Two rock crs v3 clone and v1 vs v3 differences

[rootz]

For this new build I’m working on I’m looking at Dumble like amps with every. I already build a Wonderland. It’s a beautiful amp, but I’m starting to miss the OD that my preamp (switchable HRM/normal ODD like) has to offer. My pedals don’t produce that sound!
I can find some info on the Two Rock crs v1, but not much about the v3. They are pretty different by the looks of it. The v3 has an extra node and just one triode as reverb driver. I wonder: how is this reverb done? Can’t be just an extra triode added to the v1 reverb as it would be out of phase. There has to be some kind of mixer stage for dry and wet signals. Followed by a recovery stage/half a Dumbleator? Not so sure. How can give me some insights here? Or a source of good detailed pictures.
Also I wanted to share the layout I made for a crs v1. This should be pretty accurate to a real v1 as it closely resembles pictures of it.

[Guy77]

Hi rootz. Great layout!


Cheers

Guy

[rootz]

Thanks Guy! It’s a lot of work to make that in Visio, but it helps me with building amps a lot too.

But... still no more info on the v3 (or its successor the Coral). Somebody has got to know something, right? No Dumble, but at least really Dumblesque.

[Guy77]

I believe a very similar amp is called the Bloomfield .
I posted a gut shot I found online that may help .
One thing that does seem apparent is that they are using the first half of the 2nd 12ax7 to take in part of the signal that will be used as the reverb signal . And instead of using both sides of a 12at7 to drive the reverb tank they are only using one side of the tube as you also noted.

Cheers

Bloom.jpg

[rootz]

Looks more like an ODRS to me, doesn’t it? Reverb taken from the second clean triode? OD stage is the 4th preamp tube. Classic tone stack. Low plates? Snubbers in the OD stage. Much like a #124 with reverb? Just guessing. But certainly not much like a Coral or v3 by the looks of it.

You happen to have some nice detailed gut shots of a Coral or crs v3? They seem to be very scarce...

[Guy77]

I think the link below has some inside pics further down the page on what you are looking for

Cheers

https://guitar.com/review/two-rock-clas ... signature/

[rootz]

Ha, that’s also a CRS, but not the one I mean. This is the Classic reverb signature. Bit like a Wonderland or JM amp, but with more features. Has rock/jazz, gain structure, PAB (with some kind of network with a pot and a small value PS6). This should be a 2 1/2 tube reverb with a mixer. Low plates, classic tone stack. Probably some of the best clean sounds in business and some mild OD.

But not a custom reverb signature v3

First picture is a v1. Notice one half as reverb driver, the other left unused. Like the layout I did, only I used both halves.

Second picture is a v3. Notice the extra plate resistor coming from the large power supply cap on the preamp board. Also a lot more going on on the back of the amp. Reverb send level, loop level (return?) and lead contour (front has the clean contour).

[rootz]

After a trip to Lissabon and some more thinking, I came to the conclusion that there is only one way to use a single triode reverb driver and a mixer stage (at the anodes) like I see in the crs v3 pictures I have. Apparently the idea of TR was to make a John Mayer signature amp with an OD stage. That means loop and master come before the loop like in a 'normal' ODS. Your effects will be effected by the reverb and power amp in on the back has reverb! Also the return side of the loop might be capable of amplifying line/effect level, the send side is high output impedance. Not good for driving long cables.

Anyway, a CRS v3 can be anything you want it to be. #102, #124, #183, all possible. Different feedback loops around the mixer tubes? Possible! Looks very tweakable.

Now I just have to choose: CRS v1 (or Jet!) or V3? I think both will sound great.

Time to show you the schematics of what I think are the V1 (Larry already shared a schematic years ago of this one) and v3.

[Guy77]

Hi rootz. Very cool schematics

So to get a broad understanding your are saying :

1 tube for the clean and a 2nd tube for the overdrive and then 1/2 tube reverb driver, then 1/2 tube reverb recovery . Then another tube to mix the reverb and dry signals and finally the Phase Inverter tube? 5 preamp tubes in total.

Cheers

Guy

[rootz]

Thanks Guy. That’s it, pretty normal Dumble with one triode reverb drive, one triode recovery and two triodes to do the mixing. The clean channel looks like a Wonderland or TR JM amp this way.

I got so curious that I had to build an amp based on this circuit. I went for a low plate skyliner aka #124 post 1988. Finished the amp at 9 pm, so couldn’t do much loud testing, but I like what I heard! More to come!

