Vibro Champ Reverb Amp?

[Seiche]

I'm currently building a reverb pedal and already have a trem so will try that. Do you reckon it's comparable to the amp then?

Because I would assume trem before reverb would be the more natural order, as trem pedals into amps with reverb is really common.

On the other hand, these amps pretty much predate pedals and the princeton reverb sounds really deep in videos with the opposite order, so maybe it is better that way.

[pompeiisneaks]

I think part of the point was that it's personal preference. You play both and see which you like better, and build the one the way you like the order of operations

~Phil

[Seiche]

maybe put it on a switch

Thanks guys! Great insight.

[Seiche]

This is taking longer than I thought because I got distracted with the holidays and other projects. Progress so far has been slow but steady:
- I collected most of the components, all the iron, resistors and caps based on my schematic.
- I learned how to use inkscape and designed a front plate that is based on the princeton (I'm using a princeton chassis) but with a vibro champ reverb logo. I got that made up and it turned out pretty well.
- I also made the eyelet layout and wanted to do the eyelet board myself but ended up getting a board made up at hoffman amps since this is my first amp project.
- I started assembly of most of the components, transformers and sockets to the chassis, and started the heater wiring (messed up the phase at first because I'm not using different colored heater wires).
- I actually bought a vintage drip edge vibro champ for myself for christmas (which is one of the distractions i mentioned above) It's awesome.
- I've been thinking a lot about proper grounding scheme, isolated input jacks vs regular wiring, etc. I am using a cap can.
- I'm also not entirely sure what needs to be tweaked on the power section to get proper voltages for all stages yet.

I will post some pictures once the eyelet board is here and will post the final layout and build instructions once I'm done.

One more question, for this circuit, is there any benefit to switching the tremolo out of the circuit completely (e.g. with a switched pot)? I've seen this being done with push-pull amps and referred to as the "cesar diaz mod" but not sure it works similarly here to get some more gain out of the preamp?

[Seiche]

Ok I'm basically done and it fired up first time! I used the help of a local amp builder to savely check everything out and slowly fire it up with a variac.

I got the cabinet made by belgian guy with navy bronco tolex and a wheat grill.

A few issues:
- 50hz hum which is modulated by the reverb pot. I will spend some time to figure this out, might be a grounding thing.
Edit: I got rid of the main hum by disconnecting the preamp bus from the cap can gnd (i don't have isolated input jacks so i figured this could be the ground loop via the chassis). Now the preamp is grounded at and via the jacks to the chassis. However, I now have a somewhat quieter ticking noise. Could this be Eddy Current noise? My next step would be to isolate the jacks and restore the preamp gnd bus to cap can gnd connection.
- I used the switched tremolo pot but i don't think it makes a real difference. I also used a 50k pot but i will probably change it for a 25k as the tremolo only comes on after half the pot's rotation (around 5-6 on the dial).
- Getting all components together was a real hassle, there are so many little bolts and bits one doesn't think of. I guess i was also restricted by the prefab princeton chassis I used.
- the pilot light is pretty bright, I can understand why they sometimes bend them to the side inside the chassis.

It sounds great! Just like i hoped it would, save for that hum.

So apparently Fender just introduced this same amp a few days ago as a custom 68 vibro champ reissue (with reverb). What a crazy coincidence (within days of me getting the cabinet delivered and putting it all together). I wonder if they are reading this thread

IMG_20210115_101736.jpg

IMG_20200917_230605.jpg

[Seiche]

Got rid of the ticking noise after grounding the preamp separately at the chassis (not on the same cap can gnd as the powertubes, but rather a separate bolt to the chassis). I also tried isolating the input jacks but found it made everything noisy again if the cap can gnd is shared by preamp and powertubes. Grounding the input jacks made the ticking vanish so now i have three connection points to the chassis.

There is some slight background hum and some slight residual modulation with the reverb pot but much quieter and quite tolerable. I still don't have the mesh/copper tape shielding in the cabinet ceiling yet and pretty cheap reverb cables, so there might be some room for improvement there.

I used a 5751 for the reverb and gain recovery as I am getting plenty of reverb depth (anything more than 3-4 sounds overwhelming to me).

The tremolo could be a bit deeper at 10, but it's plenty slow at 1 (i used three 20nf caps).

[Seiche]

The tremolo could be a bit deeper at 10, but it's plenty slow at 1 (i used three 20nf caps).

I changed the 68k resistor at the intensity pot wiper to a 39k and it gets plenty deep now, even though i don't really like the taper of the on/off 50kC pot that I used. The tremolo isn't really noticeable until around 4-5 on the dial. I'll leave it like it is though, as it works well.

I also replaced the amp handle by a handmade real leather one by Brookwood Leather.

I love that amp and use it exclusively since the tremolo on my vintage amp stopped working a few months ago

VCR_final.PNG

[Colossal]

Very nice! What speaker are you running?