fri Dec 29, 2017 5:46 pm Also a question about the Revibe design -- would it not be improved if the reverb could, with switchable control, cascade into the vibrato versus having the two purely in parallel?

Best .. Ian
My thoughts on this part of your question is 'it would work', BUT it may be very noisy and too gainy without some tweaks. I.e. you'd likely need to do more than just put in a switch to reroute things. Something like LNFB on to increase clean headroom etc. Similar to what other heavily driven amps do.

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Re: Sluckey's Revibe. un buffered FX loop

Post by sluckey »

Wonder if, in place of the 1M fixed, putting a 1M potentiometer at the Revibe input with wiper to the triodes would provide useful flexibility?
That simply puts another pot in parallel with your guitar volume pot. Just use the knob on the guitar.
would it not be improved if the reverb could, with switchable control, cascade into the vibrato versus having the two purely in parallel?
I think that would sound terrible. The signal coming out of the reverb circuit (top part of my schematic... red path) is only the boing, boing sound. The boing, boing sound is not very pleasing by itself. All reverb circuits I have seen always have a boing, boing signal that is mixed back with a strong dry/normal signal to produce the lush sound we all love. It's always a parallel path effect. That parallel path is really necessary.
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didit
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Re: SLuckley's Revibe. un buffered FX loop

Post by didit »

sluckey wrote: Fri Dec 29, 2017 6:33 pm
Wonder if, in place of the 1M fixed, putting a 1M potentiometer at the Revibe input with wiper to the triodes would provide useful flexibility?
That simply puts another pot in parallel with your guitar volume pot. Just use the knob on the guitar.
Not if it's going to be used on loop I/O, which was the initial query. Rather than relying the loop to provide the suitable level, a control on the effect could potentially.
would it not be improved if the reverb could, with switchable control, cascade into the vibrato versus having the two purely in parallel?
I think that would sound terrible. The signal coming out of the reverb circuit (top part of my schematic... red path) is only the boing, boing sound. The boing, boing sound is not very pleasing by itself. All reverb circuits I have seen always have a boing, boing signal that is mixed back with a strong dry/normal signal to produce the lush sound we all love. It's always a parallel path effect. That parallel path is really necessary.
Understood of course. I'd, perhaps carelessly, presumed others realize that would need to be factored into the changes. The point was, one might want cascading reverb+dry into/through vibrato versus only the dry getting the vibrato treatment. Possibly needs additional triode to get everything to come together correctly. Would need to take few minutes to sketch that out thoroughly. Starting point is, I have really enjoyed the sounds of my friend's original '62 6G12-A topped off with a matching 6G15. And that arrangement is cascading. I've never had opportunity to mess with Billy Zoom’s Little Kahuna, but gather it's cascading too.

Best .. Ian
Last edited by didit on Sat Dec 30, 2017 3:09 pm, edited 1 time in total.
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Re: SLuckley's Revibe. un buffered FX loop

Post by sluckey »

The point was, one might want cascading reverb+dry into/through vibrato versus only the dry getting the vibrato treatment.
Now that's an idea. Why don't you draw that up?
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didit
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Re: SLuckley's Revibe. un buffered FX loop

Post by didit »

sluckey wrote: Sat Dec 30, 2017 12:47 am
The point was, one might want cascading reverb+dry into/through vibrato versus only the dry getting the vibrato treatment.
Now that's an idea. Why don't you draw that up?
Not shy or shirking a challenge. Will need to start with a napkin sketch, since away with only my iPad. With time scarce could take a while.

Is your schematic in some common editable source that could be shared as a starting point - ie, versus reworking on PDF?

Best .. Ian
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Re: SLuckley's Revibe. un buffered FX loop

Post by sluckey »

All my drawings are created using Visio. I can make the original Visio file available if you like. The complete 10Meg file contains drawings that are not included in the pdf that may be of interest if you are redesigning. Or I can provide only the much smaller Visio schematic.

I'm happy using the Revibe between guitar and any amp input so I'm not likely to change mine. But, I've been thinking about how I'd attempt to put this in a typical passive loop between preamp and phase inverter. Here are some thoughts...

I would eliminate V2A and V1B and connect the input jack directly to the Dwell pot and the Level pot. Also remove the 1M from the input jack. You may even be able to remove V2B and connect the Dwell pot directly to the grid of the 6V6. The signal level produced by the preamp may be strong enough to directly drive the 6V6. If not, consider changing the 6V6 to an EL84.

The above should take care of the input signal levels. Probably need a bit of tweaking.

Now for the output. Remove the 220K/22K voltage divider from the output of V4 modulator tube (blue path). This will get the normal/vibrato signal level up enough to drive a typical phase inverter. Then cascade the unused V1B with the V1A reverb recovery amp to boost the reverb (boing, boing) signal up to match the stronger normal/vibrator signal.

I believe this basic idea (with a bit of tweaking) will work fine in an fx loop. I'll gladly provide a basic schematic showing the changes I mentioned above if anyone wants to take this idea and run with it. You'll have to do your own layout though.
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