[Guy77]

That's great rootz! Looking forward to hearing your thoughts.
I may start a similar build in several weeks and may have some questions for you. I will do mine Lowplate as well .
Just need to decide between classic or skyline tone stacks.

Cheers!

[rootz]

So I took the amp to practice last night. All I can say: WOW!!! The cleans are absolutely amazing with my Les Paul (just used the Paul) and the OD is great too. Much smoother and characterful than my Suhr Riot, but still with lots of bite and cut using an EVM12L. The other guitarist was perplexed by the sound of the OD, he thought it was stunning.

I'm really happy I went for the skyliner tone stack. I have no room for a deep switch, which I frequently used in the JM clone the amp used to be. Why? I use a small combo and the amp really can use some extra bass. Skyliner gets me all the bass and lower mids I need (YMMV).

There is an obvious downside to the amp though. The loop! I had to keep the master volume on the front of the amp down to not overdrive the effects from the send jack. And by down I mean like on lower than 9 'o clock. Which means I had to turn up the recovery master on the back of the amp. Also, driving the effects from a 1 meg master volume might not be the best idea if you use a long cable to your pedal board. The obvious solution is to build an external loop, like a dumbleator, use short cables or put a 220k/220p combo on the send jack to compensate for longer cables. Now, with just a passive loop, 1n in cable capacitance will cost approx 7 dB of high end and there is no way to compensate. Well, you could use better low capacitance cables I guess.

Will upload an updated schematic and layout shortly. That will make cloning this idea much easier for you Guy. You can make numerous variations to the ideas here, all in the reverb part. I now made the dry mixer triode like the one in the JM/Wonderland amp. 220k stopper and 10meg-47n feedback loop. But you could also make it like the recovery stage of dumbleator. I went for a presence control, but why not try a cut control instead? Or use an A250k on the treble and B250k on the mids instead of the other way around like I did!

Guy, what kind of transformers will you be using? If you're going to use one with a 5V tap: tube rectifiers are possible. Like 2x 6V6 and a GZ34, or 2x 6L6/EL34/KT66 and 2x GZ34. I choose to power the relays from the rectified 5V and a DC-DC converter. Works great that way and the converters are like $2 on Ali.

[BarryW]

Thanks for sharing this exploration. In my meager way, I've been experimenting with putting reverb in after the loop in a smaller build. I've learned a bit, but mostly that I don't really know enough not to be dangerous ;^}. It's coming along, but this gives me some things to think about as well.

[Guy77]

Thanks for the nice summary rootz! I may go with skyliner as well after hearing how much you like it.
I will probably use a Marshall style 100 watt transformer (290HX) so that I can get my B+ in the 460 - 490 range. I built a JM like this and really liked how it sounded with the higher plate voltage. I will go with a 4 x 6L6 switchable to 4 x EL34 setup . I have a a small 5v transformer that I will use for the relays.
Maybe having 3 control knobs like the dumbleator has may help your master volume issue.

I am wondering if you kept the 1meg/68K voltage divider like the JM/Wonderland amp has in the preamp?
I will probably go with a cut control, I like them a lot.

Looking forward to your update schematic/ layout!

Chat later

[rootz]

Thanks for sharing this exploration. In my meager way, I've been experimenting with putting reverb in after the loop in a smaller build. I've learned a bit, but mostly that I don't really know enough not to be dangerous ;^}. It's coming along, but this gives me some things to think about as well.

You gotta know what you're doing to not be dangerous! That being said: if you work cleanly, slowly and always keep one hand in your (back) pocket while doing measurements, you start minimising the chances that you'd electrocute yourself. What also helps, is making test setups in LTSPICE. I can highly recommend that. Always safe and as long as your parameters are right, predicted outcomes will only slightly vary from reality. For example: I designed the whole PSU in Spice and was off by about one volt.

Now what you also should do is look as much at schematics from Fender, Mesa, the ones here, etc. to get a better understanding of what circuits do. Implementing reverb is pretty simple when you use a 2 tube (4 triodes) like in many Fenders. Paralleled driver triodes (12AT7), half 12AX7 recovery and half 12AX7 mixer, just like in the schematic above. Which works, that is essentially the Two Rock Jet or the CRS v2 (and countless other amps probably). Jet users rave about their cleans and reverb (but who wouldn't after paying 2 grand for an amp that size).

Keep safe, high voltages in these amps are lethal!